TM 5-692-2 

HEADQUARTERS, DEPARTMENT OF THE ARMY 

9 DECEMBER 2005 

TECHNICAL MANUAL 

MAINTENANCE OF MECHANICAL 

AND ELECTRICAL EQUIPMENT 

AT COMMAND, CONTROL, 

COMMUNICATIONS, 

COMPUTERS, INTELLIGENCE, 

SURVEILLANCE, AND 

RECONNAISSANCE (C4ISR) 

FACILITIES 

SYSTEM DESIGN FEATURES

APPROVED FOR PUBLIC RELEASE: DISTRIBUTION IS UNLIMITED 
REPRODUCTION AUTHORIZATION/RESTRICTIONS 

This manual has been prepared by or for the Government and, except to 

the extent indicated below, is public property and not subject to 

copyright. 

Reprint or republication of this manual should include a credit 

substantially as follows: “Department of the Army TM 5-692-2 

Maintenance of Mechanical and Electrical Equipment at Command, 

Control, Communications, Computers, Intelligence, Surveillance, and 

Reconnaissance (C4ISR) Facilities – System Design Features, 9 

December 2005” 
 TM 5-692-2 

This manual supersedes TM 5-692-2 dated 15 April 2001 

 i 

Technical Manual HEADQUARTERS 

 DEPARTMENT OF THE ARMY 

No. 5-692-2 Washington, DC, 9 December 2005

APPROVED FOR PUBLIC RELEASE: DISTRIBUTION IS UNLIMITED 

MAINTENANCE OF MECHANICAL AND ELECTRICAL EQUIPMENT AT 

COMMAND, CONTROL, COMMUNICATIONS, COMPUTER, 

INTELLIGENCE, SURVEILLANCE AND RECONNAISSANCE (C4ISR) 

FACILITIES: SYSTEM DESIGN FEATURES 

CONTENTS 

 Paragraph Page 

CHAPTER 1. INTRODUCTION 

 Purpose 1-1 1-1 

 Scope 1-2 1-1 

 References 1-3 1-1 

 Standard of performance 1-4 1-1 

CHAPTER 2. SYSTEMS ENGINEERING CONSIDERATIONS 

 General systems considerations 2-1 2-1 

 Program elements 2-2 2-1 

 System design considerations 2-3 2-2 

CHAPTER 3. PRIMARY ELECTRICAL DISTRIBUTION 

 General primary electrical distribution 3-1 3-1 

 Substations 3-2 3-1 

 Overhead distribution 3-3 3-4 

 Switchgear 3-4 3-5 

 Circuit breakers 3-5 3-6 

CHAPTER 4. SECONDARY ELECTRICAL DISTRIBUTION 

 General secondary electrical distribution 4-1 4-1 

 Switchgear, switchboards, and panelboards 4-2 4-1 

 Transformers 4-3 4-1 

 Power line conditioners 4-4 4-1 

 Motor control centers 4-5 4-3 

 Protective devices, fuses, and circuit breakers 4-6 4-3 

 Switches 4-7 4-5 

 Feeder cables 4-8 4-5 

 Controls 4-9 4-5 

CHAPTER 5. UNINTERRUPTIBLE POWER SUPPLY SYSTEM 

 General 5-1 5-1 

 Battery and battery charger 5-2 5-1 

 Inverter 5-3 5-3 

 Transfer switches 5-4 5-4 

 Instrumentation 5-5 5-5 

 Operational considerations 5-6 5-5 

 Motor generator design features 5-7 5-6 
TM 5-692-2 

ii 

 Paragraph Page 

CHAPTER 6. ELECTRICAL CONTROLS 

 General electrical controls 6-1 6-1 

 Major components of an electrical control system 6-2 6-1 

CHAPTER 7. GENERATORS 

 Generator usage 7-1 7-1 

 Generator operation 7-2 7-1 

 Generator types 7-3 7-2 

 AC generators 7-4 7-2 

 DC generators 7-5 7-5 

 Major design components 7-6 7-6 

 

CHAPTER 8. DIESEL ENGINES 

 Diesel engine ratings 8-1 8-1 

 Types of diesel engines 8-2 8-1 

 Diesel engine major system components 8-3 8-1 

 Diesel engine system interfaces 8-4 8-2 

 Operation of diesel engines 8-5 8-5 

 

CHAPTER 9. GAS TURBINES 

 Applications of gas turbines 9-1 9-1 

 Gas turbine operating characteristics 9-2 9-1 

 Gas turbine system major components 9-3 9-1 

 Gas turbine system interfaces 9-4 9-4 

 

CHAPTER 10. FUEL OIL SYSTEMS 

 Simple fuel oil system 10-1 10-1 

 Complex fuel oil system 10-2 10-1 

 Fuel oil system major components 10-3 10-3 

 

CHAPTER 11. LUBE OIL SYSTEMS 

 Lube oil system design features 11-1 11-1 

 Lube oil system major components 11-2 11-9 

 

CHAPTER 12. ENGINE INTAKE AND EXHAUST SYSTEMS 

 Engine intake and exhaust system design features 12-1 12-1 

Engine intake and exhaust system major components 12-2 12-4 

CHAPTER 13. COOLING SYSTEMS 

 Cooling system design features 13-1 13-1 

 Cooling system major components 13-2 13-9 

CHAPTER 14. BOILERS 

 Types of boilers 14-1 14-1 

 Types of systems 14-2 14-1 

 Boiler system major components 14-3 14-2 

 Boiler system controls 14-4 14-3
 TM 5-692-2 

This manual supersedes TM 5-692-2 dated 15 April 2001 

 iii 

 Paragraph Page 

CHAPTER 15. INCINERATORS 

 Incineration system description 15-1 15-1 

 Incineration system major components 15-2 15-1 

CHAPTER 16. CHILLED WATER SYSTEMS 

 Chilled water systems description 16-1 16-1 

 Chilled water systems major components 16-2 16-1 

CHAPTER 17. DOMESTIC WATER SYSTEMS 

 Domestic water system description 17-1 17-1 

 Domestic water system major components 17-2 17-1 

CHAPTER 18. CHEMICAL TREATMENT 

 Chemical treatment system design features 18-1 18-1 

 Chemical treatment system major components 18-2 18-6 

CHAPTER 19. AIR HANDLING SYSTEMS 

 Air handling system design features 19-1 19-1 

 Air handling system major components 19-2 19-6 

CHAPTER 20. INDUSTRIAL WATER SUPPLY SYSTEMS 

 Industrial water supply system design features 20-1 20-1 

 Industrial water supply system major components 20-2 20-2 

 Testing 20-3 20-3 

CHAPTER 21. COMPRESSED AIR SYSTEMS 

 Compressed air system 21-1 21-1 

 Compressed air system major components 21-2 21-1 

 Compressed air system interfaces 21-3 21-8 

 

CHAPTER 22. PNEUMATIC CONTROLS 

 Pneumatic control design features 22-1 22-1 

 Pneumatic control systems major components 22-2 22-1 

 System operation 22-3 22-3 

CHAPTER 23. SANITARY WASTE SYSTEMS 

 General sanitary waste systems 23-1 23-1 

 Sanitary waste system design features 23-2 23-1 

 Sanitary waste system applications 23-3 23-1 

Treatment methods 23-4 23-2 

 Typical sanitary waste systems 23-5 23-3 

 Sludge handling, treatment, and disposal 23-6 23-7 

 Disinfection 23-7 23-7 

 Flow measurement, sampling, and process control 23-8 23-8 

CHAPTER 24. ELECTRONIC SECURITY 

 Electronic security methodology 24-1 24-1 

 Types of electronic security 24-2 24-1 
TM 5-692-2 

iv 

 Paragraph Page 

CHAPTER 25. HIGH ALTITUDE ELECTRO-MAGNETIC PULSE 

(HEMP) PROTECTION SYSTEMS 

 General HEMP protection systems 25-1 25-1 

 HEMP procedures 25-2 25-1 

 Modes of HEMP entry 25-3 25-2 

 Equipment susceptibility 25-4 25-2 

 HEMP protection systems 25-5 25-3 

CHAPTER 26. TEMPEST PROTECTION SYSTEMS 

General TEMPEST protection systems 26-1 26-1 

 Sources 26-2 26-1 

 Acquisition 26-3 26-1 

 Protection 26-4 26-1 

CHAPTER 27. GROUNDING 

 General grounding systems 27-1 27-1 

 Types of grounding 27-2 27-1 

 Grounding systems 27-3 27-3 

 Ground system materials and testing requirements 27-4 27-4 

CHAPTER 28. LIGHTNING PROTECTION 

 General lightning protection systems 28-1 28-1 

 Lightning effects on power systems 28-2 28-1 

 Principles of protection 28-3 28-2 

 Lightning protection systems equipment requirements 28-4 28-3 

CHAPTER 29. CATHODIC PROTECTION 

 General cathodic protection systems 29-1 29-1 

 Types of cathodic protection systems 29-2 29-1 

 Application of cathodic protection 29-3 29-2 

 Cathodic protection system design 29-4 29-3 

CHAPTER 30. BLAST PROTECTION AND DETECTION SYSTEM 

 General blast protection and detection systems 30-1 30-1 

 Sensors 30-2 30-1 

 Relay panels 30-3 30-1 

 Blast valve systems 30-4 30-1 

 Blast door systems 30-5 30-1 

CHAPTER 31. FIRE PROTECTION 

 General fire protection systems 31-1 31-1 

 Fire detection systems 31-2 31-1 

 Fire suppression systems 31-3 31-2 

 

APPENDIX A. REFERENCES A-1 

GLOSSARY G-1
 TM 5-692-2 

This manual supersedes TM 5-692-2 dated 15 April 2001 

 v 

LIST OF FIGURES 

Figure Title Page

Figure 10-1 Complex fuel oil system - supply 10-2 

Figure 11-1 General lube oil system – diesel engine 11-2 

Figure 11-2 General lube oil storage and dispensing system 11-3 

Figure 11-3 Lube oil purification system 11-4 

Figure 11-4 Emergency service diesel engine lube oil system 11-6 

Figure 11-5 Primary service diesel engine lube oil system 11-7 

Figure 11-6 Diesel engine standby operation lube oil heating system 11-8 

Figure 12-1 Blast-protected air intake system 12-3 

Figure 12-2 Blast-protected engine exhaust system 12-5 

Figure 12-3 Blast-protected exhaust system 12-6 

Figure 13-1 Examples of engine cooling systems (1) 13-2 

Figure 13-2 Examples of engine cooling systems (2) 13-3 

Figure 13-3 Examples of engine cooling systems (3) 13-4 

Figure 13-4 Typical primary service diesel engine cooling system 13-6 

Figure 13-5 Typical radiator diesel engine cooling system 13-8 

Figure 13-6 Typical evaporative cooling tower 13-10 

Figure 15-1 Vertical dual chamber incinerator 15-2 

Figure 16-1 Variations of centrifugal pumps 16-5 

Figure 16-2 Typical valves used in water service (1) 16-8 

Figure 16-3 Typical valves used in water service (2) 16-9 

Figure 17-1 Domestic water system with reservoir storage 17-2 

Figure 17-2 Bladder tank installation 17-4 

Figure 17-3 Electric water heater 17-5 

Figure 17-4 Instantaneous steam water heater 17-6 

Figure 17-5 Semi-instantaneous steam water heater 17-7 

Figure 17-6 Backflow preventors 17-8 

Figure 18-1 Typical fill system pot feeder installation 18-3 

Figure 18-2 Typical pot feeder bypass installation 18-4 

Figure 18-3 Open-loop chemical treatment system 18-5 

Figure 18-4 Typical steam boiler installation 18-6 

Figure 18-5 Basic water softener system 18-7 

Figure 18-6 Basic ion exchange unit 18-8 

Figure 19-1 Typical single zone air handling system 19-2 

Figure 19-2 Multizone air handling system 19-3 

Figure 19-3 Basic dual duct act handling system 19-4 

Figure 19-4 Air handling system with reheat 19-5 

Figure 19-5 Variable air volume air handling system 19-7 

Figure 19-6 Typical air handling system controls 19-15 

Figure 21-1 Typical air compressor systems 21-2 

Figure 21-2 Typical air dryers 21-3 

Figure 21-3 Typical air compressor installation 21-4 

Figure 21-4 Typical engine compressed air starting system 21-5 

Figure 22-1 Basic compressed air supply to pneumatic control system 22-2 

Figure 23-1 Typical trickling filter process treatment train 23-4 

Figure 23-2 Conventional plug flow activated sludge flow diagram 23-5 

Figure 23-3 Septic tank 23-8 

Figure 23-4 Lift station with wet pit vertical centrifugal pump 23-9 
TM 5-692-2 

vi 

Figure Title Page

Figure 23-5 Pneumatic sewage ejector 23-10 

Figure 23-6 Gate valve and swing check valve 23-11 

LIST OF TABLES 

 

Table Title Page 

Table 8-1 Typical alarm and shutdown requirements for diesel engines 8-3 

Table 9-1 Typical alarm and shutdown requirements for gas turbines 9-3 

Table 12-1 Typical bellows material failures 12-8 

 
TM 5-692-2 

1-1 

CHAPTER 1 

INTRODUCTION

1-1. Purpose

This document has been prepared to provide generic guidance to agencies responsible for the 

development and implementation of maintenance programs for site utility systems at command, control, 

communications, computers, intelligence, surveillance, and reconnaissance (C4ISR) sites. This technical 

manual (TM), TM 5-692-2, describes commonly implemented design features of various mechanical and 

electrical systems. TM 5-692-1, the companion manual to TM 5-692-2, describes the activities which 

must be performed to maintain mechanical and electrical equipment at a minimum level of operational 

readiness. 

1-2. Scope

The program guidance and system specific maintenance requirements advanced in this manual are 

applicable in part or total to all C4ISR sites. 

1-3. References

Appendix A contains a list of references used in this manual. 

1-4. Standard of performance

The program guidance and system specific features described in this manual are considered to meet the 

minimum required standards of performance for such systems and must be augmented by equipment 

manufacturer's detailed operation and maintenance instructions and other site-specific design 

requirements as local mission reliability requirements dictate. 
TM 5-692-2 

2-1 

CHAPTER 2 

SYSTEMS ENGINEERING CONSIDERATIONS 

2-1. General systems considerations 

Requirements are presented in this manual for the design of optimally reliable mechanical and electrical 

systems at command, control, communications, computer, intelligence, surveillance, and reconnaissance 

(C4ISR) facilities. These systems shall be capable of supplying services continually to the C4ISR 

installation site during any natural or man-made disruption in commercial services. Off-site power 

facilities are assumed to be adequate to supply peak power demands, but are not assumed to be 

uninterruptible. Potential threats include physical attacks; biological, chemical, and radiological warfare; 

and close-in and high-altitude nuclear blasts. 

2-2. Program elements 

The essential elements of a systems engineering program are described below. 

a. Reliability, availability, and maintainability (RAM). During design, the design agency shall 

implement RAM requirements to maximize the availability of the C4ISR systems. 

b. Human factors engineering (HFE). HFE activities will ensure that reliability, availability, and 

safety of the C4ISR systems are not degraded through human activities during operation or maintenance. 

The design agency shall accomplish the HFE program requirements through the use of established 

standard HFE design criteria and practices based on MIL-STD-1472, Human Engineering Design Criteria 

for Military Systems, Equipment, and Facilities. 

c. System safety. The C4ISR power system safety program shall ensure that the design incorporates, 

within program restraints, the highest attainable level of inherent safety. It shall eliminate or reduce the 

probability of events that can cause injury or death to personnel, or damage to or loss of equipment or 

property. For example, pipes, lines, and tanks shall be placed away from high-traffic areas. Safety 

documentation shall be provided for safety items that require designation or may cause action during 

subsequent program phases. The design agency system safety program shall be based on a philosophy 

that the most effective actions to control potential hazards are those taken early in the design process. 

 (1) When hazards cannot be controlled by design measures, including safety and warning devices, 

special operating procedures shall be developed and documented. The safety program shall provide 

support to the systems engineering (SE) program and shall ensure that the applicable requirements of 

MIL-STD-882, System Safety Program Requirements, are met. 

 (2) The systems safety program shall define and address the safety analyses that shall be performed 

during development of design. During the early design phase, an analysis that identifies conditions that 

may cause injury or death to personnel and damage or loss to equipment and property shall be performed. 

Prior to the final safety design review, the design agency shall perform a second systems safety analysis 

to determine adherence of the design to all required safety standards and criteria, and to ensure avoidance 

or reduction of identified hazards. Operating and maintenance procedures shall also be reviewed for 

compliance with all required safety standards and criteria. 
TM 5-692-2 

2-2 

 (3) The systems safety program shall include follow-up/corrective procedures to ensure that safety 

hazards identified by the systems safety analyses are eliminated or reduced to acceptable levels of risk, 

and that actions taken are fully documented. 

 (4) The design agency shall prepare specific safety program documentation. This documentation 

shall include, but not be limited to, safety analysis reports and the final systems safety report. 

 d. Consolidated system testing. The design agency shall develop a consolidated systems test program 

that covers all phases of testing, develops confidence in the system, and provides means for interim and 

final acceptance of equipment and systems. The design agency shall minimize cost through elimination 

of testing duplication and by maximizing the collection of data for each test. Final acceptance of the 

system shall follow 100 percent successful completion of these tests. 

e. Standardization. The design agency shall develop and implement a standardization program to 

minimize equipment and component stockage. Redundant systems shall be of the same design. 

f. Configuration management (CM). The CM program shall maintain effective control over design 

from criteria development through design, construction, and installation of the equipment. A government 

configuration control procedure shall be developed by the design agency for use in the C4ISR 

configuration control program. 

 g. Operations and maintenance (O&M) planning. The design agency shall identify and recommend 

essential items of the program during the design phase. Basic elements of the program are as follows. 

 (1) Data requirements shall be identified for preparation of O&M manuals. Systems functional 

descriptions shall be developed. Requirements shall be developed for data collection, including repair 

parts list, calibration requirements, special tools and test equipment, repair parts stockage level, and shelf 

life data. Repair parts list, repair parts stockage level, test equipment, and test frequency shall be 

provided the using government agency. 

 (2) Systems and equipment of high complexity or peculiarity shall be identified, and special 

training for personnel who operate and maintain such systems and equipment shall be identified. 

 (3) The design agency shall identify those items critical to accuracy and repeatability, and shall 

recommend calibration requirements. Unique calibration requirements and procedures shall be provided 

whenever necessary. 

 (4) Systems test and checkout requirements to be performed following major maintenance 

activities shall be developed during design to ensure safe and normal operation of the system. 

2-3 System Design Considerations 

a. Offsite electrical power. Two separate commercial power sources are preferred in conjunction 

with redundant feeders between the commercial power substations and the C4ISR site power plant. When 

two separate transmission lines are not available, a single commercial power source could be used to supply 

redundant distribution feeders to the power plant. The redundancy should be provided through two or more 

full capacity feeders which will be supplied from normally isolated switchgear busses in the commercial 

power substation. If the two transmission lines are used, they should be supplied by the same utility 

company; if owned by different companies, they should be supplied from the same transmission grid system 

to ensure synchronism of the two transmission lines. 
TM 5-692-2 

2-3 

b. Onsite electrical power. Operational onsite units should be capable of supplying the peak site 

demands while operating independent of any commercial power source when loaded between 60 to 80 

percent of their rated load capacities. Loading of active generating units should not exceed these 

percentages since the emergency shutdown of one unit could cause overloading and consequent shutdown 

of the other units. On the other hand, onsite generators should not be loaded below 50 percent of the 

kilowatt rating to prevent accumulation of acid and carbon (wet stacking). Onsite power system shall also 

be capable of making the transition from offsite to onsite power mode of operation in not more than one 

minute, including starting and synchronizing a sufficient number of generators to serve the required loads. 

Onsite power units shall be capable of being started using only onsite equipment and facilities. 
TM 5-692-2 

3-1

CHAPTER 3 

PRIMARY ELECTRICAL DISTRIBUTION 

3-1. General primary electrical distribution

Primary electrical distribution system is defined in this manual to be the electrical system operating above 

600 Vac. Secondary distribution system is defined as 600 Vac and below. Without electrical power to 

operate equipment, provide illumination, etc., site operations would be very difficult or impossible; 

therefore, correct operation and maintenance of the primary electrical distributions system is essential. 

3-2. Substations 

Substations control the flow of power into a facility. They are comprised of transformers for stepping 

down the voltage, high-voltage insulators, and large air/oil circuit breakers capable of interrupting 

tremendous amounts of current during fault conditions. 

 a. Transformers. A transformer utilizes electromagnetic (EM) induction between circuits of the same 

frequency, usually with changed values of voltage and current. Transformers can be classified in various 

ways, but their basic construction consists of windings, magnetic cores on which windings are coiled, 

insulation, and any special connections applying to the type of load. Substation transformers can range in 

size from a garbage can to a small house. Their main purpose is to transform alternating voltage and 

current from one level to another. At the power plant the voltage is brought up to a higher voltage for 

efficiency in transmitting the power to the end user. At the end user's locale the voltage is brought down 

to a level that is suitable for operations. 

 (1) The basic design of a transformer consists of electrical coils wrapped around an iron or steel 

core. By controlling the number of windings, or tapping into the windings, various levels of voltage 

change can occur. Nameplate information for each transformer will help in identifying the primary coil 

and the secondary coil ratings, in addition to how the transformer is configured. 

 (2) Transformers rated above 500 kVA are classed as power transformers. Transformers rated at 

500 kVA or less are classed as distribution transformers, as they usually have low tension windings of 

less than 600 volts. 

 (3) American National Standards Institute/Institute of Electrical and Electronic Engineers 

(ANSI/IEEE) C57.12.80, Standard Terminology for Power and Distribution Transformers (1992), 

identifies several classes of insulation systems for power and distribution transformers. Insulation 

classifications are based upon the insulation’s temperature rating and the method of cooling needed to 

remove the heat from the transformer. The core and the coils of dry type transformers are in a gaseous or 

dry-compound insulating material. The core and the coils of liquid-immersed transformers are contained 

in an insulating liquid. Flammable mineral oil insulation is the most frequently used liquid. Various less 

flammable liquids are used to meet National Electrical Code (NEC) code requirements. Only flammable 

and less flammable liquids are acceptable on military installations. Non-flammable insulated liquids, 

though available, are not considered environmentally acceptable. Polychlorinated biphenyl (PCB) 

insulated transformers should be removed to meet Environmental Protection Agency (EPA) requirements. 

 Replacement of liquid-filled transformers in or near buildings must take into account the latest applicable 
TM 5-692-2

3-2

NEC code restrictions, which might require an existing installation to be modified or a different type of 

insulating medium to be provided. 

 (4) All electrical component applications must meet the Electrical Electronic Enclosure 

Classifications (NEMA Standard 250 for their purposes). An outdoor transformer should be constructed 

with weather-resistant construction, suitable for service without additional protection from the weather. 

Industry standards also classify transformers as indoor units, which must be protected from the weather. 

A pole type transformer is an outdoor transformer that is suitable for mounting on a pole or a similar 

structure. A pad-mounted transformer is a unitized or compartmental type transformer, with enclosed 

compartments for medium-voltage and low-voltage cables entering from below, and is mounted on a pad. 

(5) Transformers can maintain an acceptable voltage ratio of about a two percent voltage drop 

from zero to rated output in most cases. Most distribution transformers and smaller power transformers 

have tapped windings, which permit adjusting the output voltage to broaden the range of primary voltage 

inputs. The transformer will have a manual tap changer, which can be operated if the transformer is deenergized. However, on substations which serve varying loads, such as pumping facilities, or on large 

installations with long primary feeder lines, taps may not provide sufficient voltage regulation and other 

means are necessary. 

 (6) An automatic load tap changing (LTC) feature installed on a transformer provides automatic 

tap changing under load, and normally varies the voltage to plus or minus ten percent of the system’s 

rated voltage by changing tap connections using a motor-driven, tap-changing switch. 

 (7) Sometimes voltage regulation is needed and the system transformers do not include the LTC 

feature. Voltage regulators are used to supply the control for the variations in load. A voltage regulator 

needs similar servicing to that required for a power transformer. A step-voltage regulator operates on the 

same principal as the LTC mechanism. An induction voltage regulator has a series winding and a shunt 

winding, and uses a motor to rotate the shunt winding to either add to (boost) or subtract from (buck) the 

series winding voltage. The action provided is dependent upon the voltage induced in the series winding 

and the respective polarities of each winding (that is, the respective instantaneous directions of currents 

entering the primary and leaving the secondary terminals during most of each half cycle). The switching 

mechanism in most new voltage regulators is practically maintenance free, but many of the older units 

require considerable servicing. The manufacturer’s recommendations should be followed for all 

maintenance and servicing requirements. 

 b. Insulators. The function of an insulator is to support a conductor or conducting device safely. An 

insulator, being of a non-conductive material, physically and electrically separates the supported item 

from any grounded or energized conductors or devices. Insulators are composed of porcelain, glass, 

fiberglass, or a composite compound. Maintenance is necessary to preserve their insulating ability that 

can be degraded by contamination or other damaging actions. Most insulator damage will result from gun 

shots; lightning, surge, or contamination flashovers; and wind damage. Defective insulators can also 

cause visible corona or interference voltage propagation. 

 c. Bushings. A bushing is an insulating structure that provides a conducting path though its center 

while its body isolates contact to the support structure. A bushing has a provision for mounting on a 

barrier (conducting or otherwise). The bushing insulates the conductor from the barrier and conducts 

current from one side of the barrier to the other side. The primary function of a bushing is to provide an 

insulated entrance for an energized conductor into an apparatus tank. 
TM 5-692-2 

3-3

 d. Instrument transformers. Current and potential (voltage) transformers are used to enable ammeters 

and wattmeters to monitor power conditions. An instrument transformer is designed to reproduce in its 

secondary circuit (in a definite and known proportion) the current or voltage of its primary circuit with 

the phase relations and waveform substantially preserved. 

 (1) A current transformer is a constant-current transformer that reduces line currents into values 

suitable for standard measuring devices such as ammeters and wattmeters and standard protective and 

control devices. It also isolates these devices from line voltages. The primary winding is connected in 

series with the circuit carrying the line current, or as a window type arrangement linked magnetically with 

the line conductor which eliminates the need for an integral primary winding. 

 (2) A potential transformer is basically a conventional constant-voltage transformer with primary 

and secondary windings on a common core connected in shunt or parallel to the power supply circuit to 

be measured or controlled. The secondary winding insulates devices from the power circuit. 

 e. Switches. Substation switches can be operated manually or power operated. Insulation for the 

voltage and current interrupting level may be provided by operating the contacts in air, oil, vacuum, or in 

a sulfur hexafluoride (SF6) gas medium. Switches are classified by their ability to interrupt load. 

 (1) A disconnecting switch is a device used to open, close, or change the connections in a circuit 

or system. It has no interrupting rating and is used for isolating equipment only after the circuit has been 

opened by some other means. Two special types are as follows. 

 (2) A grounding switch is a switch used to connect a circuit or piece of equipment to ground. 

 (3) A horn-gap switch is a switch provided with arcing horns to aid in dispersing any arc that may 

occur when the switch is operated. This combination is sometimes referred to as an air-break switch. It 

should not be operated except to interrupt the charging current of a short length of line, or the 

magnetizing current of a de-energized transformer. Oil switches should always be considered as 

disconnect switches, unless the switch nameplate indicates a fault closing rating suitable for the system’s 

maximum available fault. 

 (4) Interrupter switches have specific capabilities for switching one or more of the following type 

of loads: 0.8 minimum lagging power factor load, parallel or loop load, transformer magnetizing load, 

line charging load, cable charging load, and capacitor bank load. Follow the manufacturer’s instructions 

when operating interrupter switches. 

 (5) Non-fault closing type switches are equipped with means of interrupting current, at rated 

voltage, not in excess of the switch’s continuous rated current. Interrupter switches, which do not have a 

fault-closing rating, may be damaged if inadvertently closed on a short circuit. Appropriate precautions 

should be taken to avoid danger to the operator. 

 (6) Fault closing type switches are equipped with means for interrupting current, at rated voltage, 

in excess of the switch’s continuous rated current. Interrupter switches with fault-closing ratings are 

intended to provide adequate personnel protection, when closing into a short circuit, up to the 

asymmetrical fault-closing rating of the switch and when applied in accordance with the manufacturer’s 

recommendation. 
TM 5-692-2

3-4

 f. Bus structures. A bus structure is an assembly of bus conductors with associated connection joints 

and insulating supports. It can have bare or insulated conductors. A busway is a grounded metal 

enclosure, containing factory-mounted bare or insulated conductors, that are usually copper or aluminum 

bars, rods, or tubes. Each serves as a common connection between two or more circuits. 

3-3. Overhead distribution 

Overhead electrical distribution at all voltages most often uses open wire construction, although aerial 

cables of various types are employed to some extent. Poles, towers, and other supporting structures 

define overhead distribution. When several different voltages are found on these structures the hierarchy 

is the highest voltage is at the top. Voltages drop as the circuits descend downward. 

 a. Open wire construction. The basic features of open wire construction are single conductors, 

insulated supports, and wide separation, with little or no conductor covering on the conductors. The air 

space around the conductors must be large enough to allow relative conductor movement without a 

flashover. Open wire construction is mounted on insulators, either as armless or crossarm construction. 

b. Armless construction. Armless construction consists of insulators on supporting brackets mounted 

directly on the pole. When possible, this construction is preferred for use on pole replacements because 

of its more attractive appearance and lower maintenance cost. Triangular tangent construction is 

preferred over vertical tangent construction, as it requires the least conductor space and is more 

economical. Triangular construction is not suitable for configurations that require an overhead ground 

wire. It is not recommended except for the tangent and minor angle construction. 

 c. Poles. Poles are constructed of wood, metal, or concrete. Extending out from these structures are 

crossarms that support the overhead cable. The poles can be self-supporting or may require guys 

(stranded galvanized wire) or braces to hold the pole in position. 

d. Crossarm construction. Unless it conflicts with facility practice, crossarm construction should be 

phased out whenever possible, but may be necessary where equipment or line installations, utilizing 

armless construction, would result in excessive pole heights. Facility practice usually matches the local 

utility company’s open wire construction. 

 e. Overhead cable. Aerial cable has its individual conductors insulated and supported by a messenger 

(support wire) along its length. The cable is then lashed and clamped to the insulators mounted on the 

poles or towers. 

f. Overvoltage protection. Overhead lines are extremely vulnerable to direct strokes or to induced 

voltage influences. Underground systems derived from aerial lines may also be affected. Lightning 

results from the potential difference between clouds or between a cloud and earth. A lightning stroke may 

be in direct contact with an electric line and equipment. The charged clouds of a passing lightning storm 

may also cause an electrostatically induced voltage. 

 (1) The high voltage of a lightning surge, imposed on lines and devices without surge protection, 

will flash over the insulation in the majority of cases. Where flashover occurs, through air or on 

insulators, it rarely causes permanent damage, but flashover occurring through the solid insulation on 

equipment or cable can result in permanent damage. 
TM 5-692-2 

3-5

 (2) A surge limiting protective device must limit transient over-voltages or surge voltages that 

could damage apparatus. The device must bypass the surge to ground and discharge severe surge currents 

of high magnitude and long duration without injury. The device must continuously withstand the rated 

power voltage for which it is designed. The device’s protective ratio is the maximum surge voltage it will 

discharge, compared to the maximum crest power voltage it will withstand following discharge. Surge 

arresters provide the most accepted method of surge limiting protection, since they provide the highest 

degree of surge elimination. Other methods include shielding lines and equipment from direct lightning 

strokes; and providing devices designed to divert or change the waveform of the surge, such as protective 

gaps, surge capacitors, and bypass resistors. A surge arrester is a protective device for limiting surge 

voltages on equipment by discharging or bypassing surge current. Surge arresters allow only minimal 

flow of the 60 hertz power current to ground. After the high-frequency lightning surge current has been 

discharged, a surge arrester, correctly applied, will be capable of repeating its protective function until 

another surge voltage must be discharged. 

 (3) Surge arresters used for protection of exterior electrical distribution lines will be either of the 

metal-oxide or gapped silicon-carbide type. Expulsion type units are no longer used. 

3-4. Switchgear 

Switchgear is a general term covering switching and interrupting devices that control, meter, and protect 

the flow of electric power. The component parts include circuit breakers, instrument transformers, 

transfer switches, voltage regulators, instruments, and protective relays and devices. Switchgear includes 

associated interconnections and supporting or enclosing structures. The various configurations range in 

size from a single panel to an assembly of panels and enclosures. The latter is normally constructed into 

cubicles with a circuit interrupter in one and auxiliary equipment in the others. It is then normally 

connected to a transformer. Equipment rated up to 1000 volts alternating current (AC) is classed as low 

voltage. Equipment equal to or greater than 1000 volts but less than 100,000 volts AC is classed as 

medium voltage. 

 a. Medium voltage switchgear. Major elements of medium voltage switchgear are circuit breakers, 

potential transformers, current transformers, and control circuits. Construction of circuit breakers 

employed in the two types of switchgear and the methods to accomplish breaker tripping are the primary 

differences. The service entrance conductors and main bus are typical heavy-duty conductors rated for 

use between 601 volts AC and 38,000 volts AC, as required. 

 b. Circuit interrupters. These interrupters can be air circuit breakers, arc interrupters, vacuum circuit 

breakers, or oil circuit breakers. Some can be removed from their cubicle while others must be checked 

in place. 

 c. Fuses. High voltage fuses can provide current or non-current limiting features. Their use can be 

dictated by the manufacturer or end user requirements. Available types are sand filled, liquid filled, or 

vented expulsion type. 

 d. Lightning (surge) arrestors. Arrestors are provided to pass high energy surges directly to ground 

thereby protecting the other electrical equipment downstream. 

 e. Protective relays. Protective relays provide quick isolation of power systems under fault 

conditions. They can detect overcurrent, overvoltage, under-voltage, current balance, current flow, 

frequency, and impedance. 
TM 5-692-2

3-6

 f. Alarms. Various alarms available are transformer over temperature, high or low pressure, circuit 

breaker trip, ground fault, or switchgear over temperature. 

 g. Interlocks. Interlocks are provided for personnel safety to prevent operation of equipment in an 

unsafe manner. 

3-5. Circuit breakers 

Circuit breakers are a special form of switching mechanism, which can open and close circuits under both 

normal and abnormal conditions. When they are electrically controlled, they can be operated locally or 

remotely, or by both modes. Oil, SF6, vacuum, and air are the insulating mediums used on most 

installations. The selection of the insulation generally relates to the voltage level being interrupted. 

Usually the air circuit breakers have draw-out construction. This feature permits removal of an individual 

breaker from the switchgear enclosure for inspection or maintenance without de-energizing the main bus. 

 a. High-voltage breakers. Until recently most installed high-voltage circuit breakers were of the oilinsulated type. However, the use of SF6 gas insulated units is increasing as these take less space for a 

given voltage and are environmentally preferable. 

 b. Medium-voltage breakers. Newly installed medium-voltage switchgear utilizes vacuum 

construction which provides a considerable space saving over air-magnetic units. 
TM 5-692-2 

4-1 

CHAPTER 4 

SECONDARY ELECTRICAL DISTRIBUTION 

4-1. General secondary electrical distribution 

A secondary electrical distribution system is defined as an electrical distribution system having a voltage 

of 600 Vac and below. This is the electrical system that normally supplies power to process systems, 

habitability systems, and other loads within a facility. Typical equipment and components that comprise 

this system are switchgear, switchboards, and panelboards; transformers; power line conditioners; motor 

control centers; protective devices, fuses and circuit breakers; switches; feeder cables; and controls. 

4-2. Switchgear, switchboards, and panelboards 

Switchgear, switchboards, and panelboards are general terms covering switching and interrupting devices 

that control, meter and protect the flow of electric power. The component parts include circuit breakers, 

fuses, instrument transformers, transfer switches, voltage regulators, instruments, and protective relays 

and devices. The various configurations range in size from a single panel to an assembly of panels and 

enclosures. The components comprising the makeup of the main devices are usually in a grounded, metal 

enclosure. Equipment rated up to 1000 volts alternating current (AC) is classed as low voltage. 

Equipment equal to or greater than 1000 volts but less than 100,000 volts AC is classed as medium 

voltage. 

4-3. Transformers 

A transformer utilizes electromagnetic (EM) induction between circuits of the same frequency, usually 

with changed values of voltage and current. Transformers can be classified in various ways, but their 

basic construction consists of windings, magnetic cores on which windings are coiled, insulation, and any 

special connections applying to the type of load. Transformers used for secondary distribution are usually 

smaller than those for primary distribution, but depending on the voltage and demand can be large. Their 

main purpose is to transform alternating voltage and current from one level to another. At the secondary 

distribution point the voltage is brought down to a level that is suitable for operations. Small power 

transformers sometimes supply power to loads where continuity of service is critical and therefore a 

greater degree of attention is justified. While the percentage of transformer failures is low, failures that 

do occur are serious and result in extensive downtime and expense. The best assurance of continued high 

reliability is regular maintenance procedures. Transformers require very little attention when compared to 

most electrical apparatus. For a complete description of transformers see chapter 3. 

4-4. Power line conditioners 

Power line conditioning is often used to improve the quality of power for special applications such as 

computers. Although it is difficult to make any generalizations concerning the benefits that accrue from 

the use of line protective equipment, it has been estimated that clean power versus that taken directly from 

the “average” power line reduces load equipment outages by 40 percent and maintenance costs by 25 

percent. The choice to use protective equipment is both an economic and technical consideration. 
TM 5-692-2 

4-2 

 a. Isolation transformers. Isolation transformers are primarily intended to attenuate common-mode 

impulses. Some types also provide limited attenuation of normal mode impulses. Isolation transformers 

perform no voltage regulating function. Sags, surges, under voltages, or over voltages will be reproduced 

faithfully on the transformer secondary. If the power line voltage is consistently stable and highfrequency impulses or noise is the only problem, then a suitable isolation transformer may eliminate 

power line disturbance difficulties. 

 b. Line voltage regulators. Line voltage regulators do exactly what the name implies – their purpose 

is to maintain reasonably constant output voltage to the load in the face of variations in power line 

voltage. There are many different ways of accomplishing this and among the basic types there are 

innumerable variations, all with their own advantages and limitations. 

 c. Line conditioners. Line conditioners combine the functions of isolation transformers and line 

voltage regulators and thus both attenuate impulses and regulate output voltage. For this reason, a line 

conditioner can protect against the principal types of power line disturbances except for voltage dropouts 

and line interruptions. It is possible to create a line conditioner by placing separate voltage regulators and 

isolation transformers in series. Properly matching the two can be tricky, and the package is bulkier and 

generally more expensive than using a single unit designed to perform the total line conditioning function. 

 d. Motor-generator sets. Motor-generator sets consist of a motor driving an AC generator or 

alternator so that the load is completely electrically isolated from the power line. In the past, direct 

current (DC) or induction drive motors were used requiring close speed control to maintain stable 

frequency to the load. The tendency nowadays is to use synduction or synchronous motors. The 

synduction motor resembles an induction motor but runs at synchronous speed. With either of these unit 

types, alternator speed and thus frequency to the load is as stable as power line frequency. Motorgenerator sets have been widely used to supply 415 hertz power to the mainframe computers which 

require this frequency, but recently there has been a substantial shift to the use of solid-state inverters. 

 e. Uninterruptible power supplies. If continuous operation is necessary during a line voltage 

interruption lasting more than a half second or so, then an uninterruptible power supply (UPS) is required. 

 The basic UPS consists of a rectifier/battery charger that takes AC line power of the proper voltage and 

frequency, a battery bank that takes the place of the rectified DC power source if line power fails, and an 

inverter that, with suitable filtering, converts the DC power back into a sinusoidal waveform. UPS 

systems are complex, expensive, somewhat inefficient, have a high output impedance, and frequently 

require special installation facilities and increased air-conditioning capacity to dissipate the heat. The 

proper UPS will protect the load equipment from all types of power line disturbances. UPS systems are 

further described in chapter 5. 

 f. Magnetic synthesizer. The magnetic synthesizer is a static EM three-phase AC power regenerator. 

The device, powered from the AC utility line, uses no mechanically moving parts in the generation 

process, and utilizes no semi-conductor elements in the power path. The output waveform of the device 

is EM generated, and is completed isolated and independent of the input in all parameters except two: the 

phase rotation and the frequency. The output phase rotation of the device is governed by the direction of 

the input phase rotation, while the output frequency is precisely keyed to the input line frequency. There 

is no electrical connection between the input and the output of the device. The improved quality of power 

results from the synthesis of three-phase 60 hertz voltage waveforms which remain essentially constant in 

magnitude and shape over a large range of input voltage excursions in both the positive direction (surges) 

and the negative directions (sags). The device consists solely of saturable iron core reactors and 

transformers, together with capacitors, and employs the principles of ferro-resonance for its operation. 
TM 5-692-2 

4-3 

4-5. Motor control centers 

Motor control center (MCC) is the term given to a grouping of motor starters within a large enclosure. 

MCCs are used where several motors are to be operated from a single location. The starters themselves 

may be magnetic across-the-line starters or other types. A typical use would be in a boiler control room 

where the various fan, pump, conveyer, and other motors serving the boiler are all controlled from a 

central location 

a. Construction. MCCs utilize plug-in type circuit breakers and combination starters in either a front 

only or a back-to-back freestanding construction, depending on space limitations. Main bus, starters, and 

breakers are braced to withstand a short circuit current of at least 22 kA, symmetrical. A power panel 

transformer and feeder breaker complete with a 120/208 volt power panel and its own main breaker may 

be built into the MCC. 

b. Location. MCCs are strategically located to serve most of the motor loads, lighting transformers, 

motor operated devices, welding receptacles, and the like. Loads are grouped in such a manner as to 

result in relatively short feeder runs from the centers, and also to facilitate alternate power sources to vital 

services. 

c. Connections. Connections to the MCCs are usually via overhead cable tray, and thus the top 

horizontal section of the MCC incorporates ample cable training space. Control and power leads 

terminate in each compartment. MCCs can be designed with all external connections brought by the 

manufacturer to terminal blocks in the top or bottom horizontal compartments. 

4-6. Protective devices, fuses, and circuit breakers 

Design of power system protection requires the proper application of overload relays, fuses, circuit 

breakers, protective relays, and other special purpose overcurrent protective devices. 

 a. Thermal overload relays. The most common overcurrent protective device is the thermal overload relay associated with motor starting contactors. Thermal overload relays detect motor overcurrents 

by converting the current to heat via a resistive element. Thermal overload relays are simple, rugged, 

inexpensive, and provide very effective motor running overcurrent protection. Also, if the motor and 

overload elements are located in the same ambient, the thermal overload relay is responsive to changes in 

ambient temperature. The relay trip current is reduced in a high ambient and increased in a low ambient. 

The thermal overload relay combines with the short-circuit device to provide total over-current protection 

(overload and short-circuit) for the motor circuit. 

 b. Magnetic current overload relays. Basically, magnetic current relays are solenoids. These relays 

operate magnetically in response to an over-current. When the relay operates, a plunger is pulled upward 

into the coil until it is stopped by an insulated trip pin that operates a set of contacts. Magnetic relays are 

unaffected by changes in ambient temperature. Magnetic current relays may be used to protect motors 

with long starting times or unusual duty cycles, but are not an alternative for thermal relays. 

c. Fuses. A fuse is a non-adjustable, direct acting, single-phase device that responds to both the 

magnitude and duration of current flowing through it. Fuses may be time delay or non-time delay, 

current-limiting or non-current-limiting, low-voltage or high-voltage. 
TM 5-692-2 

4-4 

d. Circuit breakers. A circuit breaker is a device that allows automatic opening of a circuit in 

response to overcurrent, and also manual opening and closing of a circuit. Low-voltage circuit breakers 

are classified as molded-case circuit breakers or power circuit breakers. A molded-case circuit breaker is 

an integral unit enclosed in an insulated housing. A power circuit breaker is designed for use on circuits 

rated 1000 Vac and 3000 Vdc and below, excluding molded-case circuit breakers. Molded-case circuit 

breakers have traditionally been used in panelboards or load centers where they are fixed-mounted and 

accessible. Low-voltage power circuit breakers, on the other hand, are traditionally used in industrial 

plants and installed in metal-enclosed assemblies. All power circuit breakers are now of the drawout-type 

construction, mounted in metal clad switch-gear. Low-voltage circuit breaker trip units may be of the 

electromechanical (thermal-magnetic or mechanical dashpot) or solid-state electronic type. Low-voltage 

circuit breakers may include a number of trip unit characteristics. These characteristics include long-time 

pick-up, long-time delay, short-time pick-up, short-time delay, instantaneous pick-up, ground-fault pickup, and ground-fault delay. The continuous current rating may be fixed or adjustable. Molded-case 

breakers with solid-state trips and power breakers normally have adjustable long-time and short-time 

functions. Most molded-case circuit breakers, especially in the smaller sizes, are not provided with longtime adjustments, short-time functions, or ground-fault functions. 

 (1) The inverse-time (or thermal-magnetic) circuit breaker contains a thermal and a magnetic 

element in series and is similar in operation to time delay fuses. This circuit breaker will trip thermally in 

response to overload currents and magnetically in response to short-circuit currents. Magnetic tripping is 

instantaneous while thermal tripping exhibits an inverse-time characteristic (i.e., the circuit breaker 

operating characteristics of time and current are inversely proportional). Inverse-time circuit breakers 

have three basic current ratings: trip rating, frame rating, and interrupting rating. Trip rating is the 

minimum continuous current magnitude required to trip the circuit breaker thermally. The frame rating 

identifies a particular group of circuit breakers and corresponds to the largest trip rating within the group. 

Each group consists of physically interchangeable circuit breakers with different trip ratings. The 

interrupting rating describes the short-circuit withstand capability of a circuit breaker. 

 (2) The instantaneous-trip circuit breaker is nothing more than an inverse-time circuit breaker with 

the thermal element removed and is similar in operation to the non-time delay fuse. This circuit breaker is 

often referred to by other names, such as, magnetic circuit breaker, magnetic-only circuit breaker, or 

motor circuit breaker. Instantaneous-trip circuit breakers may be used in motor circuits, but only if 

adjustable, and if part of a circuit breaker type, combination motor controller with overload relays. Such 

an arrangement is called a Motor Circuit Protector (MCP) and provides short-circuit protection (circuit 

breaker magnetic element), overload protection (overload relays), motor control, and disconnecting means 

all in one assembly. Instantaneous-trip circuit breakers have frame and interrupting ratings but do not 

have trip ratings. They do have an instantaneous current rating which, for motor circuits, must be 

adjustable. 

e. Protective relays. Protective relays are classified according to their function, and there are a wide 

variety of protective relays available. The overcurrent relay, for example, monitors current and operates 

when the current magnitude exceeds a preset value. Other types of protective relays provide protection 

for other abnormal conditions such as overvoltage or ground faults. 

4-7. Switches 
TM 5-692-2 

4-5 

Switches are devices that typically isolate equipment from its main source of power. Large sectionalizing 

switches are used in substations as described in chapter 3. Control switches are used in lower voltage 

applications to stop and start motors, turn on lights, and to switch from one source of power to another 

source of power. Several switches may be required within the control circuit of a major component 

depending on the complexity. These may be a local switch at the device or area, a main control switch 

used for remote operation located at a main facility console, and an auxiliary switch located in another 

remote location used for emergency or abnormal operation. 

4-8. Feeder cables 

Feeder cables are generally defined as those cables providing the main source of power to a motor control 

center, panelboard, or motor. Power cables are generally made up of three components: conductor, 

insulation and protective covering. The single most important component of a cable is its insulation. The 

best way to ensure continued reliability of a power cable is through visual inspection and electrical testing 

of its insulation. They are sized based on the current requirements of the load, the distance from the 

source of power, and the short circuit withstand capability of the load. The cable sizing may also 

consider such factors as environmental conditions, location, and raceway fill. Power cables will generally 

be run in galvanized rigid steel conduit to the termination points. Distribution feeders installed in 

underground conduits and ducts inherit the highest degree of reliability/availability.

4-9. Controls 

Electric control is a method of using low voltages (typically, 24 Vac) or line voltages (110 Vac) to 

measure values and effect changes in controlled variables. Electronic controls use solid-state, electronic 

components used for measurement and amplification of measured signals and the generation of 

proportional control signals. Common duties of electrical control systems include performing automatic 

functions, monitoring equipment status, indicating trouble conditions, recording events, generating 

reports, and indicating maintenance functions. 
TM 5-692-2 

5-1 

CHAPTER 5 

UNINTERRUPTIBLE POWER SUPPLY SYSTEM

5-1. General 

An uninterruptible power supply (UPS) system is designed to provide conditioned power which offsets 

the effects of adverse normal power. There are two types of static UPS - line interactive and true on-line 

double conversion. A static UPS usually consists of a battery to provide continuous source of electrical 

power; a rectifier/charger to maintain battery charge and to provide input to inverter when utility power is 

available; an inverter to provide power to load during normal operation; a static switch to transfer load 

automatically and without disturbance between inverter and utility power; a manual switch to bypass the 

static switch for maintenance; input and output isolation transformers and filters to provide appropriate 

isolation and disturbance attenuation; and monitors, sensors, and control circuits. A flywheel driven 

rotary UPS is used for applications requiring ride-through of short duration power system outages, 

voltage dips, etc. The flywheel driven rotary UPS typically does not include batteries, and support times 

are usually on the order of a few seconds to a few minutes. The use of a generator driven rotary UPS 

(motor generator or M-G) can provide extended power for an indefinite power outage and also supply airconditioning and lighting loads. 

5-2. Battery and battery charger 

Battery power is a group of electro-chemical cells interconnected to supply a nominal voltage of direct 

current (DC) power to a suitable connected electrical load. The number of cells connected in series 

determines the nominal voltage rating of the battery is the basic factor that determines the discharge 

capacity rating of the entire battery. 

 a. Storage battery. The storage battery is constructed of a group of identically sized cells connected 

in series. The number of cells connected in series determines the voltage rating of the battery. The 

discharge capacity of the battery is basically its ability to supply a given current for a given period of time 

at a given initial cell temperature while maintaining voltage above a given minimum value. This capacity 

is stated in amperes normally abbreviated as A, at a given discharge rate. Most stationary battery cells are 

rated for 8-hour, 3-hour, 1-hour, 15-minute discharge rates to 1.75 volts per cell. 

 (1) Lead-acid cells are by far the most popular type of secondary cell. Properly sized, installed, 

and maintained, a stationary battery using lead-acid cells can have a life expectancy of 15 to 20 years in 

stationary applications, depending upon plate design, relationship between cell capacity and load demand, 

cycling, care during installation, maintenance, control of discharges and recharges, and site environmental 

conditions. 

 (2) Nickel-cadmium batteries are increasingly applied to emergency lighting and other standby 

service. The active materials are nickel hydroxide in the positive plate and cadmium oxide in the 

negative. No gases are generated during discharge, and the gases given off during charging are not 

corrosive. Initial cost of nickel-cadmium batteries is higher than lead-acid on an ampere-hour (Ah) basis. 

 However, at short rates of discharge, from 90 minutes down to 30 minutes the nickel-cadmium battery 

discharges a greater percentage of its capacity than does the lead-acid. This high discharge feature is even 

more important at extreme rates of discharge. In some applications the Ah capacity of a lead-acid battery 

must be twice the Ah capacity of a nickel-cadmium battery to do the same job. 
TM 5-692-2 

5-2 

 b. Charger. The combination of the charger and the battery becomes a system when it is connected to 

an electrical load. The load is the equipment that draws DC power from the charger and/or battery. The 

charger-battery load combination is most efficient only when all of the components are properly matched 

to each other. The charger converts alternating current (AC) power into DC power that is compatible 

with the battery’s voltage and current characteristics. The charger is the converter section of the UPS 

which charges the batteries and supplies DC to the inverter. 

 c. Floating systems. When the charger and battery are connected permanently to each other and to the 

load, and the charger regulates the voltage supplied to the load and the battery, the system is known as a 

floating battery system. The battery in such systems is mounted normally on a rack or racks housed 

inside a building or enclosure. The load in this case is the inverter. 

 d. Rectifier systems. The rectifier configuration differs from the float configuration with a rectifier, 

usually a regulated rectifier, replacing the rectifier/charger. The rectifier is used only to provide power to 

the inverter and is not used to charge the battery. A blocking diode or thyristor is used to isolate the 

rectifier from the battery. A separate battery charger is used to maintain the batteries in a fully charged 

state. 

 e. Electrolyte. The battery electrolyte is a liquid solution of dilute sulfuric acid in which the battery 

element is immersed for the lifetime of the cell. The ratio of acid weight to water is measured as specific 

gravity. Pure water has a specific gravity of 1.000. The quantity of electrolyte in a cell is specified in 

pounds, kilograms, gallons, or liters. Acid electrolyte recommended for most stationary batteries has a 

nominal specific gravity of 1.215 at 77°F (25°C), when the cell is fully charged. The specific gravity of 

acid electrolyte gradually drops as the cell is discharged. When the charger resumes operation after a 

discharge period, the charging process gradually raises the restores the specific gravity of the electrolyte. 

 f. Loads. Specification of the charger and the lead-acid battery depends on the DC load. Each single 

item of electrical equipment that will be powered by the stationary battery system must be analyzed. 

Pertinent data required for each item of the load includes: voltage range (window); current or kW draw; 

duration of operation (time); number of cycles; frequency of use; depth of discharge; and operating 

temperature range. After this data has been compiled, the battery and charger can be sized and specified. 

 g. Environmental conditions. Environmental conditions and location must also be considered when 

specifying the battery. Normally storage batteries are sized to perform at 77°F (25°C), but allowance 

must be made in the calculations for lower temperatures that require more capacity to meet the load 

criteria. Freezing of the electrolyte results in water crystals forming, but a solid mass is seldom formed. 

Such crystals damage the plates resulting in reduced life. The charger and UPS performance are 

adversely affected by altitudes higher than 3,300 feet (approximately 1,000 meters) above sea level or 

ambient temperatures above 105°F (40°C). Compensations for these factors can be designed into the 

lead-acid battery system. 

 h. Effects of temperature. Battery capacity is reduced when battery room temperature is normally 

lower than 77°F (25°C). Battery life expectancy is shortened when the battery room temperature is 

consistently higher than 85°F (29°C). 

i. Hydrogen gas evolution. During the charging and discharging process of battery operation, 

hydrogen gas is formed. Hydrogen gas is very explosive when exposed to open flames, sparks, and 

cigarettes. The room in which the battery is located should be provided with ventilation, so as to prevent 

liberated hydrogen gas. Significant amounts of hydrogen are evolved only as the battery approaches full 

charge. 
TM 5-692-2 

5-3 

When the cell is fully charged each charging ampere produces 0.016 cubic feet (.0000453 cu m) per hour 

from each cell. This volume applies at seal level when the ambient temperature is 77°F (25°C). 

j. Monitoring systems. Continuous battery monitoring equipment is available which is used in 

conjunction with a battery charging system. These systems can monitor float charge rate, voltage levels 

of individual cells or the complete bank, monitor liquid level and adjust charge cycle and rate of charge. 

5-3. Inverter 

The inverter provides three primary functions in the UPS. Inversion is the changing of the DC power to 

AC power composed of a sine wave free from harmful harmonic distortion [typically 5% total harmonic 

distortion (THD) or less]. The inverter also provides regulation of the AC voltage to a tolerance level 

acceptable to the load, typically +2 percent of the nominal voltage. Finally, current-limiting capability is 

provided by the inverter as a means of self-protection. The inverter used in a C4ISR facility shall be 

capable of supplying an inrush current of 7 times rated output current without damage or failure to 

operate. 

a. Inversion technologies. In the world of industrial inverters, two inversion technologies dominate: 

these are ferroresonant and Pulse Width Modulation (PWM). 

 (1) PWM inverters synthesize a sinusoidal output waveform from a constant height, variable width 

high frequency pulse stream. The pulse stream is stripped of its high frequency carrier (20-50 kHz) by a 

low-pass filter and reduced to a 120 Vac level through a linear power transformer. 

 (a) The PWM inverter configuration is referred to as an active regulator. Voltage and current 

feedback loops gather downstream information and deliver it to a microprocessor based control circuit 

through a series of amplifiers. The bridge circuit in modern PWM technology normally uses insulated 

gate bipolar transistors (IGBT) for power switching, although, silicon controlled rectifiers (SCR) could be 

used in high capacity, lower frequency applications. The IGBT bridge generates a positive and negative 

pulse train at approximately 3 to 6 kHz. The width of the pulses vary from narrow to wide and back to 

narrow in each half cycle; this pulse width being proportional to the transistor on-time and to the 

equivalent root mean square (RMS) AC voltage at that moment in time. The control circuit adjusts the 

transistor conduction time based on the information received from the voltage and current feedback loops 

to maintain output regulation. The driver network is a parallel power or darlington transistor array. The 

positive and negative pulse train is then coupled from primary to secondary of a linear output transformer. 

 A small (line-commutated) LC filter with harmonic traps removes the odd order harmonics from the 

pulse train to create a sine wave. 

 (b) PWM inverters offer many advantages when used in computer room applications, 

including high efficiency due to the use of IGBTs and a linear output transformer, small physical size, 

low cost, and rapid response to transient load changes. 

 (c) Disadvantages include limited fault and short circuit current availability (due to the output 

transformer being linear, a downstream short will be felt on the primary and subsequently the IGBTs; the 

inverter will shut down to protect the transistors), complex circuitry, high parts count, and intolerance to 

environmental extremes. These items can contribute to lower long-term system reliability, which is a 

major concern in an industrial facility, based on user philosophy and load architecture. When used in a 

computer room application, the advantages outweigh the disadvantages because size, cost, and heat 

dissipation are more critical issues than long term reliability, primarily due to the relatively short useful 

life of the computer equipment itself. 
TM 5-692-2 

5-4 

 (2) Ferroresonant inverters do not use linear magnetics. A line frequency square wave developed 

by the switch bridge is filtered into a sinusoidal wave shape by means of the non-linear actions of a 

saturated, resonant secondary winding. The peak current demanded by a non-linear load is supplied by 

the storage energy in the saturated secondary. The load current is not coupled to the switching bridge. 

The secondary winding also contains harmonic traps tuned to the 3rd and 5th harmonic. Ferroresonant 

inverters are uniquely compatible with switch-mode power supplies and do not have to be oversized to 

provide proper operation. 

 (a) Ferroresonant inverters are often referred to as passive regulators. Instead of using active 

feedback and control, regulation and current limiting are an inherent characteristic of the transformer 

design. The ferroresonant transformer (sometimes referred to as a regulating or constant voltage 

transformer) is the heart of the ferro inverter. The integrity of the transformer design and quality control 

associated with its manufacturer have a direct impact on inverter performance and reliability. 

 (b) The control and bridge circuits in the ferroresonant inverter consist of a simple square 

wave generator, traditionally using SCRs, however, some designs now incorporate IGBTs. This square 

wave is then driven into the primary of the ferroresonant transformer. The ferroresonant transformer is 

nonlinear, designed to operate in the saturation range of its operating curve. The square wave produced 

by the bridge saturates the transformer core, therefore, the resultant leakage reactance rounds off the 

comers during coupling from primary to secondary, creating a “pseudo sine wave.” A tuned LC circuit is 

then employed to maintain the transformer in a resonant state. Harmonic traps are designed to limit the 

3rd, 5th, 7th, etc. odd order harmonics resulting in a distortion free sine wave. A compensation winding 

is used to tighten the regulation of the transformer. 

 (c) The primary disadvantage of ferroresonant technology is size and weight, and to some 

extent cost in the higher power ranges. This is due to the mass of the ferroresonant transformer itself. 

Historically, criticism has also involved audible noise and efficiency, although the new generation IGBT 

inverters have bridged that gap tremendously. 

 (d) Low parts count, hence, inherent high reliability and ease of maintenance make 

ferroresonant inverters a good choice for industrial applications. In addition, the tuned circuit in the 

transformer secondary stores energy that can be tapped into for downstream fault clearing (most industrial 

ferroresonant inverters can deliver 500 percent of their rating for I cycle prior to current limit). This 

energy can also be used to meet the demand for non-linear current, resulting in lower distortion in the 

output waveform when the loads are predominately non-linear. Since the transformer is a current limiting 

device, it can continue to run when connected to a bolted short circuit. In summary, the transformer can 

tolerate a great deal of abuse, both operationally and environmentally without degradation in 

performance. 

b. Harmonic considerations. Reflected harmonic current from non-linear loads can cause problems 

for three-phase inverters. Theoretically, in a balanced three-phase system the neutral current should be 

zero, however, non-linear loads can induce current in the neutral due to reflected harmonic current 

(primarily 3rd 5th, 7th, and 11th harmonic) even if the phase current appears balanced. This coupled with 

the high impedance of the inverter can cause voltage distortion in the output waveform. This effect can 

be significantly reduced through the use of a Scott-Tee output connection rather than a wye because the 

triplen harmonics are in phase with one another and effectively cancelled, eliminating the 3rd harmonic as 

a problem. 
TM 5-692-2 

5-5 

5-4. Transfer switches

UPS transfer switches are often the static interrupter type unless the manufacturer’s standard product 

incorporates the use of circuit breakers necessary for protection and isolation purposes. These breakers or 

switches are controlled by logic circuits in the UPS inverters or by other circuits included in a common 

control cabinet or panel. Signals so derived cause closing of the static transfer switch when the 

monitoring circuits sense the failure of the inverter output or when the UPS module is driven into the 

“current limit” mode of operation for a preset period of time. Switching speeds as fast as 2 milliseconds 

are obtainable in standard products of major manufacturers of UPS equipment. UPS systems also usually 

incorporate a maintenance bypass switch (or breaker) with a make-before-break feature to allow 

preventative maintenance to be performed on the UPS. 

5-5. Instrumentation 

Instrumentation provided with the UPS usually includes a local status panel mounted on the UPS enclosure 

and a remote status panel which duplicates the LED status indicators and switches on the local status panel. 

5-6. Motor generator design features 

Standard motor generator sets usually provide a ride through of a transient condition for no more than 15 

to 30 cycles depending on the load and the mechanical limitations of the motor generator. Usually the 

limitation is the ability to maintain an output frequency within the tolerance on the load. The Roesel 

Motor Generator (RMG) is a continuous duty device that provides essential electrical loads with a 

continuous source of clean, regulated, and isolated 60 cycle power. When a loss or variation of input 

utility power occurs, the motor-generator continues to supply constant frequency 60 cycle power for a 

minimum of 15 seconds with full rated load on the unit. At reduced loads it will supply power for up to 

45 seconds. When the duration of the power failure is more than 15 seconds or up to 45 seconds at 

reduced load, the system automatically restarts itself and resumes normal operation when power is 

restored. 

a. Construction. The RMG is built as an inverted structure, i.e., the stator is the stationary inner 

portion with the rotor rotating around it. This provides the best method of obtaining the maximum 

amount of stored mechanical energy with the least weight in the rotor itself. Exciter coils located on the 

stator "print" poles on the ferrite lining of the rotor. This is achieved when the exciter heads receive a 

signal from the generator control and magnetize or re-magnetize the layer of permanent magnet material 

on the inside rotor surface. The resulting pole pattern is constant in poles per second and thus produces a 

constant output frequency regardless of rotor speed. The rotor's flywheel effect extends ride-through time 

from 15 to 45 seconds depending on load. This allows the RMG to provide rated output voltage and 

frequency independent of the rotor speed during a loss or variation of utility input power. The RMG 

provides 15 to 45 seconds of ride-through protection for sensitive loads during voltage disturbances. This 

is ideal where outages are infrequent and protection against voltage sags is a main concern. The duration 

of most voltage sags is typically between 10 and 20 cycles (60 cycles = 1 second). 

 b. Advantages. The RMG eliminates the need for costly battery plants [required by conventional 

uninterruptible power supply (UPS) devices] and associated maintenance, space, ventilation, and 

environmental concerns, etc. The RMG also eliminates the need for costly power conditioning equipment 

and establishes a separately derived electrical source for protection of sensitive electronic end-user loads 

such as computer workstations, file servers, data centers, telecommunication systems, and other critical 
TM 5-692-2 

5-6 

loads. Finally, the RMG provides total isolation from voltage transients and electrical noise produced by 

disturbing loads within the facility. It also provides total isolation from interference caused by harmonics 

(those produced by the protected load and those produced from other loads in the facility). 

c. Disadvantages. The problems with motor generators are mostly on the output or load side. Very 

high alternator output impedance can cause substantial voltage dips in response to sudden load changes 

such as result from large inrush motor starting current, and response to load changes is sluggish in the 

range of 0.25 to 0.5 seconds. Also, the drive motor may overheat under long term brownout or low line 

voltage conditions. Motor generator efficiency is relatively low at about 80 percent, so that electrical 

energy costs over its lifetime may be substantial. Heat dissipation, weight and bulk, and the potential for 

annoying audible noise are factors that must be considered in motor generator installation. The use of 

rotating field exciters has eliminated the need for slip rings, with the consequent brush inspection and 

replacement, but as with any rotating equipment, bearings must be inspected and periodically replaced. 

5-7. Operational considerations 

Operational considerations are another key factor in UPS selection. Efficiency and reliability often 

depend on the type of unit, the load, and the environment. The higher a unit's efficiency, the lower the 

operating cost. 

a. Noise. Noise emitted by an UPS can be a factor, depending on the surrounding environment. In 

most cases, UPSs placed in computer centers, control rooms, or office-type environments need to operate 

as quietly as possible. Noise levels vary according to the type of system. UPS manufacturers' 

specifications generally include noise-level data. 

b. Load types. The type of load being protected is an important consideration, too. Microprocessorbased equipment may require a different type of UPS unit than other loads. For example, switching 

power supplies, found in most computers, react differently to certain types of UPS systems. Today's UPS 

units should be capable of supplying non-linear type loads without derating or degradation in total 

harmonic distortion. Load size determines what size UPS is needed. Systems usually are sized in 

kilovolt-ampere ratings. Before selecting UPS capacity, a profile of critical electrical loads should be 

computed, listing the power requirements of each piece of equipment to be protected. Most UPS 

manufacturers also recommend allowing for a 25 to 30 percent future expansion factor. Systems 

generally are available in both single-phase and three-phase models to suit the application. 

c. Application. Consideration should be placed on the application of the UPS. Computer-room UPS 

components are more densely packaged to create a smaller footprint. Many times, isolation transformers 

are removed from the front end of a computer type UPS rectifier/battery charger. Although this usually is 

acceptable in most office/computer-room environments, it can be a problem in an industrial facility due to 

the presence of large equipment that may cause disturbances during starting. 
TM 5-692-2 

6-1

CHAPTER 6 

ELECTRICAL CONTROLS 

 

6-1. General electrical controls

Automation of facilities, along with technically advanced control equipment capabilities, have driven 

extensive use of sophisticated electrical control systems. Control systems, such as those associated with 

building automation, process control, and electrical system controls, are being relied on to maintain the 

integrity of site operations and missions. Common duties of electrical control systems include performing 

automatic functions; monitoring equipment status; indicating trouble conditions; recording events; 

generating reports; and indicating maintenance functions. 

6-2. Major components of an electrical control system 

Controls are broadly defined as the methods and means of governing the performance of any electric 

apparatus, machine, or system by sensing any need for a change and facilitating that change. In 

performing these duties, control circuits or systems may act to regulate, protect, indicate, open, close, or 

time an operation. Control devices execute control functions. Some of the more common control devices 

are switches, push buttons, circuit breakers, contactors, lights, rheostats, timers, alarms, batteries, coils, 

fuses, relays, solenoids, surge capacitors, lightning arresters, and transformers. Other special electrical 

equipment may be used also. 

a. Generator controls. Switchgear and related control panels contain complete controls for all 

functions of the auxiliary generator equipment. Control for voltage regulation; phase adjustment; current 

compensation; engine operating parameters as well as engine start, stop, and running speed; battery 

charging; and brightness or dimming of indicator lights are usually provided. 

b. Indicating devices. White indicating lamps with colored caps are used to show breaker positions. 

Green lights indicate open breakers; red lights indicate closed breakers. White lights, when used, are 

energized from potential transformers to indicate live circuits. Some stations include amber or orange 

lights to indicate that the circuit has been tripped automatically. Low voltage lamps, connected in series 

with appropriate resistors, are usually used to reduce lamp size and glare. Red and green lights are 

usually wired so that they are energized through the trip coil of the breaker. An opening in the trip coil 

circuit is indicated by a dark unlit lamp. Similar indicating lamps and colored caps are used to indicate 

normal and abnormal conditions for other control functions of the system. 

c. Device characteristics. Electromechanical controls are operated by magnets, thermal action, 

motors, or other mechanical or static actions. Solid-state controls perform similar functions to 

electromechanical controls, but their characteristics are affected to a much greater degree by ambient 

temperature changes and excessive electrical circuit parameters. 

d. Power sources. Control equipment may be powered from storage batteries or from an alternating 

current (AC) source. Controls will only be as dependable as their operating input. The power supply 

must be as reliable as possible, so that control and protection of the equipment is not jeopardized. 
TM 5-692-2 

6-2

e. Electronic loop controls. Pneumatic and electromagnetic (EM) controls are gradually being 

replaced by electronic loop controls, as systems are increasingly being incorporated into energy 

management control systems (EMCS) or supervisory control and data acquisition systems (SCADA). 

Sensors are used to provide units of information via conventional (hard) wiring to the field interface 

devices (FID). A sensor is installed as a component part of the electrical apparatus being controlled and 

must be maintained by electrical maintenance personnel. Control line components such as FIDs, data 

transmission links, the central processing unit (CPU), and its subcomponents are not electrical 

maintenance responsibilities. Communications lines are used, such as telephone pairs; coaxial cable; 

radio, micro-wave or power line carrier signals; and fiber optics, sometimes as a part of a local area 

network (LAN). 

f. Relays. A relay is an electrical device designed to interpret input data in a prescribed manner. 

When specific input conditions occur, the relay responds to cause contact operation or a similar sudden 

change in associated electric control circuits. Input data analyzed is usually electrical, but may be 

mechanical or thermal, or evaluate other conditions or a combination of conditions. Electrical conditions 

can be overcurrent, overvoltage or undervoltage, a combination of current and voltage, current balance, 

direction of current flow, frequency, impedance, or other electrical data. 

(1) Electric power apparatus relays and relay systems are designed to operate circuit breakers and 

contactors, usually medium-voltage units. Electric power apparatus relays operate to quickly sense 

problems and speedily isolate power systems under fault conditions. Such an action limits the extent of 

electrical equipment damage and provides a means to limit outage periods. 

(2) Industrial control relays are designed primarily for industrial control, for switching of 

communication or other low-level signals, or for any other equipment not controlling electric power 

apparatus. 

(3) Relays can be classified by functions, input operating principals, and performance 

characteristics. American National Standards Institute/Institute of Electrical and Electronic Engineers 

(ANSI/IEEE) C37.90, Standard for Relays and Relay Systems Associated with Electric Power Apparatus 

(1994), covers classifications of relays and also standard service conditions, ratings, tests, and 

temperature rise. 

(4) Relays are classified according to their primary purposes, which are protective, regulating, 

monitoring, programming, and auxiliary control. Some relays may qualify for more than one 

classification, depending on their application. Input relays are classified as such because the relay 

responds to a signal input of either voltage or current. Relays are also classified in accordance to their 

operating principles or structural features, such as electromechanical or solid-state types. 

g. Relay functions. Relays are selected to perform certain functions. To standardize on reference use, 

they are given device function numbers by ANSI/IEEE C37.2, Standard Electrical Power System Device 

Function Numbers and Contact Designations (1996). (Device function numbers also describe other 

electrical power apparatus equipment in addition to relays.) Device function numbers readily identify 

devices in drawings, diagrams, instruction books, publications, and specifications. The use of “52” for 

circuit breakers, “51” for an AC time overcurrent relay, “65” for a governor, and “86” for a lockout relay 

provide a simple brief AC method of designation of the device’s operational performance. The standard 

also covers suffix letters used for main devices (such as “N” for neutral), actuating qualities (such as “A” 

for amperes), auxiliary devices (such as “CS” for control service), operating device components (such as 

“TC” for trip coil), and auxiliary contact positions (such as “a” and “b”, “aa” and 

“bb”). 
TM 5-692-2 

6-3

 (1) Instantaneous relays act on an EM attraction operating principle wherein a plunger, solenoid, 

hinged armature, or balance beam is pulled into a coil or pole face of an electromagnet. They can be used 

in both AC and direct current (DC) power systems. 

 (2) Time-delay relays act on an EM induction operating principle, whereby torque is developed in 

a movable rotor (disc or cup) which rotates between two faces of an electromagnet. These units can only 

be used in AC circuits. Time overcurrent and time under/overvoltage relays are generally of the disc 

design type, while high-speed overcurrent, directional, differential, and distance relays are more often of 

the cup (cylinder) design type. 

 (3) Solid-state relays are extremely fast in their operation, as they have no moving parts. Other 

advantages are lower burden, high seismic-withstand, and reduced panel space. Many are programmable, 

allowing increased choices of time-current characteristics. There are no formal statistics available, but 

estimates are that 40 to 50 percent of relays sold in 1992 were solid-state units. Today it is estimated that 

85 to 95 percent are the solid-state type. Solid-state relays require no preventive maintenance, but they do 

require a periodic maintenance check. 

 (4) Protective relays detect, isolate, and/or indicate abnormal electrical conditions. The operation 

of circuit breakers or other protective devices is initiated by relays as required. Some of the electrical 

hazards protected against are short circuit, overcurrent, overvoltage, undervoltage, and phase or frequency 

irregularities. Relays installed to protect generator stator windings from internal shorts and overheating 

are sensitive to faults in the generator and do not respond to faults outside the generator. These relays act 

rapidly to prevent damage to the generator and isolate the generator from the system. Relay action 

includes de-energizing the generator field winding. Protective relays are provided in systems when 

reverse power flow occurs. Those relays operate on a succession of power reversals and current impulses 

to detect loss of synchronism. 
TM 5-692-2 

7-1 

CHAPTER 7 

GENERATORS 

7-1. Generator usage

Electric generators are devices that convert energy from a mechanical form to an electrical form. This 

process, known as electromechanical energy conversion, involves magnetic fields that act as an 

intermediate medium. 

a. Generator types. There are two types of generators: alternating current (AC) and direct current 

(DC). A generator may provide electrical power as the primary power source, standby power source, or 

emergency power source. It may be part of the primary electrical distribution system (above 600 volts) or 

part of the secondary distribution system (600 volts and below). 

b. Energy conversion. The generator provides electrical power through the introduction of 

mechanical energy to a prime mover that takes this mechanical energy and converts it to electrical energy. 

 Power companies accomplish this by using fossil and/or nuclear power to drive the prime mover. Large 

industrial sites can use their waste exhaust for such purposes. In addition, geothermal and wind turbines 

can also accomplish the same goal. However, for most Command, Control, Communications, Computers, 

Intelligence, Surveillance, and Reconnaissance (C4ISR) sites, diesel powered generators will supply 

electricity on demand when local power is not available. The less volatile diesel fuel feeds the diesel 

engine that drives the prime mover. As the prime mover rotates, it drives the generator rotor causing 

magnetic lines of force to be cut by electrical conductors. Electrical energy is thereby produced by 

electromagnetic (EM) induction. 

c. Power generation. The generator’s operation is based on Faraday’s law of EM induction. In brief, 

if a coil (or winding) is linked to a varying magnetic field, then an electromotive force (EMF) or voltage 

is induced across the coil. Thus, generators have two essential parts: one creates a magnetic field, and 

the other where the EMFs are induced. The magnetic field is typically generated by electromagnets (thus, 

the field intensity can be adjusted for control purposes), whose windings are referred to as field windings 

or field circuits. The coils where the EMFs are induced are called armature windings or armature circuits. 

 One of these two components is stationary (stator), and the other is a rotational part (rotor) driven by an 

external torque. Conceptually, it is immaterial which of the two components is to rotate because, in either 

case, the armature circuits always “see” a varying magnetic field. However, practical considerations lead 

to the common design that for AC generators, the field windings are mounted on the rotor and the 

armature windings on the stator. In contrast, for DC generators, the field windings are on the stator and 

armature on the rotor. 

7-2. Generator operation 

A generator consists of a number of conducting coils and a magnetic field. The coils are called the 

armature. Relative motion between the coils and magnetic field induces voltage in the coils. This action 

is called EMF. An AC generator needs a separate DC source to feed the magnetic field. The required DC 

is provided by an external source called an exciter. Usually, the exciter is a small DC generator that is 

driven by the generator rotor. The exciter may be mounted on the rotor shaft or rotated by belt-drive. 

Some generating systems use a static, solid-state exciter to provide DC. A voltage regulator controls the 
TM 5-692-2

7-2 

induced voltage by regulating the strength of the EM field established by the exciter. Frequency is 

controlled by the speed at which the prime mover rotates the rotor. 

7-3. Generator types 

Depending on the type of generating equipment employed, the electrical energy produced is either DC or 

AC. 

a. AC generators. AC generators are considered either brush or brushless, based on the method used 

to transfer DC exciting current to the generator field. In addition, AC generators are classified as salientpole or nonsalient-pole depending on the configuration of the field poles. Projecting field poles are 

salient-pole units and turbo-type (slotted) field poles are nonsalient-pole units. 

b. DC generators. DC generators are classified as shunt, series, or compound wound. Most DC 

generators are the compound wound type. Shunt generators are usually used as battery chargers and as 

exciters for AC generators. Series generators are sometimes used for street lights. The EMF induced in a 

DC generator coil is alternating. Rectification is needed to direct the flow of current in one direction. The 

generator rotating commutator provides the rectifying action. 

7-4. AC generators 

AC generators are classified as single-phase or polyphase. Variations include three-phase generators used 

as single-phase units by insulating and not using one phase lead. Since the lead is unused, it is not 

brought out to a terminal. The kilowatt rating is reduced from that of the three-phase unit as limited by 

the amount of current carried by a coil. A generator designed only for single-phase operation usually 

does not have coils in all of the armature slots because end coils contribute little to the output voltage and 

increase the coil impedance in the same proportion as any other coil.

a. Single-phase generators. A single-phase generator is usually limited to 25 kW or less and 

generates AC power at a specific utilization voltage. Single-phase alternators are usually used in smaller 

systems. Terminal voltage is usually 120 volts. A variation is the three wire, single-phase alternator has 

three power terminals; one from each end of the armature coil and one from the neutral. Terminal voltage 

is usually 120 volts from the midpoint to either end of the armature coil and 240 volts between the two 

ends. The load is connected between the two outside wires or between either outside wire and neutral, 

depending upon the voltage required by the load. 

b. Polyphase generators. Polyphase generators produce two or more alternating voltages (usually 

two, three, or six phases). Two-phase power is used in only a few localities. Six phase is primarily used 

for operation of rotary converters or large rectifiers. Three-phase alternators are the most widely used for 

power production. Polyphase alternators have capacities from 3 kW to 250,000 kW and voltage from 110 

V to 13,800 V. Two general types of three-phase alternator windings are the delta winding used in three 

wire, three-phase alternators, and the star or wye winding used in four wire, three-phase types. 

c. Damper windings. Damper windings on the rotor stabilize the speed of the AC generator to reduce 

hunting under changing loads. If the speed tends to increase, induction generator action occurs in the 

damper windings. This action places a load on the rotor, tending to slow the machine down. If the speed 

tends to decrease, induction motor action occurs in the damper winding, tending to speed the machine up, 

 The windings are copper bars located in the faces of the rotor pole pieces. Mounted parallel to the rotor 

axis, the bars are connected at each end by a copper ring. 
TM 5-692-2 

7-3 

d. Synchronous generators. AC generators that operate at a speed that is exactly proportional to the 

frequency of the output voltage are synchronous generators. Synchronous generators are usually called 

alternators. Today, most electric power is produced by synchronous generators. Synchronous generators 

rotate at a constant speed, called synchronous speed. This speed is dictated by the operating frequency of 

the system and the machine structure. There are also AC generators that do not necessarily rotate at a 

fixed speed such as those found in windmills (induction generators); these generators, however, account 

for only a very small percentage of today’s generated power. 

 (1) The rotor consists of a winding wrapped around a steel body. A DC current is made to flow in 

the rotor winding (or field winding), and this results in a magnetic field (rotor field). When the rotor is 

made to rotate at a constant speed, the three stationary windings experience a periodically varying 

magnetic field. Thus, EMF is induced across these windings. This EMF is AC and periodic; each period 

corresponds to one revolution of the rotor. Thus, for 60-Hz electricity, the rotor has to rotate at 3600 

revolutions per minute (rpm); this is the synchronous speed of the given machine. Because the windings 

are displaced equally in space from each other (by 120 degrees), the EMF waveform is displaced in time 

by 1/3 of a period. The machine is therefore capable of generating three-phase electricity. The machine 

has two poles since its rotor field resembles that of a bar magnet with a north pole and a south pole. 

(2) When the stator windings are connected to an external (electrical) system to form a closed 

circuit, the steady-state currents in these windings are also periodic. These currents create magnetic fields 

of their own. Each of these fields is pulsating with time because the associated current is AC; however, 

the combination of the three fields is a revolving field. This revolving field arises from the space 

displacements of the windings and the phase differences of their currents. This combined magnetic field 

has two poles and rotates at the same speed and direction as the rotor. In summary, for a loaded 

synchronous (AC) generator operating in a steady state, there are two fields rotating at the same speed: 

one is due to the rotor winding and the other due to the stator windings. 

(3) It is important to observe that the armature circuits are in fact exposed to two rotating fields, 

one of which, the armature field, is caused by and in fact tends to counter the effect of the other, the rotor 

field. The result is that the induced EMF in the armature can be reduced when compared with an 

unloaded machine (i.e., open-circuited stator windings). This phenomenon is referred to as armature 

reaction. The EMF induced in a stator winding completes one period for every pair of north and south 

poles sweeping by; thus, each revolution of the rotor corresponds to two periods of the stator EMFs. If 

the machine is to operate at 60 Hz, then the rotor needs to rotate at 1800 rpm. In general, a p-pole 

machine operating at 60 Hz has a rotor speed of 3600/(p/2) rpm. That is, the lower the number of poles 

is, the higher the rotor speed has to be. In practice, the number of poles is dictated by the mechanical 

system (prime mover) that drives the rotor. 

(4) Steam turbines operate best at a high speed; thus, two- or four-pole machines are suitable. 

Machines driven by hydro turbines usually have more poles. Usually, the stator windings are arranged so 

that the resulting armature field has the same number of poles as the rotor field. In practice, there are 

many possible ways to arrange these windings. Geometry suggests that, at any time instant, equal EMFs 

are induced across the windings of the same phase. If the individual windings are connected in series, 

their EMFs add up to form the phase voltage. 

e. Auxiliary devices. In addition to the basic components of a synchronous generator (rotor, stator, 

and their windings), there are auxiliary devices which help maintain the machine’s operation within 

acceptable limits. Three such devices are mentioned here: governor, damper windings, and excitation 

control system. 

 (1) A governor is to control the mechanical power input Pin . The control is via a feedback loop 
TM 5-692-2

7-4 

where the speed of the rotor is constantly monitored. For instance, if this speed falls behind the 

synchronous speed, the input is insufficient and has to be increased. This is done by opening up the valve 

to increase the steam for turbogenerators or the flow of water through the penstock for hydrogenerators. 

Governors are mechanical systems and therefore have some significant time lags (many seconds) 

compared to other EM phenomena associated with the machine. If the time duration of interest is short, 

the effect of governor can be ignored in the study; that is, Pin is treated as a constant. 

 (2) Damper windings (armortisseur windings) are special conducting bars buried in notches on the 

rotor surface, and the rotor resembles that of a squirrel-cage-rotor induction machine. The damper 

windings provide an additional stabilizing force for the machine when it is perturbed from an equilibrium. 

 As long as the machine is in a steady state, the stator field rotates at the same speed as the rotor, and no 

currents are induced in the damper windings. That is, these windings exhibit no effect on a steady-state 

machine. However, when the speeds of the stator field and the rotor become different (because of a 

disturbance), currents are induced in the damper windings in such a way as to keep the two speeds from 

separating. 

 (3) Modern excitation systems are very fast and quite efficient. An excitation control system is a 

feedback loop that aims at keeping the voltage at machine terminals at a set level. From a system 

viewpoint, the two controllers of excitation and governor action rely on local information (machine’s 

terminal voltage and rotor speed). In other words, they are decentralized controls. For large-scale 

systems, such designs do not always guarantee a desired stable behavior since the effect of 

interconnection is not taken into account in detail. 

f. Induction generators. A three-phase induction machine is similar to a synchronous machine, but 

the former has a much simpler rotor circuit. A typical design of the rotor is the squirrel-cage structure, 

where conducting bars are embedded in the rotor body and shorted out at the ends. When a set of threephase currents (waveforms of equal amplitude, displaced in time by one-third of a period) is applied to the 

stator winding, a rotating magnetic field is produced. Currents are therefore induced in the bars, and their 

resulting magnetic field interacts with the stator field to make the rotor rotate in the same direction. In 

this case, the machine acts as a motor since, in order for the rotor to rotate, energy is drawn from the 

electric power source. 

 (1) When the machine acts as a motor, its rotor can never achieve the same speed as the rotating 

field (this is the synchronous speed) for that would imply no induced currents in the rotor bars. If an 

external mechanical torque is applied to the rotor to drive it beyond the synchronous speed, however, then 

electric energy is pumped to the power grid, and the machine will act as a generator. 

 (2) An advantage of induction generators is their simplicity (no separate field circuit) and 

flexibility in speed. These features make induction machines attractive for applications such as 

windmills. 

 (3) A disadvantage of induction generators is that they are highly inductive. Because the current 

and voltage have very large phase shifts, delivering a moderate amount of power requires an 

unnecessarily high current on the power line. This current can be reduced by connecting capacitors at the 

terminals of the machine. Capacitors have negative reactance; thus, the machine’s inductive reactance 

can be compensated. Such a scheme is known as capacitive compensation. It is ideal to have a 

compensation in which the capacitor and equivalent inductor completely cancel the effect of each other. 

In windmill applications, for example, this faces a great challenge because the varying speed of the rotor 

(as a result of wind speed) implies a varying equivalent inductor. 
TM 5-692-2 

7-5 

7-5. DC generators 

To obtain DC electricity, one may prefer an available AC source with an electronic rectifier circuit. 

Another possibility is to generate DC electricity directly. Although the latter method is becoming 

obsolete, it is still important to understand how a DC generator works. As in the case of AC generators, a 

basic design will be used to explain the essential ideas behind the operation of DC generators. 

a. Basic theory. The stator of the simple machine is a permanent magnet with two poles labeled N 

and S. The rotor is a cylindrical body and has two (insulated) conductors embedded in its surface. At one 

end of the rotor the two conductors are connected to a pair of copper segments; these semicircular 

segments are mounted on the shaft of the rotor. Hence, they rotate together with the rotor. At the other 

end of the rotor, the two conductors are joined to form a coil. Assume that an external torque is applied to 

the shaft so that the rotor rotates at a certain speed. The rotor winding formed by the two conductors 

experiences a periodically varying magnetic field, and hence an EMF is induced across the winding. 

b. Commutation. This voltage periodically alternates in sign, and thus, the situation is conceptually 

the same as the one encountered in AC generators. To make the machine act as a DC source, viewed from 

the terminals, some form of rectification needs be introduced. This function is made possible with the use 

of copper segments and brushes. Each copper segment comes into contact with one brush half of the time 

during each rotor revolution. The placement of the (stationary) brushes guarantees that one brush always 

has positive potential relative to the other. For the chosen direction of rotation, the brush with higher 

potential is the one directly beneath the N-pole. (Should the rotor rotate in the reverse direction, the 

opposite is true.) Thus, the brushes can serve as the terminals of the DC source. In electric machinery, 

the rectifying action of the copper segments and brushes is referred to as commutation, and the machine is 

called a commutating machine. 

c. DC voltage. The voltage across the unloaded terminals is not a constant. A unidirectional current 

can flow when a resistor is connected across the terminals of the machine. The pulsating voltage 

waveform generated by the simple DC machine usually cannot meet the requirement of practical 

applications. An improvement can be made with more pairs of conductors. These conductors are placed 

in slots that are made equidistant on the rotor surface. Each pair of conductors can generate a voltage 

waveform but there are time shifts among these waveforms due to the spatial displacement among the 

conductor pairs. For instance, when an individual voltage is minimum (zero), other voltages are not. If 

these voltage waveforms are added, the result is a near constant voltage waveform. This improvement of 

the DC waveform requires many pairs of the copper segments and a pair of brushes. 

d. Armature reaction. When the generator is connected to an electrical load, load currents flow 

through the rotor conductors. Therefore, a magnetic field is set up in addition to that of the permanent 

magnet. This additional field generally weakens the magnetic flux seen by the rotor conductors. A direct 

consequence is that the induced EMF is less than those in an unloaded machine. Similar to the case of 

AC generators, this phenomenon is referred to as armature reaction, or flux-weakening effect. 

e. Brushes. The use of brushes in the design of DC generators can cause a serious problem in 

practice. Each time a brush comes into contact with two adjacent copper segments, the corresponding 

conductors are short-circuited. For a loaded generator, such an event occurs when the currents in these 

conductors are not zero, resulting in flashover at the brushes. This means that the life span of the brushes 

can be drastically reduced and that frequent maintenance is needed. A number of design techniques have 

been developed to mitigate this problem. 
TM 5-692-2

7-6 

f. Excitation. The stator winding is called the field winding, which produces excitation for the 

machine. The current in the field winding is adjusted by means of a variable resistor connected in series 

with this winding. It is also possible to use two field windings in order to have more flexibility in control. 

 The use of field winding(s) on the stator of the dc machine leads to a number of methods to produce the 

magnetic field. Depending on how the field winding(s) and the rotor winding are connected, one may 

have shunt excitation, series excitation, etc. Each connection yields a different terminal characteristic. 

7-6. Major design components 

A typical AC generator consists of a stationary stator and a rotor mounted within the stator. The stator 

contains a specific number of coils, each with a specific number of windings. Similarly, the rotor consists 

of a specific number of field poles, each with a specific number of windings. In addition to the rotor and 

stator, a generator has a collector assembly (usually consisting of collector slip rings, brushes, and brush 

holders). DC flows from the exciter, through the negative brush and slip ring, to the rotor field poles. 

The return path to the exciter is through the positive brush and slip ring. 

a. Rotor. The rotor contains magnetic fields that are established and fed by the exciter. When the 

rotor is rotated, AC is induced in the stator. The changing polarity of the rotor produces the alternating 

characteristics of the current. The generated voltage is proportional to the strength of the magnetic field, 

the number of coils (and number of windings of each coil), and the speed at which the rotor turns. 

b. Stator. The frame assembly is the main component of the stator. Insulated windings (or coils) are 

placed in slots near an air gap in the stator core. There is a fixed relationship between the unit's number 

of phases and the way the coils are connected. The stator in a four wire, three-phase unit has three sets of 

armature coils which are spaced 120 electrical degrees apart. One end of each coil is connected to a 

common neutral terminal. The other end of each coil is connected to separate terminals. Conductors 

attached to the four terminals carry the current to the system's switchgear and on to the load. 

c. Collector slip rings. Slip rings are usually made of non-ferrous metal (brass, bronze or copper); 

iron or steel is sometimes used. Slip rings usually do not require much servicing. The wearing of 

grooves or ridges in the slip rings is retarded by designing the machine with limited endplay and by 

staggering the brushes. Surfaces of the slip rings should be bright and smooth; polishing can be 

performed with fine sandpaper and honing stone. Electrolytic action can occur at slip ring surfaces 

producing formation of verdigris. Verdigris is a greenish coating that forms on non-ferrous metals. 

Electrolytic deterioration can be prevented by reversing the polarity of the slip rings once or twice a year. 

The stator of the three wire, three-phase unit also has three sets of armature coils spaced 120 electrical 

degrees apart. The ends of the coils are connected together in a delta configuration. Conductors are 

attached to the three connecting points. 

d. Exciters. An AC or DC generator requires direct current to energize its magnetic field. The DC 

field current is obtained from a separate source called an exciter. Either rotating or static-type exciters are 

used for AC power generation systems. There are two types of rotating exciters: brush and brushless. 

The primary difference between brush and brushless exciters is the method used to transfer DC exciting 

current to the generator field. Static DC excitation for the generator fields is provided in several forms 

including field flash voltage from storage batteries and voltage from a system of solid-state components. 

DC generators are either separately excited or self excited 

 e. Field flashing. Field flashing is required when generator voltage does not build up and the 
TM 5-692-2 

7-7 

generating system (including the voltage regulator) does not have field flash capability. This condition is 

usually caused by insufficient residual magnetism in the exciter and generator fields. In some cases, a 

generator that has been out of service for an extended period may lose its residual magnetism and require 

flashing. Residual magnetism can be restored by flashing the field, thereby, causing a current surge in the 

generator. Refer to the voltage regulator manufacturer's literature for procedural instructions. Solid-state 

components may be included in the voltage regulator. Perform field flashing according to the 

manufacturer's instructions to avoid equipment damage. 
TM 5-692-2 

8-1 

CHAPTER 8 

DIESEL ENGINES 

8-1. Diesel engine ratings 

Diesel engines are the most common prime movers used for remote or emergency electric power 

generation. Those engines used for this purpose commonly range from 133 hp to 6,700 hp (100 kW to 

5,000 kW), with rotational speeds ranging from 360 rpm for large prime power applications to as high as 

1,800 rpm for small standby units. Thermal efficiency ranges from 30 to over 40 percent. For C4IRS 

Facilities applications, diesel engine prime movers shall be class A for continuous duty operation and 

shall be air-started and water-cooled. Spare engines available for service shall be kept in a ready-to-run 

condition by circulation of warm lubricating oil and warm jacket cooling water. This chapter will 

primarily address the requirements of diesel engines in the middle range of capacity and speed which are 

the most common. The engine manufacturer's directions regarding maintenance practices take precedence 

over any guidance provided in this chapter. 

8-2. Types of diesel engines 

Diesel engines are used as prime movers for many applications, but they are addressed here based on their 

use in electric power generation to drive generators. 

a. Configuration. Diesel engines are available in two- or four-cycle configurations. Four-cycle 

engines are available in naturally aspirated or turbocharged models, but most engines are now purchased 

with turbocharging. Similarly, two-cycle engines are available with either a blower or turbocharger 

(some manufacturers use both in series), but turbochargers are supplied on most engines. Each type has 

its advantages in certain applications and has specific requirements for operation and maintenance due to 

the inherent differences. Two-cycle engines are frequently lighter weight for the same horsepower due to 

the fabrication of the engine block from steel plate instead of a casting and elimination of the valving 

common to four-cycle engines. In addition, they usually respond more quickly to rapidly changing loads, 

since they have less rotating mass than four-cycle engines. 

b. Applications. Two major considerations in the level and amount of maintenance required for diesel 

engines are the application of the engine (emergency standby power or prime power) and the rotational 

speed of the engines. Emergency equipment which is expected to operate very few hours per year can be 

expected to last for years with minimal maintenance and utilize higher speed engines (i.e., 1,200 to 1,800 

rpm). Prime power applications require significantly more maintenance and generally utilize lower speed 

engines (360 to 450 rpm) to maximize the useful life of components. 

8-3. Diesel engine major system components

Diesel engines have many components and subsystems. Only those components which are typically 

mounted on the engine or engine skid will be addressed here. Descriptions of engine support systems, 

such as the fuel oil system, starting system, and lubrication system, are presented later in this manual. 

a. Drivetrain. The drivetrain of the engine consists of the pistons, connecting rods, crankshaft, 

flywheel, coupling if any, and associated bearings. 
TM 5-692-2

8-2 

b. Valve train and timing. This subsystem includes the gearing from the crankshaft to the camshaft, 

camshaft, tappets, push rods, rocker arms, valves, valve springs, and guides. In addition, the camshaft 

controls the fuel injection timing and actuates the injector in most contemporary engines with unit 

injectors. The description above applies to four-cycle engines; two-cycle engines move air into the 

cylinder and exhaust out through ports in the cylinder wall which are exposed by the movement of the 

piston. Some two-cycle engines have both ports and valves. Injection timing and actuation on two-cycle 

engines are still controlled by a camshaft. 

c. Governor/control. The governor controls the speed of the engine. It is a sophisticated device 

which measures crankshaft speed and reacts to small deviations due to changes in load to maintain proper 

engine speed by adjusting the amount of fuel injected. Typically, two types of governors are used on 

diesel engines driving electric generators: self-contained mechanical-hydraulic type or remote electronic 

governor with separate engine-mounted actuator. Electronic governor systems with load sharing 

capability are the usual choice for multiple engine plants. Pulsating loads of some facilities have dictated 

the use of mechanical governors. Plants with multiple engines must have compatible governors to ensure 

proper operation of engines in parallel. Other control/safety alarm and shutdown indicators are 

summarized in table 8-1. 

d. Turbocharger/blower. The turbocharger is a centrifugal compressor which is driven by the exhaust 

gases and in turn compresses the intake air to provide an increased mass of air to the combustion 

chamber. In-line engines typically have one turbocharger, and V type engines may have one or two 

turbochargers. Turbochargers are used on both two- and four-cycle engines, but many two-cycle engines 

utilize blowers to assist in scavenging air from the combustion chamber without significant increase in the 

density of the air. 

e. Aftercooler. Turbocharged engines typically have an aftercooler downstream of the turbocharger to 

reduce the air temperature and increase the density of the air entering the combustion chamber. Cooling 

water is circulated through the aftercooler which is composed of finned tubes to cool the air to 

approximately 100°F. 

8-4. Diesel engine system interfaces

Diesel engines interface with the following supporting systems. 

a. Generators. Generators are the primary driven equipment for diesel engines. The diesel engine 

and the generator must be properly aligned and coupled, either directly or by a flexible coupling. It is 

critical that the engine and generator are properly matched and a torsional analysis of the engine/generator 

system has been performed by the engine manufacturer. 

 b. Fuel oil systems. The diesel engine is dependent on the fuel oil system to provide fuel to the 

injectors. The fuel oil must have the proper characteristics required for the specific engine installation. In 

general, larger slow-speed engines require a less volatile fuel than smaller high-speed engines. Special 

engine modifications are required where special fuels, such as Diesel Fuel Arctic (DFA) or heavy oil (No. 

6) are used. Fuel oil systems are addressed in chapter 10. 

 c. Lube oil systems. The proper lubrication of the moving parts inside a diesel engine is critical to 

obtain satisfactory operation of the engine and maximum life of its components. The lube oil must be 

approved by the engine manufacturer and analyzed on a regular basis to determine the optimum interval 

for changing the lube oil and to monitor other indicators which indicate problems or a need for 
TM 5-692-2 

8-3 

maintenance. In addition, the analysis of the lube oil should include trace metal analysis for early 

indication of abnormal wear and scheduling maintenance or repairs. Lube oil systems cool and filter the 

lube oil to provide both proper lubrication and cooling of critical components within the engine. Refer to 

chapter 11 for further discussion of lube oil systems. 

Table 8-1. Typical alarm and shutdown requirements for diesel engines 

Indication Alarm Only 

Alarm and 

Shutdown 

Engine System 

 Overspeed X 

 High Exhaust Temperature X 

 High Crankcase Pressure X 

 Low Injector Coolant Pressure X 

 High Inlet Manifold Temperature X 

Lube System 

 High Lube Oil Temperature X X 

 Low Lube Oil Pressure X X 

 Low Lube Oil Level X X 

Fuel System 

 High Fuel Oil Temperature X 

 Low Fuel Oil Pressure X X 

 High Fuel Filter Differential Pressure X 

Generator System 

 High Generator Bearing Temperature X X 

 High Generator Winding Temperature X X 

Ancillary Systems 

 High Coolant Temperature X 

 Low Coolant Level X 

 Low Jacket Water Pressure X 

 Low Starting Air Pressure X 
TM 5-692-2

8-4 

 d. Engine air system. The engine intake and exhaust systems provide filtered air to the engine and 

remove products of combustion from the engine room. These systems may incorporate such features as 

preheating or precooling of the intake air, or hardened design. Restrictions or blockage of either the 

intake or exhaust systems will severely impact engine performance. 

 e. Engine cooling system. Heat is transferred away from the engine by the cooling system and usually 

rejected to the air. The engine cooling system may consist of a single circuit which removes heat from 

the aftercooler and lube oil cooler, as well as the engine, or it may have separate circuits which allow 

lower temperatures to be maintained at the various components. The cooling system temperature is 

thermostatically maintained to ensure proper cooling and avoid thermal shock of high-temperature 

components. The heat is usually rejected directly through a radiator or indirectly via a heat exchanger to 

a cooling tower. The heat removed from the engine may be used to preheat combustion air in severe cold 

climates and also for heating the power plant building in prime power applications. 

 f. Engine starting air system. The vast majority of diesel engines installed in power plants are started 

with compressed air. Compressed air is directed by a distributor directly into the combustion chamber or 

is provided to an air motor which rotates the engine. Dedicated compressors typically provide starting air 

at 250 psig. The system must provide adequate storage to allow multiple attempts to start the engines. 

The compressed air start system will included two air compressor units, each with diesel engine-electric 

motor drive, and two main air storage tanks. The compressors will be rated at 250 psig operating 

pressure, and each will have a capacity capable of restoring any single storage receiver from 150 psig to 

250 psig in 30 minutes or less. Each main storage tank will provide adequate air to the individual air start 

tanks at each diesel engine, supply air to the utility shop air outlets, and provide a second source to air to 

the instrument air system. Each air start tank will be sized to provide two 30-second start sequences 

without recharging and will be rated at 300 psig working pressure. Each main storage tank will have a 

volume equal to three air start tanks plus a volume equal to one instrument air receiver, and an additional 

volume to supply the utility shop air requirement. 

 g. Engine control systems. The basic control of the engine is maintained by the governor during 

operation, and the control is independent for each engine. The overall control of a multiple engine power 

plant can be relatively simple or very sophisticated. Possible control options range from local or manual 

starting and synchronization of each engine to automatic starting, synchronization, and load sharing of the 

engine generators. Engine control systems in advanced applications should also be integrated as a part of 

the SCADA (Supervisory Control and Data Acquisition) system. 

h. Instrumentation. Collection of operating data is critical to planning maintenance and evaluating 

problems which may occur. In the past (and still the case at most facilities), all data were recorded by 

operating personnel from instrument panels at each engine. Many newer plants now have automated data 

logging systems which can also provide warnings for out-of-tolerance conditions and histories of unusual 

events which can improve the operation of the facility. Regardless of the type of system, data collection 

provides the basis for trend analysis which can indicate potential problems before they become severe. 

i. Ventilation systems. Diesel engines operate at high temperatures and, therefore, reject large 

amounts of heat to the surrounding space. Diesel power plants are typically ventilated to remove this heat 

and to maintain temperatures within acceptable limits for both personnel and equipment. Proper 

operation of ventilation systems is required to avoid excessive temperatures, reduced equipment capacity, 

and potential equipment failures. 
TM 5-692-2 

8-5 

8-5. Operation of diesel engines

Consult the diesel engine manufacturer's manual provided with the engine for proper operating 

procedures and normal operating conditions. The operating procedures described below provide a 

general overview of diesel engine operation. 

a. Prior to starting. Prior to starting, the engine prelube pump should be operated to ensure proper 

lubrication of the bearing surfaces. The prelube pump for a standby unit should be operated on a regular 

basis to maintain engine in "ready to start" condition. All engine auxiliary systems should be checked to 

verify proper status for engine operation. Failure to properly prelube the engine prior to starting can 

result in damage to engine components and significantly decrease engine life. 

b. Starting. Normal starting of the engine should include the following items. The engine should be 

started without load and brought up to operating temperature before load is applied, verify lube oil 

pressure is normal immediately after starting, and be prepared to shut engine down if problems occur. 

c. Normal operation. Under normal circumstances, do not operate the engine below 50 percent load 

or above 100 percent load for extended periods of time. Operation at low loads can cause carbon 

formation and rapid deterioration of the lube oil. Operation at high loads results in higher temperatures 

and pressures in the combustion chamber and can lead to more frequent maintenance or replacement of 

components. Operators should verify proper operating conditions exist on an hourly basis, and data 

should be recorded at least once per shift. Priority should be given to maintaining correct lube oil and 

coolant levels and checking the pressure difference across the inlet air filters, fuel filters, and lube oil 

filters. 

 d. Shutdown. Diesel engine should be unloaded and allowed to cool down prior to shutdown of the 

unit. The engine should be operated without load at rated speed until exhaust temperature decreases to 

recommended level and then at low idle speed, if applicable, for a minimum of five minutes without load 

or as directed by manufacturer. 
TM 5-692-2 

9-1

CHAPTER 9 

GAS TURBINES 

9-1. Applications of gas turbines 

Gas turbines, also known as combustion turbines, are common prime movers for many applications. 

Their historically high fuel consumption, especially for small units (less than 10,000 kW), as well as at 

part load, and at high inlet air temperatures has made them less desirable than diesel engines for prime 

power plant applications. They have been utilized extensively in standby and peaking applications where 

their relatively low installed cost outweighs other factors. Open or simple cycle gas turbines are used in 

virtually all power plant applications and only this type will be addressed in this chapter. Combined cycle 

systems, where heat is recovered from the gas turbine exhaust and used to make steam which then drives 

a steam turbine, have become much more common in recent years, but they will not be discussed here. 

9-2. Gas turbine operating characteristics 

Gas turbines are based on the Brayton or Joule cycle which consists of four processes: compression with 

no heat transfer, heating at constant pressure, expansion with no heat transfer, and in a closed cycle 

system, cooling at constant pressure. In open cycle gas turbines, the fourth step does not exist since inlet 

air is taken from the atmosphere and the exhaust is dumped to atmosphere. Due to its higher temperature, 

there is more energy available from the expansion process than is expended in the compression. The net 

work delivered to drive a generator is the difference between the two. The thermal efficiency of the gas 

turbine is a function of the pressure ratio of the compressor, the inlet temperature of the power turbine, 

and any parasitic losses (especially the efficiency of the compressor and power turbine). Practical 

limitations on thermal efficiency due to losses and materials technology yield a maximum of about 40 

percent at pressure ratios of 30 to 40 and temperatures of approximately 2,500°F. These temperatures and 

pressure ratios are found only in recently developed, large gas turbines. Typically pressure ratios of 5 to 

20 and turbine inlet temperatures from 1,400 to 2,000°F are common in gas turbines for this application, 

resulting in efficiencies from 20 to 33 percent. As improved materials and cooling technologies are 

introduced to smaller units, the efficiencies can be expected to improve if the cost is not prohibitive. 

9-3. Gas turbine system major components

Gas turbines can be divided into three major components or sections; these are the compressor, the 

combustor, and the power turbine. Air enters the compressor and is pressurized to a level from 10 to 50 

times that of the entering air. The compressed air then passes into the combustor where fuel is introduced 

and ignited, producing temperatures in the range of 1,400 to 2,000°F. The hot gases are then directed to 

the power turbine where they are expanded to atmospheric pressure and in turn provide power to drive 

both the compressor and the driven equipment such as a generator. Gas turbine auxiliary 

systems/components include starting, fuel supply, lubrication, governor/controls, speed reduction gear, 

inlet air, and engine exhaust. 

a. Configuration. Gas turbines are lightweight in comparison to diesel engines, are very compact, and 

due to their small, well-balanced rotating mass are able to operate at very high speeds (from 10,000 to 

25,000 rpm in sizes from 900 to 10,000 kW). Smaller gas turbines are usually single-shaft design that is 

the compressor and power turbine are mounted on the same shaft. Larger gas turbines are frequently twoshaft machines in which the power turbine is divided into two sections, one of which drives the 
TM 5-692-2 

9-2

compressor and the other which drives the generator. The two-shaft design allows the compressor section 

to be operated at a variable speed (within limits) thus varying the flow to the power turbine section as a 

function of load. 

b. Starting system components. Gas turbines utilize a variety of starting systems based on size of the 

unit and other considerations. Common starting methods include compressed air, direct current (DC) 

electric motors with dedicated batteries, or a hydraulic pump driven by an alternating current (AC) motor, 

small gas turbine, or diesel engine, which in turn drives the hydraulic motor on the gas turbine. Where 

used, an auxiliary gas turbine or diesel engine also requires a starting system, usually a DC motor and 

batteries. Regardless of the equipment used, the starting system brings the unit up to a minimum speed at 

which the burners may be ignited and the turbine is then brought up to operating speed. 

c. Fuel system components. Although gas turbines are capable of burning either gas or liquid fuels, 

only liquid fuels are addressed in this chapter since they are preferred for standby power generation. The 

following fuel system components are commonly provided as part of the gas turbine package: motor 

driven booster pump, low-pressure duplex fuel filter, main turbine driven fuel pump, high pressure filter, 

main fuel control valve (regulated by the governor), fuel manifold and injectors at the combustor, and 

igniter. 

d. Lubrication system components. Most gas turbines are provided with complete lubrication systems 

which include a cooler (air cooled), filter, pre/post lube pumps, engine driven main lube oil pump, alarms, 

oil storage tank (located in engine skid), and heater. The system is usually packaged with the gas turbine 

and only the lube oil cooler is remotely located. The lube oil system may supply the speed reduction gear 

and generator in addition to the gas turbine. 

e. Governor/control. The gas turbine speed and fuel flow are controlled by the governor in response 

to load changes. Typically two types of governors are used on gas turbines driving electric generators: 

self-contained mechanical-hydraulic type or remote electronic governor with separate engine mounted 

actuator. Electronic governor systems with load sharing capability are the usual choice for multiple 

engine plants. Plants with multiple engines must have compatible governors to ensure proper operation 

of engines in parallel. Other control/safety alarm and shutdown indications are summarized in table 9-1. 

f. Speed reduction gear. The high operating speeds of most gas turbines require that a speed 

reduction gear be installed to drive the generator at the appropriate synchronous speed, usually 1,200 to 

1,800 rpm. The reduction gear is typically an epicyclic design that permits a straight-through shaft 

arrangement, thus simplifying alignment. A variety of epicyclic designs are used and depending on the 

speed of the gas turbine, a two-stage reduction may be required. Two common designs are the standard 

planetary system and the star compound system. The reduction gear is typically lubricated by the main 

lube oil system. 

g. Inlet and exhaust components. Gas turbines require significantly more combustion air than diesel 

engines. Flows are typically four to five times as much as that required by a diesel engine of the same 

capacity. This leads to much larger air filters, intake ducts, and exhaust ducts. Proper air filtration is 

critical to gas turbine performance. Deposits on compressor and turbine blades can significantly reduce 

efficiency. 
TM 5-692-2 

9-3

Table 9-1. Typical alarm and shutdown requirements for gas turbines

Indication Alarm Only 

Alarm and 

Shutdown

Engine System 

 Impending High Blade Temperature X 

 High Blade Temperature X 

 Impending High Engine Temperature X 

 High Engine Temperature X 

 High Gas Producer Thrust Bearing Temperature X X 

 High Power Turbine Thrust Bearing Temperature X X 

 Fail to Crank X 

 Fail to Start X 

 Ignition Failure X 

Starter Dropout Failure X 

 Backup Overspeed Power Turbine X 

Overspeed Power Turbine X 

 High Vibration – Engine X X 

 High Vibration – Accessory Gearbox X X 

Lube System 

 High Oil Temperature X X 

 Low Oil Pressure X X 

 Low Prelube Oil Pressure X 

 Low Oil Level X X 

 High Oil Level X 

 Lube Filter High Differential Pressure X 

Fuel System 

 Liquid Fuel Filter High Differential Pressure X 

 Low Liquid Fuel Pressure X X 

Gearbox Systems 

 High Gearbox Output Bearing Temperature X X 

 High Vibration – Gearbox X X 

Generator Systems 

 High Generator Bearing Temperature X X 

 High Generator Winding Temperature X X 

 High Vibration – Generator X X 

Ancillary Systems 

 Low Battery Voltage X 

 Battery Charger Failure X 

 Inlet Air Filter – High Differential Pressure X X 
TM 5-692-2 

9-4 

9-4. Gas turbine system interfaces

Gas turbines interface with the following supporting systems. 

a. Generators. Generators are the primary driven equipment for gas turbines. The gas turbine and the 

generator must be properly aligned and coupled, either directly or by a flexible coupling. It is critical that 

the engine and generator are properly matched. 

b. Fuel oil systems. The gas turbine is dependent on the fuel oil system to provide fuel to the engine 

skid. The fuel oil must have the proper characteristics required for the specific engine installation. In 

general, gas turbines can utilize a wider range of liquid fuels than diesel engines. Most facilities use 

kerosene, No. 1 fuel oil, or No. 1 diesel, but some use No. 2 fuel (if acceptable to the manufacturer) since 

it is less expensive than the lighter grades of fuel. 

c. Lube oil systems. The proper lubrication of the moving parts inside a gas turbine is critical to 

obtain satisfactory operation of the engine and maximum life of its components. The lube oil must be 

approved by the engine manufacturer and analyzed on a regular basis to determine the optimum interval 

for changing the lube oil. Lube oil change intervals are much longer than those for diesel engines, since 

the oil does not become contaminated by products of combustion. Lube oil systems cool and filter the 

lube oil to provide both proper lubrication and cooling of critical components within the engine. 

d. Engine air system. The engine intake and exhaust systems provide filtered air to the engine and 

remove products of combustion from the engine room. These systems may be very simple or relatively 

complex, incorporating such features as preheating or pre-cooling of the intake air, or hardened design. 

Restrictions or blockage of either the intake or exhaust systems will severely impact engine performance. 

e. Engines starting system. Gas turbines installed in power plants may be started with compressed air, 

DC motors, or an engine driven hydraulic system. Dedicated compressors typically provide starting air at 

pressures from 150 to 500 psig, depending on the specific requirements of the gas turbine. The system 

must provide adequate storage of compressed air to allow multiple attempts to start the engines. DC 

motors are driven from batteries located at the engine skid, which are charged by a dedicated battery 

charger. Hydraulic systems are composed of a prime mover, usually a diesel engine or small gas turbine, 

hydraulic pump, drive motor, and accessories, including hydraulic reservoir, air cooled heat exchanger, 

and filter. 

f. Engine control systems. The basic control of the engine is maintained by the governor during 

operation and the control is independent for each engine. The overall control of a multiple engine power 

plant can be relatively simple or very sophisticated. Possible control options range from local or manual 

starting and synchronization of each engine to automatic starting, synchronization, and load sharing of the 

engine generators. 

g. Instrumentation. Collection of operating data is critical to planning maintenance and evaluating 

problems which may occur. In the past (and still the case at most facilities), all data was recorded by 

operating personnel from instrument panels at each engine. Many newer plants now have automated data 

logging systems that can also provide warnings for out-of-tolerance conditions and histories of unusual 

events which can improve the operation of the facility. Regardless of the type of system, data collection 

provides the basis for trend analysis that can indicate potential problems before they become severe. 
TM 5-692-2 

9-5 

h. Ventilation systems. Gas turbines operate at high temperatures and therefore reject large amounts 

of heat to the surrounding space. Power plants are typically ventilated to remove this heat and to maintain 

temperatures within acceptable limits for both personnel and equipment. Proper operation of ventilation 

systems is required to avoid excessive temperatures, reduced equipment capacity, and potential equipment 

failures. 

 
TM 5-692-2 

10-1 

CHAPTER 10 

FUEL OIL SYSTEMS 

 

10-1. Simple fuel oil system 

In a simple fuel oil system there is only one device using fuel oil and the fuel oil tank is located close to 

the equipment being served which allows the tank to supply fuel oil to the equipment and receive returned 

oil without an intermediate service tank. 

a. Storage. The fuel oil tank is a double wall, horizontal, cylindrical tank and could be located either 

above or below ground. Fuel oil is drawn out from the top of the tank by the fuel oil pump suction line. 

A top discharge is best for horizontal tanks. The suction line can be installed some distance from the 

bottom of the tank to prevent water separating from the fuel oil in the tank from entering the supply 

system. Tanks typically have a high suction and a low suction line. Normal operation is through the low 

suction line. If an accumulation of water enters the low suction line, facility operation can be switched to 

the high suction line until the accumulated water is removed. Once the water is removed, it is important 

to switch back to the low suction line. Fuel oil storage tank fill and return lines typically terminate in trap 

sections. In the event the tank is drawn down past these lines, the trap section minimizes the likelihood 

that combustible vapors can exit the tank and create a hazard within the facility. Also, the fuel oil supply 

piping has an expansion chamber which prevents expanding oil from leaking through joints and shaft 

seals or causing physical damage to the system. 

b. Fuel delivery. The fuel oil used in the facility may require heating in cold weather to reduce the 

fuel oil viscosity into the pumpable range. The heating is provided by a steam or hot water coil 

surrounded by a box-like structure to form a suction heater. Fuel oil is drawn from the tank through a 

suction strainer by a fuel oil pump. The fuel oil is pumped through a coalescing filter to remove water 

and through an oil heater to reduce the fuel oil viscosity into the atomizing range. Fuel oil not used by the 

equipment is returned to the fuel oil storage tank. If the amount of hot oil returned is likely to cause the 

storage tank to fill with oil vapor, the return oil would be cooled to below the flash point by a fuel oil 

cooler before being discharged into the tank. 

c. Fuel selection. Lighter weight fuel oils such as FS2, DF2, DFA, and JP fuels have a much lower 

viscosity, which allows them to flow more easily during cold weather. Unless the outside air temperature 

is extremely cold, pre-heaters are not normally required when using these fuels. Heavier oils such as FS4 

(and especially FS6), due to their high paraffin content, do require the heaters in cold weather. The need 

for preheating should be considered by the facility in specifying the fuel requirements for new or 

replacement equipment such as boilers. The heavier fuels have a higher BTU content and are usually less 

expensive. However, the cost of preheating the fuel can easily make the lower viscosity fuels cheaper in 

the long run. Also, the higher viscosity fuels often have a higher sulfur content, which may present an air 

quality problem in certain areas 

10-2. Complex fuel oil system 

A more complex fuel oil system is shown on figure 10-1. The complex fuel oil supply system is serving a 

diesel engine unit that can run on less costly heavy fuel oil (No. 5 or No. 6), but requires a more 

expensive light fuel oil (No. 1-D, No. 2-D, No. 1, or No. 2) for starting the engine. In this instance, the 
TM 5-692-2

10-2 

LI LT

TC

TI

LIGHT OIL

TANKHEATER

MAIN STORAGE

TANKS

STRAINER

FM

S

LT LI

S

S TH

TC

HEAVY OIL

SUCTIONHEATER

CENTRIFUGEHEATER

COOLER

CLEAN OIL TANK

TO WASTEOIL TANK

VENT

HEAVY OIL

DAY TANK

LIGHT OIL DAY TANK

VENT

TO WASTEOIL TANK

HEATER

HO

HO FUEL OIL RETURN

TI

HO

FM

3-WAYVALVE

TO DIESEL ENGINE DIESEL ENGINE

FUEL OIL RETURN

TOTALIZINGFLOW METERHAND OPERATEDEMERGENCY TRANSFERPUMP (TYP)

LEVELINDICATOR/TRANSMITTERSYSTEM

Figure 10-1. Complex fuel oil system - supply 
TM 5-692-2 

10-3 

quantity of fuel oil used by the facility requires a tank farm some distance from the point of use and the 

quality of the heavy oil requires on-site conditioning before use. Note that critical fuel oil transfer pumps 

have installed spares, and critical transfer points have hand-operated pumps in parallel with the motoroperated pumps to allow a minimum level of fuel transfer in the event of unplanned electric service 

supply outages. 

 a. Storage. The fuel oil storage tanks are equipped with level indicators and level transmitters. The 

heavy oil tank uses a suction heater to adjust oil viscosity while the light oil tank uses a whole tank 

heating system to maintain the oil above the pour point temperature. All above ground piping and oil 

transfer equipment are heat-traced. 

b. Conditioning. Because of the water and sediment in the as-delivered heavy fuel oil, the heavy fuel 

oil requires conditioning before final use. In the example system on figure 10-1, fuel oil conditioning is 

accomplished using a centrifuge. The heavy fuel oil feed to the centrifuge must be further heated to 

reduce the viscosity into the atomizing range. The fuel oil discharged from the centrifuge is passed 

through a fuel oil cooler to eliminate flash point problems before being discharged into a clean oil storage 

tank that is heated to keep the fuel oil viscosity at a pumpable level. 

c. Fuel delivery. Heavy fuel oil is transferred from the clean oil tank to a heavy oil day tank at each 

diesel engine. Light fuel oil is transferred from the light oil main storage tank to the light oil day tank at 

each diesel engine. Both day tanks are equipped with systems to circulate the fuel oil through coalescing 

filters to remove any water in the fuel oil. The heavy fuel oil day tank is equipped with a heater to 

maintain the oil viscosity at a point that will flow to the engine. Additional heating of the heavy fuel oil 

is required to reduce the oil viscosity into the atomizing range as the oil is supplied to the engine. 

 (1) The heavy fuel oil and light fuel oil are supplied to the engine through a three-way valve. On 

initial starting, the three-way valve is positioned to use light fuel oil. Light fuel oil is used until the 

engine reaches operating speed and temperatures. Once the engine operation is stabilized, the three-way 

valve is positioned to supply heavy fuel oil to the engine. During a normal shutdown, the three-way valve 

is positioned to supply light fuel oil to the engine to purge the heavy oil from the engine fuel system 

before engine operation is terminated. 

 (2) The fuel oil day tanks are positioned above the engine so fuel oil is supplied by gravity to the 

inlet of the engine-driven fuel oil pump. Some installations may require self-priming, engine-driven fuel 

oil pumps to draw fuel into the pump, or there may be an additional set of pumps between the day tanks 

and the engine-driven pump to get the fuel oil to the engine-driven pump inlet. Whenever the engine fuel 

oil system has been drained, many engine designs require that the system be filled with fuel oil before a 

normal start is attempted and a hand-operated pump is provided for this purpose. Fuel oil supplied to the 

engine-driven fuel oil pump passes through a shutoff valve and a duplex strainer. The engine-driven fuel 

oil pump discharges through a duplex fuel oil filter to the engine fuel injection system. Excess fuel oil 

passes through an air-cooled fuel oil cooler, a check valve, and an engine fuel oil system isolation valve, 

and is returned to the heavy fuel oil day tank. 

10-3. Fuel oil system major components

The fuel oil system is comprised of the following major components. 

a. Fuel oil pipeline flowmeter. The fuel oil pipeline flowmeter is a rotary displacement type 
TM 5-692-2

10-4 

flowmeter used to measure fuel oil quantities for accounting purposes. 

b. Fuel oil storage tank heaters. Fuel oil storage tank heaters for outdoor aboveground tanks will vary 

in type as follows. 

 (1) Low watt density electric heating elements are arranged on the bottom of the fuel oil storage 

tank. Sometimes they are also designed to be flange-mounted through the side of the tank. 

 (2) Hot water is circulated through heat exchanger tubes that are immersed in the fuel oil. In most 

cases, the tube assembly is mounted through the side of the tank on a flanged nozzle. 

 (3) The heating of the fuel oil storage tank is similar to that used for a hot water system; only the 

heating medium is steam. 

 (4) A suction heater is designed to be mounted on or in the fuel oil storage tank suction nozzle that 

heats the fuel as it is drawn from the tank. 

c. Fuel oil supply heat tracing. Heat tracing is installed on lines to maintain the temperature of the 

fuel oil in the lines to prevent viscosity or pour point problems. Heat-traced lines and equipment are 

generally insulated. Mechanical heat tracing is generally a tube clamped and thermally bonded to the 

outside of the fuel oil pipe. Steam or hot water is passed through the tubing. Electric heat tracing is by 

means of flexible resistance heaters that can be wrapped around the pipe. 

d. Strainers. Strainers are used to remove coarse particulate matter that may damage rotating 

equipment. Typical strainers use a screen-like mesh or perforated metal element (Y type and basket type 

strainers) or closely spaced parallel rows of sharp-edged metal bar elements (metal-edge type strainer). 

They may include magnetic elements for removal of iron and steel particles. Duplex strainers have two 

strainer elements of equal capacity connected in parallel by a valve assembly that allows the process 

stream to be diverted from one strainer element to the other without interrupting flow. Duplex units are 

used in systems that cannot be conveniently shut down for maintenance. 

e. Fuel oil filters. Fuel oil is filtered to remove particulate matter and to remove water. Filters 

designed to remove water from fuel oil are known as coalescing filters. 

 (1) Particulate filters are used to remove fine particulate from fuel oils. Filters in fuel oil systems 

are generally made up in cylindrically shaped "cartridges" or elements of a size convenient for handling. 

Unless the filter element is of the metallic, permanent type that can be cleaned, filter elements are 

typically used once and then discarded. In locations where the fuel oil system can be shut down for 

maintenance, single-element filter units are generally installed. In critical services, duplex filter units 

designed to allow switching from one bank of filter elements to another without interrupting the flow of 

fuel oil are generally used. 

 (2) Fuel oil systems typically use coalescing filters to remove water from the fuel oil. Coalescing 

filters are also extremely efficient particulate filters. 

f. Centrifuges. The fuel oil conditioning system centrifuge is utilized for purification (separation of 

liquids) and clarification (removal of solids). This unit is generally a high-speed centrifuge with a selfcleaning bowl. 

 
TM 5-692-2 

10-5 

g. Control valves. Control valves are installed in the fuel oil supply lines inlet to day tanks. The 

valves automatically open when the fuel oil in their respective day tank falls to a preset level. When the 

valve opens, fuel oil flows into the day tank. When the level in the tank reaches another preset (higher) 

level, the valves automatically close, stopping the flow of fuel. The operation of the control valves is 

controlled by level switches. 

h. Fuel oil day tanks. Fuel oil day tanks are usually located at an elevation above the engines. The 

day tanks are generally a cylindrical type tank with a capacity for storing a four- to eight-hour supply of 

fuel oil. The tank has a manhole, a supply inlet connection, a vent connection, an overflow connection, a 

fuel return connection, a fuel supply outlet connection, and two connections for the level controller and 

indicator. 

i. Waste oil storage tank. The waste oil storage tank is generally a cylindrical type and will be 

double-walled if located underground. The tank will have nozzles for vent, tank pump-out, fill, and level 

monitoring. Underground tanks may have a leak detection system, level indication, and overfill alarms. 

j. Pumps. Various types of pumps are utilized in fuel oil systems. 

 (1) The pumps used to transfer fuel oil throughout the facility may vary from installation to 

installation. The types of pumps likely to be found in fuel oil service are as follows. 

 (a) Centrifugal pumps, horizontal, are preferred for pumping from aboveground tanks with 

continuously flooded pump suction when viscosity considerations or the pressure drop of filter devices 

following the pump are not a concern. 

 (b) Vertical centrifugal pumps may be used, but are not preferred, for pumping from 

underground tanks (or from horizontal, cylindrical tanks). These pumps may have multiple stages. 

 (c) Turbine pumps, vertical, are preferred for pumping from underground tanks. 

 (d) Positive displacement pumps are used where a relatively constant flow over a range of 

system pressures may be encountered, or when the viscosity of the fluid or the oil filtering system 

components require relatively high pump discharge pressures. In installations or service where a flooded 

pump suction line cannot be ensured, the pump should be of the self-priming type. Positive displacement 

pumps are common in fuel oil service. The three most common are rotary lobe, sliding vane, and gear type 

pumps. 

 (2) Fuel oil transfer pumps are generally rotary positive displacement type pumps equipped with 

integral pressure relief valves. The pumps are typically controlled by a locally mounted pump control 

panel. 

 (3) Hand-operated pumps are recommended for limited fuel oil transfer during unexpected outages 

of the electric motor-driven transfer pumps when the arrangement of the facility does not allow filling 

service tanks by gravity. 

 (4) The engine fuel oil pump supplies fuel oil to the engine fuel injector system at the required 

pressure for proper atomization of the fuel oil when the engine is operating. The fuel oil pump is usually 

mounted on the engine and is gear-driven from the engine. The engine-driven fuel oil pump is generally a 

positive displacement pump that is usually of the rotary lobe or gear type. Depending on the equipment 
TM 5-692-2

10-6 

manufacturer, the pump may be equipped with an internal pressure relief device that will return oil to the 

inlet side of the pump in the event the discharge of the pump is blocked. 

 (5) The engine priming pump is used to fill the fuel oil system any time the fuel system has been 

drained or opened for maintenance, or the engine has been out of service for an extended period of time. 

The priming pump is generally a hand-operated pump of the positive displacement type. 

k. Fuel oil. The manufacturer's recommended fuels should only be used as specified in the equipment 

literature. In general, most fuel oils will be supplied in accordance with Federal Specification A-A52557, Fuel Oil, Diesel; For Posts, Camps, and Stations; or Military Specification MIL-F-16884J, Fuel, 

Naval Distillate. Dirty fuels or fuels not meeting manufacturer’s minimum specifications will adversely 

affect combustion, filter life, injection system performance, service life, and ability to start. They will 

also affect service life of valves, turbine blades, pistons, rings, liners, and bearings. 

 (1) A supplier should provide certified documentation prior to or with the fuel oil delivery, 

verifying that the oil has been tested by a certified laboratory and meets the specifications for the fuel oil 

used by the facility. If documentation is not provided for the fuel oil, the facility should sample and 

analyze the fuel oil prior to use. The facility should take samples of all fuel oil delivered to the facility 

and retain the samples until that lot of fuel oil is used. Even if certified test reports are provided by the 

supplier, the facility should periodically have independent analyses performed to ensure compliance with 

purchase order or contract requirements. A simple delivery test is to visually check the quality of fuel oil 

delivered by collecting a sample of every fuel oil delivery in a clear, clean, dry, glass bottle. As each 

sample is taken, tightly cap the bottle and identify the bottle with information, such as date, supplier 

identification, purchase order, specification, etc. Allow the sample to settle for at least eight hours, and 

compare it with a similar bottle containing a fuel oil known to be of acceptable quality. A cloudy 

appearance suggests that fine droplets of water are entrained in the fuel which, in time, will settle to the 

bottom of the sample. Any contamination in gasoline or kerosene (lighter fractions) will float and collect 

at the top of the bottle. Contaminants, such as pipe scale or other foreign solids, will settle and collect at 

the bottom of the sample. If doubt exists as to the quality or identity of the fuel oil after the visual 

examination, the sample should be laboratory-analyzed for compliance with the specification. 

 (2) A periodic inspection of stored fuel and fuel systems is important to ensure reliable engine 

performance. Many engine failures are caused by fuel contamination. The following in-service testing 

suggestions are given for preventing and/or detecting post delivery fuel contamination. 

 

 (a) Monitor storage tanks (main tanks, intermediate tanks, day tanks, etc.) for accumulations 

of water, and remove water frequently. 

 (b) Keep storage tanks as full as possible (especially in cold weather). 

 (c) Do not mix different grades of fuel oil. 

 (d) Use oldest fuel oil inventory first. Long-term storage may result in the formation of sludge 

or the growth of soluble and insoluble bacteria that can clog fuel filters and injectors. If sludge in filters 

is noticed, switch to a different fuel oil supply and have suspect supply tested. If suspect supply is found 

to be unacceptable, discard unacceptable fuel oil. 

 (e) When strainers are cleaned or filters are changed, carefully inspect elements for unusual 

amounts of rust, scale, or sediment. If unusual amounts are observed, inspect fuel oil storage and delivery 
TM 5-692-2 

10-7 

system upstream of the strainer or filter to determine and correct the cause of the contamination. 
TM 5-692-2 

11-1 

CHAPTER 11 

LUBE OIL SYSTEMS 

11-1. Lube oil system design features

A general facility lube oil system serving a diesel engine is shown on figure 11-1. As shown, a system 

may consist of storage tanks, interconnecting piping and piping components, instrumentation and 

controls, filtration equipment (strainers and filters), pumps, conditioning equipment (centrifuge), heaters, 

and heat exchangers. 

a. Central lube oil storage and dispensing system. A central lube oil storage and dispensing system 

may consist of a clean lube oil receiving, storage, and supply system, and a dirty lube oil return and 

storage system. Where the facility is large, the system may also include intermediate storage tanks 

located at the points of lube oil use. A central lube oil storage and dispensing system with intermediate 

storage tanks is shown on figure 11-2. It is sometimes possible to remove the contaminants from dirty 

lube oil and recycle the cleaned lube oil to the clean oil system for reuse. A typical lube oil purification 

system is shown on figure 11-3. 

 (1) Clean lube oil may be received in bulk shipment. The bulk delivery unit may be equipped 

with a self-contained pumping unit, or an external pump which is part of the facility lube oil system 

(figure 11-2) may be required. In either case, facilities should have a strainer unit installed in the main 

lube oil tank fill line to minimize particulates entering the lube oil distribution system. The clean lube oil 

tank may also receive clean lube oil from intermediate storage tank overflows. 

 (a) The main clean lube oil tank may be equipped with some type of level gauge. The gauge may 

only have local readout capabilities, or a transmitter element may be part of the gauge so that the level in 

the tank can be monitored from a remote location. The tank may also be equipped with a level switch that 

activates an alarm when the lube oil level in the tank exceeds a preset level and is in danger of 

overflowing. This level switch may also be interlocked with the tank fill pump to turn the pump off, or 

may close a valve in the fill line. Depending on local climate, lube oil tanks installed outdoors or in 

unheated spaces may be equipped with a tank heater. 

 (b) A clean oil supply pump distributes the clean lube oil to end use points (figure 11-1) or, in 

large facilities, distributes the clean lube oil to intermediate storage facilities (figure 11-2). Typically, the 

clean oil supply pump operates only as needed. In many facilities, this allows clean lube oil supply and 

dirty lube oil disposal or centrifuge feed piping to be interconnected so that one pump system serves as 

the clean oil supply pump, the dirty oil disposal pump, and the lube oil purification system feed pump. 

 (c) Intermediate storage tanks (figure 11-2) may be used in large facilities to place a supply of 

lube oil close to an operation within the larger facility and allow that operation to supply individual user 

points within the operation from the intermediate tank. The intermediate tanks may be equipped with the 

same types of gauges, level switches, and control devices as the main storage tanks. Clean lube oil may 

be delivered by gravity or, as shown on figure 11-1, by a pump to a manual dispensing point or to the 

makeup lube oil connection on a piece of equipment. 
TM 5-692-2

11-2 

PI PI NC NC NC

ENGINE

DUPLEX FILTER

NC

TO OTHER

LUBE OILUSERS

LUBE OILSUMP

DUPLEX STRAINER

ELECTRIC MOTORDRIVEN PRELUBE

PUMP

ENGINE DRIVENLUBE OIL PUMP

LUBE OILCOOLER

NO

NO

NC

TO

DISPOSAL

FROM OTHERLUBE OIL USERS

DRAIN

DIRTY LUBE

OIL TANK TANK HEATER

STRAINER

(TYP)

(TYP)

CLEAN LUBE

OIL TANK

NCNC

NO

PUMP(TYP)

TANKVENT(TYP)

FOOTVALVE(TYP)

FILL

CHECKVALVE(TYP)

SHUTOFFVALVE(TYP)

PRESSUREINDICATOR

THERMOSTATIC

VALVE

Figure 11-1. General lube oil system – diesel engine 
TM 5-692-2 

11-3 

TANK HEATER(TYP)

MAIN CLEANLUBE OIL TANK

TANKVENT(TYP)

I H

LS

LG

S

S

LG I HLS MAIN DIRTY LUBE OIL TANK

TANKS

TO OTHERINTERMEDIATE

S

LUBE OIL

SUPPLY PUMP

TANK

FILL PUMP

LG I L

LS

I H

LS

A A

 PUMP

DISPENSING

S

INTERMEDIATECLEAN LUBEOIL STORAGE

TANK

DISPENSING POINTOR CONNECTIONTO EQUIPMENT LUBEOIL SUMP

A H

FS

TANK

INTERMEDIATEDIRTY LUBEOIL STORAGE

S

DIRTY OIL

 RETURN PUMP

A

H I

LS

LG

DISCHARGE

TO TANKTRUCK TO LUBE OIL

PURIFICATIONSYSTEM

STRAINER(TYPICAL)

USED

LUBE OIL

FILLCONNECTION

FROM OTHER LUBEOIL USERS

ISOLATION VALVE(TYPICAL)

LEVEL GAUGELEVEL SWITCHHIGH, INTERLOCK

FLOW SWITCH

LEVEL SWITCHLOW, INTERLOCK,ALARM

Figure 11-2. General lube oil storage and dispensing system 
TM 5-692-2

11-4 

PI

FEEDPUMP

DIRTYOIL

STORAGE

S

PI

PI TIFS

PUMP

DISCHARGE

VALVE(TYPICAL)

HEATER

STRAINER

SLUDGEWATER/OIL TOTREATMENT PLANT

CENTRIFUGE

SAMPLE

POINT

(TYPICAL)

TO CLEAN OIL TANK,AN INTERMEDIATE TANK,OR RECYCLE TO DIRTYOIL TANK

FLOWSWITCH

PRESSUREINDICATOR

TEMPERATUREINDICATOR

ISOLATION

Figure 11-3. Lube oil purification system 
TM 5-692-2 

11-5 

 (2) When the lube oil in a piece of equipment must be changed, the dirty lube oil may be returned 

to a main dirty lube oil tank. Depending on the size of the facility, there may be an intermediate dirty oil 

storage tank and a dirty oil return pump, as shown on figure 11-2. The dirty lube oil system may have 

many of the same type of devices and controls that were discussed as part of the clean lube oil system. 

For final disposal of dirty lube oil, the dirty lube oil tank will be equipped with a discharge. Depending 

on the tank location, oil may be discharged by gravity or by pumping. Final disposal may be delivery to a 

facility waste oil tank or to a waste disposal company, or oil recycling company tank truck or railroad 

tank car. Another discharge connection from the main dirty lube oil tank may be to a lube oil purification 

unit. 

 (3) Some dirty lube oil may be cleaned (purified) and reused as clean lube oil. Some lube oil users 

dirty the lube oil with contaminants that can be easily removed with commercially available centrifugal 

separation equipment. A typical centrifuge operation is shown on figure 11-3. Chemical analysis of the 

dirty lube oil determines whether the dirty lube oil can be cleaned and reused or is ready for final 

disposal.

b. Diesel engine lube oil system. Each diesel engine is equipped with a lubrication system that 

lubricates and cools various engine components when an engine operates. Depending on the service and 

size of the diesel engine, the lube oil system components may be part of the engine package and enginemounted or mounted on the engine skid (typical of emergency service diesel engines), or may be standalone components (typical of large primary service diesel engines). The lube oil system components for 

diesel engines in either primary or emergency service generally have the same components and operate in 

a similar manner. A typical emergency service diesel engine lube oil system is shown on figure 11-4. A 

typical primary service diesel engine lube oil system is shown on figure 11-5. 

 (1) Monitoring and control of an engine lube oil system is by means of various pressure, 

temperature, and level monitoring gauges, instruments, and control valves. Typical diesel engine lube oil 

controls are shown on figures 11-4 and 11-5. Many of the instruments include switches that may prevent 

the engine from starting if the lube oil pressure, temperature, or flow does not meet some minimum 

requirement. They also may sound an alarm or shut the engine down if the oil pressure is too low, the oil 

temperature is too high, or the pressure drop across a filter is too high. 

 (2) Many diesel engines will have a lube oil heating system to maintain the lube oil near the normal 

lube oil temperature when the primary service diesel engine is in standby operation. The lube oil heating 

system may consist of a strainer, a circulating pump, and a heater. A typical primary service diesel 

engine standby operation lube oil heating system is shown on figure 11-6. 

 (3) The electric motor-driven prelube pump in an emergency service diesel engine lube oil system 

generally operates all the time when the diesel engine is not operating, but is in ready-to-operate standby 

service. 

 (4) The electric motor-driven prelube pump on a primary service diesel engine generally only 

operates for a short period of time before the diesel engine is started. Some older primary service diesel 

engines have hand-operated prelube pumps. Before starting an engine, the operator must use the handoperated pump to pressurize the lube oil system. The prelube pump on primary service diesel engines 

may also be operated for a period of time when the engine is shut down to provide for controlled cooling 

of engine components. 
TM 5-692-2

11-6 

LEGEND AND ABBREVIATIONS

XX

X X

XX

A L

PS

A L

PS

S H

PS

A L

PS

A L

PS

S H

TS

S L

PS

S L

PS

PI TT

PI

DPI

SHAFT

DPI

PI

DPT

S L

PS

TT TE

F

I M

PS

F

LUBE OILSUMP VENT

OUTDOORSINDOORS

VENTFILTER DIESEL

ENGINE

LUBE OIL SUMP

(ENGINE CRANKCASE-WETSUMP)

STRAINER

IDLELOW

DESIGN

OPERATING

SPEED

ENGINE LUBE OILDISTRIBUTIONMANIFOLD

FILTER BANKFILTER BANK

VENTDRAINVENTDRAIN

DUPLEX LUBE OILFILTER ASSEMBLY

FILTER CHANGECONTROL VALVE

COOLINGWATERSUPPLYCOOLINGWATERRETURN

LUBE OILCOOLER

ASSEMBLY

LUBE OILTEMPERATURECONTROL VALVE

DIRTY

OIL

TANK

ELECTRIC MOTORDRIVEN PRELUBEOIL PUMP

DIESEL ENGINEDRIVEN LUBEOIL PUMP

DRAIN

LUBE OIL BY-PASS (OVERPRESSURE PROTECTION)BY-PASS FILTER(OPTIONAL)

OIL PUMP

INSTRUMENTATIONTYPE OF DEVICETYPE OF DEVICEFUNCTIONOPERATION

A ALARMDPI DIFFERENTIAL

PRESSURE INDICATOR

DPS DIFFERENTAIL

PRESSURE SWITCH

DPT DIFFERENTIAL

PRESSURE TRANSMITTER

H HIGH

I INTERLOCK

L LOW

LS LEVEL SWITCHM MINIMUMPI PRESSURE INDICATORPS PRESSURE SWITCH

PT PRESSURE TRANSMITTER

S SHUT DOWN

TE TEMPERATURE ELEMENT

TI TEMPERATURE INDICATORTT TEMPERATURE TRANSMITTER

Figure 11-4. Emergency service diesel engine lube oil system 
TM 5-692-2 

11-7 

SHAFT

F

F

LUBE OILSUMP VENT

OUTDOORSINDOORS

VENTFILTER

LUBE OIL SUMP

FILTER BANKFILTER BANK

DUPLEX LUBE OILFILTER ASSEMBLY

FILTER CHANGECONTROL VALVE

LUBE OILTEMPERATURECONTROL VALVE

DRAIN

BY-PASS FILTER(OPTIONAL)

F

DRAIN

DPI

FINAL OIL FILTER

(OPTIONAL)

DRAIN

DRAIN

VENT

VENT

DRAIN

LUBE OIL FILL

LUBE OILOVERFLOW

ENGINE CRANKCASE

(DRY SUMP)

LUBE OIL PRESSURE

CONTROL VALVE

DUPLEX STRAINER

SUMP DRAIN VALVE(NORMALLY CLOSED)

LUBEPUMP

PRELUBE

PUMP

ASSEMBLY

LUBE OIL COOLER

Figure 11-5. Primary service diesel engine lube oil system 
TM 5-692-2

11-8 

DRAIN

F

OVERFLOW

LUBE OIL

LUBE OIL SUMP

(DRY SUMP)

ENGINE CRANKCASE

S

STRAINER

LUBE OIL

CIRCULATING

PUMP

LUBE OIL

HEATER

RECIRCULATING

LUBE OIL FILTER

(OPTIONAL)

Figure 11-6. Diesel engine standby operation lube oil heating system 
TM 5-692-2 

11-9 

11-2. Lube oil system major components

The lube oil system is comprised of the following major components. 

a. Pumps. Various types of pumps are utilized in lube oil systems. 

 (1) For a discussion of the types of pumps which may be used in lube oil systems for transferring 

lube oil throughout the facility, see chapter 10. 

 (2) The engine oil pump pulls oil from the lube oil sump and is the pressure pump supplying 

lubricant to the engine when the engine is operating. The main lube oil pump is usually mounted on the 

engine and is a positive displacement pump, gear-driven by the engine. 

 (3) The prelube pump is generally a close-coupled, self-priming, positive displacement pump of 

the rotary lobe or gear type. The prelube pump is driven by an electric motor. The prelube pump pulls 

oil from the lube oil sump and supplies lubricant to the engine when the engine is in standby operation. 

b. Storage tanks. Storage tanks are generally fabricated from carbon steel plate with welded joints. 

All lube oil tanks should be fabricated and operated in accordance with the general requirements of 

National Fire Protection Association (NFPA) 30, Flammable and Combustible Liquids Code (1996), for 

flammable liquid storage. Most lube oil is stored in atmospheric storage tanks. Most storage atmospheric 

tanks are either the vertical or horizontal cylindrical type. 

c. Heat exchangers. Heat exchangers are commonly used in both the lube oil cooler and lube oil 

heating subsystems. 

 (1) The lube oil cooler assembly generally uses shell-and-tube heat exchangers. Depending on the 

lube oil flow rate, a single heat exchanger may be used or two or more units may be used. When more 

than one heat exchanger unit is required, it is common to connect the heat exchangers 

in parallel. Lube oil is generally piped through the shell (outside the tubes), and the cooling fluid is piped 

through the tubes (inside the tubes). Some newer facilities may use, or may have replaced old shell-andtube units with, plate type heat exchangers. 

 (2) The heat source may be steam (preferred for high capacity heating), hot oil, hot water, or low 

density electric (low flow applications) depending on the needs of other operations at the facility. 

 (a) Lube oil storage tank heaters are generally of the convection type. The tank heater should 

be designed for insertion into the storage tank through a manhole that does not exceed 24 inches diameter. 

 Convection type heaters should have the capacity to raise the temperature of a full tank of lube oil by 

about 60°F in 24 hours. 

 (b) Lube oil in-line heaters are generally of the shell-and-tube type for liquid-to-liquid heat 

transfer or the electric bayonet type. For electric heaters, the heater should be designed so that the heating 

element can be removed without draining the heater shell. 

d. Strainers. Strainers are used to remove coarse particulate matter that may damage rotating 

equipment. 
TM 5-692-2

11-10 

e. Filters. Particulate filters are used to remove fine particulate from lube oils. 

f. Centrifuge. The lube oil purification system centrifuge is utilized for purification (separation of 

liquids) and clarification (removal of solids). This unit is generally a high-speed centrifuge with a selfcleaning bowl. Centrifuge units are generally supplied as complete units. They include: differential 

pressure gauges; sight glass elements on the water discharge; a diaphragm-operated control valve in the 

main discharge with a flow-limiting pilot and a float-operated pilot to close the main valve if the water 

level in the sump rises above a set point; an automatic, float-controlled, diaphragm-operated water drain 

valve; a manual water drain valve; a head lifting device; and automatic air release devices. 

g. Engine lube oil temperature control valves. Temperature control valves are used in engine cooling 

systems which use a lube oil bypass to maintain either a constant lube oil temperature at the engine lube 

oil outlet or a constant lube oil supply temperature. The most common engine lube oil temperature 

control valve is a self-contained, factory-set, thermostatic element-operated, sealed three-way valve unit. 

When installed to maintain a constant lube oil outlet temperature, the unit is referred to as a diverting 

valve. When installed to maintain a constant lube oil inlet temperature, the unit is referred to as a mixing 

valve. The valve is designed to maintain full lube oil flow through the engine cooling system. A 

thermostatic element in one of the valve ports controls a sliding valve assembly that controls the flow 

through that port. In the closed position, all of the flow is from the inlet port and out the other port. As 

the thermostatic element moves the sliding valve off the valve seat, a portion of the flow is from the inlet 

and through the thermostatically controlled port. At full lift, all of the flow is through the thermostatic 

port. 

 

h. Valves and piping. This subsection presents an overview of the types of piping components and 

design and testing considerations related to facility lube oil distribution and dispensing piping systems. 

Information contained in this section applies to field-installed piping. Piping design, materials, 

fabrication, assembly, erection, inspection, and pressure tests for facility piping systems should be in 

accordance with American Society of Mechanical Engineers (ASME) 31.3, Process Piping. Inspection of 

modified piping installations should include radiographic or magnetic particle inspection of welds where 

applicable. New piping should also be hydrostatic tested. During testing, system components such as 

storage tanks, filters, centrifuges, or similar equipment that was not designed for the piping test pressure 

must be disconnected and protected against damage by overpressure. 

 

(1) Valve bodies and bonnets should, as a minimum, be cast or forged carbon steel in accordance 

with American Society for Testing and Materials (ASTM) A 105, Standard Specification for Carbon Steel 

Forgings for Piping Applications (1998), for forged body valves and ASTM A 216, Standard 

Specification for Steel Castings, Carbon, Suitable for Fusion Welding, for High-Temperature Service 

(1998), Grade WBC, for cast body valves. Cast iron or bronze body valves are not suitable for lube oil 

service. The typical types of valves and valve trims used in lube oil service are as follows. 

 (a) Gate valves may be used for lube oil shutoff service where a slow closure is acceptable 

and where absolute bubbletight closure is not a critical consideration. Gate valves may be rising stem, 

outside stem and yoke (OS&Y), or double-disk type. 

 (b) Ball, butterfly, or non-lubricated plug valves are generally used where quick or frequent 

opening or closing is required. Synthetic seals or seating material in ball and butterfly valves should be 

Teflon or viton. Butterfly valves shall be high-performance type with eccentric disk shaft and camming 

action for bubbletight shutoff. 
TM 5-692-2 

11-11 

 (c) Double-seated plug or ball valves with an automatic body bleed between the seats should 

be used for separation of product services on tank shell connections and other locations critical to 

pressure testing of piping. 

 (d) Check valves are used in the lube oil system to prevent backflow through pumps, branch 

lines, meters, or other locations where runback or reverse flow must be avoided. Check valves may be of 

the swing disk, spring-loaded poppet, ball, or diaphragm-actuated types. Swing checks should be a softseated, non-slamming type with renewable seats and disks. 

 (e) Globe valves are used in lube oil systems at locations where manually controlling the flow 

rate is required. General use of globe valves should be avoided because of their high resistance to flow. 

 (f) Diaphragm type valves typically operate on the basis of pressure differential and are used 

for automatic or remote control of functions, such as flow control, pressure control, or level control. All 

diaphragm type valves should have Teflon or viton packing, seals, and trim. 

 (2) Pipe used in lube oil systems is generally, as a minimum, carbon steel conforming to the 

requirements of ASTM A 106, Standard Specification for Seamless Carbon Steel Pipe for HighTemperature Service (1999), Grade B, seamless for pipe 1-1/2 inches in diameter and smaller and ASTM 

A 53, Standard Specification for Pipe, Steel, Black and Hot-Dipped, Zinc-Coated, Welded and Seamless 

(1999), Grade B, ERW for pipe 2 inches in diameter and larger. Pipe 1-1/2 inches in diameter and 

smaller should be Schedule 80 in accordance with ASME B36.10M, Welded and Seamless Wrought Steel 

Pipe (1996), and pipe 2 inches in diameter and larger should be Schedule 40. 
TM 5-692-2 

12-1 

CHAPTER 12 

ENGINE INTAKE AND EXHAUST SYSTEMS 

12-1. Engine intake and exhaust system design features 

The function of an engine intake and exhaust system is to deliver combustion air to the engine and 

dispose of the engine exhaust with as little impact as possible on engine performance. The air intake 

system may consist of ducts, air filter elements, silencers, etc., as required to lead the combustion air to 

the engine manifold or blower (turbocharger) air inlet connection. In addition to supplying combustion 

air to the engine, another important function of the air intake system is to condition the air (usually just 

particulate removal) to protect engine parts from airborne impurities (dirt and other particulate matter). 

Air intake systems may also have devices to reduce noise transmitted from the engines. Ducted air intake 

systems permit the engine to be installed at a location remote from the supply of combustion air. A basic 

exhaust system consists of an exhaust gas discharge duct, with components to accommodate expansion of 

the duct, and an exhaust gas silencer (muffler). Some exhaust systems may include components to use 

the hot exhaust gas to provide the heat for some other process or operation (waste heat recovery), such as 

fuel oil heating, hot water production, steam generation, etc. When an engine operates within a facility 

that is protected against attack (blast-protected), the intake and exhaust system must include blast 

protection features. Maintaining the filter elements, keeping the air intake and exhaust gas discharge 

points free from obstructions, (such as severely dented or crushed duct sections) that restrict the free flow 

of combustion air to the engine and exhaust gas from the engine is very important. 

a. Basic air intake and exhaust gas systems. A typical basic air intake and exhaust system has air 

entering the system through an intake air filter. Depending on the size of the engine, the design use of the 

engine, and the location where the engine is to be used, the air intake filter may range in size from a small 

replaceable paper filter element to a large filter bank with numerous filter elements. From the intake 

filter, the air may pass through a separate air intake silencer before reaching the engine combustion air 

inlet connection. On many engines, the air intake filter may also provide the necessary air intake 

silencing eliminating the need for a separate air intake silencer. The basic air intake system described 

might be used on many different kinds of engines (diesel, gaseous fuel, and gasoline) and compressors. 

 (1) On the normally aspirated diesel engine, the combustion air passes through an air shutoff valve 

to the engine combustion air distribution manifold and then to individual engine cylinders. On the 

turbocharged (or air-scavenged) engine, a fan, blower, or compressor device provides compressed air 

(more pounds of air in the same space) through an air shutoff valve and aftercooler to the engine 

combustion air distribution manifold. Depending on the engine size and design, the turbocharger device 

may be standalone (not driven by the engine) or driven by the engine (engine-driven). An engine-driven 

turbocharger may be directly driven by the engine through a gear or belt drive by the flow of exhaust 

gases through a turbine section. At the same time the turbocharger (or air scavenger) increases the 

pressure of the combustion air supplied to the engine, the temperature of the air is also increased. Since 

the diesel engine is a compression-ignition cycle, an aftercooler may be used on diesel engines to reduce 

the air temperature low enough to prevent early ignition of the air-fuel mixture. 

 (2) The operation of a basic air intake system is usually monitored by pressure gauges at the inlet 

of the engine air intake manifold (on the inlet side of any turbocharger or air scavenger device). As the 

air intake filter elements become dirty, the vacuum slowly increases. When the vacuum increases beyond 
TM 5-692-2

12-2 

an engine manufacturer-specified value, the intake air filter elements may need to be cleaned or replaced. 

 Most systems will have temperature gauges to monitor the exhaust gas temperatures. Systems with 

turbocharger or air scavenger devices may also have pressure gauges to monitor the combustion air 

pressure at the discharge of the device. Systems with aftercoolers may also have pressure gauges to 

monitor the combustion air pressure at the discharge of the aftercooler and temperature indicators to 

monitor the combustion air temperature at the inlet and outlet of the aftercooler. 

b. Dusty environment air intake system. Engines used in dusty environments may need air intake 

filters with more face area or, depending on the dust size and frequency of dusty conditions, a series of 

filters may be required to protect the engine. In areas where the amount of dust in the air varies with 

weather, the filter system may need to be capable of responding to varying dust concentrations. A 

common dusty environment air intake and exhaust system is where the engine is installed in a building. 

Combustion air for the engine is pulled from inside the building through an intake air filter assembly, and 

the exhaust gas is ducted to outside the building and discharged through an engine exhaust silencer 

installed outside. The roll filter bank, by advancing either on a timed cycle or when the pressure drop 

across the filter reaches a preset value, responds to variable dust conditions. The extended filter surface 

bank (deep cell filter) provides a lot of total filter area compared to the face area of the filter frame to 

minimize how often filters have to be changed. 

c. Blast-protected air intake and exhaust systems. Blast protection can mean different things 

depending on the type of facility. For this discussion, a blast-protected facility refers to a facility that is 

designed to withstand a specific blast effect and continue in operation throughout the design level attack. 

 (1) Figure 12-1 shows a blast-protected air intake system. The engine (not shown on the figure) is 

located deep within the facility and pulls combustion air from inside the facility through an engine intake 

air filter. In this example, the air intake is not only providing combustion air to the engines, but is also 

providing air to occupied spaces within the facility. The example blast-protected intake system utilizes an 

intake air fan to draw air into the facility. In facilities using intake air fans, there is usually a standby fan 

installed so that fans can be removed from service for maintenance and so a spare fan is available in the 

event an in-use fan fails. The example blast-protected air intake system is installed inside a blast-resistant 

structure. Air enters the structure through an array of blast valve assemblies that are built into the blastresistant structure. See chapter 30 for a detailed description of blast valves and blast valve operation and 

maintenance. 

 (a) In addition to the roll filter assembly and the deep cell filter bank, the example blastprotected air intake system includes a prefilter element and a CBR (chemical-biological-radiological) 

filter bank. The prefilter is provided to handle short-term, very high dust and debris concentrations that 

may occur during an attack. Many systems allow intake air to bypass the prefilter during periods when 

the blast protection system is not in the blast mode of operation. If the blast protection system is in 

operation, the prefilter may also be bypassed when the filter elements become plugged. 

 (b) The CBR filter bank removes chemical and biological agents and radioactive particles 

from the intake air. As with the prefilter, many blast-protected air intake systems allow intake air to 

bypass the CBR filter elements when the blast protection system is not in the blast mode of operation. 

While this prevents the performance of the CBR filters from being impaired by a buildup of dirt, the 

reactive filter media deteriorates from exposure to air and requires replacement on a regular basis even if 

the filter bank has not been in service. 
TM 5-692-2 

12-3 

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FILTER PLENUM

BY-PASSDAMPER

BY-PASSDAMPER

INTAKEAIRFAN

CBR FILTER

BANK

DEEP CELLFILTER BANK

ROLL FILTERASSEMBLY

PREFILTER

BLAST RESISTANT

FACILITY

BLAST VALVEASSEMBLY

OUTDOORS

SENSORPORT

BLAST

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Figure 12-1. Blast-protected air intake system 
TM 5-692-2

12-4 

 (2) Figures 12-2 and 12-3 show blast-protected engine exhaust systems. On figure 12-2, the 

engine exhaust gas is discharged into a mixing chamber and the mixing chamber discharges to the 

outdoors through an array of blast valve assemblies (only one valve is shown on each figure). There are 

two features in this blast-protected engine exhaust system not usually found on engine exhaust systems in 

ordinary facilities, an exhaust cooling system and an exhaust isolation system. 

 (a) During normal operation, the engine exhaust is cooled to prevent damage to the blast valve 

assembly. During periods when the blast-protected facility is not in the blast mode of operation, other 

systems (such as cooling towers) can provide exhaust cooling by mixing with the engine exhaust. When 

the facility is in the blast mode of operation and many normal operations are curtailed, a water spray 

system similar to the system shown on figure 12-2 may be used. 

 (b) Another blast-protected exhaust system option is shown on figure 12-3. In this example, 

each engine exhaust duct has a high-temperature blast valve in the exhaust duct. When blast sensors trip 

the valve, an exhaust system relief valve (poppet valve) diverts the exhaust to an unoccupied space within 

the blast-protected facility. The exhaust systems on units not in operation are potential points of 

contaminant (exhaust gases from operating units, chemical or biological agents, radioactive particles, etc.) 

entry into protected spaces. Therefore, exhaust systems in blast-protected facilities may include valves 

(or dampers) in the exhaust duct system that automatically close when a unit is not in operation and the 

facility is in the blast mode of operation. The example blast-protected exhaust system shown on figure 

12-2 has two isolation valves in series with an air purge in between to prevent backflow through the 

exhaust system of an out-of-service unit. 

12-2. Engine intake and exhaust system major components 

Descriptions of major system components for engine air intake and exhaust systems will be limited to 

components directly related to the operation of the engine. These components include combustion air 

particulate removal filters, intake air silencers, exhaust silencers, and air intake and exhaust duct materials 

of construction and duct system components. Items which impact the operation of the air intake and 

exhaust systems that are part of other systems (such as blast protection, compressed air, and industrial 

water) are described in other chapters of this manual. 

a. Combustion air particulate removal filters. Common combustion air particulate removal filters are 

either wet type or dry type. Within the filter types, the filter elements may be either permanent (clean and 

reuse) or disposable. 

 (1) Three common wet type filters used to remove particulate matter from combustion air include 

the following. 

 

 (a) Viscous impingement filters are packed with fine strands of wire coated with oil. Air 

passing through the filter element impinges on the wires, and the oil coating traps the dust particles. 

 (b) Oil bath filters have a reservoir of oil. The filter housing is arranged to sweep the surface 

of the oil bath with the combustion air passing through the filter that agitates the bath. The oil coats and 

traps the particles, and the oil-coated particles collect in the oil reservoir. 
TM 5-692-2 

12-5 

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BLAST RESISTANT

FACILITY

BLAST VALVEASSEMBLY BLAST

SENSOR

PORT

FILTER ASSEMBLY

INTAKE AIR

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OPERATIONWITH COOLEXHAUST AIR

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ISOLATION VALVE

NORMALLY UNOCCUPIEDGALLERY, TUNNEL,HALL, ETC.

TEMPERATUREELEMENT

MIXINGCHAMBER

EXHAUST COOLINGSPRAY NOZZLEASSEMBLY

ISOLATION 

VALVE

HIGH PRESSURE

WATER SUPPLY

ENGINE

STRAINER (TYP)

SOLENOIDVALVE (TYP)

CHECK VALVE

PRESSURE REGULATINGVALVE COMPRESSED AIR

SUPPLY

Figure 12-2. Blast-protected engine exhaust system 
TM 5-692-2

12-6 

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STONE FILLEDEXHAUST SHAFT

POPPETVALVE

BLASTVALVE

Figure 12-3. Blast-protected exhaust system 
TM 5-692-2 

12-7 

 (c) Traveling screen filters are a combination of the viscous impingement and oil bath filters. 

A moving wire screen is continuously passed through an oil bath to be coated with oil. Air passing 

through impinges on the wire screen, and the oil coating traps the dust particles. As the wire screen 

passes through the oil bath, the dust particles are washed off the screen and collect in the oil reservoir. 

Most wet type filter elements are considered to be permanent elements. 

 (2) Many materials can be used to make filter media for dry type combustion air filters. Typical 

materials are fiberglass, polyester, cotton (a form of cellulose), and paper (also a form of cellulose). 

Common combustion air filter media types using these materials are woven, felted, pad, and mesh (or 

blanket). Most common combustion air dry type filter elements are replaceable elements. However, 

some units with a prefilter section designed to remove small volumes of relatively large diameter particles 

may use permanent filter elements. 

 b. Intake air and exhaust silencers. Common silencer units reduce (attenuate) the noise transmitted 

through the system by decreasing the velocity of the gas stream and absorbing the sound or by canceling 

sound waves with other sound waves from the same source. Most engine silencer units (intake and 

exhaust) are installed in-line with the duct system. Silencer units are usually several times larger in 

diameter than the duct. Silencer units may be a perforated flow-through tube which allows noise to 

escape into side chambers where the noise is absorbed. Silencer units may also be a baffled unit where 

changes in direction first separate and then recombine the gas stream causing sound waves to cancel each 

other. Common silencer units used with internal combustion engines have an internal volume equal to six 

to eight times the displacement of the engine. Noise transmitted through most combustion air intake 

systems has much less energy than noise transmitted through the exhaust gas system. The reduced noise 

energy in the intake system can be abated by the intake air filter media acting as a baffle and a noise 

absorbing mass. Therefore, most combustion air intake systems do not have a separate silencer unit. 

Some engines with turbocharger units that are driven by a turbine section turned by the exhaust gases may 

not require an exhaust silencer. 

c. Intake and exhaust duct and duct components. Many materials may be used to fabricate the duct 

system and duct system components. One common material is carbon steel and another is stainless steel. 

The material selection is usually an economic decision during the initial design that considers the cost of 

the initial installation and future maintenance costs. Without careful study, repairs to existing systems 

should use the same materials and material thickness used in the original installation. 

 (1) The most common method for moving gases under moderate pressures is by means of some 

type of fan. There are two broad categories of fans: axial flow and centrifugal. Axial fans use propellers 

to move the air and are generally classed into three subtypes: propeller, tube axial, and vane axial. 

Centrifugal fans use fan wheels to move the air and are also classed into three subtypes according to the 

basic characteristics of the wheel used: forward curved, backward curved, and radial. 

 (2) A common expansion joint used to isolate rotating equipment from connected loads and to 

control thermal movements is a bellows type joint. These joints can accommodate axial, lateral, and 

angular motion, or limited combinations of each motion. For a specific set of operating conditions and a 

specific material of construction, the wall thickness of the expansion joint section, the outside diameter of 

the bellows, and the number of convolutions determine the amount of movement the expansion joint can 

accommodate. 

(a) Bellows type joints can be fabricated from a wide variety of materials. Metal expansion 

joints are typically used in diesel engine air intake and exhaust gas systems. A common material of 
TM 5-692-2

12-8 

construction for these expansion joints is stainless steel. Expansion joints should be sized and constructed 

in accordance with the Standards of the Expansion Joint Manufacturers Association, the appropriate 

sections of the American National Standards Institute (ANSI) Power Piping Codes, and the appropriate 

sections of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Codes. 

 (b) Expansion joint failures are common maintenance problems. Common failure modes and 

the cause of the failures are shown in table 12-1. When faced with an expansion joint failure, maintenance 

personnel may make repairs to keep critical systems in operation. However, most field repairs change the 

response characteristics of the system that may cause problems in other parts of the system (e.g., engine 

manifold cracking, duct hanger deformation or failures, facility structural member deformation or failures, 

etc.). Repairs to expansion joints should be considered temporary, and arrangements should be made to 

replace the expansion joint as soon as possible. Except for the failure associated with chlorides leaching 

from insulating materials, all of the listed failure modes are the result of the expansion joint design not 

conforming to existing conditions. When the expansion joint is replaced, the design of the new expansion 

joint should reflect the current operating conditions. However, if there is a significant change in response 

characteristics of the replacement expansion joint relative to the original expansion joint, other 

modifications in the duct system may be required. This makes evaluating expansion joint problems and 

maintaining expansion joints a maintenance and facility engineering responsibility. If expansion joints 

fail because the actual movements to be accommodated by the joints exceed the capacity of the joints, the 

system needs to be reanalyzed and appropriate modifications need to be designed. 

Table 12-1. Typical bellows material failures 

Failure Mode Most Frequent Cause(s) 

 Stress Corrosion 

 Fatigue 

 Carbide Precipitation 

 Squirm and Burst 

Chlorides, caustic, high temperature 

sulfurous gas acting on nickel alloys, 

leaching of chlorides from insulation. 

Unanticipated vibration, 

unanticipated temperature changes. 

Use of unstabilized materials at high 

temperatures. 

Over pressurization. 

 (3) Butterfly or slide gate type valves (or dampers) are commonly used to provide isolation in 

blast-protected exhaust gas systems. Butterfly valves should have an offset operating shaft design so that 

the disk contacts a continuous disk-sealing surface. While a variety of materials may be used in the valve 

body, valve trim components are typically stainless steel or materials with similar heat- and corrosionresisting properties. 
TM 5-692-2 

13-1 

CHAPTER 13 

COOLING SYSTEMS 

13-1. Cooling system design features 

Diesel engines are heat-generating sources cooled by circulating a water-based coolant through a water 

jacket which is part of the equipment. The coolant is circulated through piping to a device to remove the 

heat added to the coolant by the engine and then back to the engine. Typical components associated with 

the cooling loop serving an engine are pumps, air separators, coolant expansion (or surge) tanks, 

temperature control valves, temperature switches, temperature and pressure indicators, and the coolant 

heat removal device. 

 

a. General. Cooling systems are either closed or open. In closed systems, the system is designed to 

prevent significant losses from the system so the same coolant is used over and over. The quality of the 

coolant is easier and less costly to maintain in a closed system. Open systems either waste a coolant (use 

once and discharge to a drain) or re-circulate the coolant through systems that cool the coolant by 

evaporation, resulting in a buildup of impurities in the coolant stream. See figures 13-1, -2, and -3. 

 (1) Because of the need to carefully control coolant chemistry to prevent fouling of heat transfer 

surfaces and the need to closely control engine temperatures, closed cooling systems are generally used to 

cool diesel engines. The closed engine cooling system may also provide cooling for other components 

supporting the operation of the diesel engine, such as the lube oil cooler and the combustion air aftercooler on turbo-charged engines. Depending on the cooling needs of each device associated with the 

engine, all the devices may be cooled by a single-loop system, or multiple loops may be required. 

 (2) In an open system, water is re-circulated through an air contact cooling system, such as a 

cooling tower, cooling pond, or spray pond. Because of maintenance concerns relating to water quality, 

open cooling systems are generally not used on land-based diesel engines (or similar equipment), except 

as short-term emergency backup to a closed system. 

 (a) Although open cooling systems are usually not used to provide direct cooling to devices 

like diesel engines, re-circulating cooling water systems using cooling towers, cooling ponds, and spray 

ponds may be an important part of the overall cooling system for a facility. A large facility may have a 

lot of equipment that is water-cooled. The quantity of water required by each water-cooled device may 

not be significant, but the total quantity of cooling water required adds up to a large water bill or cannot 

be provided by the resources available to the site. And even if resources are available, some blastprotected facilities must disconnect from outside resources when in the blast mode of operation. 

 (b) Common devices used to remove heat from cooling water and supply re-circulating 

systems are cooling ponds (or open reservoirs), spray ponds, and cooling towers. The primary heat 

transfer mechanism for these devices is evaporation. When water evaporates, most of the impurities in 

the water are left behind that increases the impurities in the re-circulating water. These impurities can 

form scale on heat exchanger heat transfer surfaces, the walls of water distribution and return piping, and 

cooling tower surfaces, and will require maintenance to be performed to remove (or at least significantly 
TM 5-692-2

13-2 

C

B

A

F

P

D

E

D

P

F

A

B

C

VENT

OR

PRESSURE RELIEF OR

PRESSURE CONTROL VALVE

DASHED LINES

INDICATE 

ALTERNATE

LOCATIONS

G

VENT

LOW TEMPERATURE ENGINE

 SINGLE LOOP

INTERMEDIATE TEMPERATURE ENGINE

WITH COOLANT BY-PASS

E

SEE FIGURE 8-3 FOR LEGEND

Figure 13-1. Examples of engine cooling systems (1) 
TM 5-692-2 

13-3 

E

P

F

A

B

G

VENT

HOT WATER

UNIT HEATER

(TYP)

VENT

D

F

A

B

C

G

D

C

B

K

P (2 SECTIONS)

ENGINE WITH HEAT RECOVERY

TURBOCHARGED INTERMEDIATE

TEMPERATURE ENGINE

E E

SEE FIGURE 8-3 FOR LEGEND

Figure 13-2. Examples of engine cooling systems (2) 

 
TM 5-692-2

13-4 

K

B

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VENT

G

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B

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E

F

P

STEAM HEADER

LEGEND 

A ENGINE

B PUMP

C AIR SEPARATOR

D EXPANSION TANK

 W/LEVEL GAUGE

E MAKE-UP COOLANT

 CONNECTION

F LUBE OIL COOLER

G TEMPERATURE

 CONTROL VALVE

H BACK PRESSURE VALVE

J CONDENSATE RECEIVER

K AFTERCOOLER (OR

 TURBOCHARGEED ENGINE)

L EXHAUST SILENCER WITH

 HEAT RECOVERY

M STEAM CONDENSER

N FLASH TANK

P COOLANT COOLING

 DEVICE/SYSTEM

HIGH TEMPERATURE ENGINE

WITH EXHAUST HEAT RECOVERY

E

Figure 13-3. Examples of engine cooling systems (3) 
TM 5-692-2 

13-5 

reduce) the built-up scale. Chemical treatment of and blowdown from open re-circulating water systems 

are tools for reducing the build up of contaminants. 

b. Typical primary service diesel engine cooling system. A typical engine cooling system for a large 

stationary, primary service, turbo-charged diesel engine is shown on figure 13-4. The cooling system 

consists of three cooling loops: a loop for the engine, a loop for the lube oil cooler, and a loop for the 

combustion air after-cooler. Heat is removed from the closed engine cooling system in the jacket water 

heat exchanger that is a liquid-to-liquid heat exchanger. The cooling water supply for the jacket water 

heat exchanger is a closed re-circulating cooling water system using a cooling tower. The cooling water 

supply for the after-cooler is also from the cooling tower system, while the cooling water supply for the 

lube oil cooler is from an industrial water re-circulating system that uses an open cooling reservoir. 

 (1) Hot coolant from the engine is piped to a temperature control valve (thermostat). The 

temperature control valve modulates the coolant flow between a branch that flows through the jacket 

water heat exchanger and a branch that bypasses the heat exchanger. After cooling, the total coolant 

stream enters an air separator unit. (Many cooling systems do not use an air separator unit.) The air 

separator is designed to separate gas bubbles from the coolant stream so the bubbles can be vented from 

the system. The coolant is then piped to the inlet of an engine-driven coolant pump that circulates water 

through the engine cooling water jacket. The expansion tank which, in the example system, is connected 

into the system through the air separator unit serves three equally important functions. The expansion 

tank provides space for coolant expansion, provides space for entrained gases to be removed from the 

system, and provides a static head which controls coolant flashing to steam in the system operating near 

the boiling point and prevents cavitation in the coolant circulating pump. 

 (2) The typical engine cooling system is equipped with a "keep warm" system. The keep warm 

system operates when the engine is not operating, but is in the standby ready to start mode. The keep 

warm system uses an electric motor-driven circulating pump to circulate jacket cooling water through a 

heater unit (usually an electric immersion heater) and then into the engine water jacket. The immersion 

heater heats the coolant to a temperature near the design coolant temperature for the engine. This 

minimizes startup wear on the engine and prolongs engine life. Maintaining the coolant, and hence the 

engine, near operating temperature also helps ensure that the engine will start. 

 (3) In the typical primary service diesel engine cooling system, the cooling water supply to the 

jacket water heat exchanger and lube oil cooler is either on or off. Temperature regulation of the engine 

coolant and lube oil temperatures is by bypass temperature control valves within the engine and lube oil 

cooling systems. The after-cooler cooling water supply also contains an on-off valve, but the temperature 

of the combustion air is regulated by a bypass valve in the cooling water piping at the after-cooler. When 

the engine receives a start signal, the engine controls open the on-off valves in the cooling waterlines. 

When the flow switches in the discharge lines indicate that cooling water flow has been established, the 

engine is allowed to start. 

 (4) In the typical primary service diesel engine cooling system, a number of pressure and 

temperature indicators are shown throughout the system. Readouts from these devices are important 

measures of how the system is operating. The readout units of these devices are usually mounted on the 

local control panel mounted at the diesel engine. The two main control devices for the engine cooling 

system are the two temperature indicators with output switches that either alarm on high engine coolant 

temperature or shut down the engine because of high engine coolant temperature. The alarm set point is 

usually set lower than the shutdown set point to permit the operator to investigate and correct the problem 

or start a standby engine before a high-temperature shutdown occurs. 
TM 5-692-2

13-6 

A H

LS

A L

LS

LG

FS

S H

TI

A H

TI

PI

TI

FS

TT TCV TI

FS

TI

TCV

FS

TCV

TIFS

MEZZANINE

LEVELMAIN

OPERATING

FLOORLEVEL

TOWER COOLING WATER RETURNTOWER COOLING WATER SUPPLY

COOLING TOWER

O/C

TI

JACKET WATERHEAT EXCHANGER

O/C

NC

EXPANSIONTANK

AIR

SEPARATOR

NC

NO NO

KEEP WARM

HEATER

KEEP WARMCIRCULATING

PUMP

COOLANT MAKE-UP

STORAGE AND 

DISPENSING SYSTERM

NC

ENGINE

ENGINE DRIVEN COOLANTCIRCULATING PUMP

TURBOCHARGERAFTERCOOLER

O/C

INDUSTRIAL

WATER HEADERS

SUPPLYRETURN

O/C

LUBE OILCOOLER

NC

TI

LUBE OIL

FS

XX

X X

XXX

XX

ISOLATION VALVEGLOBE VALVEVALVE WITH OPERATOR CHECK VALVESAFETY RELIEF VALVE3-WAY VALVE WITHOPERATORFLOW SWITDHPUMPINSTRUMENTATIONTYPE OF DEVICEFUNCTIONOPERATION

AFSHLLGLSNCNOO/CSTCVTITT

ALARMFLOW SWITCHHIGHLOWLEVEL GAUGELEVEL SWITCHNORMALLY CLOSEDNORMALLY OPENOPEN/CLOSE OPERATIONSHUT DOWNTEMPERATURE CONTROLVALVETEMPERATURE INDICATORTEMPERATURE TRANSMITTER

LEGEND AND

ABBREVIATIONS

Figure 13-4. Typical primary service diesel engine cooling system 
TM 5-692-2 

13-7 

c. Typical radiator diesel engine cooling system. A typical stand-alone engine cooling system for a 

turbo-charged diesel engine is shown on figure 13-5. The cooling system consists of two cooling loops: 

a loop for the engine, and a loop for the lube oil cooler and combustion air after-cooler. Heat is removed 

from the closed engine cooling system in the jacket water radiator and the lube oil/after-cooler radiator 

which are liquid-to-air heat exchangers. The use of radiators with fan motors powered from the engine 

electrical system makes the engine cooling system independent of other facility systems and is typical of 

cooling systems for emergency service diesel engines. However, radiator cooling systems are also used 

in many primary service diesel engine installations where the radiator fan motors may be powered by the 

engine electrical systems or driven by an electric motor powered from the facility electrical distribution 

system. 

d. Coolant makeup storage and dispensing systems. Most facilities with diesel engines have a coolant 

makeup storage and dispensing system. In large facilities, one system can usually serve all of the engines. 

 At a minimum, the system will consist of a tank for preparing and storing large quantities of engine 

coolant with a pump and distribution piping to dispensing points near the makeup coolant fill points on 

equipment. Most systems are directly connected to the makeup coolant fill points. Most systems also 

include storage so that coolant drained from an engine during maintenance can be reused. In some 

systems with used coolant storage, there is either a separate coolant drain pump or the coolant distribution 

and drain piping is connected into a manifold that allows the makeup coolant dispensing pump to serve as 

both a dispensing and drain pump. 

e. Coolant quality. Water treatment is critical to the operation of the engine cooling systems. It is 

important that a coolant quality monitoring and treatment program for a facility be developed and 

followed. Because of the wide variation in water supplies available and the likelihood of seasonal 

variations within a single source, no single coolant treatment program will work at every facility. Each 

facility requires a program tailored to the equipment used in the facility and the quality of the available 

water supply. A minimum water treatment program must provide for control of coolant quality 

parameters as follows. 

 (1) In outdoor installations, engine operations that may be shut down in cold weather must 

be protected against freezing. 

 (2) Only water with a hardness value of 0 (zero) should be used to make engine coolant. 

 (3) The pH value of the coolant solution should be between 8.0 and 9.5. 

 (4) The total solids concentration of the coolant should not exceed 3,500 parts per million. 

 (5) The oxygen content of the coolant should be maintained at a value of 0 (zero) by the addition 

of oxygen scavenging compounds, or the metal surfaces of the engine need to be protected against 

corrosion by the addition of corrosion inhibiting compounds. 

 f. Typical cooling tower system. A typical cooling tower (evaporative cooler, spray cooler, etc.) is 

shown on figure 13-6. Tower re-circulating cooling water flows from the pan section through a strainer 

built into the pan section into the spray (tower circulating) pump. The spray pump provides water to the 

spray header (or as a circulating pump discharges water into an open channel water distribution header). 

The downward flow of water in the cooling tower flows over the outside surface of the cooling coil. The 
TM 5-692-2

13-8 

evaporation of tower cooling water absorbs heat transferred through the cooling coil tube wall from the 

facility re-circulating cooling water stream. FS FS

A L

LS TCV

ISOLATION VALVEGLOBE VALVECHECK VALVE3-WAY VALVE WITHOPERATOR

FLOW SWITCH

PUMP

INSTRUMENTATIONTYPE OF DEVICEFUNCTIONOPERATION

AFSHLLSTCVTITT

ALARMFLOW SWITCHHIGHLOWLEVEL SWITCHTEMPERATURE CONTROLVALVETEMPERATURE INDICATORTEMPERATURE TRANSMITTER

LEGEND AND ABBREVIATIONS

KEEP WARM

HEATER

FS TT

ENGINE

S H

TS

TI

A H

TS

PI

TCV

PI

TI

AIR

SEPARATOR

TANK

AFTERCOOLER

LUBE OILCOOLER

TI

PI

LUBE OIL/AFTERCOOLER

RADIATOR

JACKET WATERRADIATOR

A L

LS

PI PRESSURE INDICATOR

VENT

EXPANSION TANK

W/LEVEL GAUGE

COOLANT MAKE-UP STORAGEAND DISPENSING SYSTEM

ENGINE DRIVENCOOLANT PUMP

ENGINE MOUNTEDEQUIPMENT

ENGINE DRIVEN

COOLANT PUMP

MAKE-UP

TURBOCHARGER

AIRIN

ELECTRIC MOTOR DRIVENKEEP WARM CIRCULATINGPUMP
TM 5-692-2 

13-9 

Figure 13-5. Typical radiator diesel engine cooling system 

 (1) As water evaporates, impurities are left behind. The quality of the tower cooling water may be 

controlled by discharging (blowing down) a portion of the tower water and adding fresh water and 

chemical treatment. Most towers have a blowdown valve located in the discharge piping of the spray 

pump. While some large towers may have water quality sensing equipment that controls the operation of 

the blowdown valve, most towers have a manual valve. A manual blowdown valve is usually adjusted to 

discharge water at a rate equal to the evaporation rate when the tower is operating at design conditions. 

Water is added to the pan section to maintain a constant level through a makeup water control valve. 

Most towers utilize float-operated makeup water control valves. 

 (2) Most cooling tower designs use fans to circulate air through the cooling tower. On many 

cooling tower units, the fans are integral with the unit. However, it is not uncommon for the fan to be a 

separate installation connected to the cooling tower by a duct system. Several cooling tower fan 

arrangements are shown on the left side of figure 13-6. The temperature of the facility re-circulating 

cooling water discharged from the cooling tower can be controlled by controlling the flow of air through 

the cooling tower. Reducing airflow increases temperature. The flow control damper may be part of the 

tower as shown on figure 13-6 or may be installed at the inlet or discharge of the fan. Most towers are 

equipped with mist eliminators. Mist eliminators reduce the amount of water droplets carried out of the 

cooling tower. 

 (3) In facilities with variable facility re-circulating cooling water demands, several cooling tower 

units may be manifolded in parallel. As the cooling load decreases, cooling tower units may be taken out 

of service so that the facility re-circulating cooling water temperature can be maintained at the proper 

value. In multiple cooling tower installations, valves are usually installed so that the tower is completely 

isolated from the facility re-circulating system. These valves may be remote-operated as shown on figure 

13-6. Multiple cooling tower installations with all of the towers discharging into a common air discharge 

duct may also isolate the air side of the tower with an isolation damper. The isolation damper may be in 

addition to the airflow control damper. The isolation damper prevents moist air from other units from 

backflowing into the facility through an out of service unit. The isolation damper also allows personnel 

entry into out of service units to perform maintenance activities. 

13-2. Cooling system major components

Cooling systems are generally comprised of the following major components. 

a. Heat exchangers. Diesel engine installations utilize heat exchangers to control the temperature of 

engine coolant, lube oil, fuel oil, and combustion air. Temperature is controlled by heat transfer through a 

tube wall or plate surface to another fluid (gas or liquid). Control of the above temperatures maintains the 

engine temperature. The most common type of heat exchanger used in the diesel engine cooling system is 

a tubular heat exchanger. Engine coolant heat exchangers are usually air-cooled or water-cooled. Aircooled units are referred to as radiators. A radiator consists of an inlet box and a discharge box connected 

by many small diameter tubes arranged so that air flows through the tube bundle around the outside of the 

tubes. The tubes usually have fins on the outside surfaces to enhance the heat transfer between the tube 

surface and the cooling air. Radiator units are usually equipped with a thermostatically controlled fan that 

moves air through the tube bundle. 
TM 5-692-2

13-10 

CONTROL DAMPER

DC

TT

COOLWATERHOTWATER

REMOTE OPERATINGVALVE

COOLING COIL

LOUVERED COOLINGAIR INLET (TYP)

SPRAYPUMPSTRAINER

OVERFLOWDRAIN

MIST ELIMINATOR

SPARY WATERFLOW CONTROLVALVEBLOWDOWNCONTROLVALVE

COOLING AIR FLOW

POSITIONCONTROLLERDAMPER

TEMPERATURETRANSMITTER

ALTERNATE OPEN

CHANNEL WATER

DISTRIBUTION SYSTEM

ALTERNATE TOWER ARRANGEMENTS

FAN

FAN

FAN

FLOAT OPERATED MAKE UPWATER CONTROL VALVEMAKE-UP WATER SUPPLY

Figure 13-6. Typical evaporative cooling tower 
TM 5-692-2 

13-11 

b. Air separators. Some diesel engine cooling systems use air separators to remove air (gas) bubbles 

that have become entrained in the cooling fluid. Some air separators are just a tank constructed so the 

coolant inlet is not in a direct line with the coolant outlet. The surface area of the tank is large compared 

to the coolant piping. The slowing of the coolant stream and change in direction allows gas bubbles to 

rise to the surface of the tank or into the coolant expansion tank to be vented. A very common air 

separator is a mechanical separator with a tangential entry that causes the coolant stream to spin from an 

upper entry to a lower discharge. The resulting turbulence enhances gas separation. Tangential entry 

mechanical separators generally require less space than tank type separators, but require that the 

circulating pump is capable of producing higher differential pressures. 

c. Expansion tanks. When coolant is heated, it expands. If the cooling system was completely closed, 

the forces generated by expansion of the coolant could damage the engine. The expansion tank provides 

space for coolant expansion. The expansion tank also provides added coolant capacity to make up for 

small losses. The expansion tank is generally installed some distance above the engine to provide a static 

head to prevent coolant flashing to steam which might result in cavitation in coolant circulating pumps. 

d. Pumps. Various types of pumps are utilized in cooling systems. 

 (1) The pumps that circulate coolant when the engine is operating are generally mounted on the 

engine and are gear-driven by the engine. The pumps are generally furnished by the engine manufacturer 

with the engine so the design of the pump may vary from manufacturer to manufacturer. The most 

common pump design is a single-stage, end suction, centrifugal pump. The pump housings are generally 

cast iron, and the pump impeller and shaft bearings are generally bronze. 

 (2) The keep warm circulating pump circulates engine coolant through a keep warm heater when 

the engine is not operating. The keep warm pump is typically a single-stage, end suction, centrifugal type 

driven by an electric motor. Pump housings are generally cast iron or carbon steel, and the pump impeller 

and shaft bearings are generally bronze. The pump is generally direct-connected to the electric motor. 

 (3) The type of pump used to circulate cooling water in facility recirculating cooling water 

systems varies with the design of the system. The pumps are generally driven by direct-connected 

electric motors. Common types of pumps that may be used are as follows. 

 (a) Centrifugal pumps, horizontal, are preferred for pumping from aboveground water supplies 

which continuously flood the pump suction. These pumps may also be used to pump from reservoirs 

below the pump if the net positive suction head capability of the pump is not exceeded. When drawing 

from reservoirs below the pump, it is common practice to install foot valves at the inlet to the suction 

piping, so the suction piping remains full when the pump is not in operation. 

 (b) Centrifugal pumps, vertical, may be used, but are not preferred, for pumping from pits, 

ponds, or reservoirs, or from horizontal tanks where the pump extends down into the fluid to be pumped 

from a platform above the fluid. These pumps may have multiple stages. 

 (c) Turbine pumps, vertical, are preferred for pumping from pits, ponds, reservoirs, or 

horizontal tanks where the pump extends down into the fluid to be pumped from a platform above the 

fluid. 

 (d) Positive displacement pumps are not generally used in facility re-circulating cooling water 

systems. 
TM 5-692-2

13-12 

e. Keep warm heaters. Keep warm heaters are generally low density electric immersion units 

supplied as a package with thermostatic control units. The heaters are sized to keep engine coolant 

circulated by the keep warm pump at the design operating temperature of the keep warm system. The 

operating temperature of the keep warm system depends on the needs of the engine. Keep warm systems 

may provide temperatures as low as 70°F to temperatures just below the coolant temperature in an 

operating engine. 

f. Engine coolant temperature control valves. Temperature control valves are used in engine cooling 

systems which use a coolant bypass to maintain either a constant coolant temperature at the engine 

coolant outlet or a constant coolant supply temperature. The most common engine coolant temperature 

control valve is a self-contained, factory-set, thermostatic element-operated, sealed, three-way valve unit. 

When installed to maintain a constant coolant outlet temperature, the unit is referred to as a diverting 

valve. When installed to maintain a constant coolant inlet temperature, the unit is referred to as a mixing 

valve. The valve is designed to maintain full coolant flow through the engine cooling system. A 

thermostatic element in one of the valve ports controls a sliding valve assembly that controls the flow 

through that port. In the closed position, all of the flow is from the inlet port and out the other port. As 

the thermostatic element moves the sliding valve off the valve seat, a portion of the flow is from the inlet 

and through the thermostatically controlled port. At full lift, all of the flow is through the thermostatic 

port. (Some valves operate the opposite of the preceding description.) 

g. Engine instrumentation and controls. Typical instrumentation and controls used in engine cooling 

systems include the following. 

 (1) Pressure indicators are located throughout the engine cooling system with pressure ranges 

varying according to function. 

 (2) Level indicators are installed on all coolant expansion tanks for local indication. 

 (3) Level transmitters are installed where needed to provide a signal to a remote location or 

control room for engine coolant level indication. 

 (4) Level controllers usually provide control signals for high level alarm, transfer pump start and 

stop, and low level alarm. 

 (5) Temperature switches may be used to activate a high coolant temperature alarm. Temperature 

switches may also be used to shut the engine down when coolant temperatures reach the point where 

further operation may result in damage to the engine. 

 (6) A flow switch can be located in an overflow line out of the top of each day tank. When flow is 

detected by a flow switch, the fuel oil transfer pumps will deactivate. 

 
TM 5-692-2 

14-1 

CHAPTER 14 

BOILERS 

14-1. Types of Boilers 

The two most general classifications of heating boilers pertain to the method of manufacture, i.e., by 

casting (cast iron boilers) or fabrication (steel boilers). Those that are cast usually use iron, bronze, or 

brass in their construction. Those which are fabricated use steel, copper, or brass, with steel being the 

most common material. 

a. Steel boilers. Steel boilers can be generally divided into two types: fire tube and water tube. 

 (1) In fire-tube boilers, gases of combustion pass through the inside of the tubes with water 

surrounding the outside of the tubes. The advantages of a fire-tube boiler are its simple construction and 

less rigid water treatment requirements. The disadvantages are the excessive weight per pound of steam 

generated, excessive time required to raise steam pressure because of the relatively large volume of water, 

and inability to respond quickly to load changes, again due to the large water volume. The most common 

fire-tube boilers used in facility heating applications are often referred to as scotch or scotch marine 

boilers, as this boiler type was commonly used for marine service because of its compact size (firebox 

integral with boiler section). 

 (2) In the water-tube boiler, the water is inside the tubes and gases of combustion pass around the 

outside of the tubes. The advantages of a water-tube boiler are a lower unit weight per pound of steam 

generated, less time required to raise steam pressure, a greater flexibility for responding to load changes, 

and a greater ability to operate at high rates of steam generation. 

b. Cast iron boilers. Cast iron boilers are made in three general types: horizontal sectional, vertical 

sectional, and one-piece. Most of the sectional boilers are assembled with push nipples or grommet type 

seals, but some are assembled with external headers and screw nipples. Horizontal, sectional, cast iron 

boilers are made up of sections stacked one above the other, like pancakes, and assembled with push 

nipples. Vertical, sectional, cast iron boilers are made up of sections standing vertically, like slices in a 

loaf of bread. One-piece cast iron boilers are those in which the pressure vessel is made as a single 

casting. 

14-2. Types of systems 

Boilers are generally used to provide a source of steam or hot water for facility heating and process needs. 

a. Steam and condensate. In steam and condensate systems, heat is added to water in a boiler causing 

the water to boil and form steam. The steam is piped to points requiring heat, and as the heat is 

transferred from the steam to the building area or process requiring heat, the steam condenses to form 

condensate. In some very low-pressure saturated steam heating applications, the steam distribution piping 

may be sized to slope back to the boiler so that the steam distribution piping also acts as the condensate 

return piping (single-pipe system). In other low-pressure applications there may be steam supply piping 

and condensate return piping (two- pipe system) although the condensate system is open to the steam 

system. In typical packaged steam boiler operations, the boiler system may generate steam at about 150 

psig for distribution throughout the facility and be lowered to the operating pressure of equipment 
TM 5-692-2 

14-2 

supplied through point-of-use pressure reducing stations. As heat is transferred from the steam, 

condensate is formed which collects in discharge legs until enough condensate is present to operate a trap 

that isolates the steam distribution system from the condensate system. In common facility heating 

applications, the condensate system is at atmospheric pressure and the system is arranged to drain the 

condensate to a central condensate receiver, or into local smaller receivers which pump the condensate 

back to the central condensate receiver. 

b. Hot water. A boiler is used to heat water that is circulated through a closed loop piping system for 

general facility and service water heating. Low-temperature systems generally operate below 200°F. 

Medium-temperature systems generally operate at temperatures between 200 and 250°F. A feature of hot 

water systems is an expansion tank to accommodate the expansion of the water in the system as the water 

is heated. The expansion tank, when piped into the system on the suction side of the circulating pumps, 

also pressurizes the system to prevent flashing in the circulating pump, piping, and piping components. 

In many low- and medium-pressure systems, pressurization is maintained by flash steam in the expansion 

tank. In a few hot water systems, pressurization is maintained by maintaining a compressed gas blanket 

above the water level in the expansion tank. 

c. High-Temperature Hot Water. High-temperature hot water systems, which operate above 250°F, 

are basically the same as hot water systems. High-temperature systems are generally installed when a 

process requires the higher temperature, a number of locations require small quantities of low-pressure 

steam that the high-temperature hot water can generate in a local converter, or high-temperature drop 

equipment can be used at end use points to minimize the size of water circulation piping required. 

d. Fuels. Most facility boiler systems are fired using a combustible gas (typically natural gas or 

propane) or fuel oil. In many facilities, the boilers are designed to fire both a combustible gas fuel and a 

fuel oil. In these facilities, the combustible gas fuel is generally natural gas that is considered the primary 

fuel and fuel oil is considered to be the backup fuel. For an expanded discussion of fuel oil properties and 

fuel oil delivery systems, see chapter 10. 

14-3. Boiler system major components 

Boiler systems are comprised of the following major components. 

a. Feedwater heaters. Feedwater heaters are energy recovery devices generally found only in large 

steam generating plants where all of the steam generated is not reduced to condensate by the steam user. 

This "waste steam" is reduced to condensate for return to the boiler in the feedwater heater. The boiler 

feedwater is used as a cooling medium to reduce the steam to condensate that increases the temperature of 

the feedwater and thereby increases the thermal efficiency of the boiler. 

b. Fuel heaters. Many boilers firing heavy fuel oil require fuel heaters to reduce the fuel viscosity, so 

the fuel can be atomized by the burner system for complete combustion. For an expanded discussion of 

fuel oil properties and the function of fuel oil heaters, see chapter 10. 

 c. Deaerators. A deaerator is a special case of feedwater heater that is designed to promote the 

removal of non-condensable gases from the boiler feedwater. The principal gases of concern are oxygen, 

carbon dioxide, and ammonia, which are major contributors to boiler, and steam and condensate piping 

corrosion problems. In small steam plants, a portion of the steam generated by the boiler is used to 

operate the deaerator if "waste steam" is not available. Failure to maintain and properly operate the 

deaerator can lead to early failure of the boiler, steam using equipment, and the steam and condensate 
TM 5-692-2 

14-3 

piping. 

d. Pumps. In most hot water systems, the system circulating pumps are electric motor-driven, end 

suction centrifugal pumps. In steam systems, the condensate return pumps are typically electric motordriven, end suction, centrifugal or turbine type pumps. Feedwater pumps are generally electric motordriven, multiple-stage, end suction centrifugal pumps. The shutoff head of the pump must be greater than 

the steam or hot water system operating pressure. 

e. Combustion air blowers. In many packaged boiler installations, the combustion air fan is designed 

and provided by the boiler manufacturer and is integral with the boiler housing. In installations where a 

stand-alone fan is provided, low-pressure centrifugal blowers are commonly used. An important 

characteristic of the blower is the ability to maintain a relatively constant air pressure over a wide range of 

airflows. 

 f. Flues. Flues (boiler firebox exhaust duct or boiler discharge stack) must be large enough to 

conduct the products of combustion away from the boiler with a minimum of duct friction loss. Flues 

may be fabricated from any material suitable for the operating temperature and pressure. Common 

materials of construction associated with packaged boiler installations are carbon steel and stainless steel. 

14-4. Boiler system controls 

The control configuration for a boiler installation depends on the size of the boiler, the requirements of 

the insurance company providing coverage for the facility, and the building codes of the locality in which 

the facility is located. The overall boiler control system is typically integrated through a control panel 

known as the burner management system which controls the boiler operation to maintain the system set 

point conditions and shuts down the boiler if an equipment damaging and life threatening condition is 

sensed. For most packaged boiler installations, the basic boiler control is a single-element, proportional 

control device. In the case of a steam boiler, the control device is a pressure sensing element that sends a 

signal to the burner management system to adjust the burner firing rate to maintain a set pressure in the 

steam distribution system. In a hot water boiler, the control device is a temperature sensing element. In 

large steam boiler installations, the control system may be a three-element, proportional-integralderivative controller that not only responds to the system set pressure, but may also respond to the rate of 

change in parameters, such as pressure, steam flow, water level, etc. In multiple boiler installations, the 

burner management systems of each boiler may be controlled by a master plant controller (sometimes 

referred to as a lead-lag controller) to stage boiler operation to minimize on/off operation. They may also 

minimize frequent burner cycling which can cause thermal stresses leading to tube and tube sheet leaks. 

While a brief description of the common types of control components associated with packaged boilers 

follows, the best guide to facility boiler operation and boiler controls is the manufacturer's operating and 

maintenance instructions provided with the boilers. 

a. Common controls. The following control devices are common to all boilers. 

 (1) The forced draft fan motor drives forced draft fan directly to provide combustion air. 

 (2) The forced draft fan motor starter energizes forced draft fan motor. 

 (3) The forced draft fan furnishes all air, under pressure, for combustion of pilot fuel and main 

fuel, and for purging prior to burner ignition and after burner operation termination. 
TM 5-692-2 

14-4 

 (4) The ignition transformer provides high-voltage spark for ignition of gas pilot or light oil pilot. 

 (5) The modulating motor operates the rotary air damper and fuel valves through a cam and 

linkage system to provide proper air-fuel ratios under all boiler load conditions. 

 (6) The low fire switch is an internal auxiliary switch, cam-actuated by the modulating motor 

shaft, which must be closed to indicate that the air damper and fuel metering valve are in the low fire 

position before an ignition cycle can occur. 

 (7) The burner switch is a manually operated start-stop switch for directly starting and stopping 

operation of burner. 

 (8) The manual-automatic switch, when set at "automatic," subsequently operates at the command 

of the modulating control which governs the position of the modulating motor in accordance with load 

demand. When set at "manual," the modulating motor, through the manual flame control, can be 

positioned at a desired burner firing rate. The primary purpose of the manual position is for testing and 

setting the air-fuel ratio through the entire firing range. 

 (9) The manual flame control is a manually operated potentiometer that permits the positioning of 

the modulating motor to a desired burner firing rate when the manual-automatic switch is set on manual. 

It is used primarily for initial or subsequent setting of fuel input throughout the firing range. It has no 

control over the firing rate when the manual-automatic switch is set on "automatic." 

 (10) The modulating motor transformer reduces control circuit voltage to required voltage for 

operation of modulating motor (typically reduces 115 volt alternating current to 24 volt alternating 

current). 

 (11) Indicating lights provide visual information of flame failure, load demand, fuel valve (valve 

open), and low water. 

 (12) The program relay and flame safeguard control (flame safety system) automatically 

programs each starting, operating, and shutdown period in conjunction with operating limit and interlock 

devices. This includes, in a timed and proper sequence, the operation of the blower motor, ignition 

system, fuel valve(s), and damper motor. The sequence includes air purge periods prior to ignition and 

upon burner shutdown. The flame detector portion of this control monitors both oil and gas flames and 

provides protection in the event of loss of a flame signal. The control recycles automatically during 

normal operation, or following a power interruption. It must be manually reset following a safety 

shutdown caused by a loss of flame. Incorporated is an internal checking circuit, effective on every start, 

that will prevent burner operation in the event anything causes the flame relay to hold in during this 

period. 

 (13) The combustion air proving switch is a pressure sensitive switch actuated by air pressure 

from the forced draft fan. Its contacts close to prove presence of combustion air. The fuel valves cannot 

be energized, unless this switch is satisfied. 

 (14) The combustion air damper controls combustion air in proportion to fuel input for various 

load demands. It may be of the butterfly, opposed blade, or rotary type. 

b. Steam controls (all fuels). The following control devices are used with steam systems.
TM 5-692-2 

14-5 

 (1) The steam pressure gauge indicates boiler internal pressure. 

 (2) The operating limit pressure control breaks a circuit to stop burner operation on a rise of boiler 

pressure above a selected setting. It is adjusted to stop or start the burner at a preselected pressure setting. 

 (3) The high limit pressure control breaks a circuit to stop burner operation on a rise of pressure 

above a selected setting. It is adjusted to stop the burner at a preselected pressure above the operating 

limit control setting. This control is normally equipped with a manual reset. 

 (4) The modulating pressure control senses changing boiler pressures and transmits this 

information to the modulating motor to change the burner firing rate when the manual-automatic switch is 

set on automatic. 

 (5) The low water cutoff and feedwater pump control (typically float-operated) responds to the 

water level in the boiler. The control starts and stops the feedwater pump or operates the feedwater 

control valve to maintain the proper water level in the boiler. If the water level drops below the lowest 

safe water level for the boiler, the control shuts down the boiler. 

 (6) Most jurisdictions required two independent low water cutoff devices. The auxiliary low 

water cutoff also provides a signal to shut down the boiler if the water level drops below the lowest safe 

water level for the boiler. 

 (7) The water column provides visual indication of boiler water level. The water column and low 

water cutoff devices for a boiler are typically incorporated in the same piping assembly. 

 (8) The test valve allows the boiler to be vented during filling and facilitates routine boiler 

inspection. The test valve is typically incorporated in the same piping assembly as the water column and 

the low water cutoff. 

 (9) Safety valves relieve the boiler of pressure higher than the design pressure. Safety valves and 

discharge piping must conform to the American Society of Mechanical Engineers (ASME) Boiler and 

Pressure Vessel Code requirements. 

c. Hot water controls (all fuels). The following control devices are used with hot water systems. 

 (1) The water temperature gauge indicates the internal water temperature. 

 (2) The water pressure gauge indicates the pressure in the boiler. 

 (3) The operating limit temperature control breaks a circuit to stop burner operation on a rise of 

boiler temperature above a selected setting. It is adjusted to stop or start the burner at a preselected 

operating temperature. 

 (4) The high limit temperature control breaks a circuit to stop burner operation on a rise of 

temperature above a selected setting. It is adjusted to stop the burner at a preselected temperature above 

the operating control setting. The high limit temperature control normally is equipped with a manual 

reset. 
TM 5-692-2 

14-6 

 (5) The modulating temperature control senses changing boiler temperature and transmits this 

information to the modulating motor to change the burner firing rate when the manual-automatic switch is 

set on automatic. 

 (6) The low water cutoff breaks the circuit to stop burner operation if the water level in the boiler 

drops below a safe operating level. 

 (7) Most jurisdictions require two independent devices to terminate boiler operation in the event 

of low water. The auxiliary low water cutoff also provides a signal to stop burner operation if the water 

level in the boiler drops below a safe operating level. 

 (8) Relief valves relieve the boiler of pressure higher than the design pressure. Relief valves and 

discharge piping must conform to the ASME Boiler and Pressure Vessel Code requirements. 

d. Gas controls. The following control devices are used with gas-fired boilers.

 (1) The gas pilot valve is a solenoid valve that opens during the ignition period to admit fuel to the 

pilot. It closes after main flame is established. The sequence of energizing and de-energizing is 

controlled by the program relay and flame safeguard control. Some jurisdictions may require two 

independent gas pilot valves installed in series. 

 (2) When two independent gas pilot valves are required, a normally open vent valve is usually 

required to vent the section of gas piping between the valves whenever both gas pilot valves are deenergized. The vent valve closes when the gas pilot valves are energized. 

 (3) The gas pilot shutoff cock is a manually operated, non-lubricated plug valve for isolating the 

gas supply from the gas pilot valve. 

 (4) The gas pilot adjusting cock is a manually operated valve used to regulate the size of the gas 

pilot flame. 

 (5) The gas pilot aspirator is a venturi device using combustion air to improve the flow of gas to 

the pilot burner. 

 (6) The gas pilot pressure gauge indicates gas pressure in the supply line to the gas pilot. 

 (7) The gas pilot pressure regulating valve reduces incoming gas pressure to suit the requirements 

of the pilot burner. Most pilot burners require a gas pressure in the range of 5 to 10 inches of water 

column. 

 (8) The main burner gas flow control valve is modulated through a mechanical linkage to the 

modulating motor to regulate the flow of gas to the burner in proportion to the boiler load. 

 (9) The gas modulating cam is an assembly consisting of a quadrant, a series of adjustable allen 

head screws, and a contour spring to adjust gas input at any boiler load condition to attain the required 

air-fuel ratio. The position of the quadrant is controlled by the modulating motor. 

 (10) The main gas cock is a manually operated, non-lubricated plug valve for isolating the gas 

supply from the main gas valves. 
TM 5-692-2 

14-7 

 (11) Most jurisdictions require two independent main gas valves in series. Main valves will open 

only after the program relay and flame safeguard control signals that a pilot flame has been established. 

 (12) The main gas vent valve is a normally open solenoid valve installed between the two main 

gas valves to vent gas to atmosphere should any be present in the main gas line when the gas valves are 

de-energized. 

 (13) The low gas pressure switch is a pressure-actuated switch that is closed whenever the 

pressure in the gas supply line is above a preselected pressure. If the gas pressure in the gas main drops 

below the set pressure, the low gas pressure switch opens breaking the circuit to the main gas valves 

which causes the main gas valves to close, terminating burner operation. 

 (14) The high gas pressure switch is a pressure-actuated switch that is closed whenever the gas 

supply line pressure is below a preselected pressure. If the gas pressure in the gas main rises above the 

set pressure, the high gas pressure switch opens breaking the circuit to the main gas valves which causes 

the main gas valves to close, terminating burner operation. 

e. Oil controls. The following control devices are used with oil-fired (or dual fuel) boilers. 

 (1) The oil drawer switch is a limit switch which remains open preventing the burner from 

operating until the oil drawer burner gun is latched in the forward position. 

 (2) The atomizing air proving switch is a pressure switch that closes allowing the burner to operate 

when there is sufficient atomizing air pressure for proper burner operation. Oil valve(s) will not operate 

or will not remain open, unless the atomizing air proving switch remains closed. 

 (3) The air pump module provides the compressed air required to atomize the fuel oil for proper 

burner operation. It is started automatically by the program in the program relay and flame safeguard 

control system. 

 (4) The air pump motor drives the air pump and an air-cooling fan. The control for the motor 

operates in parallel with the forced draft fan motor. 

 (5) The air pump provides air for atomizing the fuel oil. 

 (6) The air filter, typically, an oil bath or viscous film filter element (see chapter 7 for an expanded 

discussion of air filter assemblies) is used to clean the air supply prior to entering the air pump. 

 (7) The check valve prevents lubricating oil and compressed air from surging back through the 

pump and air filter when the air pump stops. 

 (8) The air-oil receiver tank holds a supply of oil for lubricating the air pump. It separates lube oil 

from atomizing air before delivery to the burner nozzle. 

 (9) The atomizing air pressure gauge indicates the pressure in the atomizing air supply system 

near the connection to the burner. 
TM 5-692-2 

14-8 

 (10) The lube oil level sight glass indicates the level of lubricating oil in the air-oil receiver tank. 

 (11) The lube oil cooling coil cools the lubricating oil before the oil enters the air pump. A fan 

driven by the air pump motor circulates cooling air over the coil. 

 (12) The lube oil strainer filters lubricating oil before the oil enters the air pump. 

 (13) The lube oil fill pipe and strainer are used when adding oil to the air-oil receiver tank. 

 (14) Some jurisdictions require a low oil pressure switch. When required, this pressure-actuated 

switch opens when the pressure in the fuel oil supply system drops below a set value. 

 (15) The oil solenoid valve opens when energized by the program relay and flame safeguard 

control system allowing fuel oil flow from the oil metering valve to the burner nozzle. Many jurisdictions 

require two independent oil solenoid valves in series for boiler fired-on light oils. 

 (16) The fuel oil controller is an assembly combining into a single unit the gauges, regulators, and 

valves required for regulating the flow of fuel oil. Most controllers have the following integral parts. In 

addition to the parts listed below, controllers on systems burning No. 6 or heavier fuel oil required 

additional parts that are described in paragraph 14-4.f. 

 (a) The oil metering valve is operated through a mechanical linkage to the modulating motor. 

The valve regulates the fuel oil supply to the burner nozzle in proportion to the boiler load. 

 (b) The oil modulating cam is an assembly consisting of a quadrant, a series of adjustable 

allen head screws, and a contour spring to adjust gas input at any boiler load condition to attain the 

required air-fuel ratio. The position of the quadrant is controlled by the modulating motor. 

 (c) The oil burner pressure gauge indicates the pressure in the fuel oil supply line at the inlet 

connection to the oil metering valve. 

 (d) The oil pressure regulator may be required to reduce the pressure in the facility fuel oil 

delivery system to a pressure compatible with the oil burner fuel oil supply regulating components. 

 (17) The oil relief valve bypasses excess fuel oil and maintains the fuel oil system pressure 

indicated on the oil supply pressure gauge. 

 (18) When a light oil pilot system is used, a solenoid valve is provided to control the flow of fuel 

to the pilot nozzle. The pilot valve is energized at the appropriate time by the program in the program 

relay and flame safeguard control system. It shuts off the flow of fuel to the pilot when the control 

system receives a signal that the main burner flame has been established. (Note: Many oil burners use a 

gas pilot system consisting of the components described in paragraph 14-4d.) 

 (19) The back pressure orifice is a restriction located in the oil return line immediately 

downstream of the fuel oil controller to maintain a set pressure in the fuel supply system. A back pressure 

orifice is generally only used on systems that do not use an oil relief valve. 

f. Heavy oil controls. The following additional control devices are used when firing heavy oil. 
TM 5-692-2 

14-9 

 (1) The oil heater switch is a manual disconnect for electric power to fuel oil heater system. 

 (2) The oil heater – electric – is used for heating sufficient fuel oil for operating burner at low fire 

during cold starts before steam or hot water is available for fuel oil heating. On steam boiler units, the 

electric heater is typically integral with the steam fuel oil heater. On hot water boiler units, the electric 

heater is typically a stand-alone unit. The electric heater must be turned off during extended boiler lay-up 

or at any time fuel oil transfer is terminated. 

 (3) The oil heater – steam or hot water – heats the fuel oil to attain the proper fuel oil viscosity for 

full atomization of the fuel oil. On steam boilers operating at 15 psig or less, the steam heater typically 

operates at the same pressure as the boiler. On higher pressure steam boiler units, a pressure reducing 

station is typically installed in the supply line to the fuel oil heater to limit the steam pressure in the oil 

heater to 15 psig or less. 

 (4) The oil heater thermostat – electric and steam – senses fuel oil temperature. On electric 

heaters, energizes or de-energizes the electric heater to maintain the proper fuel oil temperature. On 

steam heaters, controls the operation of the steam flow control valve in the supply line to the heater to 

maintain temperature. 

 (5) The oil heater thermostat – hot water – senses fuel oil temperature and starts and stops a 

booster water pump which circulates hot water from the boiler through the oil heater to control the 

temperature of the fuel oil. 

 (6) The booster water pump circulates water from the hot water boiler through a hot water fuel oil 

heater. Operation of the pump is controlled by the hot water oil heater thermostat. 

 (7) The oil heater valve is a normally open solenoid valve opened by the steam boiler heater 

thermostat to allow flow of steam to the steam heater to maintain the temperature of the fuel oil. 

 (8) The steam heater supply check valve is installed in the steam supply line ahead of a steam oil 

heater, the check valve prevents oil contamination of the waterside of the pressure vessel should any 

leakage occur in the oil heater. 

 (9) The steam heater pressure regulator is used on steam boiler units that operate at pressures 

higher than 15 psig to reduce the steam pressure supplied to the steam oil heater to pressures compatible 

with the equipment. 

 (10) The steam trap drains condensate and prevents loss of steam from the steam oil heater. The 

discharge of the steam trap on the steam oil heater unit is typically discharged rather than recovered to 

eliminate the possibility of contaminating the waterside of the boiler in the event of a leak in the oil heater 

unit. 

 (11) The steam heater discharge check valve prevents air entry during shutdown periods when 

cooling action may create a vacuum within the steam heater. 

 (12) The oil supply pressure gauge is installed in the fuel oil supply line between the discharge of 

the fuel oil heater and inlet to the fuel oil controller unit oil pressure regulator. 

 (13) The low oil temperature switch is a temperature-actuated switch that prevents the burner 
TM 5-692-2 

14-10 

from firing or terminates burner operation if the fuel oil temperature is lower than required for proper oil 

burner operation. 

 (14) High oil temperature switch. Some jurisdictions require a temperature-actuated switch that 

prevents the burner from firing or terminates burner operation if the fuel oil temperature is above a set 

temperature. This is the high oil temperature switch. 

 (15) The fuel oil controller units for boilers firing heavy oil require the following. 

 (a) The fuel oil thermometer indicates temperature of fuel oil being supplied to the fuel oil 

controller. 

 (b) The back pressure valve ensures that a minimum fuel oil supply system pressure is 

maintained for proper fuel oil controller operation. 

 (c) The oil return pressure gauge indicates the oil pressure on the return side of the fuel coil 

controller. 

 (d) The manual bypass valve is used when making a cold start. When open, bypasses control 

elements and allow oil circulation through the supply and return system to allow oil heaters to adjust the 

temperature of the fuel oil before firing the burner is attempted. The valve must be closed prior to firing 

the boiler. 

 (e) The orifice oil control valve may be opened prior to startup to aid in establishing fuel oil 

flow through the controller. Prior to firing the boiler, the valve must be closed. 

 (16) The air purge valve is a solenoid valve that opens simultaneously with closing of oil 

solenoid valve at burner shutdown allowing compressed air to purge oil from the burner nozzle and 

adjacent piping. This oil is burned by the diminishing flame which continues burning for approximately 

four seconds after the oil solenoid valve closes. 

 (17) The air purge orifice nozzle limits purging air to proper quantity for expelling unburned oil 

at the normal delivery rate. 

 (18) The air purge orifice nozzle filter filters the purging air of any particles that might plug the 

air purge orifice nozzle. 

 (19) The air purge check valve prevents fuel oil from entering the atomizing air line. 

 (20) The air purge relay, when energized, controls the operation of the air purge valve. 

g. Additional controls for dual-fuel burners. Boilers with dual-fuel burner systems require a selector 

switch to tell the control system which set of fuel controls to operate. 

 

h. Economizer. An economizer is an energy recovery device that uses the hot exhaust gases from the 

boiler (waste heat) to heat combustion air or feedwater. 

i. Steam traps. Steam traps are installed throughout steam systems to remove condensate (spent 

steam), air, and non-condensable gases from the steam system. There are five types of steam traps in 
TM 5-692-2 

14-11 

general use today. While other types have been designed and built, the requirements of industry have 

centered around the five basic types described below. 

 (1) The heart of a balanced pressure thermostatic trap is the flexible bellows that moves the valve 

head from its seat to discharge the condensate. The bellows is filled with a volatile fluid and hermetically 

sealed. The fluid has a pressure-temperature relationship that closely parallels, but is approximately 10°F 

below that of steam. 

 (2) The liquid expansion steam trap has for its operating element a liquid-filled cartridge. Within 

this cartridge is a hermetically sealed bellows which is attached to the valve head and plunger. 

 (3) Float and thermostatic steam traps provide immediate and continuous discharge of condensate, 

air, and non-condensables from a steam system as soon as they reach the trap. The trap consists of a ball 

float connected by a lever assembly to the main valve head. As condensate reaches the trap, the ball float 

rises, positioning the valve to discharge the condensate at the same rate as it reaches the trap. 

 (4) The inverted bucket steam trap is a type of trap with an inverted bucket attached to the valve 

head by a lever mechanism and operates to open and close the trap. When condensate enters the trap, a 

water seal is formed around the bottom of the inverted bucket which, since it is filled with air, becomes 

buoyant and rises and closes the trap. A small hole in the top of the inverted bucket allows air to escape 

with condensate taking its place inside the bucket. The inverted bucket loses its buoyancy and sinks to 

the trap bottom, opening the valve to discharge the condensate. 

 (5) Thermodynamic steam traps are a type of steam trap which responds to differences in kinetic 

energy between steam and condensate to open and close the valve for discharging condensate. 

j. Piping. Piping 2 inches and smaller used in steam and hot water systems is typically schedule 80, 

American Society for Testing and Materials (ASTM) A 106, Standard Specification for Seamless Carbon 

Steel Pipe for High-Temperature Service (1999), Grade B, steel pipe with threaded joints and carbon steel 

fittings. Piping larger than 2 inches is typically standard weight, ASTM A 106, Grade B, steel pipe with 

flanged joints and carbon steel fittings. 
TM 5-692-2 

15-1 

CHAPTER 15 

INCINERATORS 

15-1. Incineration system description

Incineration of waste is an operation that includes feeding the furnace, burning the waste, exhausting the gases 

to the atmosphere, and removing the residue from the furnace. This chapter presents an overview of 

incinerators and associated fans, burners, and control equipment required for a complete refuse disposal 

system. Typical incineration system equipment is described, as well as guidelines for maintenance of such 

systems. 

a. Waste classification. Incinerators and associated equipment are available in a wide variety of designs 

based on the type of refuse, unit capacity, and degree of process automation. For the purpose of this manual, 

discussion will be limited to manually fed, low capacity units (less than 250 pounds per hour) with dry paper 

as the primary waste. Dry paper matter is classified as a Type O waste with the following characteristics. 

 

 Moisture content Less than 10 percent 

 Incombustible solids 5 percent 

 BTU value per pound 8,500 

 Weight per cubic foot 8 - 10 pounds 

b. System design features. The feed system for incinerators may be automatic or manual (batch); however, 

for small scale systems associated with paper waste, the waste is typically batch-fed into a charging hopper or 

directly into the furnace. Auxiliary gas or oil burners assist in the combustion of the waste and help in 

maintaining the desired combustion temperature. The required furnace draft is provided by the stack or by an 

induced draft fan, and is monitored closely to ensure that the proper negative air pressure is maintained in the 

furnace. Residue generated from burning dry paper consists of a relatively fine, light ash. Removal of this 

residue from the furnace may be by automatic equipment or by manual means. For manually fed, low 

capacity incinerators as described in this chapter, ash removal is generally manual through cleanout doors 

located below the furnace grate. 

15-2. Incineration system major components

Incineration systems are comprised of the following major system components. 

a. Combustion chambers. The combustion chamber(s) of an incinerator enclose the combustion area 

and are typically constructed of an outer shell and an inner refractory material lining. Shell materials vary 

with size and age of the incinerator, and are usually brick for older built-up units and steel or cast iron for 

newer packaged units. The refractory lining serves to protect the shell from the high temperatures 

generated in the chamber. Incinerators may have one or two combustion chambers. Newer packaged 

incinerators generally will have two chambers (figure 15-1), primary (lower) and secondary (upper), 

whereas older built-up incinerators may have only a single combustion chamber. 

 (1) The primary combustion chamber houses the fixed grate or hearth, waste charging door, ash 

removal doors, and primary burner. Initial burning of the waste occurs in this chamber, with combustion air 
TM 5-692-2 

15-2 

SPARK SCREEN

REFRACTORY

LINED STACK

SECONDARY

CHAMBER

COMBUSTION

AIR BLOWER

SECONDARY

BURNER

CHARGE

DOOR

PRIMARY CHAMBER

BURNER

ASH

DOOR

PRIMARY

CHAMBER

ACCESS 

DOOR

Figure 15-1. Vertical dual chamber incinerator 

supplied in the grate area by air vents or by a combustion air blower. Partial combustion occurs in the primary 

chamber, with the hot gases generated flowing up into the secondary combustion chamber. The temperature 

within the primary chamber is maintained around 1,300o

F by controlling the combustion air and the firing rate 

of the burner. 

 (2) Further combustion of the gases occurs in the secondary combustion chamber that is usually 

located above the primary chamber. Secondary combustion is augmented by an auxiliary burner, with air 
TM 5-692-2 

15-3 

supplied by additional vents or blowers. To minimize pollution, the temperature within the secondary 

chamber should be maintained at 1,800°F, and the residence time should be a minimum of two seconds. The 

combustion gases exit the secondary chamber and are discharged to the stack. 

b. Burners. Incinerators will have auxiliary burners to assist in the combustion of the waste. Burners 

serving the primary combustion chamber heat and ignite the waste. Burners serving the secondary 

combustion chamber aid in maintaining the temperature required to minimize emissions. Incinerator 

burners may be natural gas or oil fired, with controls ranging from manual on/off operation to fully 

automatic modulating operation. Safety controls are typically provided to ensure proper burner ignition 

and operation, and to prevent flow of fuel into the chamber if ignition has not occurred. 

c. Fans. Fans serving incinerator systems may be provided to supply combustion air (forced draft 

fans) or to aid in exhausting the flue gases from the incinerator to the stack (induced draft fans). The 

combustion air fans are generally the centrifugal type and are mounted on or near the combustion 

chambers. The induced draft fan is located in the flue gas stream between the incinerator and the stack. 

Induced draft fans are usually of centrifugal or axial design, and are constructed to handle the high 

temperatures and particulate of the combustion gases. Controlling the forced draft and induced draft fan 

output enables the proper temperature and draft (pressure) to be maintained within the incinerator. Fan output 

may be controlled by dampers or by variation of motor speed. Damper control generally consists of 

adjustable fan discharge dampers or adjustable fan intake dampers (inlet vanes). Motor speed control can be 

accomplished by several methods including use of variable speed direct current (DC) motors, use of multiple 

speed alternating current (AC) motors, or electronically adjustable motor drives. The pressure within the 

incinerator is usually monitored by a draft gauge calibrated in inches of water. 

d. Air pollution control equipment. For the purpose of this manual, it is assumed that the low 

capacity incinerators located on existing sites are not equipped with air pollution (emission) control 

devices. A brief discussion of this equipment is provided since it is likely that systems may be 

required to be retrofitted in the future due to increasingly stringent regulations. Emission 

regulations vary from state to state, but generally speaking, low capacity (250 to 500 pounds per 

hour) incinerators are exempt from emission equipment requirements. Most states do, however, 

require that a temperature of 1,800o

F be maintained within the incinerator to ensure more complete 

combustion, thereby reducing emissions. Pollution control equipment serving incinerators includes 

wet and dry scrubbers, electrostatic precipitators, and baghouses. Any one or a combination of these 

devices may be used depending on the incinerator size, waste to be incinerated, system configuration, 

and emission regulations. Wet and dry scrubbers are generally used to neutralize the acid gases that are 

generated in the combustion process. The flue gases also contain a fine particulate matter that may be 

collected by an electrostatic precipitator or baghouse for complete emission control. Addition of 

pollution control equipment to an incinerator system will generally mandate the use of an induced draft 

fan to overcome the significant air resistance caused by this equipment.
TM 5-692-2 

16-1 

CHAPTER 16

CHILLED WATER SYSTEMS

 

16-1. Chilled water systems description 

A chilled water system is a means by which heat, generated in a space or by a process, is conveyed from 

that space and ultimately released to the outside. This chapter is intended to acquaint the facility operator 

with chilled water systems and identify a minimum level of maintenance activities that must be performed 

to maintain a chilled water system for continuous day-to-day operation. Each chilled water system is 

designed to transfer heat by the most efficient and cost-effective method. While there is no right way to 

design a chilled water system, chilled water systems have common characteristics and use common types 

of components. Due to these differences in chilled water systems, the individual chilled water system 

equipment manufacturer's directions regarding maintenance practices take precedence over any guidance 

provided in this chapter. 

a. System functions. Basically, a chilled water system circulates the chilled water through a loop 

piping system. Pumps force the water from the water chiller through the heat transfer components and 

back to the chiller via the piping system. Heat is transferred to the chilled water as it circulates through 

the heat transfer device that causes the temperature of the chilled water to increase. The portion of the 

system that supplies the water from the chiller to the heat transfer equipment is typically designated the 

chilled water supply system. Once the water is through this heat transfer equipment, the piping system 

delivering it back to the chiller is termed the chilled water return system. 

b. Piping systems. There are two common types of chilled water piping systems: two-pipe and dualtemperature, with numerous variations of each. Two-pipe systems for comfort air conditioning typically 

operate with a design supply temperature of 40 to 55o

F and a system pressure of approximately 125 psi. 

Antifreeze or brine solutions may be used for chilled water systems (usually process applications) that 

require supply temperatures below 40o

F. In addition, well water type chilled water systems can use 

supply temperatures of 60o

F or higher. Dual-temperature systems are a combined water heating and 

cooling system that circulate hot and/or chilled water to heat or cool with common piping and terminal 

heat transfer apparatus. This chapter will consider two-pipe chilled water systems that supply 40 to 55o

F 

supply water only; however, much of the information presented in this chapter will apply to dualtemperature systems as well. 

16-2. Chilled water systems major components 

Chilled water systems are generally comprised of the following major system components. 

a. Chillers. The most common chilled water air-conditioning system is a single compressor and 

refrigerant circuit using a water-cooled condenser. It is relatively simple and compact. Compression type 

refrigeration liquid chilling equipment ranges in size from quite small to those with capacities in the 

thousands of tons (1 ton equals 12,000 BTU per hour of cooling). The three categories of chillers that 

will be discussed in this chapter are those which use reciprocating compressors, centrifugal compressors, 

and rotary screw type compressors. Control of water chillers is typically based on the return water 

temperature. The return water temperature indicates the cooling load in the facility at any given time. 

The warmer the chilled water return temperature, the larger the facility cooling loads. Occasionally, the 

chiller is controlled by the leaving water (supply) temperature. This is typical for process chilled water 
TM 5-692-2

16-2 

applications. In this case, the rotary screw compressor or the centrifugal compressor will usually respond 

best and will provide modulating control to meet the load. 

 (1) Reciprocating type chiller compressors are available in capacities from about 2 to 200 tons. 

Reciprocating water chillers may have one, two, or more compressors, each of which is matched to a 

separate tube circuit in a common shell, and each with its own expansion valve, service valves, dryer, 

piping, and controls. The compressors may be piped to use a common water-cooled condenser or may 

each have their own water-cooled condensers. Chillers are also built with air-cooled condensers as part of 

a package for outdoor use, or can be built for use with a remote air-cooled condenser or an evaporative 

condenser. The principles of operation of all reciprocating compressors are much the same. Suction gas 

(from the evaporator) is drawn into the compressor through the suction shutoff valve to the suction 

chamber and on through a suction filter. The filter separates the lubricating oil from any liquid refrigerant 

that is mixed with the refrigerant gas. Since reciprocating compressors are made to pump refrigerant gas 

only, any liquid refrigerant must be separated from the gas to keep from doing any damage to the 

compressor valves. The gas then flows through the crankcase and then to the cylinders. The piston in the 

cylinder compresses the refrigerant that is discharged through the discharge opening. Water chillers 

which use reciprocating type compressors are of three main groups: hermetic, semihermetic, and open 

direct drive type. 

 (a) A hermetic unit uses a hermetic compressor with the electric motor totally enclosed in the 

refrigerant atmosphere. The possibility of refrigerant leakage to the outside through a shaft seal is totally 

eliminated, and motor operating noise is subdued by the housing. Because this type of forced refrigerant 

cooling of the motor is very effective, smaller, less expensive motors can be used. The need for a heavy 

external base to preserve motor-compressor shaft alignment is eliminated. Hermetic machines are less 

expensive than external drive machines, have slightly greater power consumption, and are quieter. 

However, should the motor fail, the repair cost is higher, and the unit must be replaced with a like unit or 

sent back to the manufacturer for service. These compressors are used in most cases for a small 

refrigeration or air-conditioning system. 

 (b) The semihermetic compressor, like the hermetic type, has both the compressor and its 

drive motor in the same casing. The term "semihermetic" means that the case in which both the 

compressor and motor are sealed may be opened for service or repair. 

 (c) Open direct drive type compressors are those in which the crankshaft, which is fitted with 

a shaft seal, extends from the housing. They do not have a drive motor as an integral part, but the drive 

motor in most cases is placed on the same base with the compressor. The motor may be joined to the 

compressor with a direct drive coupling or belt drive. 

 (2) Centrifugal compressors which are used as part of many large refrigeration and airconditioning systems move a large volume of refrigerant at low pressures. They are made in sizes as 

great as 10,000 tons. The only wearing parts in a centrifugal compressor are the main bearings and the 

main seals. However, hermetic type centrifugal chillers do not have main seals. All centrifugal 

compressors do not have pistons. In this type of compressor, the refrigerant gas from the evaporator is 

pulled through the suction line into the center of the impeller. The impeller which is rotating at a high 

speed forces the gas flow to the outside edge of the impeller and out the impeller housing. The hot, highpressure refrigerant gas then flows to the condenser. A centrifugal compressor may have one or more 

stages. These stages may be in the same or in separate impeller housings. 

 (3) The rotary screw type compressor uses a mated pair of special helical rotors. They trap and 
TM 5-692-2 

16-3 

compress the refrigerant gas as they revolve in an accurately machined compressor cylinder. The helical 

rotors are made with the male rotor having four lobes and the female rotor having six interlobe spaces. 

The male rotor often drives the female rotor, but in some cases they are both gear-driven. These 

compressors are built in either external drive or semihermetic construction. They are used in larger 

systems that range in size from 20 to 800 tons. These compressors are commonly used with R-134a, R22, and R-717 (ammonia) refrigerants. An oil injection system is used that gives high-efficiency and 

smooth operation. As the lobe of the male rotor starts to unmesh from an interlobe space of the female 

rotor, a void is made and gas is drawn in through the inlet port. As the rotors continue to turn, the 

interlobe space increases in size and more gas flows into the compressor. Just prior to the point at which 

the interlobe space leaves the inlet port, the entire length of the interlobe is filled with refrigerant gas. As 

rotation continues, the trapped gas in the interlobe space is moved circumferentially around the 

compressor housing at a constant pressure. Further rotation starts the meshing of another male lobe with 

the female space on the suction end and progressively compresses the gas in the direction of the discharge 

port. Thus, the occupied volume of the trapped gas within the interlobe space is decreased, and the gas 

pressure as a result increases. As this gas is discharged, a fresh charge of refrigerant is drawn through the 

inlet on the opposite side. 

 b. Water chiller auxiliary systems. Auxiliary systems used to enhance chiller performance and to aid 

maintenance activities include the following. 

 (1) Purge units are required for centrifugal liquid machines using low pressure refrigerants (such 

as R-123), because evaporator pressure is below atmospheric pressure. If a purge unit was not used, air 

and moisture would accumulate in the refrigerant over time. These noncondensables drastically reduce 

the capacity and efficiency of the chiller operation. A purge unit is designed to prevent the accumulation 

of noncondensables and ensure internal cleanliness of the liquid chiller. Purge units may be manual or 

automatic, compressor-operated, or compressorless. 

 (2) A refrigeration transfer unit may be provided for centrifugal liquid chillers using refrigerants 

with a boiling point below ambient temperature at atmospheric pressure (R-134a, R-22). This system is 

used for adding and removing refrigerant to and from the chiller. The unit consists of a small 

reciprocating compressor with electric motor drive, a condenser (air-cooled or water-cooled), an oil 

reservoir, an oil separator, valves, and interconnecting piping. 

 (3) Air-conditioning equipment is generally selected on the basis of maximum design condition 

and is then expected to cope with a variety of conditions, some of which may force the equipment outside 

of its stable operating range. At light cooling loads, operating the chiller at its maximum capacity will 

cause frosting of the coil, excessive compressor cycling, and possible liquid carry-over. Hot gas bypass is 

a system that, at some predetermined partial loading, allows flow of hot refrigerant gas from the highpressure side to the low-pressure portion of the refrigerant system. This reduces the condenser capacity to 

produce refrigeration, because the gas returned to the low-pressure side produces no useful cooling; 

instead it becomes an evaporator load. This enables the chiller to operate over a broader range of 

conditions and avoid freeze-ups and cycling problems. 

c. Pumps. The type of pump used to distribute chilled water through the chilled water system varies 

with the system design. There are two basic types of pumps: positive displacement and centrifugal. 

 (1) Positive displacement pumps trap the liquid in internal cavities and move it from the inlet of 

the pump to the discharge. This action increases the velocity and pressure of the liquid which flows in the 

discharge pipe. Positive displacement pumps are rarely used in chilled water systems. 
TM 5-692-2

16-4 

 (2) Centrifugal pumps are the most commonly used pumps in refrigeration and air-conditioning 

systems and are classified by their mechanical features, installation arrangement, mounting position, and 

method of connection to the electrical motor. figure 16-1 shows several types of centrifugal pumps. 

Centrifugal pumps have three main parts: a prime mover (typically electric motor), an impeller, and a 

body. The motor is often connected to the pump shaft by a flexible type coupling. Some centrifugal 

pumps are built with the motor and pump impeller on the same shaft. In all cases, the pump impeller is 

connected to the shaft and turns the same speed as the motor. The impeller is the part of the pump that 

causes the water to move through the pump body. Impellers vary widely in their construction. The 

centrifugal force that comes from the rotating impeller moves the water or other liquids through the 

channels that run between the vanes. The outward-moving water streams are directed by the volute in a 

single stream that flows out of the pump discharge. This action of the impeller builds up the pressure of 

the water at the pump outlet. 

 d. Expansion tanks. Expansion tanks are used in chilled water systems for two purposes. First, 

expansion tanks allow for thermal expansion of the chilled water that, if not for the expansion tank, could 

damage the piping system. Secondly, the expansion tank provides a location for makeup water to be 

admitted to the system. The expansion tank is connected to the chilled water system on the inlet (suction) 

side of the distribution pump(s) by a branch line. The makeup water line is typically connected to this 

branch line between the expansion tank and the main pump inlet pipe. 

 e. Control valves. Control valves are used in chilled water systems to control the flow of chilled 

water through the piping system. The control system positions the valve through a valve operator or 

actuator that is directly attached to the valve stem. The valve operator or actuator uses electricity, 

compressed air, or hydraulic fluid to move the valve stem through its operating range. 

 f. Thermal storage. Thermal storage is the temporary storage of high- or low-temperature energy for 

later use. The purpose of thermal storage is to lower overall energy costs by generating and storing 

cooling medium during periods when electrical rates are at their lowest (off-peak). This occurs typically 

during the night or during periods of light air-conditioning loads. 

 (1) There are two types of storage strategies: full storage and partial storage. In full storage 

systems, the entire cooling load for a design period of time is generated during the off-peak time and 

stored for use during the following design period. In partial storage systems, only a portion of the design 

period cooling load is generated and stored during the previous off-peak period. During the peak period, 

the cooling load is satisfied by simultaneous operation of the cooling equipment (chillers) and withdrawal 

from storage. 

 (2) There are two thermal storage system options available for large commercial and industrial 

cooling applications: chilled water storage and ice storage. 

 (a) Chilled water storage systems use conventional chillers, pumps, and piping systems. They 

also require large storage tanks for chilled water. In this system, chilled water is generated during offpeak periods and stored in a storage tank. During peak cooling periods, the stored chilled water is 

pumped from the tank to the cooling equipment (air handler coils, etc.) and then returned to the storage 

tank. 

 (b) There are several types of ice storage systems that are used to store thermal energy. Ice 

storage typically has the advantage over chilled water storage in that it requires less space. 
TM 5-692-2 

16-5 

CIRCULATOR

CLOSE-COUPLED

END SUCTION

FRAME-MOUNTED

END SUCTION

BASE-MOUNTED

HORIZONTAL SPLIT CASE

SINGLE-STAGE

DOUBLE-SUCTION

BASE-MOUNTED

HORIZONTAL SPLIT CASE

MULTISTAGE

VERTICAL INLINE

VERTICAL TURBINE

SINGLE-STAGE OR

MULTISTAGE

*COOLING TOWER

*CONDENSER WATER

*CHILLED WATER

*PRIMARY AND SECONDARY

*HOT WATER

*BOILER FEED

*CONDENSATE RETURN

*CONDENSATE RETURN

*BOILER FEED

*HOT WATER

*PRIMARY AND SECONDARY

*CHILLED WATER

*CONDENSER WATER

*COOLING TOWER

SUMP-MOUNTED

CAN PUMP

Figure 16-1. Variations of centrifugal pumps 
TM 5-692-2

16-6 

g. Heat exchangers. A heat exchanger is any device that affects the transfer of thermal energy from 

one fluid to another. In the simplest exchangers, the hot and cold fluids mix directly; more common are 

those in which the fluids are separated by a wall. Common heat exchangers include the flat-plate, shelland-tube, and cross-flow types. A double-pipe heat exchanger, the simplest form of the shell-and-tube, 

can have the fluids both flow in the same direction. It is referred to as a parallel-flow type. If they flow 

in opposite directions, it is referred to as a counter-flow type. A shell-and-tube exchanger may also have 

several tubes, two-passes, and baffles. In cross-flow heat exchangers, the fluids flow at right angles to 

each other. The evaporator and condenser sections of water chillers are examples of shell-and-tube type 

heat exchangers that are an integral part of the water chiller package. Heat exchangers are also designed 

and used as stand-alone thermal heat transfer devices in chilled water systems, heating water systems, and 

steam systems. 

h. Strainers. Strainers are defined as closed vessels with cleanable screen elements designed to 

remove and retain foreign particles down to 0.001 inch diameter from various flow fluids. A strainer 

differs from a filter in that strainers trap particles that are typically visible to the naked eye. Strainers are 

typically installed in chilled water systems on the inlet (suction) side of the distribution pumps. 

i. Air separators. All chilled water systems use air separators to remove air (gas) bubbles that have 

become entrained in the water. One type of air separator is simply a tank constructed so that the chilled 

water inlet is not in a direct line with the outlet from the tank. The diameter of the tank is large compared 

to the chilled water piping. As the chilled water enters the expansion tank, the flow is slowed down 

considerably. This slowing of the flow, together with the change in direction of the chilled water flow, 

allows the air to rise to the surface of the tank or into the expansion tank to be vented. A more common 

type of air separator is a mechanical type air separator with a tangential entry that causes the chilled water 

to spin down from an upper entry to a lower discharge. The resulting turbulence enhances the air 

separation. Tangential entry mechanical separators generally require less space than tank type separators, 

but require that the circulating pump be capable of producing higher differential pressures. The air 

separator is typically installed in the chilled water supply piping between the chiller and the distribution 

pump. Air separators should be fabricated, tested, and certified in accordance with the appropriate 

sections of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code for 

unfired pressure vessels. 

j. Valves. Valves installed in the chilled water system are used to control water flow and to isolate 

equipment for ease of maintenance. Most valves in a chilled water system are manually operated with a 

handwheel or lever operator. 

 (1) Valves are rated in terms of saturated steam pressure; nonshock cold water, oil, or gas pressure 

(WOG); or both. Valve ratings are usually stamped or cast into the valve body. A valve with the 

markings "125" or "200 WOG" will operate safely at 125 psig of saturated steam or 200 psig of cold 

water, oil, or gas. 

 (2) Valves generally should be installed with the stem in the vertical up or horizontal position. 

Gate valves should be installed with the stem in the horizontal position and the bottom half of the valve 

disk opening in the direction of flow. Check valves are best-suited for horizontal installation, unless 

specifically designed for vertical installation. Special care must be taken when welding, soldering, or 

brazing valve end connections. All valve components not capable of withstanding the temperatures 

generated should be removed or cooled during installation. Valves are typically installed at the following 
TM 5-692-2 

16-7 

locations. 

 (a) On the inlet and outlet connection of each piece of equipment, including chillers, pumps, 

reducing valves, control valves, tanks, coils, and other equipment that requires periodic maintenance. 

 (b) On the supply and return branch lines at the point of connection to the main supply and 

return piping headers. 

 (c) Drain valves are installed at low points in the water distribution system to facilitate 

draining of the system. 

 (d) Vent valves should be installed at all high points in the chilled water piping system for 

manual venting of air from the system and to help in the draining of the piping. 

 (3) The most common types of valves utilized in chilled water systems include gate, ball, 

butterfly, globe, check, and pressure regulating valves. The general characteristics of these valves are 

described below. Illustrations of these valves are located on figures 16-2 and 16-3. 

 (a) Gate valves are identified by a wedge-shaped disk that is raised to open or lowered to close 

the valve. Gate valves are intended to operate fully open or fully closed, and have very low resistance to 

flow in the open position, since the disk rises out of the flow path. The gate valve 

should not be operated in the partially open position, as this may cause vibration and premature wear on 

the disk. The gate valve may be used for shutoff service where a slow closure is acceptable and where an 

absolute bubbletight closure is not a critical consideration. Gate valves may be rising stem with outside 

screw and yoke (OS&Y), rising stem with inside screw, or non-rising stem. The rising stem type makes 

viewing of the valve position possible, while the non-rising stem type requires less clearance above the 

operator, since the stem does not rise from the body. 

 (b) Ball valves use a ball as the opening/closing mechanism to control fluid flow. The ball is 

rotated 90 degrees from full open to full closed; therefore, it is well-suited for applications which require 

quick or frequent opening and closing. The ball seals by fitting tightly against resilient seats located on 

each side of the ball. Ball valves are generally selected for on/off service and are most common in sizes 3 

inches or less. Ball valves are available in three port sizes, including standard, full, and reduced port. 

Full port has the same opening size as the connecting pipe, standard port is usually one pipe size smaller 

than the valve size, and reduced port may be up to two pipe sizes smaller than the valve body size. 

 (c) Butterfly valves in the chilled water system are most common in the larger sizes due to the 

ease of operation, low cost, and superior shutoff characteristics. The butterfly valve usually consists of a 

wafer-shaped body with a rotating disk that closes against a resilient seat located within the valve body. 

Like the ball valve, a 90-degree rotation of the operating mechanism results in valve travel from closed to 

full open. The butterfly valve is well-suited for both on/off service or throttling service. 

 (d) Globe valves are primarily used for throttling service and are not well-suited for full flow 

applications due to the high resistance to flow designed into the valve. The standard valve consists of a 

round disk or tapered plug that seats against a round opening. Angle valves and needle valves are 

variations of the standard globe valve and use a similar method of closure. Unlike the gate and ball 

valves, globe valves must be installed in the proper direction of flow. Flow should enter through the disk 
TM 5-692-2

16-8 

seat and push up against the valve disk. Reverse installation will result in valve chatter, vibration, and 

premature valve failure. 

GATE VALVE ANGLE VALVE

GLOBE VALVE BUTTERFLY VALVE

Figure 16-2. Typical valves used in water service (1) 
TM 5-692-2 

16-9 

BALL VALVE PISTON CHECK VALVE

PLUG VALVE

LIFT CHECK VALVE SWING CHECK VALVE

Figure 16-3. Typical valves used in water service (2) 
TM 5-692-2

16-10 

 (e) Check valves are used in the chilled water system to prevent reversal of flow at pumps and 

equipment, with swing checks and lift checks as the most common types. The swing check has a 

swinging disk that is held open by the fluid flow. Closure results from reverse flow and gravity acting on 

the disk. Lift check valves consist of a disk that is lifted by upward fluid flow. Reversal of flow pushes 

down on the disk, stopping flow. The swing check valve has less resistance to flow due to its straightthrough flow design, but is more prone to water hammer than the lift check. Swing and lift check valves 

generally are only suited for horizontal installations, unless specifically configured for vertical 

installation. 

 (f) Water pressure regulating valves are used in the chilled water system to limit the water 

supply pressure to equipment within acceptable levels. The two common types of water pressure 

regulating valves include the direct-acting type and the pilot-operated type. The direct-acting regulator 

consists of an inner valve connected to a diaphragm. The diaphragm is held in position by a spring that is 

externally adjustable to give the desired downstream reduced pressure. The direct-acting regulating valve 

is simple and relatively inexpensive, but is not capable of maintaining constant downstream pressures if 

the upstream pressure varies or if the flow rate varies significantly. The pilot-operated regulator is more 

accurate than the direct-acting type, as it employs a small direct-acting valve (pilot valve) that maintains a 

constant pressure on the main valve diaphragm. Variations in upstream pressure have little effect on the 

resulting downstream pressure. 

k. Piping. Piping 2 inches and smaller used in chilled water systems is typically standard weight, 

continuous weld steel pipe with threaded joints and cast iron fittings. In addition, Type L hard copper 

pipe can be used in this size range. Copper piping uses soldered joints with wrought copper fittings. For 

chilled water piping larger than 2 inches, steel pipe conforming to American Society for Testing and 

Materials (ASTM) A 53, Standard Specification for Pipe, Steel, Black and Hot-Dipped, Zinc-Coated, 

Welded and Seamless (1999), is used. Joint types for this size of pipe are welded, flanged, or grooved. 

Fittings for ASTM A 53 type pipe are wrought steel, cast iron, and malleable or ductile iron. 
TM 5-692-2 

17-1 

CHAPTER 17

DOMESTIC WATER SYSTEMS 

17-1. Domestic water system description 

Domestic water (potable water) is water that is free from any significant impurities that would cause 

disease or harmful physiological effects to humans, and is in compliance with the water quality 

requirements of the Health Service having jurisdiction. 

a. System functions. The purpose of the domestic water system is to provide the occupants of a 

facility an adequate quantity of domestic water for drinking and for the proper operation of plumbing 

fixtures utilized for personal health and hygiene. The domestic water system must also protect the water 

it conveys from harmful substances that would damage the water quality and make it unfit for human 

consumption. The domestic water system is comprised of a water supply; a water distribution system; 

auxiliary components such as water heaters, pumps, storage equipment, and backflow prevention devices; 

and the termination point of use that are the plumbing fixtures. 

b. Water supply. The water supply may be from a public or private onsite system. Public systems are 

generally very reliable, however, for critical facilities, the use of a private system in conjunction with a 

storage system or a private onsite water supply will ensure the availability of water at all times. 

 (1) An example of a typical domestic water system with reservoir storage (under normal 

operation) is shown on figure 17-1. In this arrangement, under normal conditions, the plumbing fixtures 

are supplied with water directly from the public water supply. The public water supply is metered and 

then distributed throughout the facility. The supply of water to equipment and uses that may contaminate 

the domestic system is provided through a backflow preventer. The water downstream of the backflow 

preventer is referred to as nonpotable, and is not for human consumption. 

 (2) During periods when the public water system is out of service, water is drawn from the 

reservoir and supplied to the facility through the use of the reservoir pump (emergency operation). The 

pump is controlled by a pressure switch, and system pressure is maintained by the hydropneumatic tank 

as the pump cycles. Check valves in the system prevent water flow back into the public system when the 

reservoir pump is operating and prevent backflow through the pump when it is not operating. The 

reservoir is kept filled with water when operating from the public system; however, the reservoir water 

must be pumped out and refilled on a regular basis to prevent stagnation and contamination of the stored 

water. 

17-2. Domestic water system major components 

Domestic water systems are generally comprised of the following major components. 

a. Water storage. Water storage systems may be associated with a private water system in which case 

the storage would act as a buffer to maintain a relatively constant supply pressure. Water storage systems 

also may function as an emergency backup supply in the event that the public water supply is taken out of 

service. The principle types of water storage are tanks, reservoirs, and bladder tanks. All storage 

structures utilized for domestic water must be constructed of nontoxic materials that resist corrosion, and 

must be disinfected prior to use. 
TM 5-692-2 

17-2 

M

DOMESTIC

WATERHEATER

TO

PLUMBING

FIXTURES

HOT WATERCIRCULATING

VALVE

WATER SUPPLY TONONPOTABLE SYSTEMPREVENTER

ISOLATION VALVE (TYP)WATER PRESSUREREGULATING VALVE

RELIEF

BACKFLOW

AIR

WATER

PS

DOMESTICPUMP

GAUGE GLASS

CHLORINE SOLUTION TANKHYPOCHLORINATOR

AIR CHARGE CONNECTIONHYDROPNEUMATIC TANK

DOMESTICRESERVOIR

PRESSURE SWITCHRESERVOIR PUMP

CHLORINE SOLUTION TANKHYPOCHLORINATOR

PUBLIC

WATER

SUPPLY

WATER

SUPPLY

WELL

WATER METERFILL VALVE

PUMPSUCTION

CIRCULATION

Figure 17-1. Domestic water system with reservoir storage 
TM 5-692-2 

17-3 

 (1) The discussion will focus on two types of aboveground tanks: ground-mounted and elevated. 

The elevated storage tank is used in flat-land areas where the terrain does not offer the advantage of a 

high point near the water use point in which a ground-mounted tank could be located. The elevated 

storage tank consists of a tank (usually steel), structural support legs, and water standpipe. The groundmounted tanks are also usually constructed of steel, and are typically mounted on a concrete foundation. 

The pump and piping arrangement serving the storage tanks is dependent on the tank elevation. If the 

tank is well above the water use point (60 to 100 feet), the water supply is pumped into the tank to 

maintain a certain water level, and the tank is not pressurized. The water pressure at the use point is 

equivalent to the water elevation in the tank (100 feet = 43 psig). If the water storage tank is at or near 

the same elevation of the use point, the tank is usually pressurized if it is used as a constant water supply 

system. If the tank is used for emergency purposes only, it may have pumps on the discharge and then 

would not be pressurized. 

 (2) Reservoirs are typically underground concrete water storage structures. Typically the reservoir 

is not pressurized and is fed from a private or public water system, or in some cases may be spring fed. It 

is common for pumps to draw from the reservoir and pump into the pressurized water system at a facility. 

Reservoirs typically have an access for maintenance personnel and a vent to prevent pressure buildup. 

 (3) Bladder tanks, also referred to as hydropneumatic tanks, consist of a steel tank that is divided 

into an air section and a water section by a rubber bladder. The air section is charged with air to a 

pressure equivalent to the minimum desired pressure in the water supply system. A bladder tank is 

commonly installed on a private water supply system to provide some storage capacity and to act as a 

buffer for the supply pumps (figure 17-2). Typically, one third of the total tank capacity is available for 

storage (a 200 gallon tank would result in 70 gallons of useful storage). 

 b. Water heaters. The purpose of the domestic water heater is to provide hot water at the desired 

temperature to the plumbing fixtures and to any other point of use. System water temperatures range 

from 120 to 140o

F for typical plumbing fixtures, up to 165oF for laundry, and 180 to 190oF for 

dishwashing and sanitizing applications (see figures 17-3, 17-4, and 17-5). 

 (1) Heat energy sources include oil, propane and natural gas, electricity, and steam. Oil and gas 

units are generally referred to as fuel type direct-fired water heaters. Electric water heaters employ a 

direct conversion of electrical energy into heat. Indirect water heating is accomplished through the use of 

remote heat sources (usually boilers) which supply steam to the water heater. The water heater then uses 

steam as an energy source to heat the domestic water. 

 (2) Water heaters are also classified as to their storage capacity and recovery rate. The recovery 

rate is the amount of water in gallons per hour (gph) that can be raised +100° F at a given heat input. The 

storage capacity allows large volumes of hot water to be drawn from the system at flow rates that exceed 

the recovery capacity of the heater. Instantaneous heaters have a high recovery rate and very little 

storage, while storage type heaters have a lower recovery rate and significant storage capacity. A semiinstantaneous heater is a variation of the above two types, with limited storage and moderate recovery 

rates. 
TM 5-692-2 

17-4 

WATER

AIR

PI

PS

WATER SUPPLY

WATER SUPPLY OR

BOOSTER PUMP

BLADDER ACCESS

CONNECTION

CONNECTION

AIR CHARGE

TANK BLADDER

RELIEF VALVE

PRESSURE

PRESSURE

TO WATER

DRAIN VALVE

DISTRIBUTION SYSTEM

SWITCH

INDICATOR

CHECK VALVE

ISOLATION

VALVE (TYP)

Figure 17-2. Bladder tank installation 

c. Plumbing fixtures. The plumbing fixture is the termination point of the domestic water system and 

is the beginning of the sewer system. Since the quantity of water consumed by the plumbing fixture 

presents a load on both the domestic water supply system and the sewage disposal/treatment system, all 

plumbing fixtures should be maintained to minimize water usage. All plumbing fixtures should be 

provided with shutoff valves on the water supply to allow for servicing. The most common plumbing 

fixtures are water closets, urinals, lavatories, service sinks, general purpose sinks, and drinking fountains. 

d. Backflow preventers. Backflow preventers are devices used to prevent the contamination of the 

domestic (potable) water system. Backflow preventers can be classified into four basic types, with the 

proper application of each type dependent upon the piping arrangement and the degree of hazard 

involved. The basic types of backflow preventers are illustrated on figure 17-6. 
TM 5-692-2 

17-5 

WATER

OUT VACUUM

RELIEF

TEMPERATURE

AND PRESSURE

RELIEF VALVE

RELIEF VALVE

FULL SIZE OF

RELIEF PIPE

TO SPILL OVER

FLOOR DRAIN

IMMERSION

ELEMENT (TYP)

DRAIN VALVE

DRAIN

HOT

SUPPLY

WATER

COLD VALVE

ISOLATION

VALVE

(TYP)

Figure 17-3. Electric water heater 

e. Valves and piping. A variety of valves and piping materials are commonly used in domestic water 

systems. 

 (1) Valves installed in the domestic water system are to control water flow and to isolate 

equipment for ease of operation and maintenance. Most valves in a domestic water system are manually 

operated with a hand wheel or lever operator. 
TM 5-692-2 

17-6 

STEAM SUPPLY

PI PI

T

TE HOT WATER

OUT

COLD WATER

SUPPLY

ISOLATION

STEAM TRAP

CONDENSATE

RETURN

VALVE (TYP)

(TYP)

WATER COILS

STRAINER (TYP)

PRESSURE INDICATOR

(TYP)

STEAM CONTROL

VALVE

ELEMENT

TEMPERATURE

PRESSURE AND

TEMPERATURE

RELIEF VALVE

VALVE

CHECK

Figure 17-4. Instantaneous steam water heater 

 (2) Piping materials that convey domestic water must be specifically approved for this use. 

Typical code-approved piping materials for water distribution include brass pipe, copper tube or copper 

pipe, galvanized steel pipe, ductile iron pipe, and approved plastic pipe. Pipe and fittings for use in 

domestic water systems shall not contain more than 8 percent lead. Solder used for joining copper tubing 

shall not contain more than 0.2 percent lead. 

 (a) Piping systems should be inspected and tested prior to being concealed and put in service. 

Minimum test pressure should be 80 psig or the working pressure, whichever is greater. A visual 

inspection should be made to identify proper installation, including joints and connections, supports, 

access to valves, and cross connections. Pipelines should be identified as to the fluid contained by color 

coding or identification tags. An adequate quantity of unions or flanges should be provided at all pieces 

of equipment to allow for servicing of the equipment. Drain valves should be installed at low points of 

the piping system to facilitate draining of the system for maintenance. Installation of pipe over electrical 

equipment should be avoided or should be provided with drip pans. 

 (b) Brass pipe is an alloy of copper and zinc and is found on a limited basis in domestic water 

systems. The most common use is for gauge piping and for piping of equipment accessories. Available 

sizes range from 1/8 inch up to 12 inch. Smaller diameter fittings are usually screwed whereas larger 

diameter fittings are flanged type. 
TM 5-692-2 

17-7 

ISOLATION

SUPPLY

VALVE (TYP)

T

DRAIN

COLD WATER

HOT WATER

RETURN

(IF PROVIDED)

CIRCULATING PUMP

(TYP)

STEAM COILS

TE

PI PI

T

STEAM TRAP

(TYP)

CHECK VALVE

(TYP)

CONDENSATE

RETURN

INDICATOR

PRESSURE

STEAM

(TYP)

STEAM

CONTROL

VALVE

SUPPLY

RELIEF VALVE

TEMPERATURE

PRESSURE AND

THERMOMETER

ELEMENT

TEMPERATURE

HOT WATER OUT

Figure 17-5. Semi-instantaneous steam water heater 

 (c) Copper pipe and tubing is common in domestic water service and distribution systems. 

Copper pipe is used on a limited basis for applications similar to that of brass pipe. Copper tubing, 

however, is used extensively for water service and distribution, especially in pipe sizes 3 inch and 

smaller. Copper water tube is designated as Type K, L, or M, and is available in drawn (hard) or annealed 

(soft) tempers in sizes from 1/8 to 12 inch. Copper tubing is also color-coded with a stripe to designate 

Type K (green), Type L (blue), or Type M (red). Type K tube is the heaviest of the three types and is 

used primarily for underground water services. Type L tube is used widely for underground water 

services and for interior water distribution piping. Type M tube is the lightest weight of the three tube 

types. Type M tube is approved for interior water distribution; however, it is preferable to use the heavier 

Type L tube for this application. 

 (d) Galvanized steel pipe is available in three basic weight categories including standard 

weight, extra-strong, and double extra-strong. American Society for Testing and Materials (ASTM) A 

53, Standard Specification for Pipe, Steel, Black and Hot-Dipped, Zinc-Coated, Welded and Seamless, 

Grade B, standard weight (Schedule 40) galvanized steel pipe is the most common type of steel pipe used 

for domestic water application. Fittings are generally malleable-iron and threaded. Galvanized steel 

domestic water systems require more maintenance than non-ferrous systems due to the deterioration of 

the zinc-coating (galvanizing) and the natural oxidation of the steel over the lifetime of the system. 
TM 5-692-2 

17-8 

BACKFLOW PREVENTER WITH

INTERMEDIATE ATMOSPHERIC VENT

HOSE BIBB VACUUM BREAKER

PRESSURE TYPE VACUUM BREAKER

ATMOSPHERIC VACUUM BREAKER

REDUCED PRESSURE PRINCIPLE

BACKFLOW PREVENTER

DOUBLE CHECK VALVE ASSEMBLY

Figure 17-6. Backflow preventers 

 (e) Ductile iron pipe is typically used for underground water services and for water 

distribution in pipe sizes of 4 inch and larger. Fittings are generally push-joint for underground 

applications and flanged or mechanical joint for aboveground applications. Ductile iron pipe and fittings 
TM 5-692-2 

17-9 

for domestic water systems must be cement mortar lined per the requirements of the American Water 

Works Association (AWWA) C104, Cement-Mortar Lining for Ductile-Iron Pipe and Fittings for Water 

(1995). 

 (f) Plastic pipe is available in various types, some of which are approved for domestic water 

services and others which are approved for domestic water distribution. Generally polybutylene (PB), 

polyvinyl chloride (PVC), and polyethylene (PE) are approved for underground water services, whereas 

interior water distribution systems are limited to chlorinated polyvinyl chloride (CPVC) and PB pipe and 

tubing. PVC and CPVC fittings are available in solvent weld, threaded, and flanged types. PB and PE 

fittings are available in thermal fusion and compression types. Metal insert fittings are also available for 

PB pipe. Plastic pipe has excellent characteristics for resistance to corrosion, therefore, it is well-suited 

for corrosive atmospheres or for use in soils where corrosion protection would be required for metallic 

piping systems. An interior plastic water distribution system will require considerably more pipe supports 

than a metallic system due to the poorer strength characteristics of plastic. Also, the combustion qualities 

of plastic pipe prevent its use in some building areas, including spaces used as air plenums. 

 f. Pumps. Pumps are most commonly used in domestic water systems for boosting water pressure 

and for hot water circulation. There are two basic types of pumps: positive displacement and centrifugal. 

g. Water treatment equipment. Water treatment equipment generally associated with domestic water 

systems includes hypochlorinators and water softeners. Hypochlorinators are used to disinfect well water 

and water reservoirs, whereas water softeners are used to remove dissolved solids from the water supply. 
TM 5-692-2 

18-1 

CHAPTER 18

CHEMICAL TREATMENT SYSTEMS 

18-1. Chemical treatment system design features 

This chapter presents an overview of common chemical treatment processes that may be required to 

maintain water, steam, and condensate utility systems in good operating condition. The descriptions in 

this chapter are provided as a reference for the reader in applying the terminology, uses of equipment, and 

recommended maintenance practices. The need for chemical treatment depends on the quality of the 

water supplied to the facility and the types of equipment in service at the facility. There is no one 

treatment program or system that is right for all facilities or systems within the facilities. The chemical 

treatment examples are based on the facility being supplied with water either from a municipal supply 

system or from a well system dedicated to the facility. The water supplied to the facility generally meets 

drinking water standards and is used to supply potable water and process water systems within the 

facility. 

a. Applications. The systems for which treatment practices are discussed as follows. 

 (1) Well water delivered to facility domestic and industrial water reservoirs 

 (2) Closed-loop recirculating water systems (chilled water, recirculating cooling water, and hot 

water heating) 

 (3) Open recirculating water systems (cooling tower spray water or recirculating cooling water in 

an open cooling tower loop) 

 (4) Steam boiler system (makeup water, feedwater, and steam and condensate) 

b. Water supply disinfection. Although the water supplied to the facility is already drinking water 

quality, additional disinfection may be required to control the growth of biological contaminants, such as 

algae, in the potable and industrial water reservoirs where long-term storage may provide conditions for 

growth. This additional disinfection may be direct treatment of the water supplied to the facility, 

treatment of a recirculating stream at the reservoirs, or a combination of both. Operator involvement is 

limited to testing the water to determine the amount of treatment required, adjusting the pump stroke 

and/or the hypochlorite solution strength to obtain the desired dosage, and keeping an adequate supply of 

hypochlorite solution in the local storage tank. 

c. Process water systems. Process water refers to systems, such as chilled water systems, hot water 

heating systems, and recirculating water equipment cooling systems. The three primary reasons that 

process water chemical treatment may be required are to control corrosion, scale formation, and the 

growth of biological agents. Because corrosion and scale control chemicals can change the pH of the 

circulating water stream, the pH of a system may also require monitoring and adjustment. Process water 

streams may be closed-loop systems or open systems. 

(1) In closed loop systems, there are negligible losses from or additions into a known volume 

system. Once the initial volume is chemically treated, the quality of the circulating fluid needs to be 

monitored on a regular basis and additional chemicals added as required to maintain recommended 

residual concentrations of treatment chemicals. When chemical treatment of a closed-loop water 
TM 5-692-2 

18-2 

circulating system is required, the chemicals are usually introduced into the system by means of a pot 

feeder. The chemical treatment can be accomplished as the system is filled or during normal operation of 

the system using a pot feeder in a bypass loop. A typical pot feeder fill system installation is shown on 

figure 18-1, and a typical pot feeder bypass installation is shown on figure 18-2. 

 (a) In cold service closed-loop systems, the system may only need to have chemical treatment 

when the system is filled initially and any time the system has been open for maintenance. Cold service 

recirculating systems are usually treated to prevent corrosion from dissolved oxygen. Scale formation is 

usually not a problem in cold systems. 

 (b) In warm or hot service closed-loop water circulating systems, regular monitoring and 

chemical additions may be required to prevent corrosion from dissolved oxygen and scale formation from 

precipitation of minerals in the water. 

 (2) In open recirculating cooling water systems there is constant loss from the system due to 

evaporation and a constant addition of makeup water into the system which constantly changes the quality 

of the recirculating stream. Also, as water evaporates from the system, impurities in the water are left 

behind which causes an increase in the concentration of these impurities. These impurities are generally 

referred to as total dissolved solids. Open systems typically control total dissolved solids by blowdown 

from the system. Additionally, the methods used to reduce the temperature of open recirculating water 

streams allow oxygen, which is a primary cause of corrosion, to be entrained in the recirculating stream. 

 (a) This constant change in the system quality may require frequent water quality monitoring 

along with the frequent addition of chemicals to control corrosion, scale formation, and growth of 

biological agents. Some combinations of chemicals used may also change the pH of the system 

significantly which will require pH monitoring and adjustment. If an open system requires chemical 

treatment, treatment program options range from the operator periodically sampling the water and making 

slug additions of chemicals into the basin to a continuous water quality analyzer controlling the operation 

of metering pumps which inject controlled doses of chemicals into the circulating stream to maintain a 

uniform water quality. 

 (b) A typical automated open-loop water quality monitoring and control system is shown on 

figure 18-3. In the example automated system, a sample stream passes through a water quality analyzer 

which has probes that monitor pH and conductivity (a measure of total dissolved solids). The pH meter 

controls a metering pump that injects a pH adjustment solution (usually an acid) into the circulating 

stream. The conductivity meter controls the operation of the blowdown valve. A signal from a water 

meter in the makeup waterline controls the corrosion inhibitor metering pump. A timer in the water 

quality analyzer activates the biological growth control metering pump. Some automated systems may 

have a corrosion sensing probe, rather than a water meter, to control the corrosion inhibitor metering 

pump. A likely alternate to the fully automated system is metering pumps controlled by timers. Based on 

a periodic water sample, the operator sets the timers and adjusts the metering pumps to provide the 

desired level of chemical treatment for the system. 
TM 5-692-2 

18-3 

FEEDER FILL POINT

VENT

ASSEMBLY

POT FEEDER

DRAIN

BE TREATED

STREAM TO

Figure 18-1. Typical fill system pot feeder installation 

 (3) The elevated temperatures at which even low-pressure boilers operate increase the likelihood 

of corrosion and scale formation problems from contaminants in the water. Other common boiler 

problems caused by poor water quality control are foaming and caustic embrittlement of metal 

components (usually not a concern for boilers operated below 600 psig). Steam boiler water quality 

control is typically accomplished by a combination of chemical treatment, deaeration, and blowdown. A 

typical steam boiler installation is shown on figure 18-4. 

 (a) In the example installation, the quality of the makeup water is adjusted by a water softener, 

a dealkalizer, or an ion exchange unit. In areas where only treatment to reduce hardness is required, a 

water softener is used to reduce the total dissolved solids in the makeup water that helps control scale 

formation and foaming. In areas where only treatment to reduce alkalinity is required, a dealkalizer is 

used. In areas where combined treatment is required, an ion exchange unit is 
TM 5-692-2 

18-4 

SUPPLY

RETURN

SCREW ON LID

DRAIN/SAMPLE

CLOSED LOOP SYSTEM

CIRCULATING PUMP

POT FEEDER

ASSEMBLY

VENT

Figure 18-2. Typical pot feeder bypass installation 

used. In an ion exchange unit, a section known as the cation exchanger removes metals, such as calcium 

and magnesium (hardness), and a section known as the anion exchanger (alkalinity control) may remove 

bicarbonates (corrosion and embrittlement), sulfates (hard scale), chlorides (foaming), and soluble silica 

(hard scale). A typical water softener unit is shown on figure 18-5, and a typical ion exchange unit is 

shown on figure 18-6. Dealkalizer units operate the same as water softeners, but use different resin bed 

materials and require strong caustic or acid regeneration. The makeup water is passed through a treated 

resin bed where the contaminants in the water are collected through a chemical exchange process. When 

the bed becomes saturated with contaminants, the bed is backwashed, treated with a concentrated 

electrolyte, rinsed, and placed back in service. For critical or continuous operations, treatment units may 

be dual-column units that allow switching from a saturated column to a regenerated standby column so 
TM 5-692-2 

18-5 

HEAT

EXCHANGER

INHIBITOR

CORROSION

CONTROL

GROWTH

BIOLOGICAL

P H CONTROL

CONTROLLER

QUALITY

WATER

COOLING TOWER

PUMP

DRAIN

SUPPLY

WATER

MAKE UP

VALVE

BLOW DOWN

WATER METER

WH

SV

Figure 18-3. Open-loop chemical treatment system 

that service is not interrupted for routine column regeneration. Ion exchange units may also be used to 

provide water for engine cooling systems and closed-loop process water systems. The use of water 

softener-treated water for engine cooling loops is discouraged by many engine manufacturers. 

 (b) The next step in boiler water quality control is deaeration of the combined makeup water 

and condensate return stream. A deaerator unit heats the water to the boiler point at the operating 

pressure of the unit which encourages release of non-condensable dissolved gases, such as oxygen and 

carbon dioxide, which are significant contributors to corrosion in the boiler and condensate system. As 

the feedwater flows from the deaerator to the boiler, various chemicals may be injected into the feedwater 

to further control corrosion, scale formation, foaming, and caustic embrittlement. (Some systems, as 

shown in the example, may also inject treatment chemicals into the steam header.) A typical feedwater 

treatment system consists of a chemical feed tank, an agitator, a strainer, a chemical feed pump, a check 

valve, and appropriate isolation valves. The operation and control of the metering pumps is dependent on 

the type of boiler and the boiler operation cycle, and the control options are similar to those discussed for 

open systems in paragraph 18-1c(2). Treatment chemicals such as hydrazine and sodium sulfite are used 

to control corrosion by reacting with dissolved oxygen and are generally referred to as oxygen 

scavengers. Chemicals known as neutralizing amines (injected into the feedwater) and filming amines 

(injected into the steam lines) provide protection against carbonic acid formed by the reaction of carbon 

dioxide and carbonates. Scale control chemicals generally act to keep precipitated solids soft and fluid. 

 (c) As water evaporates to form steam, contaminants are left behind which increase the 

concentration of total dissolved solids in the boiler. Even if fluid, a coating of solids on heat transfer 
TM 5-692-2 

18-6 

10N EXCHANGE UNIT

DEALKALIZER OR

WATER SOFTENER,

VENT

DEAERATOR SYSTEM

STEAM DISTRIBUTION

BOILER

TO DRAIN

BLOWDOWN

PUMP (TYPICAL)

CHEMICAL FEED

(TYPICAL)

FEED TANK

CHEMICAL

(MIXER)

AGITATOR

SUPPLY

WATER

RAW

RETURN

CONDENSATE

PUMP

FEEDWATER

Figure 18-4. Typical steam boiler installation 

surfaces, can reduce the capacity of equipment or create conditions which may lead to equipment failure. 

The concentration of total dissolved solids is controlled by blowing down the boiler. Boiler blowdown 

may be a combination of bottom blowdown and surface blowdown. Many boilers utilize a continuous or 

automated surface blowdown. Hot water boilers, which are used to provide hot water consumed in 

facility operations and, therefore, require substantial quantities of makeup water, may have makeup and 

feedwater treatment needs and blowdown operations similar to similarly sized steam boilers. 

18-2. Chemical treatment system major components 

Chemical treatment systems are comprised of the following major components. 

a. Chemicals. The list that follows includes generic or families of chemicals which may be used to 

condition water and the typical condition that the chemical is used to treat. The specific name of the 

treatment product containing the listed chemical and the form of the chemical used will depend on the 

manufacturer. Most chemical treatment manufacturers have developed proprietary "brand names" which 

combine a number of the chemicals discussed below and include other agents to enhance the performance 

of the product. Facilities should use the technical service departments of water treatment chemical 

suppliers to tailor the facilities’ chemical treatment needs to local conditions, and to establish procedures 

for safe chemical storage and handling. 
TM 5-692-2 

18-7 

O - OPEN C - CLOSED

VALVE OPERATION

FUNCTION 2 3 4 5 6 7

C

O

C

C

O

O

C

C

C

O

C

C

C

C

O

C

C

C

O

C

C

C

C

O

1

O

O

C

C

RINSE 

BRINE

BACKWASH

ON-LINE

FLOW

BRINE

OUTLET

SOFT WATER

INLET

RAW WATER

BRINE

TANK

WATER

SOFTENER

DRAIN

TREATMENT

FLOW 

SOFTENER

BED

BACKWASH

FLOW

CUT AWAY OF

WATER SOFTENER

COLUMN

5

7

3

1

4

2 6

Figure 18-5. Basic water softener system 

 (1) Copper sulfate - Controls algae in reservoirs and open systems. 

 (2) Sodium hydroxide (NaOH - caustic soda) - Increases alkalinity, raises pH, precipitates 

magnesium. 

 (3) Sodium carbonate (Na2CO3 - soda ash) - Increases alkalinity and pH, precipitates calcium in 

the form of carbonate. 

 (4) Sodium phosphates (NaH2PO4, Na2HPO4, Na3PO4, NaPO3) - Precipitates calcium as 

hydroxyapatite (Ca10(OH)2(PO4)6). Stream pH must be kept high for this reaction to occur. 

 (5) Sodium aluminate (NaAl2O4) - Precipitates calcium and magnesium. 

 (6) Chelants (EDTA, NTA) - Control scaling by forming heat-stable soluble complexes with 

calcium and magnesium. 

 (7) Polymers (polyacrylates, etc.) - Disperse sludge and distort crystal structure of calcium 

deposits. Prevent fouling due to corrosion products. 
TM 5-692-2 

18-8 

(8) Tannins, starches, glucose, and lignin derivatives - Prevent feed line deposits by coating scale 

crystals to produce sludge that will not readily adhere to boiler surfaces. DRAIN

(OPTIONAL)

FILTER

CARBON

ACTIVATED

INLET

RAW WATER

COLUMN

ION EXCHANGE

CUT AWAY OF

FLOW

BACKWASH

BED

RESIN

FLOW 

TREATMENT

DRAIN DRAIN

EXCHANGER

CATION

EXCHANGER

ANION

OUTLET

WATER

DEIONIZED

TANK

ACID

TANK

CAUSTIC

PI

PI PI

PI

Figure 18-6. Basic ion exchange unit 

 (9) Seaweed derivatives (sodium alginate, sodium mannuronate) - Minimize carry-over from 

boiler by keeping scale forming sludge fluid. 

 (10) Sodium sulfite (Na2SO3) - Prevents oxygen corrosion. 

 (11) Hydrazine (N2H4 - normally supplied as a liquid) - Prevents oxygen corrosion. 

 (12) Filming amines (octadecylamine, etc.) - Control condensate line corrosion by forming 

protective film on metal surfaces. 

 (13) Neutralizing amines (cyclohexylamine, morpholine, etc.) - Control condensate line corrosion 

by adjusting condensate pH. 

 (14) Sodium nitrate (NaNO3) - Inhibits caustic corrosion. 

 (15) Antifoams (polyglycols, polyamides, silicones) - Reduce foaming tendency of highly 

concentrated boiler water. 

 (16) Nitrite-borax (three parts sodium nitrite and one part borax) - Inhibits corrosion and controls 

cylinder line cavitation in diesel engine cooling systems. 
TM 5-692-2 

18-9 

 (17) Soluble oils - Inhibit corrosion in diesel engine cooling systems. 

 (18) Chromates - Inhibit corrosion in diesel engine cooling systems. Not compatible with ethylene 

glycol base, antifreeze solutions and are extremely toxic. Do not use without major command permission. 

b. Chemical feed pumps. Most chemical feed pumps are referred to as metering pumps. Because the 

pump has to inject a treatment chemical into what is frequently a high pressure stream, common chemical 

feed pumps are positive displacement units which use a reciprocating (piston) action to alternately fill a 

pumping chamber and discharge a fixed volume of solution. In many units, the piston acts through a 

flexible, noncorrosive diaphragm that isolates the mechanical elements of the pump from the chemical 

stream. Chemical metering pump discharge quantities can usually be varied by adjusting the stroke 

length of the pump by means of an external stroke length adjustment knob. The stroke adjustment of 

many electric motor-driven metering pumps alters a mechanical linkage that can be damaged if the pump 

is not operating when adjustments to stroke length are made. 

c. Pot feeders. Pot feeders are used to add chemicals to systems that do not require frequent chemical 

treatment. The flow of the stream or part of the stream to be treated through a pot feeder charged with 

chemical solutions adds the chemical to the stream. Typical pot feeder installations are shown on figures 

18-2 and 18-3. 

d. Valves and piping. This paragraph presents an overview of the types of piping components and 

design and testing considerations related to chemical treatment piping. Information contained in this 

section applies to field-installed piping. Piping design, materials, fabrication, assembly, erection, 

inspection, and pressure tests for facility piping systems should be in accordance with American Society 

of Mechanical Engineers (ASME) B31.1, Power Piping. Major modifications of existing piping systems 

should include hydrostatic testing and radiographic or magnetic particle inspection of welds where 

applicable. During testing, system components that have not been designed for the piping test pressure 

must be disconnected and protected against damage by overpressure. 

 (1) Common valve materials compatible with typical facility chemical treatment systems are 

carbon or stainless steel. Valve bodies from these materials should be cast or forged. In low-pressure 

systems, plastic valves from materials similar to polyvinyl chloride (PVC) may be used. In general, 

unless the valve has failed after only a short period of use, replace valves (and other piping components) 

with new valves constructed from the same materials. Typical types of valves that may be found in 

chemical treatment systems are as follows. 

 (a) Gate valves may be used for lube oil shutoff service where a slow closure is acceptable 

and where absolute bubbletight closure is not a critical consideration. Gate valves may be rising stem, 

outside stem and yoke (OS&Y), or double-disk type. 

 (b) Ball or non-lubricated plug valves are generally used where quick or frequent opening or 

closing is required. 

 (c) Check valves are used in chemical treatment systems to prevent backflow through pumps, 

branch lines, meters, or other locations where runback or reverse flow must be avoided. 

 (d) Globe valves are used in systems at locations where manual control of the flow rate is 

required. General use of globe valves should be avoided, because of their high resistance to flow. 
TM 5-692-2 

18-10 

 (2) Common piping materials used in chemical treatment systems are carbon steel pipe, and 

stainless steel pipe and tubing. Some low-pressure systems may use plastic pipe components. In general, 

when modifying or repairing a system, replace existing piping components or add to the system using 

piping components of the same materials of construction of the existing system, provided the service life 

has been good. 

 (3) Many piping systems will have one or more pipe test sections installed in the system. A test 

section is a short section of pipe that can be easily isolated and removed from the system to make a 

thorough visual inspection of the interior of the pipe system possible. Visual inspection confirms the 

need for or the effectiveness of a chemical treatment program. 
TM 5-692-2 

19-1 

CHAPTER 19

AIR HANDLING SYSTEMS 

19-1. Air handling system design features 

An air handling system is a means of providing conditioned air to the space in order to maintain the 

environmental requirements. Not all air handling systems will contain the components presented in this 

chapter, nor is there a standard arrangement for the devices and equipment for various facilities. While 

there is no "one correct way" to design an air handling system, all air handling systems have basic 

components that are used. To meet the whole sensible and latent cooling needs of a space with the cool 

air they supply, these systems use air handling units and, in most cases, chilled water coils to give cooled 

and dehumidified air to the space. These systems may use low-, medium-, or high-pressure air 

distribution systems. All air systems are subdivided into single-zone, multizone, dual-duct, reheat, and 

variable air volume systems. 

a. Single-zone systems. Single-zone systems serve just one temperature control zone and are the 

simplest type of all air systems. For this type of system to work properly, the load must be uniform all 

through the space, or else there may be a large temperature variation. Single-zone systems are, in most 

cases, controlled by varying the quantity of chilled water or refrigerant, adding reheat, adjusting face or 

bypass dampers, or a combination of these. If a close control of the humidity is required while in the 

cooling mode, a reheat system must be used. Figure 19-1 is the schematic for a typical single-zone 

central air handling system. 

b. Multizone systems. Multizone systems are used to serve a small number of zones with just one 

central air handling unit. The air handling unit for multizone systems is made up of heating and cooling 

coils in parallel to get a hot deck and a cold deck. For the lowest energy use, hot and cold deck 

temperatures are, as a rule, automatically changed to meet the maximum zone heating (hot deck) and 

cooling (cold deck) needs. Zone thermostats control mixing dampers to give each zone the right supply 

temperature. A typical multizone air handling system is shown on figure 19-2. 

c. Dual-duct systems. Dual-duct systems are much like multizone systems, but instead of mixing the 

hot and cold air at the air handling unit, the hot and cold air are both brought by ducts to each zone where 

they are then mixed to meet the needs of the zone. It is common for dual-duct systems to use 

high-pressure air distribution systems with the pressure reduced in the mixing box at each zone. A simple 

dual-duct system is shown on figure 19-3. 

d. Reheat systems. Reheat systems supply cool air from a central air handler as required to meet the 

maximum cooling load in each zone. Each zone has a heater in its duct that reheats the supply air as 

needed to maintain space temperatures. Reheat systems are quite energy-inefficient and have become rare 

in new buildings as the cost of energy has gone up. Most reheat systems are constant volume, thus the 

reduction of air volume to each zone as the cooling load gets less will keep down the use of the reheat 

units and reduce energy consumption significantly. Energy may also be saved by automatically resetting 

the temperature of the cold air, allowing it to rise as the temperature of the outside air falls. More energy 

savings may be found through the recovery of the refrigeration system's rejected heat and the use of this 

heat to reheat the air. An example of a reheat system that uses terminal reheat units shows on figure 19-4. 
TM 5-692-2 

19-2 

SUPPLY RETURN

RETURN AIR

CEILING PLENUMOR RETURN DUCT

FAN

RELIEF DAMPERRETURN AIRDAMPER

EXHAUST AIR

FAN

SUPPLY

OUTSIDE AIRDAMPER

HEATING

COIL

COOLING

COIL

OUTSIDE

AIR

RETURN

Figure 19-1. Typical single zone air handling system 
TM 5-692-2 

19-3 

SUPPLY RETURN

RETURN AIR

CEILING PLENUMOR RETURN DUCT

FAN

RELIEF DAMPER

RETURN AIRDAMPER

EXHAUST AIR

FAN

SUPPLY

HOT DECKHEATING COILOUTSIDE AIRDAMPER

COLD DECKCOOLING COIL

OUTSIDE

AIR

(TYP) (TYP)

ZONE 1 ZONE 2 ZONE 3

ZONE DAMPERS

(TYP)

RETURN

Figure 19-2. Multizone air handling system 
TM 5-692-2 

19-4 

SUPPLY RETURN

RETURN AIR

CEILING PLENUMOR RETURN DUCT

FAN

RELIEF DAMPER

AIRDAMPER

EXHAUST AIR

FAN

SUPPLY

AIRDAMPER

COIL

COIL OUTSIDE

AIR

(TYP) (TYP)

ZONE 1 ZONE 2 ZONE 3

MIXING BOXES

(TYP)

HEATING

COOLING

RETURN

RETURNOUTSIDE

Figure 19-3. Basic dual duct air handling system 
TM 5-692-2 

19-5 

SUPPLY RETURN

RETURN AIR

CEILING PLENUMOR RETURN DUCT

FAN

RELIEF DAMPERRETURN AIRDAMPER

EXHAUST AIR

FAN

SUPPLY

OUTSIDE AIRDAMPER

COIL

OUTSIDE

AIR

(TYP) (TYP)

ZONE 1 ZONE 2 ZONE 3

TERMINAL REHEATUNITS (TYP)

COOLING

RETURN

Figure 19-4. Air handling system with reheat 
TM 5-692-2 

19-6 

 e. Variable air volume systems. The one feature that is common to all variable air volume systems is 

they change the volume of air in response to a change in load, rather than a change in the supply air 

temperature. Figure 19-5 shows a variable air volume, single-duct, multizone system. Variable air 

volume systems may change the volume of the whole airflow and/or the volume of each individual zone. 

Total system airflow may be varied by the use of inlet vanes, discharge dampers, speed control, and 

variable pitch blades. Zone airflow may be modulated in coordination with total system flow modulation 

or it may be varied by passing the excess flow right to the return air system with no variation in total 

system flow. Note that fan horsepower savings, which in most cases are found with variable air volume 

systems, are obtained from systems which modulate total system volume in response to zone volume 

modulation. 

19-2. Air handling system major components 

Air handling systems are comprised of the following major components. 

a. Air handling units. Air handling units may consist of a supply fan and coil section with a chilled 

water or direct expansion coil, preheat or reheat coil, heating coil section, filter section, mixing box, or 

combination mixing box filter section. In some larger units, a return fan may be added to the unit. Air 

handling units are configured to be either blow-through or draw-through units. Blow-through unit is 

when one of the coil sections is located downstream of the supply fan. Draw-through unit is when one of 

the coil sections is located upstream of the supply fan. Draw-through units can be further configured to 

be either horizontal units or vertical units. 

b. Computer room air conditioners. Computer room air conditioners are typically factory-assembled 

units. Indoor units typically consist of fan(s); chilled water or direct expansion coil; steam, electric, or 

hot water reheat coil; steam or electric humidifiers; and filter section. Hermetic compressor(s) are added 

to the units when direct expansion coil is used. The outdoor units typically are air-cooled condensing 

units. Units typically consist of copper tube and aluminum fin coil, direct-drive propeller type fan, and 

integral electric control panel. On split systems, the condensing unit is the same as described above, 

except the hermetic compressor is located at the unit instead of being located in the indoor unit. 

c. Chilled water coils. Fin coils generally consist of rows of round tubes or pipes that may be 

staggered or placed in-line with respect to the airflow. Flattened tubes or those with other non-round 

internal passageways are sometimes used. The inside surface of the tubes is usually smooth and plain, but 

some designs have various forms of internal fins or turbulence devices (turbulators) to improve 

performance. The individual tubes in a coil are usually interconnected by return bends (U-bends) to form 

the serpentine arrangement of multipass tube circuits. Chilled water coils usually have aluminum fins and 

copper tubes, although copper fins on copper tubes are also used. 

 d. Hot water coils. Hot water coils are basically the same as described for chilled water coils. 

However, the most common circuiting arrangement is often called single-row serpentine or standard 

circuiting. With this arrangement, all tubes in each coil row are supplied with an equal amount of water 

through a manifold, commonly called the coil header. 

e. Direct expansion coils. Coils for refrigerants present more complex cooling fluid distribution 

problems than water coils. The fin coil that is used for evaporators in most air handling units is typically 

constructed from copper tubes with aluminum fins. Fin spacings are generally from 6 to 14 fins per inch 

(2 to 4 mm). Most manufacturers offer a wide choice of fin space and a number of tube rows, usually two 

to eight in a single casing. The whole tube and fin assembly is enclosed in a galvanized steel casing. 
TM 5-692-2 

19-7 

SUPPLY RETURN

RETURN AIR

CEILING PLENUMOR RETURN DUCT

FAN

RELIEF DAMPER

AIRDAMPER

EXHAUST AIR

FAN

SUPPLY

AIRDAMPER

HEATING

COOLING

OUTSIDE

AIR

(TYP) (TYP)

ZONE 1 ZONE 2 ZONE 3

COIL

COIL

VOLUME CONTROLBOXES

RETURN

RETURNOUTSIDE

Figure 19-5. Variable air volume air handling system 
TM 5-692-2 

19-8 

f. Steam coils. Coils generally consist of a steam header and a condensate header joined by finned 

tubes. The headers may be both at a side of the unit, with U-bends between them, or sometimes an 

internal steam tube is used to carry the steam to the remote end of an outer finned tube. Vertical headers 

may be used with horizontal finned tubes, or sometimes horizontal headers at the bottom of the unit 

supply vertical finned tubes. Copper and aluminum are the materials most commonly used in the 

fabrication of low-pressure steam coils. Low-pressure steam coils are usually designed to operate up to 

150 to 200 psig (1.0 to 1.4 MPa). For pressures higher than 200 psig, tube materials, such as red brass, 

Admiralty, or Cupro-Nickel, are used. Tubing made of steel or various copper alloys, such as CuproNickel, are used in applications where corrosive materials or chemicals might attack the coils from either 

inside or outside. 

g. Dehumidifiers. A dehumidification system is one that takes the water vapor from the air. It may do 

this by cooling the air below its dew point or by chemical means. The more generally used types will be 

discussed herein. The three most common types of dehumidification equipment are those which use 

refrigerant liquid type absorbents and solid-state absorbents. The term "absorb" means to drink in or soak 

up, like a sponge, by chemical or molecular action. The word "adsorb" means to collect in condensed 

form on a surface and may be done with a gas, liquid, or dissolved substance. 

 (1) The refrigeration type of dehumidifier is the most commonly used system. Most cooling 

systems depend on the dehumidification process to take the moisture out of the air, to achieve the desired 

comfort level in the room. The refrigerated system has its limitations. The coil temperature can only be 

cooled to the point where the moisture on the coil does not freeze. If the refrigerated system cannot 

remove enough moisture from the air, other dehumidifiers, such as solid-state absorbents, are typically 

used. 

 (2) Solid adsorbents are those which have the ability to make moisture cling to their surface. The 

products that are used the most are silica gel, activated alumina, and molecular sieve. These desiccant 

materials will take the water vapor from air or gas with physical or chemical change. The water vapor 

that they pick up can be released by passing hot dry air across the surface of the product. These products 

have submicroscopic cavities that hold the particles of adsorbed water vapor. 

 (3) The systems that use a liquid absorbent to take the moisture from the air are designed to 

achieve close moisture control in the room that it is serving. These systems can be used as the only 

means of temperature/humidity control or can be used with a total air-conditioning system to give 

complete environmental control. 

h. Humidifiers. Steam humidifiers are generally used for central air handling systems. But, in order 

to ensure the advantages of steam humidifiers over other humidifiers, steam humidifiers must provide 

three performance characteristics: conditioning, control, and distribution. The humidifier must condition 

the steam to be completely dry and free of significant matter. It must respond immediately to control, 

provide precise output, and distribute steam as uniformly as possible into the air. Failure of the 

humidifier to provide these characteristics will result in improper humidification. 

i. Three-way control valves. Three-way control valves are usually used in air handling systems to 

control the flow of chilled water or hot water to their respective coils. The valve has one inlet and two 

outlet connections, and two separate disks and seats. It is used to direct the flow to either of the outlets or 

to proportion the flow to both outlets. Generally, this valve is used because the pumping system used 

must maintain a constant flow, i.e., as the valve closes, the flow to the coil decreases, therefore, the water 
TM 5-692-2 

19-9 

must be diverted to the return side of the system to maintain constant flow. 

j. Control valves. Control valves are designed to control the flow of steam, water, gas, and other 

fluids within an air-conditioning system. Valves must be properly sized and selected for the particular 

application. The valves are made of materials best-suited to the fluid handled, depending upon operating 

temperature and pressure. Internal parts of valves, such as the seat ring, throttling plug or V-port skirt, 

disk holder, and stem, are sometimes made of stainless steel or other corrosion-resistant metals, 

depending upon the fluid handled. 

k. Fans. Fans are used to move air or other gases or vapors with a fan wheel that makes use of 

centrifugal or propeller action. Fans can be put into two general classifications: centrifugal fans and 

axial fans. Centrifugal fans have the flow directed radially outward from the fan wheel. Centrifugal fans 

are able to move more air at higher pressures and with less noise than axial fans. Axial fan flow is moved 

parallel to the shaft on which the fan wheel is mounted. All fans have three basic parts: an impeller, 

motor, and housing. The impeller is the part of the fan that moves the air. In order for an impeller to 

move air, it must rotate. This is done by power from the motor. Housings are made to fit the individual 

fan types. Materials used in fan construction are generally steel. They are also built of aluminum and can 

be made of special materials, such as stainless steel or epoxy-bound fiberglass. Fans can be coated with 

compounds that are especially suited to the many kinds of corrosive atmospheres in which they must 

work. In some cases, spark-proof construction is required. 

 (1) Small fans, especially those whose blades or wheel turn at higher speeds, are equipped with 

direct-connected motors. For larger size fans, and those that operate at lower speeds, V-belt drives are 

used. Belt drives have the advantage of giving a lower fan speed than the motor speed and have a built-in 

shock-absorbing ability. 

 (2) In some air handling systems, there is a need to change the volume of air that is produced by 

the fan. Where such a change is made infrequently, the pulley or sheave on the drive motor, or on the fan, 

may be changed to vary the speed of the fan and thus change the air volume. Dampers may be placed in 

the duct system to vary the air volume. Variable-speed pulleys and drives, such as electric or fluid drives, 

may be used to change the fan speed. Two-speed motors and variable fan inlet vanes may also be used to 

control the airflow rate. Tubeaxial and vaneaxial fans have adjustable blades that vary the airflow rate as 

required. 

 (3) A centrifugal fan is built with a wheel that is mounted on a horizontal shaft and turns in a 

housing. Air enters near the axis of the wheel and is discharged through the housing outlet. Air may enter 

the fan wheel at one or at both ends of the wheel's axis. The fans that are in use for air- conditioning, 

heating, and ventilating systems normally do not exceed 10 inches of water (2,488 Pa) static pressure. 

The main feature that distinguishes one type of centrifugal fan from another is the curvature and the 

inclination (slope) of the fan wheel blades. The slope largely determines the operating characteristics of 

the fan. The three principal types of blades are the forward-curved blade, the radial blade, and the 

backward inclined blade. 

 (a) The forward-curved blade fans are used primarily for the low-pressure heating, ventilating, 

and air-conditioning application. Domestic furnaces, low-pressure central station air handling units, and 

packaged air-conditioning units, such as window and rooftop air-conditioning units, use this type of fan. 

 (b) In the radial blade fan wheel, the tip of the blade projects straight out from the fan shaft. 

The radial blade fan can work at a higher pressure than either the forward-curved or the 
TM 5-692-2 

19-10 

backward-inclined blade fans. However, to move the same amount of air as the other two types, the 

radial fan wheel requires more horsepower. Due to its low efficiency, the radial blade fan generally is not 

found in heating, ventilating, and air-conditioning (HVAC) applications. It is used more for material 

handling applications, since the wheels are of simple construction and they can be fixed in the field. 

 (c) In the backward-inclined blade fan wheel, the tip of the blade is inclined backwards away 

from the direction of the rotation of the fan wheel. This lets the backward- inclined fan move air at higher 

pressures than the forward-curved fan. It is more efficient (uses less horsepower) for many air volume 

and pressure ranges than the forward-curved blade fan. The backward-inclined blade wheel is also built 

with blades that are made in an airfoil shape. This wheel is the most efficient of all types and is the 

quietest at high static pressure. The backward-inclined fans are generally used in medium to large air 

handling systems. They are normally used for medium- and high-pressure systems, although they are, at 

times, used in low-pressure systems. 

(4) An axial fan may consist of a fan wheel mounted on a motor shaft or it may have one, or in 

some cases two, fan wheel(s) mounted on a shaft and confined inside a housing or tube. Axial fans use 

either a direct drive or a belt drive. The three main types of axial fans are propeller fans, tubeaxial fans, 

and vaneaxial fans. Axial fans do not develop their static pressure by centrifugal force. The static 

pressure is gained from the change in velocity of the air when it passes through the fan wheel. 

 (a) A propeller fan consists of a multiblade impeller within an inlet ring or plate. Propeller fans 

are low-pressure, high-capacity units built either with the blades mounted on the shaft of an electric motor 

or a shaft for V-belt drive. 

 (b) A tubeaxial fan consists of an axial flow wheel within a cylinder or tube. Tubeaxial fans may 

be used on low- and medium-pressure systems. 

 (c) Vaneaxial fans are tubeaxial fans with guide vanes that straighten out the axial spiral 

airflow. Vaneaxial fans can be used in low-, medium-, and high-pressure systems. 

l. Variable air volume terminal units. A variable air volume system controls the temperature in a 

space by varying the volume of supply air rather than varying the supply air temperature. Variable air 

volume terminal units or boxes are used to vary this airflow in each zone or space. There are generally 

five different types of units that are used: pressure-independent volume units; pressure-dependent, 

airflow-limiting, maximum volume units; pressure-dependent units; bypass (dumping) units; and supply 

outlet throttling units. One other type of unit that is used is the fan-powered variable air volume terminal 

unit. 

 (1) Pressure-independent volume units regulate the flow rate in response to its respective 

thermostat's call for heating or cooling. The thermostat controls airflow to the space by varying the 

position of a simple damper or volume regulating device located in the unit. The required flow rate is 

maintained, regardless of the fluctuation of the system pressure being supplied by the air handling unit 

supply fan. These units can be field- or factory-adjusted for maximum and minimum airflow settings. 

 (2) A pressure-dependent, airflow-limiting, maximum volume unit regulates maximum volume, 

but the flow rate below maximum varies depending upon inlet pressure at the unit. Generally, airflow 

will oscillate when system pressure varies. These units are less expensive than pressure-independent 

units. These units can be used where pressure independence is required only at maximum airflow, where 

system pressure variations are relatively small, and where some degree of fluctuation or "hunting" is 
TM 5-692-2 

19-11 

tolerable. 

 (3) Pressure-dependent units do not regulate the flow rate, but position the volume regulating 

device in response to the thermostat. These units are the least expensive and should only be used where 

there is no need for maximum or minimum airflow control and the air handling unit system pressure is 

stable. 

 (4) Generally, in small air handling systems, the cost of a variable air volume system is too high. 

However, by using bypass (dumping) units in certain zones or spaces, the constant volume system can 

have variable airflow control. The thermostat controls airflow to the space by varying the position of the 

volume regulating device. If less air is required to the space, the regulating device closes down and 

bypasses or diverts some of the air to the return ceiling plenum or return air duct. 

 (5) Supply outlet throttling units are usually linear diffusers. The area of the throat or the 

discharge opening varies in approximate proportion to the air volume to maintain throw patterns. The 

thermostats are usually located at the outlet of the diffuser for easy temperature adjustment. Since these 

units are pressure-dependent, constant pressure regulators are usually required in the duct system. Noise 

is a concern when using these units in occupied spaces. 

 (6) Fan-powered variable air volume units are available in two types: parallel and series flow 

units. The units have the same components as pressure-dependent or pressure-independent volume units, 

and in addition, a fan and usually an electric or hot water heating coil. Fan-powered variable air volume 

units, both series and parallel, are often used for building perimeter heating, because they move more air 

through a room at low cooling loads and during the heating cycles compared to variable air volume reheat 

or perimeter radiation systems. 

m. Dampers. Dampers are devices used to control or restrict the airflow. They fall primarily into 

three types: volume, backdraft, and fire dampers. 

 (1) Volume dampers are devices used to vary the volume of air that passes through an air outlet, 

inlet, duct, fan, air handling unit, cooling tower, or condenser unit. They may vary the volume from 0 to 

100 percent of capacity. Some volume dampers can be opened and closed by hand, while others are 

opened and closed by a pneumatic or an electric operator. The largest use of manual controlled volume 

dampers in cooling systems is for air balancing. 

 (2) Backdraft dampers are devices used to limit the airflow within a duct to one direction and to 

stop airflow through a duct or opening when the fan is shut off. Backdraft dampers are opened 

automatically by the force of the airflow on the damper blades. They are closed automatically by a spring 

or weight counterbalance and by gravity. The counterbalances can be adjusted to allow the damper to 

pass the needed airflow. Backdraft dampers, because they are free to open and close easily, may rattle 

and make noise. To eliminate this, felt or vinyl strips can be placed on the damper edges, which will also 

help minimize the air leakage. 

 (3) Fire dampers are devices used to close off individual sections of a building during a fire. Fire 

dampers are normally installed where a duct passes through a wall, partition, floor, or ceiling which is 

specifically designed to provide fire resistance. If ducts pass through barriers having a fire rating of up to 

and not more than one hour of fire resistance and can be assumed to present no further fire hazard, there is 

no need for fire dampers. If the wall, partition, ceiling, or floor is required to have a fire resistance rating 

for more than one hour, a fire damper is then required to properly protect the opening where the ductwork 
TM 5-692-2 

19-12 

penetrates the wall. Fire damper blades are held open by a fusible link (replaceable) during normal 

operation of the building. If a fire occurs, the fusible link melts and the damper blades close 

automatically. For a cooling system to operate properly, all fire dampers must be open all the way. 

Broken or damaged fusible links should always be changed, and fire dampers should never be wired 

open. Break-away type connections should be used to connect the ductwork to the fire dampers; solid 

connections should never be used. 

 (4) Smoke dampers are used for either smoke containment or for smoke control. The damper is 

basically the same as a volume damper, except the damper is classified and listed in accordance with 

Underwriters Laboratories, Inc. (UL) 555S, UL Standard for Safety Smoke Dampers Fourth Edition 

(1999). The damper is a two-position damper, i.e., the damper is either open or closed depending upon 

the control requirements. The dampers are opened and closed by a pneumatic or electric operator. The 

damper usually has low leakage characteristics. 

n. Unit heaters. A unit heater is an assembly of a fan and motor, a heating element, and an enclosure 

whose function is to heat a space. Generally, unit heaters use five different types of heating media: 

steam, hot water, gas indirect-fired, oil indirect-fired, and electric. Propeller fan units are the most 

popular units used; however, sometimes centrifugal fan units are used. Unit heaters are used for spot or 

intermittent heating, such as large outside doors. Unit heaters are used to heat garages, factories, 

warehouses, stores, etc. 

o. Ductwork. Ductwork is the system of ducts and ductwork accessories that are used to connect air 

handling units and fans with the rooms, spaces, or exhaust hoods with which they are associated. The 

material used for a duct system must be based on the availability of the material, expertise of the duct 

installer, the type of duct already installed, the location of the installed duct, and the environment it is 

planned to be used in. For example, a fume hood that handles corrosive fumes should be connected with 

a non-metallic polyvinyl chloride (PVC) or stainless steel duct. Metallic ducts are usually built from 

sheets of aluminum or galvanized steel. The ducts may either be built with round or rectangular cross 

sections. Non-metallic ducts are usually built from fiberglass duct board, except for ducts handling 

corrosive fumes that are constructed from a PVC material. Fiberglass duct board sheets are generally in 

locations where the duct will not be damaged by objects or personnel. All joints should be sealed with a 

special pressure-sensitive tape made for this purpose; standard duct tape should not be used. Round PVC 

duct systems are built from standard PVC duct and standard fittings. Fittings and ducts are connected 

with glue. Rectangular PVC ducts are of a special construction and should be made by people who are 

skilled in this work. Flexible ducts can be bought and used directly without further fabrication. They are 

available either insulated or noninsulated. 

p. CBR filters. CBR (chemical-biological-radiological) filters remove chemical and biological agents 

and radioactive particles from the intake air. Many blast-protected air intake systems allow intake air to 

bypass the CBR filter elements when the blast protection system is not in the blast mode of operation. 

While this prevents the performance of the CBR filters from being impaired by a buildup of dirt, the 

activated carbon filter element deteriorates from exposure to air over time and requires replacement on a 

regular basis, even if the filter bank has not been in service. 

q. Air filters. All of the air that is drawn into an air handling system is "contaminated" to some 

degree. Such contamination may be as solid particles, liquids, fumes, smoke, or bacteria. The process 

used to remove these contaminants from the air mechanically, electrically, or by absorbing them, is called 

air filtration. 
TM 5-692-2 

19-13 

 (1) Viscous impingement filters are of the panel or roll type with a viscous (tacky) coating on the 

media to hold the particles to the media. The coating is called an adhesive. Viscous impingement filters 

are made to trap large dust particles from the airstream. Most air-conditioning systems have this type of 

filter. There are four types of these filters: throwaway, cleanable, automatic renewable media, and 

automatic self-cleaning media. 

 (2) Dry media filters, as their name suggests, do not have the tacky coating that is on viscous 

impingement filters. The dry media filters take out particles from the air by interception and straining. 

Interception means to filter out particles using the natural forces of attraction between molecules. 

Straining means to take out particles that are too large to pass through the openings between the fibers. 

 (3) A filter made of activated carbon will get rid of solid particles, as well as odor-causing gases 

and bacteria from the airstream. It is possible to clean and reuse the carbon filters. However, this is best 

done by the manufacturers, who will take out the carbon and process it to be used again. 

 (4) The inability of standard dry or viscous type filters to take out fine dust particles from 

airstreams has led to the development of the electrical precipitator. The precipitation method consists of 

giving an electrical charge to each dust particle in the airstream by passing the air between electrodes and 

then collecting the dust on parallel plates as the air flows between the plates. 

r. Condensers and condensing units. Condensers can be put in the following groups: water-cooled, 

air-cooled, and evaporative. The term "evaporative," when used in reference to the condensing process, 

refers to the cooling effect brought on by the natural evaporation of water exposed to air currents. The 

heat rejected by a condenser comes from the heat absorbed by the evaporator and the heat of compression 

that is added by the compressor. Since the compressor and condenser work as one to compress and 

condense refrigerant vapor, these two parts, when combined into one package, are called a condensing 

unit. 

 (1) Shell-and-tube condensers are used for most of the water-cooled refrigeration systems. The 

shell-and-tube type of water-cooled condenser is like the direct expansion water chiller. But most shell 

type water-cooled condensers have the cooling water flowing inside the tubes, and the refrigerant that it 

condenses is inside the shell, but outside the tubes. 

 

 (2) Air-cooled condensers are most popular in areas where water is in short supply, where there is 

a costly water supply, or where the use of water for air conditioning is restricted at times. They also find 

wide use in those jobs where low maintenance is a prime need. In addition, air-cooled condensers are 

used in a lot of installations, because they keep down the cost and do away with the installation of water 

pipe. They also do not require drainage to keep them from freezing in areas where the climate changes a 

lot and the cooling system must be turned on and off several times in a year. Propeller fan air-cooled 

condensers use a fin-and-tube coil like the coil described in the Direct-Expansion Coils section. The 

refrigerant vapor is condensed inside its tubes by giving up heat to air which flows across the coils. 

These condensers are, in most cases, placed outdoors, or at least the air is taken to the outdoors. 

s. Diffusers, registers, and grilles. These are devices used in air handling systems for the supply, 

return, and exhaust air at intakes and outlets. 

t. Pumps. The type of pump used to distribute chilled or hot water through the coils in air handling 

units varies with the system design. There are two basic types of pumps: positive displacement and 

centrifugal. 
TM 5-692-2 

19-14 

u. Airflow control devices. Devices that sense the condition of air in a space or in an airflow system 

act upon other devices to make the air behave in the manner desired. 

 (1) A thermostat or other temperature control device may move a damper that directs the path of 

an airstream. It may also change the temperature of an airstream by directing its flow through a coil, or it 

can control the volume of air flowing in a duct system. Through the action of a valve, it also may change 

the temperature of an airstream. 

 (2) Pressure controls operate to control the pressure of air in a room, or the duct system through 

the action of dampers. Figure 19-6 shows how a static pressure controller, along with thermostats and 

dampers, can be used to control static pressure in a variable volume system. The damper being controlled 

is in the inlet duct to the supply fan, but it could equally well be an inlet vane damper or an outlet damper. 

 The pressure controller could also operate a blower drive speed control. In this control, the pitch of 

motor and fan pulleys is varied by a device in response to a signal from the pneumatic static pressure 

controller. 

 (3) Control of fan speed to control pressure and airflow volume results in less noise than when 

inlet vanes or outlet dampers are used. In certain installations, the use of speed control also cuts down the 

horsepower that is needed by the fan or blower drive motor. 

 (4) Airflow switches are mounted on the side of a duct with the blade inserted into the duct. The 

blade of the switch will move according to airflow in the duct, and it will make electrical contacts when 

air flows and break the contacts when airflow stops. The sensitivity of the switch to the airflow may be 

adjusted. Another control for the same purpose as the ones described above is the differential pressure 

switch that senses velocity pressure in the duct. This controller also has an adjustable pressure range. 

v. Valves and piping. Valves installed in the air handling system are to control water flow and to 

isolate equipment for ease of operation and maintenance. 
TM 5-692-2 

19-15 

SPACETHERMOSTAT(TYP)DIFFERENTIAL STATICPRESSURE CONTROLLER

PIPE LINE TOREFERENCE POINT

STATICPRESSURE SUPPLY 

FAN DAMPER

Figure 19-6. Typical air handling systems controls 
TM 5-692-2 

20-1 

CHAPTER 20 

INDUSTRIAL WATER SUPPLY SYSTEMS 

20-1. Industrial water supply system design features

This chapter presents an overview of industrial cooling systems and their various components. The 

industrial cooling system is the means by which heat generated by facility equipment (diesel engines, 

thermal storage refrigeration, and chillers, typically) is removed from the facility. Under normal 

operating conditions, this heat will be rejected to the outside by cooling towers and the condenser water 

piping system. When the cooling towers are not operating, this condenser water is circulated through the 

industrial cooling system and reservoir(s). Each industrial cooling water system is designed to transfer 

heat by the most efficient and reliable method. While there is no right way to design an industrial cooling 

system, all industrial cooling water systems have common characteristics and use common types of 

components. 

a. Terminology. For the purposes of this manual, the term "industrial cooling system" refers to any 

heat removal system that uses a body of water as a heat sink. A condenser water system refers to a 

system that removes heat with cooling towers. There may be some confusion in the use of this 

terminology because some facilities refer to an industrial cooling water system as that which removes heat 

with both cooling towers and a heat sink (industrial reservoir). A condenser water system and an 

industrial cooling system both serve the same function, heat removal. In addition, these two systems 

share much of the same piping, valves, and additional system components. 

b. System functions. Industrial cooling is used in the event of failure of the normal condenser water 

system, or if cooling towers are to handle the facility head load. The system may also be used during a 

variety of operating scenarios including testing, blowdown of the condenser water system, maintenance, 

crew training, load shedding, or blast conditioning. The primary function of the industrial cooling system 

is to serve as a backup for the condenser water system. The condenser water gains heat as it is circulated 

through the facility equipment (chiller condensers, diesel engine jacket water heat exchangers, diesel 

engine lubricating oil heat exchangers, thermal storage refrigeration units, etc.). This warm condenser 

water then travels through the cooling towers, giving up the heat it gained, and is pumped through the 

circuit again by the condenser water pumps. 

c. Reservoir water supply. The reservoir water supply system has the function of providing industrial 

water to each facility for storage in the industrial reservoirs. Water is supplied to the reservoirs by one of 

two ways. One method is by water wells located on or outside of the facility. The second method is by 

pumping stations that deliver the water into the facility from an external water treatment or monitoring 

facility. With either method, the pumps can be controlled locally or from a remote control station, and 

they can be manually started or operated automatically by a level controller located at the reservoir. 

Another source of water to the industrial reservoir may be underground spring water. 

d. Reservoir cooling system. During industrial reservoir cooling, the cooling towers and condenser 

water pumps are turned off, reservoir pumps are activated, and control valves are positioned to divert 

water around the towers and pumps. The warm condenser water (now referred to as industrial water) is 

delivered to the industrial reservoir. As the returned industrial water makes its way through the reservoir 

to the reservoir pump suction, the reservoir acts as a heat sink by dissipating the heat gained by the 

industrial cooling water. The heat capacity of the industrial reservoir is dependent on facility cooling and 
TM 5-692-2 

20-2 

electrical loads, and volume of water in the reservoir. When industrial reservoir cooling has been 

operating for an extended period of time, the industrial reservoir will lose its ability to dissipate heat from 

the returned industrial water. This occurs when the reservoir reaches a certain temperature. At that 

temperature, reservoir dump is begun. Reservoir dump is simply the removal of the hot reservoir water 

from the facility. 

e. Makeup water system. The industrial cooling system requires makeup water at all expansion tanks. 

The makeup water system replaces water lost in the condenser water or industrial water systems. As 

pressure in the expansion tank decreases, the makeup water valve will open allowing makeup water to 

enter the system until the pressure increases to a point above the setting of the makeup water valve. 

Makeup water does not apply to the industrial reservoirs, since water is continuously supplied to the 

reservoir based on the water level in the reservoir. As the water level in the reservoir falls, the water level 

controller will automatically activate the supply pumps to replenish any water lost from the reservoir. 

f. Water treatment. Water treatment consists of maintaining approximately 1 ppm (part per million) 

residual chlorine in the industrial reservoir of the industrial cooling system. A hypochlorinator unit is 

used to inject chlorine into the reservoir piping system. The industrial reservoir water should be checked 

(tested) daily to determine whether chlorine is needed. If the reservoir residual chlorine is in excess, 

reservoir water should be drained while adding fresh water from the supply system until the residual 

chlorine is approximately 1 ppm. This should only be done during normal operating conditions. 

Additional water treatment may be required at the cooling towers and for the condenser water system. 

20-2. Industrial water supply system major components 

Industrial water supply systems are generally comprised of the following major components. 

a. Reservoirs. Water storage reservoirs are used for both domestic water and industrial cooling. The 

reservoirs are unlined rock chambers that extend, mostly horizontal and slightly down, from a common 

audit area. The reservoirs may include a steel bulkhead or concrete dam in front to retain the water within 

the reservoir. In addition, the reservoir may include a pump platform, located above the water level, from 

which the reservoir water is drawn by the distribution pumps. 

b. Tanks. Surge tanks are used in the reservoir water supply system to absorb water surging or water 

hammer shock in the industrial water supply line between the reservoir and the supply pumps. The tank 

is a closed tank pressurized with compressed air which absorbs the water surges caused by starting and 

stopping of pumps. A liquid level control maintains a constant air pressure in the tank by modulating an 

air supply valve. Expansion tanks are used in industrial cooling (condenser) water systems to allow for 

thermal expansion and to provide a location for makeup water to be admitted to the system. 

c. Wells. Wells extract water from permeable water bearing layers called aquifers. The wells used for 

industrial water supply systems typically have an 8- or 6-inch casing which fills with water. A pump 

forces the water up to the surface. 

d. Pumps. For an expanded discussion of pumps which can be used in industrial water systems, see 

chapter 11. 
TM 5-692-2 

20-3 

e. Control valves. Control valves are used in condenser/industrial water systems to control the flow of 

water through the piping system. The control system positions the valve through a valve operator or 

actuator that is directly attached to the valve stem. Control valves must be carefully sized and selected for 

the particular design conditions. Control valves used in condenser/industrial water are typically equipped 

with a throttling plug or V-port that is specially designed to provide the desired flow characteristics. 

f. Valves. For a discussion of the types of valves which may be used in industrial water systems, see 

chapter 16. 

g. Strainers. Strainers are defined as a closed vessel with cleanable screen element designed to 

remove and retain foreign particles down to 0.001 inch diameter from various flow fluids. A strainer 

differs from a filter in that strainers trap particles that are typically visible to the naked eye. Strainers are 

typically installed in condenser water systems on the inlet (suction) side of the distribution pumps. 

h. Piping. Pipe used in industrial/condenser water systems for sizes two inch and smaller is typically 

standard weight, continuous weld steel pipe with threaded joints and cast iron fittings. For 

industrial/condenser water piping larger than two inches, steel pipe conforming to American Society for 

Testing and Materials (ASTM) A 53, Standard Specification for Pipe, Steel, Black and Hot-Dipped, ZincCoated, Welded and Seamless (1999), is used. Joint types for this size of pipe are welded, flanged, or 

grooved. Fittings for A 53 type pipe are wrought steel, cast iron, and malleable or ductile iron. 

20-3. Testing

The industrial reservoir(s) plays a critical role in the success of a given facility's mission. Because the 

industrial water system is required to be operational before the systems it supports can operate, it is 

probably the most important system in the facility. Due to this fact, the reservoir should be placed 

through a series of tests periodically to provide reassurance that the industrial reservoir maintains a high 

level of reliability and will perform adequately when needed. The following items should be considered 

when developing a testing procedure for the industrial reservoir. 

a. Record information. Prior to beginning any test on the industrial reservoir, always record the 

following information: the reservoir water temperature, the water level or the amount of water in the 

reservoir, individual condenser water flow rates through all equipment, entering and leaving temperatures 

of condenser water through all equipment, total condenser water flow to the cooling towers, and 

condenser water supply temperature to and return temperature from the cooing towers. Always record the 

date and exact time the test was begun. In addition, record the time any significant changes occur in flow 

rates and temperatures in the system, along with this new data. Always record the ending time of the test. 

b. Manual switchover. The ability of the condenser water system to switch to industrial reservoir 

cooling should be tested manually by opening/closing valves locally, and starting and stopping the 

appropriate condenser water and industrial reservoir pumps, also from local control stations. Personnel 

should be assigned specific tasks and timed as to how long is required for manually switching the entire 

condenser water system over to industrial reservoir cooling. 

c. Remote switchover. The ability of the condenser water system to switch to industrial reservoir 

cooling by initiating reservoir cooling from a central control room should be tested. 

d. Automatic switchover. The ability of the condenser water system to switch to industrial reservoir 

cooling automatically by simulating a blast as detected from the blast sensors should be tested. 
TM 5-692-2 

20-4 

e. Temperature. Once industrial reservoir cooling is initiated, the temperature of the reservoir should 

be monitored and recorded at regular time intervals until the completion of the test. In addition, the flow 

rate into and out of the reservoir should be continuously monitored and recorded, again until the test is 

completed. 

f. Reservoir dump. If reservoir dump is initiated, the starting time, flow rate, temperature of reservoir 

water, and stopping time should be recorded. 

g. Fresh water. If fresh water is added to the reservoir during testing, the following should be 

recorded: the supply water temperature to the reservoir, the exact starting time that water is supplied, the 

flow rate of water to the reservoir, the temperature of the reservoir when the water was added, the 

temperature of the reservoir when the supply to the reservoir stopped, and the exact time when the supply 

to the reservoir stopped. 

 
TM 5-692-2 

21-1 

CHAPTER 21 

COMPRESSED AIR SYSTEMS 

 21-1. Compressed air system 

There is no specific way to compress air; however, each system consists of certain typical components. 

Figures 21-1 through 21-4 provide a depiction for these components and their arrangements. The critical 

missions of C4ISR facilities require the compressed air start system to be designed adequately to handle 

two 30-second standby generator start sequences without recharging. More specifics on the requirements 

can be found in chapter 8 – Diesel Engines. 

a. Components. Compressed air systems consist of compressor units with drives, controls, 

intercoolers, and inlet air filtration; compressed air-conditioning equipment consisting of aftercoolers, 

receivers, filters, separators, traps and drains, and air dryers; and air distribution systems, including 

piping, valves, control valves, filters, pressure regulators, drains, lubricators, etc. 

 b. Applications. Compressed air is probably one of the most universal operations within a plant 

environment. It transcends industries, operations, and applications. Compressed air is used to power 

tools, move conveyers, transport products, and make process applications possible. Considered a power 

source, compressed air systems are increasingly more reliable and predictable. It is often considered the 

fourth utility. 

21-2. Compressed air system major components 

Compressed air systems are comprised of the following major components. 

a. Compressor. The compressor is the main component of the system. The key issues involved in 

ensuring the compressor performs as necessary are reliability, cost-effectiveness, ease of operation, and 

maintainability. Compressor reliability is based on the type of control system, ambient temperature, 

motor design, and the cooling system. 

 (1) Modern day use of electronic controls has eliminated many problems associated with 

mechanical switches and relays. Older pneumatic compressor controls using compressed air taken before 

the air dryer can prove troublesome because moisture in the air leads to sluggish performance and damage 

to the compressor. The rubber diaphragms used with these pneumatic control systems are a common 

weak link in control systems. The control system should be easy to use and provide required data. 

(2) The compressor must be capable of operating in ambient temperatures approaching 110-115°F 

because compressor rooms are five to ten degrees warmer than the outdoor temperature. Higher 

temperature ratings mean longer, more reliable periods between maintenance. 

(3) As a minimum, motor insulation must be class F. Temperatures inside the sound attenuating 

enclosures for motor and compressors are warmer than the ambient air. Summertime operation gives 

internal temperatures from 110 to 115°F. Standard Class B insulation motors are designed for a 

maximum installed temperature of only 104°F. 

(4) During operation, the compressor produces a tremendous amount of heat that must be removed. 

The compressor oil removes some of heat. Lubricated compressors remove even a higher portion of the 

heat since the oil is in the compression chamber. The oil is then cooled in a forced draft 
TM 5-692-2 

21-2 

RECEIVER

A

PS

MS I

IF

F

T

D

T

T

INLETFILTER

MOTORSTARTER

DRAIN(TYP)

TRAP(TYP)

FILTER*

DRYER

INTERCOOLERAFTERCOOLER

PRESSURESWITCH

SINGLE ACTING, TWO STAGERECIPROCATING COMPRESSOR DISPLACEMENT COMPRESSOR

FILTER

OIL FLOODED ROTARY POSITIVE

T

T

D F

T

IF

MS

PS

RECEIVER

A

PT

I

IF

F

T

D

T

INTERCOOLER

TWO STAGE CENTRIFUGAL COMPRESSOR

MOTOR

OIL COOLER

OIL SEPARATOR PS

MS IF

F

T

D

T

T

DRY ROTARY POSITIVE

DISPLACEMENT COMPRESSOR

S A

T

SEPARATOR

SAFETYRELIEFVALVE

SAFETYRELIEFVALVE

T

A S

T

T

D F

T

IF

I

MOTOR

RECEIVER

RECEIVER

INTERCOOLER

DOUBLE ACTING, TWO STAGERECIPROCATING COMPRESSOR

S

T

STRAINER

PC

S

T

VALVECONTROLLERPRESSURETRANSMITTER

MOTOR

(TYP)

EXHAUSTSILENCER

BY-PASSVALVE

* SOMETIMES LOCATED AFTER DRYER, OR BOTH BEFORE AND AFTER DRYER, DEPENDING ON TYPE OF DRYER.

OILCOMPRESSED AIRCONTROL SIGNAL

ISOLATIONVALVE (TYP)

Figure 21-1. Typical air compressor systems 
TM 5-692-2 

21-3 

DRAIN(TYP)

TRAP(TYP)

DELIQUESCENT DRYER 

S

AFTERCOOLER

A

T

RECEIVER C

VALVE (TYP)

COMPRESSOR SEPARATOR

DRYER

P

T

A

PREFILTER(OPTIONAL)

AFTERFILTER(OPTIONAL)

DRY

AIR

PREFILTER(OPTIONAL)

T

DRYER

SEPARATOR COMPRESSOR

VALVE (TYP)

C

RECEIVER A

AFTERCOOLER

DELIQUESCENT DRYER 

DRAIN(TYP)

DRY

AIR

AFTERFILTER(OPTIONAL)

PREFILTER(OPTIONAL)

A P

T

SEPARATOR COMPRESSOR

VALVE (TYP)

C

RECEIVER

T

A

AFTERCOOLER

S

REFRIGERATION DRYER 

TRAP(TYP)

DRAIN(TYP)

DRY

AIR

AFTERFILTER(OPTIONAL) PREFILTER

(OPTIONAL) A

PT

SEPARATOR COMPRESSOR

VALVE (TYP)

C

RECEIVER

T

A

AFTERCOOLER

S

DESICCANT REGENERATION DRYER 

TRAP(TYP)

DRAIN(TYP)

T S

T

PACKAGEDDRYER UNIT

REFRIGERATIONCOMPRESSOR

REFRIGERANTCONDENSER

DESICCANTCOLUMNS

REGENERATIONCONTROLS

Figure 21-2. Typical air dryers 
TM 5-692-2 

21-4 

TI

PREFILTER(OPTIONAL)

P

T

SEPARATOR

T

AFTERCOOLER

S

T

D

IF

INLETFILTER

INLETFILTER

IF

A

TI TI

TI

PI

PI

RECIEVER

T

LIQUIDTRAP

PI PI

A

T

AFTERFILTER

PI

PLANT

AIR

CONTROL SIGNAL

COMPRESSOR

COOLINGFULID

BLOWDOWN

VALVE

CHECK VALVE(TYP)

BACK PRESSUREVALVE

AIR DRYER

GLOBEVALVE

PRESSUREINDICATOR(TYP)

INSTRUMENT

AIR

COMPRESSOR

IF

INLETFILTER

INLETFILTER

IF

TI TI

I

INTERCOOLER

TI

COOLINGFULID

S

SEPARATOR

COMPRESSOR

TI

SEEABOVE

RESERVOIRW/SIGHTGLASS

TWO STAGE (MULTISTAGE) 

SAFETYRELIEFVALVE

PI PI

STRAINER

ISOLATION

VALVE

TEMPERATUREINDICATOR

SINGLE STAGE

Figure 21-3. Typical air compressor installation 
TM 5-692-2 

21-5 

PREFILTER

PT

SEPARATOR

T

AFTERCOOLER

S D

IF

INLETFILTER

INLETFILTER

IF

A

PS

PI

RECIEVER

T

TRAP

COMPRESSOR

AIR DRYER

T

PT

AFTERFILTER

(TYP)

PRESSURESWITCH

S

LUBRICATOR

L

PS PI

R

ISOLATIONVALVE

CONNECTIONS TO OTHER

DIESEL ENGINE AIR

START SYSTEMS

PRESSUREINDICATOR

CHECKVALVE

ENGINE

MOUNTED

REMOTE

FROMENGINE

FLEXIBLECONNECTION

OPTIONAL FORREDUNDANT SYSTEMS

PRESSURE SWITCH ACTIVATEDLOW AIR PRESSURE ALARM

STRAINER

PNEUMATIC

RELAY VALVE

AIR MOTORS

SOLENOID VALVEINTERLOCKED WITH LUBE OIL PRESSURE

MANUALBARRING

VALVE

Figure 21-4. Typical engine compressed air starting system 

 

air-cooled heat exchanger. That portion of the heat remaining is removed in intercooler and aftercoolers 

of sufficient capacity to permit continuous, fully loaded compressor operation in high ambient 
TM 5-692-2 

21-6 

temperatures. The aftercooler approach temperature, that is, the temperature difference between the 

compressed air outlet and ambient air temperature, should be in the 15 to 20°F range. 

 (5) The compressor should be easily accessible for maintenance. If enclosed, the panels should be 

easily removed. Leave at least three feet of clearance around the compressor. The primary maintenance 

items on a compressor are the inlet filter, oil drain, oil fill, motor greasing, condensate traps, and control 

calibration. Each should be easily accessible. Service indicators help guarantee timely maintenance. In 

lubricated compressors, the oil travels downstream and must be replenished regularly. Synthetic 

lubricants provide superior lubricating characteristics, longer service life, and lower vaporization rates. 

Polyglycols extend changeout intervals to 8,000 hours, have the lowest vaporization rate, and are 

biodegradable. Oil-free compressors require limited amounts of lubricant for bearings and gears. 

 b. Air purification. The air purification system is an integral part of the process because it ensures that 

the air produced is of a high quality to preclude deterioration of the piping system and associated valving. 

 The primary functions of the air purification system are to deliver the required air quality, maintain air 

quality during upsets, and minimize operating costs. Generally, air purification falls into one of three 

categories: filters, dryers, and receivers. 

 (1) Filters remove condensed liquids, particulates, and oil vapors. Coalescing filters to remove 

water and oils have efficiencies from 99.98% at 0.01 micron particle size to 99.9999% at 0.1 micron. The 

filters should have a maximum wetted pressure drop of 3 to 3.5 psi. The maximum pressure drop, 

normally 10 psi, determines the service life of these filters. Expect to replace the filter elements every six 

to twelve months. High-performance coalescing filters require changeout every five years. Although 

these filters have a higher first cost, the lower pressure drop and reduced energy and maintenance costs 

provide a simple payback of less than one year. Particulate filters installed downstream of a desiccant 

dryer should have a different pressure gauge to indicate the condition of filter elements rated for a 

nominal efficiency of 99.95% at 1 micron particle size and initial pressure drop of 1 psi. Coalescing 

filters must have high-quality automatic condensate drains. Vapor removal and filters absorb oil vapors 

with activated charcoal. Location and the oil concentration determine filter element life. Normal pressure 

drop for a vapor removal filter is 1 psi. 

 (2) Air dryers are a very important part of the overall system because an aftercooler discharging 

compressed air at 100°F passes 67 gallons of water per 1,000 standard cubic feet/minute (scfm) per 24 

hours. Instrumentation fails when water and lubricant condense as the air is further cooled in the piping 

system or as the air expands through the orifices. The air exiting the aftercooler is saturated and any 

further temperature drop results in more condensation. A useful rule of thumb states that "a 20 degree 

reduction in temperature condenses one half the water vapor in saturated air." 

(a) Air dryers reduce the moisture content as measured in terms of a pressure dew point (pDp) 

that is based on a specific set of inlet conditions to the dryer. Dew point is the temperature at which water 

vapor condenses -- saturated, 100% relative humidity. Pressure dew point is the dew point of the air at 

operating pressure. Atmospheric dew point refers to air expanded to atmospheric conditions. To avoid 

confusion, specify dryer performance in terms of pressure dew point. 

(b) The instruments and the lowest expected ambient temperature determine the drying 

method. The most common dryer is a refrigerated unit that cools the compressed air, condenses water and 

oil vapors, separates them, and drains them from the system. The “dried” compressed air is then fed to 

the instrument air system. 

(c) Dryer performance is specified as a pressure dew point class that is based on specific inlet 

and ambient conditions. The lowest pressure dew point class with a refrigerated dryer is Class H. This 
TM 5-692-2 

21-7 

class delivers a pressure dew point of 33 to 39°F. Refrigerated dryers should not operate below the Class 

H range because the water vapor will freeze in the dryer. The highest practical pressure dew point for a 

refrigerated dryer is 60°F because higher pressure dew points give condensation in downstream piping. 

In the United States, most dryer manufacturers base the pressure dew point performance on standard 

conditions: inlet air flow, 100°F inlet air temperature, 100 psig operating pressure, 100°F maximum 

ambient temperature (air-cooled units), 85°F cooling water temperature (water-cooled units), and 5 psi 

maximum pressure drop. 

 (d) Adjust air dryer sizing to account for deviation from standard conditions. For example, 

elevating the inlet air temperature 10 degrees increases the load on the dryer by more than 25 percent and 

raises the outlet pressure dew point above 50°F. Maintaining the original 33 to 39°F dew point now 

requires a dryer 35 percent larger. 

 (e) Non-cycling and cycling are the two types of refrigerated dryers. On a non-cycling dryer, 

the refrigeration compressor runs continuously regardless of dryer load. A thermostatic expansion valve 

and hot gas bypass valve regulate the flow of refrigerant into the heat exchanger to maintain dew point 

and minimize "freeze-up." Since the unit uses full input power at all times, a non-cycling dryer should be 

selected for systems with a constant air flow. In cycling dryers, the refrigerant cools an intermediate fluid 

that cools and "dries" the air. During low-load operation, the refrigeration circuit stops its compressor 

and restarts it when the fluid temperature rises. The cycling type dryer conserves energy and minimizes 

dryer freeze-up making cycling dryers the choice with fluctuating air flow and inlet temperatures. Oversized cycling dryers provide additional drying capacity for future air system upgrades. 

 c. Air receivers. The final major components needed are the air receivers. Air receivers provide 

storage capacity to prevent rapid compressor cycling; reduce wear and tear on compression module, inlet 

control system, and motor; eliminate pulsing air flow; avoid overloading purification system with surges 

in air demand; and damp out the dew point and temperature spikes that follow regeneration. A rule of 

thumb is to provide a minimum of one gallon of receiver capacity for each cubic foot of compressor flow. 

 d. Piping. Consideration must be given to critical pipe lengths of the air discharge pipe, and certain 

lengths must be avoided to prevent resonance. The critical lengths vary with the type and size of air 

compressor, and can be determined from air compressor manufacturers. Consideration will also be given 

to surge volume between reciprocating compressors and aftercoolers to minimize vibration and wear in 

the tubes and tube supports or baffles in the aftercoolers. Pulsation dampers or surge bottles at the 

compressor discharge will increase the installation cost, however, they may reduce maintenance costs 

because attenuation of discharge pulsations reduces wear and the potential of tube failures. 

 e. Safety valves. A safety valve must be provided between a positive displacement compressor 

discharge and any block valve or other flow restricting device, as well as between the compressor and an 

internally finned tube aftercooler. This is particularly true with lubricated compressors. If deposits should 

clog the aftercooler, proper protection would be afforded. Safety valves should be connected directly into 

the piping at the pressure point it is sensing, without unnecessary additional piping or tubing. Safety 

valve discharge should be directed away from personnel areas and traffic lanes. 

 f. Other components. Other components that are part of the system are various control valves, control 

switches, pressure switches, drains, electrical controls, and wiring. 
TM 5-692-2 

21-8 

21-3. Compressed air system interfaces 

The compressed air system interfaces with many other systems within the plant or site. Primary interfaces 

are with the electrical system and the various process systems that the compressed system serves. 
TM 5-692-2 

22-1 

CHAPTER 22 

PNEUMATIC CONTROLS 

 

22-1. Pneumatic control design features 

Pneumatic controllers for the most part rely on compressed air as described in the previous chapter. 

Additional air dyers and filters may be added locally in the area of interest in addition to those back at the 

compressor station. 

a. Components. The next stage in control is the pressure regulator or regulators. At this point one or 

more operating pressures are set for the equipment in the area with each operating pressure having its own 

dedicated line. From this line(s) various pieces of equipment can operate. The simplest would be 

pressure gauges that measure the process relative to atmosphere or another set pressure. Next would be 

control switches that would activate either electrical circuits or pneumatic circuits based on pressure set 

point or set points. For example, the reset state could be set at a different set point from the initiation set 

point. Then there are thermostats, a control switch that operates based on the process temperature or in 

another case the outside temperatures to which the process is exposed. See figure 22-1 for an example of 

this case. At the next level are pressure transmitters and controllers. This class of service acts as a 

pneumatic amplifier to send pressure changes over greater distances and/or to generate enough energy to 

operate a valve or piston. There are many variations to these devices to allow for feedback proportional 

and derivative control. For maintenance review, site process drawings, data sheets, and manufacturers’ 

information should be used. 

b. Applications. Tools and appliances driven by compressed air are known as pneumatic devices. 

Examples of these devices are rock drills, jackhammers, spray painters, and air brakes. In some cases, air 

suction instead of compression is used to operate the tool or appliance, as in the familiar vacuum cleaner. 

Pneumatic devices are flexible, efficient, and safe. An air device creates no sparks. This is an important 

consideration for work in dangerous areas. Air compressors used in pneumatic tools and appliances may 

be either reciprocating--that is, driven by the up-and-down motion of a piston in a cylinder--or rotary, in 

which the air is compressed by a device similar to a centrifugal or axial pump. 

22-2. Pneumatic control systems major components 

Pneumatic control systems are comprised of the following major components. 

a. Air motors. Pneumatic devices are operated by two types of air motors: rotary and reciprocating. 

These air motors are the opposite of reciprocating or rotary air compressors. In a rotary device, also 

known as an air turbine, compressed air enters the motor housing, pushes on the rotary blades, and rotates 

a central shaft or spindle. Small devices can be run at speeds up to 30,000 revolutions per minute. 

Reciprocating pistons are driven as compressed air enters the cylinder, expands, and forces the piston to 

move. The return stroke is triggered either by compressed air pushing on the other side of the piston or 

by spring action. Pneumatic tools are commonly supplied with compressed air at or above 100 pounds 

per square inch (690 kilopascals). Air motors do not become hot when overloaded and can stand repeated 

stalling and rapid reversals without damage. Pneumatic tools of different sorts are used for a variety of 

purposes. Portable pneumatic tools are normally powered by rotary air motors and include grinders, 

buffers, drills, screwdrivers, chipping hammers, and various specialty tools such as paint mixers, concrete 
TM 5-692 

22-2 

COMPRESSED

AIR SUPPLY

SYSTEM

MAIN

TO OTHER

CONTROLLERS

THERMOSTAT

M B

BRANCH

ACTUATOR

VALVE

Figure 22-1. Basic compressed air supply to pneumatic control system 

vibrators, and spike drivers. Rock drills are heavy-duty machinery used for mining and rock excavation 

and are powered by reciprocating piston motors. Here, a high-carbon steel drill is held loosely in a chuck 

at the end of a cylinder and is struck by rapid blows from the freely moving piston. Major pneumatic 

devices include jackhammers, pneumatic drills and wrenches, spray guns, pneumatic conveyor systems, 

and brake systems. They have wide application in home and industrial use. Jackhammers, or paving 

breakers, are powered by a reciprocating piston that strikes a solid street drill that usually has a wedgeshaped end. Heavy jackhammers are used to break up road surfaces, concrete, and boulders; lighter 

versions are used on light concrete floors, frozen earth, and ice. 

b. Instrumentation. Instruments are the means for monitoring or measuring physical variables. The 

basic element of instrumentation is the transformation of one form of energy into another form. 

Producing meaningful information from physical variables requires conversion and processing. 

Electronic instruments require that physical variables be converted to electrical signals through a process 

of transduction, followed by signal conditioning and signal processing to obtain useful results. 

 (1) The measured parameter can be one of many physical variables; the type depends on the 

application. For example, in process control, typical measured parameters can include pressure, 

temperature, and flow. 
TM 5-692-2 

22-3 

 (2) Transducers convert one form of energy to another. To be useful for an electronic instrument, 

a transducer must produce an electrical output such as voltage or current to allow required signal 

conditioning and signal processing steps to be completed. A variety of transducers are available to meet 

measurement requirements and can be compared based on their operating principles, measurement range, 

interface design, and reliability. 

c. Process control. Process control typically involves some mechanical system that needs to be 

operated in such a fashion that the output of the system remains within its design operating range. The 

objective of a process control loop is to maintain the process at the set point under the following dynamic 

conditions. 

 (1) The set point is changed. 

 (2) The load on the process is changed. 

 (3) The transfer function of the process is changed or a disturbance is introduced. 

d. Closed-loop operation. The classical control system representation is a feedback-loop system. A 

feedback (or closed-loop) system contains a process, a sensor, and a controller. A process is a system that 

produces a motion, a temperature change, a flow, a pressure, or many other actions as a function of the 

actuator position and external inputs. The output of the process is called the process value. If a positive 

action in the actuator causes an increase in the process value, then the process is called direct acting. If 

positive action in the actuator decreases the process value, it is called reverse acting. 

 (1) A sensor is a pneumatic, fluidic, electronic or other device that produces some kind of signal 

indicative of the process value. 

 (2) The set point is the desired value for a process output. The difference between the set point 

and the process value is called the process error. 

 (3) A controller sends signals to an actuator to effect changes in a process. The controller 

compares the set point and the process value to determine the process error. It then uses this error to 

adjust the output and bring the process back to the set point. The controller gain dictates the amount that 

the controller adjusts its output for a given error. 

 (4) An actuator is a pneumatic, fluidic, electric, or other device that performs any physical action 

that will control a process. 

22-3. System operation 

As discussed in the previous sections, the major operation of the pneumatic control system is controlled 

by the compressed air system. Various variables can affect the proper operation and require strict control 

and maintenance processes. 

a. Disturbances. An external disturbance is any effect that is unmeasured or unaccounted for by the 

controller. 

b. Time constant. The time constant of a sensor or process is a quantity that describes the dynamic 

response of the device or system. Often the time constant is related to the mass of an object or other 

dynamic effect in the process. For example, a temperature sensor may have a protective sheath around it 

that must first be warmed before the sensor registers a change of temperature. Time constant can range 

from seconds to hours. 
TM 5-692 

22-4 

c. Dead time. The dead time or lag time of a process is the time between the change of a process and 

the time this change arrives at the sensor. The delay time is not related to the time constant of the sensor, 

although the effects of the two are similar. Large dead times must be properly treated by the control 

system to prevent unstable control. 

d. Hysteresis. Hysteresis is a characteristic response of positioning actuators that result in different 

positions depending on whether the control signal is increasing or decreasing. 

e. Dead band. The dead band of a process is that range of the process value in which no control 

action is taken. A dead band is usually used in two-position control to prevent “chattering” or in splitrange systems to prevent sequential control loops from fighting each other. 

f. Control point. The control point is the actual, measured value of a process (i.e., the set point + 

steady-state offset + compensation). A direct-acting process will increase in value as the signal from the 

controller increases. A reverse-acting process will decrease in value as the signal from the controller 

increases. 

g. Stability. The stability of a feedback control loop is an indication of how well the process is 

controlled or, alternatively, how controllable the process is. The stability is determined by any number of 

criteria, including overshoot, settling time, correction of deviations due to external disturbances, etc. 
TM 5-692-2 

23-1 

CHAPTER 23 

SANITARY WASTE SYSTEMS 

 

23-1. General sanitary waste systems 

 

A sanitary waste system is a system that conveys and handles sewage and excludes storm, surface, and 

ground water. Sewage is any liquid waste containing animal or vegetable matter in suspension or 

solution, including liquids containing chemicals in solution. The purpose of the sanitary waste system is 

to collect the waste generated at the plumbing fixtures, floor drains, and equipment drains, and to convey 

and dispose of this waste in an environmentally safe manner.

23-2. Sanitary waste system design features 

Treatment requirements will be determined on the basis of meeting stream and effluent requirements set 

by either U.S. or State governments or foreign governmental agencies. Methods of treatment are grouped 

below. 

 a. Preliminary treatment. Preliminary treatment is defined as any physical or chemical process at the 

wastewater treatment plant that precedes primary treatment. Its function is mainly to protect subsequent 

treatment units and to minimize operational problems. Pretreatment at the source to render a wastewater 

acceptable at the domestic wastewater treatment facility is not included. 

 b. Primary treatment. Primary treatment is defined as physical or, at times, chemical treatment for the 

removal of settleable and floatable materials. 

 c. Secondary treatment. Secondary wastewater treatment is defined as processes that use biological 

and, at times, chemical treatment to accomplish substantial removal of dissolved organics and colloidal 

materials. Land treatment can be classified as secondary treatment only for isolated locations with 

restricted access and when limited to crops that are not for direct human consumption. 

 d. Advanced wastewater treatment. Advanced wastewater treatment is defined as that required to 

achieve pollutant reductions by methods other than those used in conventional treatment (sedimentation, 

activated sludge, trickling filter, etc.). Advanced treatment employs a number of different unit operations, 

including ponds, post-aeration, microstraining, filtration, carbon adsorption, membrane solids separation, 

and specific treatment processes such as phosphorus and nitrogen removal. This treatment is very 

effective in removing over 90 percent of organics and suspended solids. Low phosphorus and nitrogen 

can also be reached through advanced treatment. 

23-3. Sanitary waste system applications 

Listed below are some of the fundamental processes with their applications. 

 a. Preliminary. Covers neutralization, equalization, screening, grit removal, temperature adjustment, 

and nutrient addition. 

 b. Primary treatment. Covers sedimentation and dissolved-air floatation. 
TM 5-692-2 

23-2 

 c. Secondary treatment. Covers activated sludge (aeration and secondary sedimentation), aerated 

pond w/secondary sedimentation, aerobic-anaerobic ponds, trickling filter, chemical oxidation, chemical 

mixing flocculation and clarification, gravity filtration, pressure filtration, dissolved-air flotation 

w/chemicals, and anaerobic contact. 

 d. Advanced wastewater treatment. Covers activated carbon adsorption, micro straining filtration, 

land treatment, subsurface disposal, and ground water recharge. 

 e. Sludge. Covers anaerobic digestion, aerobic digestion, autoclaving, elutriation, vacuum filtration, 

centrifugation, sand beds, presses, incineration, wet oxidation, land disposal, and sanitary landfill. 

23-4. Treatment methods 

Listed below are some of the methods used in waste water treatment. 

 a. Preliminary treatment. This includes screening, grinding, grit removal, flotation, equalization, and 

flocculation. Screens, grinders and grit removal are provided for the protection of other equipment in the 

treatment plant. Air flotation and flocculation aid in the removal of suspended solids and oil in the 

primary clarifier and reduce the biological loading on secondary treatment processes. Pre-chlorination or 

pre-aeration may be required to prevent odor problems and to eliminate septic conditions where 

wastewater has abnormally long runs to the plant. Equalization structures are used to dampen diurnal 

flow variations and to equalize flows to treatment facilities. 

 (1) The primary function of bar screens is protection of downstream facilities rather than effective 

removal of solids from the plant influent. 

 (2) Comminuting devices are shredders that incorporate mechanisms that cut the retained material 

without removing it from the sewage flow. Comminutors are generally located between grit chambers 

and the primary settling tanks. Each comminuting device must have a bypass for maintenance and repair 

purposes. The bypass will include a bar screen, described as coarse screens. 

 (3) The primary purpose of grit chambers is to protect pumps and other mechanical equipment. 

Grit chambers will be located ahead of pumps and comminuting devices. 

 (4) Dissolved air flotation is a unit process whereby particulate matter is separated from a 

wastewater, causing the matter to float to the liquid surface. 

 (5) Flocculation units will be used and will immediately precede clarification units when a 

chemical precipitation process is employed as part of primary, secondary, or advanced wastewater 

treatment schemes. 

 (6) Dissolved air flotation is a unit process whereby particulate matter is separated from a 

wastewater, causing the matter to float to the liquid surface. 

 b. Primary treatment. The purpose of primary treatment is to remove solids that are not removed 

during preliminary treatment. Processes that provide primary treatment are primary sedimentation 

(clarification) and Imhoff tanks. In most facilities, primary treatment is used as a preliminary step ahead 

of biological treatment. 
TM 5-692-2 

23-3 

 (1) Sedimentation tanks allow solids to drop out of the wastewater. They usually take two forms. 

One is the rectangular tank with a minimum length of flow from inlet to outlet of ten feet in order to 

prevent short circuiting of flow in the tank. In existing installations, tank length-to-width ratio varies 

between 3:1 and 5:1. Tanks will be designed with a minimum depth of seven feet except final tanks in 

activated sludge plants, which will be designed with a nine foot minimum depth. The other tank type is 

the circular tank. Circular tank diameters range from 25 to 150 feet. Side-water depths are seven feet as a 

minimum, and tank floors are deeper at the center. A circular sludge-removal mechanism with peripheral 

speeds of five to eight feet per minute will be provided for sludge collection at the center of the tank. 

Chemical precipitation may be introduced at this point to alleviate problems such as phosphorous, odor, 

industrial waste, or plant overload. 

 (2) Imhoff tanks provide removal of settleable solids and the anaerobic digestion of these solids in 

the same unit. They are two-level structures that allow the solids to settle out in the upper level. The 

settled solids then fall through slots into the lower level where they undergo digestion. The gas produced 

during digestion escapes through the vent areas along the sides of the upper level. 

 c. Secondary treatment. Secondary treatment is the use of secondary sedimentation tanks to allow the 

biological solids in the wastewater leaving the trickling filter to settle out. This produces an effluent for 

discharge, and the settled solids can be recirculated to the trickling filter to enhance its performance. 

23-5. Typical sanitary waste systems 

The following systems are used at the sites for waste treatment. 

 a. Trickling filter process. These have been justified by their low initial cost, low operating and 

maintenance costs, and relative simplicity of operation. Although the effluent from trickling filter plants 

of earlier design was of poorer quality than that from activated sludge plants, the performance of trickling 

filters designed more recently is comparable to that of activated sludge plants. Both processes offer 

certain advantages, with trickling filters providing good performance with minimal operator care and few, 

if any, energy requirements. An example of a typical trickling filter treatment process appears in figure 

23-1. Although not shown, dual or parallel trains are appropriate for all treatment systems having a 

design capacity rating equal to or greater than 0.5 million gallons per day. 

 b. Activated sludge process. The activated sludge process is capable of meeting secondary treatment 

effluent limits. All designed processes will include preliminary treatment consisting of bar screen as a 

minimum and, as needed, comminutor, grit chamber, and oil and grease removal units. In a conventional 

(plug-flow) activated sludge plant (figure 23-2), the primary-treated wastewater and acclimated microorganisms (activated sludge or biomass) are aerated in a basin or tank. After a sufficient aeration period, 

the flocculent activated sludge solids are separated from the wastewater in a secondary clarifier. The 

clarified wastewater flows forward for further treatment or discharge. A portion of the clarifier underflow 

sludge is returned to the aeration basin for mixing with the primary-treated influent to the basin and the 

remaining sludge is wasted to the sludge handling portion of the treatment plant. 

 c. Stabilization pond process. A wastewater stabilization pond is a relatively shallow body of 

wastewater contained in an earthen basin that is designed to treat wastewater. ("Oxidation pond" is a 

synonymous term.) They are used to treat a variety of wastewater’s, from domestic wastewater to 

complex industrial waters, and they function under a wide range of weather conditions, i.e., tropical to 

arctic. Ponds can be used alone or in combination with other treatment processes. If sufficient land is 
TM 5-692-2 

23-4 

available, ponds are a cost-effective means to provide wastewater treatment. In addition, their operation 

is easy and their maintenance requirements are minimal. Below are listed the different types of ponds. 

Figure 23-1. Typical trickling filter process treatment train 

 (1) An aerobic stabilization pond contains bacteria and algae in suspension; aerobic conditions 

(the presence of dissolved oxygen) prevail throughout its depth. There are two types of aerobic ponds: 

 (a) Shallow oxidation ponds obtain their dissolved oxygen via two phenomena: oxygen 

transfer between air and water surface, and oxygen produced by photosynthetic algae. 

 (b) An aerated pond is similar to an oxidation pond except that it is deeper and mechanical 

aeration devices are used to transfer oxygen into the wastewater. 

 (2) Three zones exist in an aerobic-anaerobic pond. They are the following. 

 (a) A surface zone where aerobic bacteria and algae exist in a symbiotic relationship; 

 (b) An anaerobic bottom zone in which accumulated solids are actively decomposed by 

anaerobic bacteria; and 
TM 5-692-2 

23-5 

Figure 23-2. Conventional plug flow activated sludge flow diagram 

 

 (c) An intermediate zone that is partly aerobic and partly anaerobic in which the 

decomposition of organic wastes is carried out by facultative bacteria. In these ponds, the suspended 

solids in the wastewater are allowed to settle to the bottom. As a result, the presence of algae is not 

required. The maintenance of the aerobic zone serves to minimize odor problems because many of the 

liquid and gaseous anaerobic decomposition products, carried to the surface by mixing currents, are 

utilized by the aerobic organisms. 

 (3) Controlled discharge ponds have long hydraulic detention times and effluent is discharged 

when receiving water quality will not be adversely affected by the discharge. Controlled discharge ponds 

are designed to hold the wastewater until the effluent and receiving water quality are compatible. 

 (4) Complete retention ponds rely on evaporation and/or percolation to reduce the liquid volume 

at a rate equal to or greater than the influent accumulation. 

 d. Advanced wastewater treatment processes. A number of different unit operations are used in 

various configurations to make up an advanced wastewater treatment system. There are no advanced 

wastewater treatment process trains that can be considered typical or most applicable to a C4ISR 

installation. Effluent quality standards exceeding established secondary treatment level standards will 

dictate the advanced treatment unit processes and their combinations that will provide the necessary 

degree of treatment. Unit operations typically used in advanced treatment are presented below. 

 (1) Wastewater treatment ponds may be used as a practical and economical method for upgrading 

existing secondary treatment facilities to obtain improved organic and suspended solids removal. Both 

aerobic and aerobic-anaerobic ponds can be used for this purpose. Ponds used for polishing purposes are 
TM 5-692-2 

23-6 

subject to the same operating characteristics as those used for primary or secondary treatment, and the 

same precautionary design considerations must be applied. 

 (2) Post-aeration can be accomplished by diffused, cascade, U-tube, or mechanical aeration. 

Diffused aeration is carried out in tanks 9 to 15 feet deep and 10 to 50 feet wide (depth-to-width ratio is 

maintained at less than two), with detention time of about 20 minutes. The maximum air requirement is 

approximately 0.15 cubic feet per gallon of wastewater treated. Mechanically aerated basins are eight 

feet deep and require 15 to 50 square feet per aerator. The drop required for cascade aeration in a 

stepped-weir structure or in a rapidly sloping channel filled with large rocks or concrete blocks will 

depend on the desired oxygen uptake: two feet of drop will be provided for each milligram per liter of 

dissolved oxygen increase required. 

 (3) A microstrainer consists of a rotating drum supporting a very fine, stainless steel or plastic 

screen. Wastewater is fed into the inside of the drum and filters radially outward through the screen, with 

the mat of solids accumulating on the screen inside the drum. The solids are flushed into a removal 

trough at the top of the drum by a pressurized backwash system. From this trough, the solids are returned 

to the head of the system. Process effluent wastewater can be used for the backwash. 

 (4) The function of filtration is to remove as much of the suspended solids in the waste stream as 

possible through the use of filters. A filter consists of various sizes of media bounded by a container. 

Media in this case consists typically of different grades of sand, gravel, anthracite coal, etc. The 

effectiveness is derived from the type and size of filter media, depth of filter, amount of backwash, 

chemical pretreatment dosage, and filter rate and duration. 

 (5) Activated carbon adsorption beds can provide filtration but their primary function is to remove 

non-biodegradable organics, taste and odor compounds, and reduce color in the waste stream. 

 (6) Mineral addition and lime addition are the principal methods for in-plant removal of 

phosphorus from wastewater. The most commonly used of these metal salts are: alum, a hydrated 

aluminum sulfate, sodium aluminate, ferric sulfate, ferrous sulfate, ferric chloride, and ferrous chloride. 

Mineral addition is usually followed by anionic polymer addition, which aids flocculation; the pH may 

require adjustment depending on the particular process. In lime addition, phosphorus removal is attained 

through the chemical precipitation of hydroxyapatite. Addition can take place at the primary or 

secondary treatment stage. 

 (7) Land application systems are the use of land and biomass growth as a wastewater treatment 

area. Because land treatment of wastewater entails a higher risk than other treatment processes of 

introducing pathogenic micro-organisms and toxic chemicals into groundwater and surface water, land 

treatment system design must carefully consider all possible means to prevent water supply 

contamination. 

 (8) Soil biota are capable of stabilizing most organic wastes, including oily sludges. Today, only 

about 25 percent of sludges are spread on land; even less is composted. However, the organic materials in 

sludges are beneficial in restoring fertility to soils disturbed by mining, gravel operations, or poor 

agricultural practices. There are, however, some major limitations. Concentrated sludges (if not 

composted or otherwise stabilized) placed on land should be immediately covered to prevent odor 

production and insect breeding. Sludges can be sliced or injected into soil or into stubble, using special 

equipment. Deep snow and deep frost will stop land spreading operations. 
TM 5-692-2 

23-7 

 (9) Nitrification occurs in two steps: first NH is converted by Nitrosomonas bacteria; then 

converted by Nitrobacter bacteria. This process is limited by the relatively slow growth rate of 

Nitrosomonas. 

 (10) Denitrification is performed by heterotrophic anaerobic organisms 

and, therefore, requires an organic carbon source and anaerobic conditions. Suspended growth 

denitrification will provide gentle mixing (no aeration) with the mixed liquor being clarified. The 

effluent is aerated to provide dissolved oxygen and to drive off entrained nitrogen, and the sludge is 

recycled to the contact tank. 

 (11) Three-stage biological systems. Three-stage biological systems are essentially a combination 

of separate stage nitrification and denitrification. The advantage of this system is its flexibility of 

operation and the main disadvantage is the capital cost involved. This configuration also works to 

prevent short circuiting, which can be a problem in nitrification-denitrification when plug flow is not 

achieved. 

 (12) In anaerobic contact process, a further development of the high-rate digestion process allows 

separation and recycling of digested sludge solids. Like the activated sludge process, detention and mean 

cell residence times are controlled. Denitrification within these contact vessels approached 95 percent. 

e. Small installations. Septic tanks, biological package treatment plants, and stabilization ponds are 

cost effective and require less operational and maintenance attention than other treatment options. 

Therefore, these treatment methods are especially applicable to C4ISR installations having design 

capacities of less than 100,000 gallons per day. See figures 23-3 through 23-6 for depictions of a septic 

tank, lift station, sewage ejector, and valves associated with these installations. 

23-6. Sludge handling, treatment, and disposal 

Sludge, or residual solids, is the end product of wastewater treatment, whether biological or 

physical/chemical treatment. Primary sludge is from three to six percent solids. Treatment objectives are 

reduction of the sludge and volume, rendering it suitable for ultimate disposal. Secondary objectives are 

to utilize the generated gas if anaerobic digestion is selected as part of the sludge management strategy. In 

addition, an attempt should be made to sell/utilize the sludge as a soil conditioner rather than paying to 

dispose of it. 

23-7. Disinfection 

Disinfection is a process in which pathogenic organisms are destroyed or inactivated. This process may 

be accomplished by physiochemical treatment or addition of chemical reagents. Improved coliform and 

virus removal can be obtained by utilizing flash mixing and acid feed for pH reduction. Chlorine, as 

liquid chlorine or in the form of chlorine compounds, is the most common chemical used to disinfect 

wastewater treatment plant effluents. Calcium hypochlorite or sodium hypochlorite will only be used as 

chlorinating agents for very small installations (less than 20,000 gallons per day). Ozone has been an 

effective disinfectant when used in the water treatment field, and its use as a disinfectant for wastewater is 

being seriously considered. This interest has developed mainly because zonated effluents have normally 

shown no toxic effects on the receiving water biota as have residual chlorine compounds; however, for 

certain industrial wastes, epoxides have been found. The major disadvantage of ozonation is the high 

capital and operational cost associated with its generation. 
TM 5-692-2 

23-8 

ACCESS COVER

BAFFLE

EFFLUENT

SCUM

SLUDGE

Figure 23-3. Septic tank 

23-8. Flow measurement, sampling, and process control 

Monitoring is required by Environmental Protection Agency (EPA) when National Pollutant Discharge 

Elimination System (NPDES) permits are issued to assure compliance with the permit. Additionally, 

certain operational monitoring is required to ensure that proper treatment plant performance is 

maintained. Below is a listing of the instrumentation used. 

 a. Continuous recording of flow. Wastewater flow rates will be monitored and recorded for purposes 

of evaluating treatment plant performance and will also be used when treatment changes are involved. 

Continuous flow measurement is necessary in order to monitor diurnal variations in flow which may 

affect treatment plant efficiency. Flow rates must also be taken into account when sampling wastewater 

quality. 

 b. Types of flow measuring devices. The following paragraphs describe the types that are suitable for 

use in wastewater treatment plants. 

 (1) Venturi meters are not to be used for measuring wastewater or sludge flow unless sufficient 

hydraulic head is available, or unless the Venturi tube is so constructed as to prevent solids accumulation 

at the upstream side of the throat. Clogging of the pressure tubes is avoided by providing cleanout taps 

and discharging a stream of fresh water through them into the sewer. Positive separation of potable water 

supply from this connection must be assured. 
TM 5-692-2 

23-9 

Figure 23-4. Lift station with wet pit vertical centrifugal pump 

 (2) Weirs will be located in a channel so that the flow will not be disturbed by turbulence and in 

such a manner that the depth of flow over the weir can be observed and recorded. When continuous 

recording is required, the float will be installed in a chamber separated from the main channel of flow but 

connected thereto by piping. 
TM 5-692-2 

23-10 

TO SEWER

AUTOMATIC THREE WAY

PNEUMATIC VALVE

COMPRESSED AIR

BUILDING 

SUB-DRAIN OR

GRAVITY DRAIN

VALVE

CHECK VALVE

SEWAGE

EJECTOR

CHECK VALVE

FORCED 

DISCHARGE

FLOAT SWITCH

TO OPERATE

THREE WAY

PNEUMATIC

VALVE& VENT

VALVE

VENT 

PIPING

FINISHED FLOOR

INLET

Figure 23-5. Pneumatic sewage ejector 

 (3) Parshall flumes have many advantages: the loss of head is minimal; it is self-cleaning; flow 

measurement can be made in open-channel flow; and it has no moving parts to malfunction. The 

downstream water-surface elevation above the flume approach floor must not exceed 65 percent of water 

elevation upstream of the flume. The flume will be designed with the narrowest throat practicable for the 

conditions under consideration. This is particularly important where a Parshall flume is utilized to control 

the velocity through a grit chamber. 

 (4) Magnetic flow meters can be used for flow measurement in wastewater treatment plants. 

There are many types of magnetic flow meters, however, and direct contact with the manufacturers is the 

quickest and generally most practical way to determine their application to specific wastewater 

measurements. 

 (5) Ultrasonic devices are being used to measure levels in Parshall flumes. A pulsing signal is 

bounced to the receiver where the level is related to the time elapsed. Since no components are in contact 

with the liquid, this device is applicable to many types of wastes and situations. 

 c. Sampling. Wastewater sampling at various points in the sewage treatment process is useful in 

evaluating operation efficiency. This can be used internally to optimize the process and is also used by 

regulatory agencies to judge whether treatment plant regulations are satisfied. Sampling is also used to 

establish changes when treating industrial wastes. Provisions for sampling sites must be made in the plant 

design. The type of sampling provisions (flow proportional, composite, or grab-sample collection) will 

be dictated by the type of sampling required in any discharge permit. Forward flow, recycled flow, 

sludge flow, chlorine residual, pH and dissolved oxygen are some of the process control parameters that 

can be monitored on a continuous basis. 
TM 5-692-2 

23-11 

GATE VALVE CHECK VALVE

Figure 23-6. Gate valve and swing check valve 

 d. Monitoring equipment for process control. Monitoring equipment will be used to indicate and/or 

record flow quantities and, if justified, pressure, temperature, liquid levels, velocities, and various quality 

parameters such as dissolved oxygen, biochemical oxygen demand, total suspended solids, ammonia, 

nitrate, and pH. 

 (1) In sewage pumping stations, flow measurement is necessary to control periodic pump 

operation. Watt-hour meters and pump-time meters will be used to ensure uniform pump wear in 

multiple-pump installations. 

 (2) Monitoring primary treatment processes will require only flow measurement and recording and 

perhaps grit level monitoring. When digestion of the primary sludge follows, raw sludge flow rates must 

be monitored and controlled. In digestion, gas flow rates, tank pressures, and sludge temperatures will be 

monitored, and digester operation adjusted accordingly. 

 (3) Trickling filter monitoring will include flow measurement of influent, effluent and 

recirculation lines, and also volume of sludge pumped to or from the digesters. These parameters are used 

in determining and controlling hydraulic and organic loading as well as in controlling settling tank 
TM 5-692-2 

23-12 

efficiencies. Activated 

sludge treatment will require the same monitoring with the addition of mixed-liquor, volatile suspended 

solids, and air supply monitoring. 

 (4) In sludge elutriation, sludge and elutriant flows will be measured in order to determine 

required sludge conditioner quantities. Sludge filtration will require measurements and control of sludge 

and sludge-cake flows and chemical feed rates. All chemical feed lines will be monitored and controlled, 

whatever their function. Sludge incineration and drying processes will require temperature monitoring at 

various points, pressure gauges, and sludge weighing equipment. Fuel flow rates, whether waste gas or 

auxiliary fuel, must be measured and controlled. 
TM 5-692-2 

24-1 

CHAPTER 24 

ELECTRONIC SECURITY

24-1. Electronic security methodology 

Electronic security is an intrusion detection system (IDS) installed to adequately protect valuable assets 

against adversaries who pose a threat to these assets. Electronic security systems (ESS) are used to alert 

responsible personnel, such as security guards, to intrusions at protected facilities. In some cases, the 

system may cause actuation of physical barriers to prohibit intruders’ access. 

a. Physical barriers. At most facilities, three barriers are utilized to form lines of defense to 

physically protect valuable assets. Perimeter barriers are normally found at the edge of the protected 

property and are considered to be the first line of defense. This may be a fence, wall, or a natural barrier, 

such as a river, lake, cliff, ravine, or other terrain that is difficult to traverse. The second line of defense is 

building exterior walls and roof. Interior building rooms, safes, and vaults make up the third line of 

defense. These physical barriers are mentioned because they establish areas where intrusion detection 

may be warranted. Depending on the type, configuration, location, and other conditions of the protected 

area, applicable ESSs are selected from several different types. At property lines and large building 

walls, intrusion detectors covering large areas are required as opposed to a room within a building or a 

vault. Also, exterior applications require weatherproof enclosures and are sometimes subjected to a wide 

temperature range. 

b. Detection systems. There are many types of electronic security systems in use at military 

installations. All require frequent tests and checks, in some instances as often as once a day. The 

emphasis is on operational tests to ensure the continued functionality of the designed system, rather than 

on routine maintenance of component parts. Before the advent of low-cost computer multiplexed 

hardware, security systems were simple hardwired alarm systems, providing a minimum level of intrusion 

detection. Today, the system may be a fully redundant computer-based system interfaced with a 

redundant looped time-division-multiplexed communication network for gathering alarm data from 

sensors and for sending commands to release locked doors under the card-access control subsystem. The 

remote multiplexer may be microprocessor-based units, capable of data collection, communication with 

the host computer, and performing limited-access control functions. The security system provides 

location information as well as delay time for the guards. By successive detections, the security force can 

track the intruder and relay location information via portable radio communications equipment to the 

responding guards. In turn, the guards can constantly inform the security force on the progress of their 

work or the need for additional assistance. The cameras, using various means of target intensification, 

can “see” better than the human eye. Guard patrols are also used to detect unusual activity. Perimeter 

detection is accomplished by the application of electronic detection systems. 

24-2. Types of electronic security 

Electronic security systems can be placed into two categories – perimeter detection and interior detection. 

a. Perimeter detection. Perimeter detection is that used to prevent entry into a restricted area and the 

devices are usually located to protect the exterior premises. 
TM 5-692-2 

24-2 

 (1) Microwave detection links are devices mounted on posts inside the fence. Transmitters radiate 

amplitude modulated X-band energy, and receivers detect and process the received energy. Thus, an 

invisible energy envelope is produced that will detect an intruder. 

 (2) Infrared detection links are devices that are post-like and mounted inside the fence. 

Transmitters radiate multiple beams of modulated infrared energy, and the receivers detect and process 

the energy. Penetration of the invisible infrared shield will alarm the system. 

 (3) E-field links are transmitter wires and receiver wires are strung horizontally from mounting 

posts located inside the fence or mounted on the fence. A radio-frequency energy field is generated 

around the wires. The intrusion of a person into the invisible field will “short” energy, creating an alarm. 

 (4) Buried sensor links are devices sensing seismic pressure, [or electromagnetic (EM) 

disturbances for a combination of these] are buried inside the fence, and alarm upon the intrusion of 

someone into the field of detection. 

 (5) Other systems are available that can be used in combination with the previously mentioned 

systems. The probability of detection by these outdoor devices depends on their application. Perimeter 

detection equipment must be applied with consideration of the environmental limitations of the device’s 

technology. 

b. Interior detection. If the intruder penetrates the perimeter detection, the protected area has been 

breached. The interior detection then must be in place to prevent further entry into controlled or protected 

buildings. 

 (1) Visual or closed-circuit television surveillance may detect the intruder. 

(2) Entry into a building is provided by the application of a balanced magnetic switch on doors and 

openings. This device uses an internal bias magnet to balance a delicate reed switch in the field of the 

external magnet attached to the door. Should the door be opened, even a fraction of an inch, or should 

another magnet be introduced in an attempt to defeat it, the switch will change state and alarm. 

(3) Other devices for detection of an intruder may be applied inside the building, including 

microwave and infrared motion detection, photoelectric or laser beams, seismic, sound detection, passive 

infrared, and other devices.
TM 5-692-2 

25-1 

CHAPTER 25 

HIGH ALTITUDE ELECTRO-MAGNETIC PULSE (HEMP) PROTECTION 

SYSTEMS 

 

25-1. General HEMP protection systems 

Command, Control, Communications, Computer, Intelligence, Surveillance, and Reconnaissance (C4ISR) 

facilities contain miniature solid-state electronics. These devices will fail when subjected to voltages that 

exceed the dielectric strength of the component or when the device melts as a result of heating from 

currents induced by a radio frequency (RF) pulse. Most people are familiar with the effects of lightning 

upon solid-state equipment. Other sources are High Power Microwave (HPM), Ultra Wide Band (UWB) 

waveforms, and High-Altitude Electromagnetic (EM) Pulse (HEMP). A nuclear weapon detonated 300 

km above the United States can blanket the entire continental United States with the HEMP effects. 

a. Reliance on electronic technology. Military facilities are becoming increasingly reliant on 

automated systems that take advantage of modern electrical and electronic technology. Facilities are 

equipped with state-of-the-art computerized systems for expeditious, reliable, and cost-effective 

operations. However, the EM properties of many electronic components can make entire systems 

susceptible to upset or permanent damage due to the environmental effects of HEMP. Systems are also 

susceptible to the compromise of security information by the unintentional intelligence-bearing 

emanations of EM signals. Thus, with the benefits of automation has come an increased vulnerability. 

b. Early planning. Techniques to protect a facility are usually selected during the early design phase. 

If it is anticipated that a facility may someday acquire equipment that must be protected, early planning 

can avoid costly retrofitting later. The decision to harden will be based on the interaction of mission 

criticality, EM environment, security requirements, and costs. 

c. Far-reaching effects. HEMP is dangerous because this event has far-reaching effects at distances 

where other nuclear environments are either nonexistent or inconsequential and because of its high level 

of broad spectral energy. However, the spectrum included under HEMP does not cover all EM 

environments. For example, the characteristic pulse rise time and possible conducted current waveforms 

for lightning differ from those for HEMP; thus, hardening against HEMP does not necessarily protect 

against lightning. 

25-2. HEMP procedures 

HEMP is defined as EM pulses produced by nuclear explosions at high altitudes. HEMP hardened 

facilities are intended to provide vital communications at a time when unhardened facilities are likely to 

fail. If initial HEMP hardness for a facility degrades during day-to-day operations, then unexpected 

system failures could seriously compromise communication assets as a result of a nuclear event. Because 

degradation in HEMP hardness has little effect on the normal facility operations, specific surveillance, 

maintenance, and operational procedures must be employed to detect and repair degradation in facility 

hardness. 
TM 5-692-2 

25-2 

25-3. Modes of HEMP entry 

Modes of HEMP entry include diffusion, leakage through apertures, antennas, and conductive 

penetrations. 

a. Diffusion through the shield. HEMP fields diffuse through imperfectly conducting walls of 

shielded enclosures. The diffusion is greatest for magnetic fields and is a low-pass filtering event, as 

shown by the magnetic shielding effectiveness curve. Thus, the field that reaches the inner region of a 

shielded enclosure is basically a low-frequency magnetic field. This effect is greatest in an enclosure 

with solid metal walls. It is also seen somewhat in enclosures with metal rebar or wire mesh 

reinforcement. The reduced shielding effectiveness at high frequencies for rebar and wire mesh structures 

allows a significant fraction of the incident HEMP environment to penetrate to electronics inside the 

enclosure. 

b. Leakage through apertures. Openings and other shielding compromises include doors, windows, 

holes for adjustments and display units, seams, improperly terminated cable shields, and poorly grounded 

cables. Unless properly treated, each opening is a leak through which the HEMP field can couple directly 

into the shielded enclosure. Leakage through an aperture depends on its size, the type of structure 

housing it, and its location. The aperture responds to both total magnetic and electric fields at the site of 

the leak. 

c. Intentional and inadvertent antennas. Intentional antennas are designed to collect EM energy over 

specified frequency bands. However, there will also be an out-of-band response to HEMP. Because the 

incident HEMP field has a broad frequency spectrum and high field strength, the antenna response must 

be considered both in and out of band. Analytical models are available for determining the different 

antennas’ responses to HEMP. These models, along with the incident field, yield the HEMP energy that 

appears at the connecting cable. This energy later reaches the electronic systems inside the enclosure at 

the other end of the connecting cable. Inadvertent antennas are electrically conducting, penetrating 

external structures, cables, and pipes that collect HEMP energy and allow its entry into the enclosure. As 

a rule, the larger the inadvertent antenna, the more efficient energy collector it is in producing large, 

transient levels in the enclosure. The coupling for inadvertent antennas can be analyzed using 

transmission line and simple antenna models. 

d. Conductive penetrations. Many factors affect the coupling of EM energy to penetrating 

conductors. The HEMP waveform characteristics, such as magnitude, rate of rise, duration, and 

frequency, are each important. Further, the observer’s position with respect to the burst is a factor. 

Because the interaction between fields and conductors is a vector process, the direction of arrival and 

polarization is also important. Conductor characteristics also affect HEMP coupling. These include 

conductor geometry (length, path, terminations, distance above or below the earth’s surface), physical and 

electrical properties that determine series impedance per unit length (including diameter, resistivity, and 

configuration), and the presence and effectiveness of shielding. For overhead or buried conductors, the 

electrical properties of soil affect coupling. Many elements of a facility can act as efficient collectors and 

provide propagation paths for HEMP energy. HEMP can couple to structures such as power and 

telephone lines, antenna towers, buried conduits, and the facility grounding system. Actual antennas, 

nonelectrical penetrators such as water pipes, and any other conductive penetration can couple HEMP 

energy into a structure. In addition, if the structure is not shielded or is not shielded well enough, HEMP 

can couple to the cables between equipment inside. 
TM 5-692-2 

25-3 

25-4. Equipment susceptibility

System damage or upset from HEMP is caused by currents and voltages induced in conductors exposed to 

a free-field or partly attenuated EM pulse coupled to circuits. The narrow resonance results from circuits 

of high Q (quality factor) which have low resistive dissipation of energy. External conductors, structures, 

and internal conductors act as unintentional receiving antennas and “coupling” paths. They can deliver 

the resulting HEMP-induced currents and voltages to sensitive components of electronic equipment. The 

HEMP-induced currents on exterior long-line penetrators, such as power and telephone lines, can have 

amplitudes as high as thousands of amperes. Currents induced on internal cable runs can be as high as 

hundreds of amperes for most structures and even higher in facilities with lower systems engineering 

(SE). It is important to note that exterior voltage transients can be in the megavolt range, and it would be 

normal to expect an order of thousands of volts from internal coupling. 

 a. Effects of transients. Transients of these magnitudes can be delivered to electronic circuits, such as 

integrated semiconductor circuits, which can be damaged by only a few tens of volts, a few amperes, or 

less. These circuits also operate at relatively low levels (e.g., five volts and tens of milliamperes) and can 

be upset by HEMP currents of similar values. If the large exterior coupled transients were allowed to 

enter a structure that had no HEMP protection treatment, even relatively “hard” devices, such as relay 

coils, could suffer damage. 

b. Equipment responses. HEMP produces two distinct responses by equipment and system 

components: upset and damage. Upset is a non-permanent change in system operation that is selfcorrecting or reversible by automatic or manual means. Damage is an unacceptable permanent change in 

one or more system parts. 

c. Damage thresholds. The passive elements most susceptible to damage from HEMP-induced 

currents are those with very low voltage or power ratings and precision components for which a small 

change is significant. Resistor failures due to high-level pulsed currents are caused by energy-induced 

thermal overstress and voltage breakdown. Resistor failure threshold can be calculated from the resistor’s 

parameters and the empirical relation. Exposure of capacitors to transient currents sets up a voltage 

across the capacitor that increases with time. For non-electrolytic capacitors, this voltage keeps rising 

until the capacitor’s dielectric breakdown level is reached. That point is typically ten times the direct 

current (DC) voltage rating. For electrolytic capacitors, the voltage relationship holds until the zener 

level of the dielectric is reached. After that, damage can occur. The damage threshold for electrolytic 

capacitors in the positive direction is three to ten times their DC voltage rating. For the negative direction 

it is one-half their positive failure voltage. Transformer and coil damage due to HEMP-induced currents 

results from electric breakdown of the insulation. The pulse breakdown voltage is typically 5500 volts 

for power supply transformers and 2750 volts for small signal transformers. 

25-5. HEMP protection systems 

Traditional methods of electromagnetic interference (EMI) isolation often use metal enclosures to prevent 

unwanted radiation from entering the circuit. These shields provide effective protection along with good 

grounding techniques, therefore, HEMP protection systems are static as they do not have any moving 

parts. An exception to this is finger stock material that springs into place when doors or windows are 

closed. Only during an electromagnetic pulse (EMP) environment does the system function to shield the 

hardened facility. HEMP protection system components should not be disturbed or disconnected. 
TM 5-692-2 

25-4 

 a. Electronic surge arresters. An area in which care must be taken to ensure compatibility in EM 

integration is surge protection. Some surge arresters used for lightning do not clamp fast enough to 

protect against HEMP. Some used for HEMP may not have great enough current carrying capacity for 

lightning protection in all situations. 

b. Shielding. For HEMP-hardened facilities, some kind of EM shielding is essential. Shielding 

involves the use of a barrier or series of barriers to reduce the magnitude of the EM energy incident upon 

the electronic or electrical system to be protected. Shielding philosophy can be developed around 

different approaches. 

 (1) Global shielding (or hardening) is a protection concept that uses an overall shield to 

encompass the entire facility. In this approach, all conducting penetrations and all apertures are protected 

at the shield. The intent is to keep all HEMP fields and HEMP-induced transients outside the protected 

volume. The global shield could be placed on the entire outer walls, ceiling, and floor (surface) of the 

facility, or it could be reduced to a smaller volume that contains all sensitive equipment to be protected. 

The most common shield material for global shielding of ground-based facilities is sheet steel with 

welded seams, although other designs can provide adequate global HEMP shielding. 

 (2) Tailored shielding is a protection concept in which shielding is designed and constructed 

according to specific protection requirements for the equipment involved. After defining the system to be 

protected, its possible operating configurations, the expected HEMP environment, coupling paths, 

equipment sensitivities, and subsystem/system criticalities, the required protection levels for various 

subsystems or groups of subsystems can be defined. Tradeoff studies may be performed for comparing 

various shielding arrangements to verify that they meet safety margins in protection, cost-effectiveness, 

maintainability, survivability, flexibility, and other requirements. The objective is to optimize protection 

for the specific mission-critical system. Tailored shielding options may include global shielding, zonal 

shielding, shielding of cabinets or components, or combinations thereof. In a typical tailored protection 

design, discrete protection will be provided to eliminate specific, localized deficiencies. 

 (3) Zonal or topological shielding is a concept in which a facility is divided into zones, with 

shielding barriers located topologically in a shield within a shield configuration. The outer zone is 

designated zone zero; zone one is inside shield one but outside shield two. Zones and shields are assigned 

increasingly larger numbers as they progress toward the more deeply nested areas. 

 (4) The term “system configuration” identifies which way the cables, wires, equipment, and 

subsystems are laid out in relationship to each other, as well as the relationship of these items to the 

topological boundaries. In some instances, the cables, connectors, and equipment casings are actually 

part of the topological protection. System configuration as defined does not directly attenuate the 

environment, but it is an important element in the topological protection concept. The system 

configuration influences protection design requirements since some configurations are easier to protect 

than others (e.g., co-location of all mission-critical equipment). Thus, the system configuration should be 

coordinated with the protection design and the protection topology will be optimal for a specific 

configuration. During the facility life cycle, the protection design may be required to accommodate some 

changes in configuration. To ensure that the configuration’s design modifications do not compromise or 

defeat the protection, careful configuration management is necessary. The topology should be designed 

to tolerate configuration changes that are totally within a boundary. The boundary can never be violated 

(for example, opened)--only extended. All modifications must be subjected to review by HEMP experts 

to ensure continual compliance with the HEMP hardening requirements. 
TM 5-692-2 

25-5 

 (5) Conductive or metallic cable shielding or conduit is used in the zonal/topological protection 

concept to extend the boundary formed by equipment enclosures and thus provide a way to interconnect 

elements while maintaining boundary continuity. Cable shielding is also used to protect a wire or wires 

as they travel from one boundary to another. This would be the case with a shielded RF signal traveling 

from its entrance into a building to the RF receiver. From a HEMP standpoint, the shielding attenuates 

coupling of radiated energy within the first boundary as the signal travels to the receiver. Of course the 

shield is somewhat reciprocal in that it also prevents signals from radiating out of the cable. The main 

feature of cable shielding is continuity of the boundary provided by the cable shield/connector 

combination that may require special joints. 

 (a) Another way to maintain this continuity and provide cable shielding is by using steel 

conduit to house all wires and cables. The steel conduit will provide substantially higher shielding levels 

than the cable shields. 

 (b) Both cable shields and conduit connected to a shielded zone must have equal or greater 

shielding effectiveness than the shield. 

 c. Grounding. The grounding system for a HEMP protected facility shall use an equipotential ground 

and is connected to a welded stud that does not penetrate the shield. Another stud welded to the opposite 

side of the shield then will be connected to the exterior grounding system. 

d. Shield penetration protection. All shielded zones will require penetrations to allow entry of 

equipment, personnel, electric power, communications, control signals, ventilation, water, fuel, and 

various fluids. Without protection, these penetrations compromise the shield. 

 (1) Large access doors are often necessary to provide an entry for equipment, supplies, or vehicles 

into HEMP hardened facilities. In facilities that require blast overpressure protection, large blast doors 

are used. These doors generally use one or more thick steel plates to provide protection. The door’s 

inherent shielding ability is thus high, but its large size presents a difficult gasketing problem. If blast 

protection is not required, it is still necessary to design the door with a high degree of structural strength. 

This step is to ensure that the door can provide the necessary gasket compression force and that proper 

mechanical alignment of closure contact surfaces is maintained. 

 (2) Two concepts are commonly used for personnel entrances: conventional HEMP/radio 

frequency interference (RFI) shielded doors and personnel tunnels that act as waveguides below cutoff. 

The shielded doors generally use metal fingerstock or EMI/RFI gaskets to provide an EM seal around the 

door jamb periphery. Currently available gasket and fingerstock doors require regularly scheduled 

maintenance and/or replacement to maintain required shielding levels. The gaskets are relatively easily 

damaged and also require replacement. Air-expandable doors may also be used, although they typically 

have more maintenance problems. These doors generally use a movable subassembly of two shielding 

plates on a framework that is moved on rollers in and out of a steel-framed opening. When closed, air 

expansion tubes cause the two shielding plates to make uniform surface contact with the frame inner 

surfaces. 

e. Electrical penetrations. A common feature for electrical penetrations in a global protection 

approach is a cable entry vault to prevent large currents on external conductors from being conducted into 

the facility. Ideally, all penetrations should enter a single vault. In some cases, however, it may be 

necessary to separate the vault into two compartments or to use two vaults for penetrations by different 

types of lines: power, signal and control, and antenna. The vault must be connected directly to the 
TM 5-692-2 

25-6 

external facility ground system. Conductive penetrations, such as a conduit, waveguide, or shielded 

cable, must have a circumferential weld or other means of providing good electrical connection at the 

intersection with the entry vault. The cable entry vault serves three purposes: 

 (1) To insure that penetrating conductors do not cause conducted HEMP energy to enter the 

protected topology. 

 (2) To contain and divert penetrator-conducted HEMP energy to the boundary exterior. 

 (3) To contain or divert radiant EM energy resulting from the activation of transient suppression 

devices subjected to a conducted pulse. 

f. Transient suppression devices and filters. Transient suppression devices fill a critical gap in the 

concept of topological protection. The necessity of supplying power to a facility and of communicating 

over cables or antennas are two major factors contributing to their use. Power lines entering a facility are 

typically connected to an unshielded power grid so that large, conducted currents must be bled off to 

prevent their entry into a facility. These currents are diverted to the exterior boundary of the topology. 

This boundary can be an overall external shield or an enclosed entrance vault. Antennas, such as for 

high-frequency (HF) communications, are designed to gather EM signals (at wavelengths in the HEMP 

frequency spectrum) and to apply these signals to the center conductor of a shielded cable. The HEMP 

transients associated with an HF antenna can be, by far, the largest single signal entering a facility. 

Transient suppressors often are used in conjunction with filters. Filters are frequency-selective whereas 

surge suppressors are amplitude-selective. Filters often are used to attenuate transients associated with 

the non-linear operation of surge arresters. They also are used for selectively passing (or stopping) 

frequency bands as in the case of antenna cable penetrations. Transient suppressors are an integral part of 

the EM topology, demanding specific installation techniques as will be seen later. A spark gap is a surge 

suppressor that provides a conducting path to ground when the voltage across the device exceeds the gap 

breakdown level. Spark gaps with a high current capacity do not operate quickly enough to block all 

HEMP energy transients entering the vault. For this reason, it may be necessary to use other protection 

devices in conjunction with the spark gap. 

g. Electromagnetic isolation. The EM isolation concept involves the use of elements either immune 

to interaction with EM radiation or which provide a current path interruption. Optical fibers are examples 

of elements immune to EM radiation that can be used to reduce the number of conductive penetrations. 

For practical purposes, optical fibers can be used for long communications links without signal 

interference from HEMP. Further, they can be used to enter shielded zones through waveguide below 

cutoff penetrations without compromising the EM shielding effectiveness. 

 h. Dielectric isolation. Other isolation techniques include using dielectric isolators for shield 

penetration when external metallic EM energy collectors are involved. Examples are control rods or 

cables (normally metallic), piping systems for fluids, and metallic duct systems for air. Dielectric 

sections are installed at or near the shield to prevent the energy induced on the external metallic part from 

being conducted through the shield. Dielectric control rods can enter through a shield in the same way as 

optical fibers, that is, through a waveguide-below-cutoff section. 

i. Isolation switching. Although not recommended now, isolation switching has been provided at 

facilities so they can use commercial electric power during routine operation, but can switch to internal 

generators or power systems in the event of an emergency such as nuclear attack. Since the commercial 

power wiring is a source of significant HEMP energy injection through a shield, switching to internally 
TM 5-692-2 

25-7 

generated power is an obvious advantage when advance warning of impending nuclear attack is received 

and throughout the entire nuclear attack cycle. This concept applies to communications lines and control 

lines as well as power lines. Switching used in past facility designs has been called “alert attack” 

switching. Such switching must provide adequate switch contact separation to prevent arcing, and must 

be designed to reduce coupling interactions between wiring and switch contacts to acceptable levels. 
TM 5-692-2 

26-1 

CHAPTER 26 

TEMPEST PROTECTION SYSTEMS 

 

26-1. General TEMPEST protection systems 

This chapter addresses systems constructed to prevent adversaries acquiring compromising information 

from facilities containing classified information. Facilities house equipment that are sources of 

electromagnetic (EM) waves and stray currents/voltages with characteristics which are related to the 

information content of the signals being processed. If these unintentional emissions are intercepted and 

studied, the analyst can reconstruct the original data and can obtain access to classified national security 

information. TEMPEST (military code-name) protection systems will, preclude the presence of 

analyzable signals in uncontrolled areas by controlling EM energy and, thus, provide communication 

security. 

a. Scope. TEMPEST is a U. S. Department of Defense program to develop methods of preventing the 

compromise of government and military information. This is accomplished by reducing or eliminating 

unintended electric or EM radiation emanations from electronic equipment. The present approach focuses 

on "threat-based systems approach" in an effort to reduce the high cost of TEMPEST efforts. Emission 

Security (EMSEC) is another term that has found favor and covers all emanations with potential to 

compromise national security information and the measures employed to prevent unauthorized disclosure. 

b. Objectives. The TEMPEST problem is nearly the inverse of the High-Altitude Electromagnetic 

Pulse (HEMP) event. TEMPEST is the unclassified name for the studies and investigation of 

compromising emanations. Equipment within the facility can be the source of EM waves and stray 

currents/voltages with characteristics that are related to the information content of signals being 

processed. Thus, HEMP and TEMPEST protective measures must each control EM energy, the former 

protecting system equipment from externally generated signals and the latter containing emissions from 

internal sources. The functional similarities imply that a common treatment can be employed for the two 

purposes. 

26-2. Sources 

Compromising emanations may be generated by any electrical information processing equipment. Some 

of them are microchips, computers, monitors, printers, and electronic typewriters. These emanations can 

be propagated through space, over telephone lines, power lines, water pipes, grounding wires, ducts, 

drains, and conduits. 

26-3. Acquisition 

Using specialized antennae, low noise pre-amps, filters, and top end receivers with computer interfaces it 

is possible to access sensitive information for immediate interpretation or analysis later. Unclassified 

estimates place interception ranges at one km. 
TM 5-692-2 

26-2 

26-4. Protection 

To mitigate or eliminate compromises in security, several techniques are used. 

a. Evaluation. TEMPEST measures shall be weighted based on the sensitivity of information, the 

amount of classified information, and the probability of facility becoming an intercept target. 

b. Personnel control. Equipment must be kept physically secure by providing physical controls to 

prevent, delay, and detect unauthorized access to the central computer facility, internal controlled areas, 

peripheral devices, remote terminals, and storage media. In many cases, the physical controls consist of 

determining what personnel may enter or leave a given site, and what equipment must be kept under 

controlled circumstances. The current emphasis in military systems is on dedicated computer systems. 

c. Compartmentalization. TEMPEST protection requires that information under one classification 

and compartment be isolated from other classifications and compartments. The separation requirements 

are based on “Equipment Radiation Transmission Zone (ERTZ).” Emanations are allowed within the 

ERTZ as determined by engineering estimates, ambient noise levels (masking), facility construction, and 

distance from source. 

d. Physical controls. It is a requirement that electronic equipment used for classified processing be 

shielded or designed to reduce or eliminate transient emanations. 

 (1) One method is to shield the area in which the information is processed so as to contain EM 

emanations or to specify control of certain distances or zones beyond which the emanations cannot be 

detected. In many cases, facilities are required to be kept within complete metal enclosures to prevent 

EM leakages, and vacuum seals to prevent sonic leakages. High noise environments are sometimes 

artificially generated to make the detection of signals very difficult. Shielding can also be applied to 

equipment cabinets and chassis via radio frequency interference (RFI) seals and honeycomb filter doors. 

 (2) Unless the wiring (telephone lines, electrical wiring, network cables, etc.), is shielded the other 

shielding methods discussed will not stop emanations from leaking to the outside world. All conductors 

must be isolated at the point of egression, including drains, pipes, ducts, cable trays, and conduits. 

 (3) Separating classified and unclassified equipment transmission paths can eliminate this form of 

cross cable leakage. Power lines for classified equipment must be isolated. 

 (4) EM signal strength can be minimized by filtering signals on the electrical leads. This is 

accomplished by using ferrites and optically coupled filters. Power lines for classified equipment must be 

filtered. 

(5) Station earth ground point must not be shared by any other facility. Classified equipment must 

be properly grounded. 
TM 5-692-2 

27-1 

CHAPTER 27 

GROUNDING SYSTEMS 

27-1. General grounding systems 

Reasons for grounding include human and equipment safety, effective lightning protection, diminishing 

electromagnetic coupling (EMC), and protection against electromagnetic pulses (EMP). Grounding 

practices and stipulations are well defined in documents published by the Institute of Electrical and 

Electronics Engineers, Inc. (IEEE), American National Standards Institute (ANSI), National Fire 

Protection Association (NFPA), and U.S. Department of Defense (DoD). Grounding is provided to limit 

potential (voltage) differences to values that will not cause undue hazards to personnel and equipment. A 

ground system that provides adequate current-carrying capacity and a low resistance path to an earthing 

connection will dissipate, isolate, or disconnect overpotential areas resulting from fault overcurrents or 

surge overvoltages. A ground path can consist of single or multiple conductors whose connection 

provides adequate thermal and conductance capacities. The earthing connection is generally a metallic 

electrode such as a rod, a water pipe, a counterpoise, or a ground grid system installed below grade. 

27-2 Types of grounding 

Electrical power distribution systems can be either ungrounded, solidly grounded, or resistance grounded. 

 

 a. Ungrounded system. An ungrounded system is one in which there is no intentional connection 

between the neutral or any phase and ground. Ungrounded system implies that the system is capacitively 

coupled to ground. The neutral potential of an ungrounded system under reasonably balanced load 

conditions will be close to ground potential because of the capacitance between each phase conductor and 

ground. When a line-to-ground fault occurs on an ungrounded system, the total ground fault current is 

relatively small, but the voltages to ground potential on the unfaulted phases will be high. If the fault is 

sustained, the normal line-to-neutral voltage on the unfaulted phases is increased to the system line-to-line 

voltage (i.e. square root of three times the normal line-to-neutral value). This, over a period of time, 

breaks down the line-to-neutral insulation and hence results in insulation failure. Ungrounded system 

operation is not recommended because of the high probability of failures due to transient overvoltages 

caused by restriking ground faults. The remaining various grounding methods can be applied on system 

grounding protection depending on technical and economic factors. The one advantage of an ungrounded 

system that needs to be mentioned is that it generally can continue to operate under a single line-toground fault without an interruption of power to the loads. 

b. Solidly grounded system. A solidly grounded system is one in which the neutral (or occasionally 

one phase) is connected to ground without an intentional intervening impedance. On a solidly grounded 

system, in contrast to an ungrounded system, a ground fault on one phase will result in a large magnitude 

of ground current to flow, but there will be no increase in voltage on the unfaulted phase. Solid 

grounding is commonly used in low voltage distribution systems. Solid grounding has the lowest initial 

cost of all grounding methods. It is usually recommended for overhead distribution systems supplying 

transformers protected by primary fuses. However, it is not the preferred scheme for most industrial and 

commercial systems, again because of the severe damage potential of high magnitude ground fault 

currents. 
TM 5-692-1 

27-2 

 c. Resistance grounded system. Limiting the available ground fault current by resistance grounding is 

an excellent way to reduce damage to equipment during ground fault conditions, and to eliminate 

personal hazards and electrical fire dangers. It also limits transient overvoltages during ground fault 

conditions. The resistor can limit the ground fault current to a desired level based on relaying needs. At 

the occurrence of a line-to-ground fault on a resistance grounded system, a voltage appears across the 

resistor that nearly equals the normal line-to-neutral voltage of the system. The resistor current is 

essentially equal to the current in the fault. Therefore, the current is practically equal to the line-toneutral voltage divided by the number of ohms of resistance used. The grounding resistances are rated in 

terms of current and its duration for different voltage classes. 

 (1) Low resistance grounding refers to a system in which the neutral is grounded through a small 

resistance that limits ground fault current magnitudes. The size of the grounding resistor is selected to 

detect and clear the faulted circuit. Low resistance grounding is not recommended on low voltage 

systems. This is primarily because the limited available ground fault current is insufficient to positively 

operate series trip units and fuses. These trip units and fuses would be dependent upon both phase-tophase and phase-to-ground fault protection on some or all of the distribution circuits. Low resistance 

grounding normally limits the ground fault currents to approximately 100-600A (amperes). The amount 

of current necessary for selective relaying determines the value of resistance to be used. 

 (2) High resistance grounding refers to a system in which the neutral is grounded through 

predominantly resistive impedance whose resistance is selected to allow a ground fault current through 

the resistor equal to or slightly more than the capacitive charging current of the system. Because 

grounding through a high resistance entails having a physically large resistance that is both bulky and 

costly, high resistance grounding is not practical and is not recommended. However, high resistance 

grounding through a grounding transformer is cost effective and accomplishes the same objective. High 

resistance grounding accomplishes the advantage of ungrounded and solidly grounded systems and 

eliminates the disadvantages. It limits transient overvoltages resulting from a single phase-to-ground fault 

by limiting ground fault current to approximately 8A. This amount of ground fault current is not enough 

to activate series overcurrent protective devices; hence no loss of power to downstream loads will occur 

during ground fault conditions. Special relaying must be used on high resistance grounded systems in 

order to sense that a ground fault has occurred. The fault should then be located and removed as soon as 

possible so that if another ground fault occurs on either of the two unfaulted phases, high magnitude 

ground fault currents and resulting equipment damage will not occur. High resistance grounding is 

normally applied in situations where it is essential to prevent unplanned system power outages, or 

previously the system has been operated ungrounded and no ground relaying has been installed. Once the 

ground point has been established through the resistor, it is easier to apply protective relays. The user 

may decide to add a ground overcurrent relay. The relay may be either current actuated using a current 

transformer or voltage actuated using a potential transformer. Depending on the priority of need, high 

resistance grounding can be designed to alarm only or provide direct tripping of generators off line in 

order to prevent fault escalation prior to fault locating and removal. High resistance grounding (arranged 

to alarm only) has proven to be a viable grounding mode for 600V systems with an inherent total system 

charging current to ground of about 5.5A or less, resulting in a ground fault current of about 8A or less. 

This, however, should not be construed to mean that ground faults of a magnitude below this level will 

always allow the successful location and isolation before escalation occurs. Here, the quality and the 

responsiveness of the plant operators to locate and isolate a ground fault is of vital importance. To avoid 

high transient overvoltages, suppress harmonics and allow adequate relaying, the grounding transformer 

and resistor combination is selected to allow current to flow that equals or is greater than the capacitive 

changing current. 
TM 5-692-2 

27-3 

27-3. Grounding systems 

Basically six types of grounding systems are used. They are static grounds, equipment grounds, system 

grounds, lightning grounds, electronic (including computer) grounds, and maintenance safety grounds. 

All of these systems are installed similarly. However, their purposes are quite different. Some of the 

systems carry little or no current. Others carry small to moderate currents at 50 or 60 Hz. Still others 

must be able to carry currents over a very broad range of frequencies in order to be considered effective. 

 a. Static grounds. A static ground is a connection made between a piece of equipment and the earth 

for the purpose of draining off static electricity charges before a spark-over potential is reached. The 

ground is applied for more than just the comfort of the equipment operator. The possibility of an 

explosion ignited by an electrical spark must be considered. Dry materials handling equipment, 

flammable liquids pumps and delivery equipment, plastic piping systems, and explosive storage areas all 

need static ground protection systems installed and functioning properly. Static ground systems are 

generally not called upon to conduct much current at any given frequency. Smaller gauge, bare 

conductors, or brushes with metallic or conductive bristles make up most parts of the static ground 

system. 

 b. Equipment grounds. An equipment ground pertains to the interconnection and connection to earth 

of all normally non-current carrying metal parts. This is done so the metal parts with which a person 

might come into contact are always at or near zero volts with respect to ground thereby protecting 

personnel from electric shock hazards. Equipment grounding consists of grounding all non-current 

carrying metal frames, supports, and enclosures of equipment. All these metallic parts must be 

interconnected and grounded by a conductor in such a way as to ensure a path of lowest impedance for 

the flow of ground fault current from any line to ground fault point to the terminal at the system’s source. 

An equipment grounding conductor normally carries no current unless there is an insulation failure. In 

this case the fault current will flow back to the system source through the equipment grounding 

conductors to protect personnel from electrical shock. The equipment grounding conductor must never be 

connected to any other hot lines. Equipment grounding systems must be capable of carrying the 

maximum ground fault current expected without overheating or posing an explosion hazard. Equipment 

grounds may be called upon to conduct hundreds to thousands of amperes at the line frequency during 

abnormal conditions. The system must be sized and designed to keep the equipment surface voltages, 

developed during such abnormal conditions, very low. An example of this system is the bare copper wire 

(green conductor) connected to the frames of electric motors, breaker panels, outlet boxes, etc. Electrical 

supporting structures such as metal conduit, metal cable trays, or metal enclosures should be electrically 

continuous and bonded to the protective grounding scheme. Continuous grounding conductors such as a 

metallic raceway or conduit or designated ground wires should always be installed from the ground grid 

system to downstream distribution switchboards to ensure adequate grounding throughout the electrical 

distribution system. Part of the equipment ground is also formed by the switchgear ground bus. 

 c. System grounds. A system ground refers to the condition of having one wire or point of an 

electrical circuit connected to earth. This connection point is usually made at the electrical neutral 

although not always. The purpose of a system ground is to protect the equipment. This ensures longer 

insulation life of motors, transformers, and other system components. A system ground also provides a 

low impedance path for fault currents improving ground fault relaying selectivity. In a properly grounded 

system the secondary neutral of a power transformer supplying a building or facility is connected to a 

transformer grounding electrode. The transformer neutral is a part of the service entrance point that 

bonds to the grounding electrode system of the building. According to the National Electrical Code 
TM 5-692-1 

27-4 

(NEC), NFPA 70, articles 250-81 and 250-83, metal underground water pipes, metal building frames, 

encased electrodes, rods, and plates are among the items that can make up the grounding electrode system 

of a building. The NEC article 250-83 requires that the size of the grounding electrode iron or steel rod 

must be at least 5/8 inches in diameter and driven eight feet deep. The resistance of the electrode to 

ground cannot exceed 25 ohms (NEC 250-84). Otherwise a second electrode should be added, and the 

distance between the two electrodes must be at least six feet. However, in some systems the 25 ohms 

resistance value cannot achieve the goals of grounding. They require ground resistance values below ten 

ohms. If the main building load is composed of computers or sensitive electronic equipment, the earth 

ground resistance should not exceed five ohms. There are many methods of system grounding used in 

industrial and commercial power systems, the major ones being ungrounded, solid grounding, and low 

and high resistance grounding. Factors which influence the choice of selection include voltage level of the 

power system, transient overvoltage possibilities, types of equipment on the system, cost of equipment, 

required continuity of service, quality of system operating personnel, and safety consideration including 

fire hazards. 

d. Lightning protection. Main lightning protection grounding requirements are dependent upon the 

structure, component, or system to be protected. See chapter 30 for detailed discussion of lightning 

protection systems. 

e. Electronic and computer grounds. Grounding for all electronic systems, including computers and 

computer networks, is a special case of the equipment ground and the system ground carefully applied. In 

fact, grounding systems for electronic equipment are generally the same as for system ground with an 

additional requirement: the degree of performance required. Electronic equipment grounding systems 

must not only provide a means of stabilizing input power system voltage levels, but also act as the zero 

voltage reference point. However, the need to do so is not restricted to a low frequency of a few hundred 

hertz. Grounding systems for modern electronic installations must be able to provide effective grounding 

and bonding functions well into the high frequency megahertz range. Effective grounding at 50-60 Hz 

may not be effective at all for frequencies above 100 kilohertz. There are several aspects to the 

requirement for good grounding performance for electronic equipment, all of which are due to electrical 

circuit behavior. Good electronic system grounding performance is achieved with a properly laid out 

distribution of multipoint, well bonded grounding connections. This system can use bare, braided, sheet, 

or stranded copper conductors for grounding or bonding functions. This system requires conduit and 

equipment enclosure bonding at all junction points. In other words, simple metallic contact between the 

enclosures, wiring conduits, and power panels is not enough. The multipoint bonding provides low 

impedance grounding for the electronic equipment. The low impedance between the separate items of 

electronic equipment keeps the noise voltages at or near zero between them and, therefore, provides an 

“equipotential plane”. This system is much easier to inspect and test. No special requirements must be 

met during modifications or expansion of the electrical system. All power panels and all supply 

transformers feeding an installation with this type of grounding system must be grouped and bonded 

together using short lengths of bare, braided, sheet, or stranded copper conductors in order to achieve the 

effective high frequency grounding performance described above. A single area of power entry with a 

large equipotential ground plane and short equipment grounding conductors forms the preferred 

grounding system for large automated data processing (ADP) and computer applications. 

 f. Maintenance safety grounds. Grounds used for maintenance work are usually intentional, but 

temporary, connections between equipment power conductors and ground. These connections are always 

applied after the power source has been turned off and the circuit(s) have been tested and are known to be 

de-energized. The ground is intended to protect maintenance personnel from an inadvertent reenergization of the circuit. The ground is removed after maintenance operations have been completed. 
TM 5-692-2 

27-5 

27-4. Ground system materials and testing requirements 

Several factors can degrade initial good grounds. These factors indicate the importance of continuous 

periodic testing of grounding systems. For example, water tab1es are gradually falling in many areas. 

Also, there are more underground installations of non-metallic pipes and conduits which do not provide 

low resistance ground connections. There are electric systems that are continually expanding with an 

associated fault current increase which may require a decrease in grounding resistance. And there are 

corroded connections that may increase the resistance of the ground system. 

 a. Testing. Periodic testing should be done to assure grounding system effectiveness. The following 

are points that should be addressed during inspection and maintenance: 

 (1) Inspect and test single point, isolated ground systems after every electrical system 

modification. Visually inspect outlets and panels for conductors forming loops between the equipment 

ground and the isolated ground. 

 (2) Test the ground to neutral voltage at each power distribution panel included in the particular 

system. The voltage should be taken using a high impedance AC voltmeter and an accurate record should 

be kept. The voltage should be very low; on the order of 10-150 millivolts (0.01-0.150V). Any sudden 

changes or increasing trends should be investigated and the cause corrected. 

 (3) The made electrode, rod, plate, or selected ground body contact point should be tested every 

12-24 months. A record should be kept. Any increasing impedance indicates a need for remedial action. 

b. Piping systems. The ground grid of the plant should be the primary system. In some cases a 

metallic underground water piping system may be used in lieu of a plant ground grid, provided adequate 

galvanic and stray current corrosion protection for the piping is installed, used, and tested periodically. 

This practice is not acceptable in hazardous areas and is not recommended if the piping system becomes 

sacrificial. 

c. Resistance goals. The plant ground grid should have a system resistance of ten ohms or less. 

Ground grid system resistance may be decreased by driving multiple ground electrode rods. A few rods, 

deeply driven and widely spaced, are more effective than a large number of short, closely spaced rods. 

Solid hard copper rods should be used, not copper plated steel. When low resistance soils are deep, the 

surface extension rods may be used to reach the low resistance stratum. Bonding of ground conductors to 

rods should be by permanent exothermic weld (preferred) or compression sleeve, and not by bolted clamp 

(corrosion results in high resistance connection). Resistance at each rod in a multiple system should not 

exceed 15 ohms. 

d. Ground rods. Grounding electrodes (driven into the earth) maintain ground potential on all 

connected conductors. This is used to dissipate (into the earth) currents conducted to the electrodes. The 

resistance of a ground electrode is primarily determined by the earth surrounding the electrode. Test data 

given in IEEE 142, IEEE Recommended Practice for Grounding of Industrial and Commercial Power 

Systems (1991), indicate that about 90 percent of the total resistance of a ground lies within six to ten feet 

(1.8 to 3 meters) from the electrode. The diameter of the rod has only a negligible effect on the resistance 

of a ground. The resistance of the soil is dependent upon the type of soil and its moisture content. 

Electrodes should be long enough to penetrate a relatively permanent moisture level and should extend 

well below the frost line.
TM 5-692-1 

27-6 
TM 5-692-2 

28-1 

CHAPTER 28 

LIGHTNING PROTECTION 

 

28-1. General lightning protection systems

Lightning protection is essential for the protection of humans, structures, contents within structures, 

transmission lines, and electrical equipment from thermal, mechanical, and electrical effects caused by 

lightning discharges. Lightning cannot be prevented, but it can with some success be intercepted, and its 

current can be conducted to a grounding system without side flashes where it is harmlessly dissipated. 

28-2. Lightning effects on power systems 

Lightning surges entering a power system through direct strokes are the primary concern in planning 

surge protection. These strokes may hit phase conductors directly, or they may strike the overhead 

ground wires or masts that shield the conductors. In either case, it is necessary to understand the 

associated surge currents and voltages produced before a protection system can be designed. 

 a. Flashover. A lightning stroke terminating directly on phase conductors or equipment terminals 

develops a very high voltage, which, with no surge protection, will flash over the insulation in the 

majority of cases. If the flashover occurs through air or across porcelain insulation, it rarely causes 

permanent damage. If, on the other hand, the flashover occurs through solid insulation such as in a 

transformer or cable, permanent damage results. 

b. Shielding. The magnitude of surge voltages applied to equipment and line insulation systems can 

be limited by providing grounding masts or ground wires to intercept direct strokes. Even with a 

shielding network, though, there is some chance of flashover, depending on stroke current magnitude, 

impedance of the shielding system, and the amount of insulation between the network and the energized 

circuits. 

c. Induced surges. A lightning stroke terminating near a transmission line can induce a voltage in the 

circuit that seldom exceeds 500 kV. Lines, shielded with overhead ground wires and operating at 69 kV 

and above, generally have sufficient insulation to prevent flashover by voltages in this range. The same 

applies to some well insulated 34.5 kV lines. Lower voltage lines, however, with insulation levels 

appreciably below 500 kV, may be flashed over by induced surges. In most cases, these circuits do not 

have ground wires, and are, therefore, subject to flashover each time they are contacted by a direct stroke. 

 In general, flashovers by induced surges do not create a significant problem since the number of 

flashovers from direct strokes far exceeds those from induced strokes. 

d. Traveling waves. A lightning stroke terminating on a power system initiates traveling waves that 

propagate within the system. To determine the resulting surge voltages and currents in various parts of 

the system, a traveling wave analysis is required. Simple networks with linear impedances can be 

analyzed manually; more complicated networks, characteristic of practical power systems, require analog 

or digital computer analysis. 

e. Surge voltages. In protecting power systems against lightning, surge voltages and currents must be 

considered. In general, lightning protection is primarily concerned with surge voltages; surge currents 
TM 5-692-2 

28-2 

cause less concern. A lightning stroke to a power system develops very high surge voltages across 

equipment and line insulation systems. If these voltages exceed the insulation strength, a flashover 

occurs. Once lightning enters a power system, the surge current is unlikely to cause any damage. 

Although the current may be extremely high, it is very short lived and can easily be handled by a small 

conductor. The largest recorded conductor to be fused or vaporized by a direct stroke was an American 

Wire Gage (AWG) No. 10. The size of conductors, installed expressly for conducting lightning currents, 

is usually determined by mechanical strength considerations, rather than by current-carrying capacity. On 

some rare occasions, overhead ground wires have been severed by lightning at the point of contact. This 

is probably due to the stroke channel heating the conductor at the point of impingement, rather than from 

simply conducting the lightning current. 

28-3 Principles of protection 

Main lightning protection requirements are dependent upon the structure, component, or system to be 

protected. According to National Fire Protection Association (NFPA) 780, Standard for Installation of 

Lightning Protection Systems (1997), there are two classifications for a building. Class I is a building 

with less than 75 feet height. The Class II building is higher than 75 feet or has a steel frame with any 

height. 

a. Shielding. Shielding masts are commonly used in substations, and overhead ground wires are used 

in both substations and on transmission lines. Both use the lightning rod principle. The voltage at the top 

of the mast is significantly less than the 2,000 kV that would be developed for the same stroke on a 

conductor. Grounded masts and grounded wires, then, offer an important reduction in the magnitude of 

surge voltages. 

b. Arresters. Even with an effective shielding system, the surge voltages must be limited to 

magnitudes consistent with practical and economical equipment insulation levels to allow for voltages 

developed by strokes to the shielding network. On rare occasions, strokes may also bypass the shielding 

system and terminate directly on the energized circuits. For these situations, an arrester is used to control 

and limit surge voltages to a safe level. The arrester, applied on or near the terminals of the protected 

equipment, is connected from phase to ground. Under normal operating conditions, the arrester has no 

effect on the power system. Under surge conditions, the arrester will spark over and conduct the surge 

current to ground, limiting the voltage applied to the equipment insulation to a safe level. After 

conducting the surge current to ground, the arrester will interrupt the power-follow current and restore 

itself to its normal operating conditions. There are two general types of arrester designs: valve type and 

expulsion type. The valve type has one or more sets of spark gaps (series connected) which establish 

spark-over voltage, interrupt the flow of current, and prevent high current flow. The expulsion type has 

an arc-extinguishing chamber in series with the gaps to interrupt the power frequency current that flows 

after the gaps have been sparked over. Design refinements include using oxide film coated components 

and sealing the inner components in a chamber filled with an inert gas. Aluminum cells are used in some 

units. 

 c. Air terminals. Air terminals are used to intercept lightning discharges above facilities. Air 

terminals will be in accordance with Underwriters Laboratories, Inc. (UL) 96, UL Standard for Safety 

Lightning Protection Components, Fourth Edition (2000), and 96A, UL Standard for Safety Installation 

Requirements for Lightning Protection Systems, Tenth Edition (1998), NFPA 780, or MIL–HDBK-419A, 

Grounding, Bonding, and Shielding. Where building roof is not metal and building construction includes 

steel framing, air terminal connection assemblies are required. 
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28-3 

 d. Grounding. Grounding generally will conform to NFPA 780, unless otherwise specified. 

Guidance for grounding for purposes such as electromagnetic pulse (EMP), electromagnetic interference 

(EMI) shielding, and electronic facility grounding, are subjects of other engineering manuals that govern 

grounding requirements. Those grounding systems will also serve as grounding of the lightning 

protection system. Where separate systems are installed, such systems will be bonded below grade to any 

other independently installed exterior grounding system such as for EM shielding not suitable for 

complete lightning protection system. However, exterior protection grounding system will be bonded to 

static electricity exterior grounding system. 

e. Ground rods. Ground rods are generally not less than ten feet in length, nor less than 3⁄4-inch 

diameter pipe or equivalent solid rod. Rods are driven so that tops are at least six inches below finished 

grade, and three to eight feet beyond perimeter of building foundation. Where ground rods are used with 

a counterpoise, tops are driven to same elevation as counterpoise below finished grade. Contact with 

chemically injurious wastewater or other corrosive soils is avoided. Where avoidance of chemically 

injurious or corrosive soils is impracticable, stainless steel rod and magnesium anode protection is used. 

Where buried metal pipes enter a building, the nearest ground rod will be connected thereto. 

f. Counterpoise. Each earth electrode subsystem or counterpoise consists of one or more closed loops 

or a grid arrangement of No. 1/0 AWG bare copper conductors installed around facility perimeter not less 

than two feet below earth surface. Larger conductors should be used when installed in highly corrosive 

soils. A second loop, if used, should not be less than ten feet beyond the first and inner loop. At least two 

ground rods are provided at each corner of each counterpoise loop where earth-seeking current tend to 

concentrate. Counterpoise will extend not less than three feet nor more than eight feet beyond the 

perimeter of building walls or footings. 

 g. Radial systems. A radial system of grounding consists of one or more No. 1/0 AWG copper 

conductors not less than 12 feet long, extending away from each ground rod or grounding connection. 

The use of multiple radials is an effective form of grounding, offering substantially lower reactance to the 

high frequency of lightning current wave fronts than do single straight conductors. Installation of 

grounding radials takes advantage of crags and cracks in surface rock formations in obtaining maximum 

available earth cover. 

h. Structural components. Lightning protection is provided on the outside of exterior surfaces without 

reliance upon components of the building for conductors. Reinforcement steel may be used for down 

conductors in conformance with NFPA 780 and if approved by the using agency. Joints are made in no 

fewer than every fifth reinforcement rod and at corners of buildings. Joints are made electrically 

conductive and are connected top and bottom for connections to roof conductors and to grounding 

electrodes, respectively. Grounding pigtails from bottoms of reinforcement fabric are connected to 

exterior grounding system at same or lower elevation as that where pigtails leave walls and footings. 

28-4. Lightning protection systems equipment requirements 

All system components are made of copper, anodized aluminum, or stainless steel. Standard down 

conductors are usually large bare copper or aluminum stranded conductors that are constructed 

particularly for the lightning protection industry. A recent advancement is a coaxial cable that reduces the 

surge impedance as well as flashover. However, this cable is more costly than the conventional 

conductors. Interconnecting conductors are as important as other components. Tests in high-voltage 

laboratories demonstrate that a steep voltage wave front, such as created by lightning, causes the surge 

impedance in conventional conductors to increase to the point that side flashes occur. Installation of 
TM 5-692-2 

28-4 

multiple grounding conductors for buildings and a roof grid system creating a faraday cage reduces the 

magnitude of current flow in any one conductor. However, side flashes can still occur. 
TM 5-692-2 

29-1 

CHAPTER 29 

CATHODIC PROTECTION 

 

 29-1. General cathodic protection systems 

Cathodic protection is a system utilized to inhibit corrosion of structures, such as underground pipes, 

tanks, etc. Corrosion is an electrochemical process in which a current leaves a structure at the anode site, 

passes through an electrolyte, and reenters the structure at the cathode site. For example, because it is in a 

soil with low resistivity compared to the rest of the line, current would leave the pipeline at that anode 

site, pass through the soil, and reenter the pipeline at a cathode site. Current flows because of a potential 

difference between the anode and cathode. The anode potential is more negative than the cathode 

potential, and this difference is the driving force for the corrosion current. The total system – anode, 

cathode, electrolyte, and metallic connection between anode and cathode is termed a corrosion cell. 

For corrosion to occur, the following conditions are required. 

a. Electrodes. An anode and cathode must be present. 

b. Electrical potential. An electrical potential between the anode and cathode must be present. 

Several conditions may cause this potential. 

c. Conductive path. A metallic conductive path electrically connecting the anode and cathode must 

exist. In the case of a metallic pipeline, the pipe itself is this conductive path. 

d. Electrolyte. The anode and cathode are immersed in an electrically conductive electrolyte that is 

ionized. Usual soil moisture or water fulfills this condition. 

e. Current. When these conditions exist, an electric current will flow, and where the current leaves a 

metallic object, metals will be consumed. Cathodic protection reverses the current flow by installing 

ground beds of sacrificial anodes. No longer does the current leave the structure. Now the structure 

receives current flow, inhibiting corrosion. The structure is the cathode, and thus, the term cathodic 

protection. 

29-2. Types of cathodic protection systems 

Cathodic protection is a method to reduce corrosion by minimizing the difference in potential between 

anode and cathode. This is achieved by applying a current to the structure to be protected (such as a 

pipeline) from some outside source. When enough current is applied, the whole structure will be at one 

potential; thus, anode and cathode sites will not exist. Cathodic protection is commonly used on many 

types of structures, such as pipelines, underground storage tanks, locks, and ship hulls. There are two 

main types of cathodic protection systems: galvanic and impressed current. 

a. Galvanic systems. A galvanic cathodic protection system makes use of the corrosive potentials for 

different metals. Without cathodic protection, one area of the structure exists at a more negative potential 

than another, and corrosion results. If, however, a much less inert object (that is, with much more 

negative potential, such as magnesium anode) is placed adjacent to the structure to be protected, such as a 

pipeline; and a metallic connection (insulated wire) is installed between the object and the structure, the 
TM 5-692-2 

29-2 

object will become the anode and the entire structure will become the cathode. That is, the new object 

corrodes sacrificially to protect the structure. Thus, the galvanic cathodic protection system is called a 

“sacrificial anode cathodic protection system” because the anode corrodes sacrificially to protect the 

structure. Galvanic anodes are usually made of either magnesium or zinc because of these metals higher 

potential compared to steel structures. 

b. Impressed current systems. Impressed current cathodic protection systems use the same elements 

as the galvanic protection system, only the structure is protected by applying a current to it from an 

anode. The anode and the structure are connected by an insulated wire, as for the galvanic system. 

Current flows from the anode through the electrolyte onto the structure, just as in the galvanic system. 

The main difference between galvanic and an impressed current system is that the galvanic system relies 

on the difference in potential between the anode and structure, whereas the impressed current system uses 

an external power source to drive the current. The external power source is usually a rectifier that 

changes input alternating current (AC) power to the proper direct current (DC) power level. The rectifier 

can be adjusted, so that proper output can be maintained during the system’s life. Impressed current 

cathodic protection system anodes typically are high-silicon cast iron or graphite. 

29-3 . Application of cathodic protection 

Before deciding which type, galvanic or impressed current, cathodic protection system will be used and 

before the system is designed, certain preliminary data must be gathered. 

 a. Dimensions. One important element in designing a cathodic protection system is the structure's 

physical dimensions (for example, length, width, height, and diameter). These data are used to calculate 

the surface area to be protected. 

 b. Layout. The installation drawings must include sizes, shapes, material type, and locations of parts 

of the structure to be protected. 

 c. Insulators. If a structure is to be protected by the cathodic system, it must be electrically connected 

to the anode. Sometimes parts of a structure or system are electrically isolated from each other by 

insulators. For example, in a gas pipeline distribution system, the inlet pipe to each building might contain 

an electric insulator to isolate in-house piping from the pipeline. Also, an electrical insulator might be 

used at a valve along the pipeline to electrically isolate one section of the system from another. Since 

each electrically isolated part of a structure would need its own cathodic protection, the locations of these 

insulators must be determined. 

 d. Short circuits. All short circuits must be eliminated from existing and new cathodic protection 

systems. A short circuit can occur when one pipe system contacts another, causing interference with the 

cathodic protection system. When updating existing systems, eliminating short circuits would be a 

necessary first step. 

 e. Corrosion history. Studying the corrosion history in the area can prove very helpful when 

designing a cathodic protection system. The study should reinforce predictions for corrosivity of a given 

structure and its environment; in addition, it may reveal abnormal conditions not otherwise suspected. 

Facilities’ personnel can be a good source of information for corrosion history. 

 f. Electrolyte resistivity. A structure's corrosion rate is proportional to the electrolyte resistivity. 

Without cathodic protection, as electrolyte resistivity decreases, more current is allowed to flow from the 
TM 5-692-2 

29-3 

structure into the electrolyte; thus, the structure corrodes more rapidly. As electrolyte resistivity 

increases, the corrosion rate decreases. Resistivity can be measured either in a laboratory or at the site 

with the proper instruments. The resistivity data will be used to calculate the sizes of anodes and rectifier 

required in designing the cathodic protection system. 

 g. Electrolyte pH. Corrosion is also proportional to electrolyte pH (see glossary for definition of pH 

and other terms). In general, steel's corrosion rate increases as pH decreases when soil resistivity remains 

constant. For existing structures, the potential between the structure and the electrolyte will give a direct 

indication of the corrosivity. According to National Association of Corrosion Engineers (NACE) 

Standard RP-0169, Control of External Corrosion on Underground or Submerged Metallic Piping 

Systems (1996), the potential requirement for cathodic protection is a negative (cathodic) potential of at 

least 0.85 volt as measured between the structure and a saturated copper-copper sulfate reference 

electrode in contact with the electrolyte. A potential that is less negative than -0.85 volt would probably 

be corrosive, with corrosivity increasing as the negative value decreases (becomes more positive). 

h. Current density. A critical part of design calculations for cathodic protection systems on existing 

structures is the amount of current required per square foot (called “current density”) to change the 

structure’s potential to -0.85 volt. The current density required to shift the potential indicates the 

structure's surface condition. A well coated structure (for example, a pipeline well coated with coal-tar 

epoxy) will require a very low current density (about 0.05 milliampere per square foot); an uncoated 

structure would require high current density (about ten milliamperes per square foot). Current 

requirements can be calculated or estimated based on coating efficiency and current density (current per 

square foot) desired. The efficiency of the coating as supplied will have a direct effect on the total current 

requirement. Coating efficiency is directly affected by the type of coating used and by quality control 

during coating application. The importance of coating efficiency is evident in the fact that a bare 

structure may require 100,000 times as much current as would the same structure if it were well coated. 

Caution should be used when estimating, however, as underprotection or overprotection may result. A 

coating's resistance decreases greatly with age and directly affects structure-to-electrolyte resistance for 

design calculations. The coating manufacturers supply coating resistance values. 

 i. Verification of need. For existing structures, the current requirement survey will verify the need for 

a cathodic protection system. For new systems, standard practice is to assume a current density of at least 

two milliamperes per square foot of bare area will be needed to protect the structure. However, local 

corrosion history may demand a different current density. In addition, cathodic protection is mandatory 

for underground gas distribution lines (Department of Transportation regulations - Title 49, Code of 

Federal Regulations) and for water storage tanks with a 250,000-gallon capacity or greater. Cathodic 

protection also is required for underground piping systems located within ten feet of steel reinforced 

concrete because galvanic corrosion will occur between the steel rebar and the pipeline. 

29-4. Cathodic protection system design 

The process required to design a cathodic protection system is described below. 

a. Galvanic systems. Eight steps are required for applying a galvanic protection system. 

 (1) The site of lowest resistivity will likely be used for anode location to minimize anode-toelectrolyte resistivity. In addition, if resistivity variations are not significant, the average resistivity will 

be used for design calculations. 
TM 5-692-2 

29-4 

 (2) Galvanic anodes are usually either magnesium or zinc. Zinc anodes are used in extremely 

corrosive soil (resistivity below 2000 ohm- centimeters). Data from commercially available anodes must 

be reviewed. Each anode specification will include anode weight, anode dimensions, and package 

dimensions (anode plus backfill). In addition, the anode’s driving potential must be considered. 

 (3) The net driving potential for the anodes must be determined. 

 (4) Determine the number of anodes needed to meet groundbed resistance limitations. 

 (5) Determine the number of anodes for the system's life expectancy 

 (6) Select number of anodes to be used. 

 

 (7) Select ground bed layout. 

 (8) Determine the life-cycle cost for proposed design. 

b. Impressed current systems. Eleven steps are required for applying an impressed current protection 

system. 

 (1) Review soil resistivity. 

 (2) Review current requirement test. 

 (3) Select anode. 

 (4) Determine the number of anodes needed to satisfy the current density limitations. 

 (5) Determine the number of anodes for the system's life expectancy. 

 (6) Determine the number of anodes needed to meet the maximum anode groundbed resistance 

requirements. 

 (7) Select anodes to be used. 

 (8) Select the area for placement of the anodes. 

 (9) Determine the total circuit resistance. 

 (10) Calculate the rectifier voltage. 

 (11) Select a rectifier. 
TM 5-692-2 

30-1 

CHAPTER 30 

BLAST PROTECTION AND DETECTION SYSTEM 

 

30-1. General blast protection and detection systems 

Blast protection and detection systems guard hardened facilities from the effects of an attack external to 

the facility. These systems consist of blast sensors, relay panels, blast valve systems, blast door systems, 

and the electrical system. 

30-2. Sensors 

Blast sensors are located in the control circuit of the valve closure system. These sensors are physically 

located on the exterior surface of the facility or opening to be protected. When a sudden increase in air 

pressure is sensed, as a result of an external explosion, the sensor activates the valve closure through a 

relay and also provides a visual and audible alarm. 

30-3. Relay panels 

The relay panels in the blast system are a part of the electrical system and contain the relaying necessary 

for the controls of the protective functions afforded by the blast valve system. 

30-4. Blast valve systems 

Blast valves are used as intake and outlet air ventilation valves in blast protected buildings to block out 

the destructive effects of explosions. All valve types are tested with multiple blast loads over the entire 

load range from high peaked short duration load to quasi-static long duration blast load.

 a. Mounting. Self-acting blast valves consist of blast valve units and mountings. Openings and 

supports to accommodate the proposed valve system are designed using loads computed from the blast 

overpressures specified or indicated. 

b. Operation. Blast valve units are installed in each opening of the facility and close under the 

positive blast overpressures specified or indicated and are fully operational after the blast. The actuation 

of the valve then seals the opening to prevent entry of undesirable environmental conditions and to allow 

the facility to remain habitable, protecting the safety of the facility occupants. Units operate under a zero 

rise time, with a sustained (infinite duration) blast overpressure. Casing-mounted exhaust valve units 

operate under a zero rise time, sustained (infinite duration) blast overpressure. Blast valve units are 

removable from casings or other mountings. Except for airflow openings, any penetrations through the 

valve system shall be sealed against blast leakage through the penetration. Valve casing supports are 

structural steel fabricated. Valves installed in piping systems are flange connected. 

30-5. Blast door systems 

Entrances that do not incorporate decontamination facilities are provided with an airtight door behind a 

pair of blast proof exterior doors resulting in two contiguous chambers: a blast lock and a vestibule. 
TM 5-692-2 

30-2 

a. Blast lock. The blast lock between the blast doors allows opening of one blast door at a time. This 

permits ingress and egress without loss of interior air pressure, interruption of the blast protection, or 

direct entry of air into the facility. Mounted above the exterior blast door is a blast closure and above the 

inner blast door an anti-backdraft valve. These fittings are connected in series by a blast proof ceiling 

cavity above the blast lock. This allows continuous exhaust of air from the vestibule under a controlled 

pressure differential independently from the use of the blast lock. 

b. Vestibule. The vestibule between the blast door and the airtight door is a pressurized and ventilated 

air lock that allows for dilution and exhaust of any outside air introduced in the vestibule by the 

movement of personnel through the inner blast door. Mounted above the airtight door separating the 

vestibule from the rest of the facility is an air pressure regulator to supply scavenging air to the vestibule 

under a controlled pressure differential 
TM 5-692-2 

31-1 

CHAPTER 31 

FIRE PROTECTION 

 

 

. 31-1. General fire protection systems

The fire protection system consists of basic fire suppression systems, such as automatic sprinklers and 

carbon dioxide systems, as well as fire detection and alarm systems. The purpose of the fire suppression 

system is to protect property and life from the consequences of a fire and to provide fire control until 

professional fire fighters arrive. Whether the combustion is controlled or extinguished by the suppression 

system depends on the hazard being protected against; the type of system selected to protect the hazard; 

the type of suppression agent selected; and of utmost importance, the design of the suppression system. It 

is imperative that the National Fire Protection Association (NFPA) Fire Code standards and 

manufacturer's recommendations relative to each suppression, detection, and alarm system be consulted 

before any operation or maintenance is performed on any of these systems. 

31-2. Fire detection systems 

The concept of defense in depth is applied in fire protection when an early warning fire detection system 

is used to communicate plant or equipment status to a central location or assigned staff. The first line of 

defense is the early warning fire detection system designed to detect the particles of combustion formed 

before overt signs of fire appear, followed by systems designed to detect fire and release extinguishing 

agents. The system’s purpose is to provide the earliest possible warning of a potential fire hazard, 

principally by the extensive use of ionization smoke detectors. 

a. Type of detectors. The three basic types of detectors can detect smoke, heat, and flame. 

 (1) Ionization and photoelectric are two types of smoke detectors that are used. Ionization smoke 

detectors contain a small amount of radioactive material which ionizes the air in the sensing chamber, 

thus rendering it conductive and permitting a current flow through the air between two charged 

electrodes. When smoke particles enter the ionization area, the detector circuit responds with an alarm or 

buzzing. Photoelectric spot type detectors contain a chamber that has either overlapping or porous covers 

of light that allows the entry of smoke. The unit contains a light source and a special photosensitive cell 

in the darkened chamber. The cell is either placed in the darkened chamber at an angle different from the 

light path or has the light blocked from it by a light stop or shield placed between the light source and the 

cell. With the admission of smoke particles, light strikes the particles and is scattered and reflected into 

the photosensitive cell. This causes the photosensing circuit to respond to the presence of smoke particles 

in the smoke chamber. 

 (2) Heat detectors can be configured as spot type or line type. In spot type detectors the sensing 

element is concentrated at a particular location. Line type detectors sense temperature changes along the 

length of a metal wire. When heat above a predetermined level reaches the lines strung throughout an 

area to be protected, an alarm or alarm and fire-suppression system is triggered. Heat detectors are fixedtemperature, rate-compensated, or rate-of-rise types. A fixed-temperature detector is a device that 

responds when its operating element becomes heated to a predetermined level or higher. A ratecompensated detector is a device that responds when the temperature of the air surrounding the device 
TM 5-692-2 

31-2 

reaches a predetermined level, regardless of the rate of temperature rise. A rate-of-rise detector is a 

device that responds when the temperature rises at a rate exceeding a predetermined amount. 

 (3) A flame detector is a device that responds to the appearance of radiant energy visible to the 

human eye or to radiant energy outside the range of human vision. 

 (a) A photoelectric flame detector is a device that the sensing element is a photocell that either 

changes its electrical conductivity or produces an electrical potential when exposed to radiant energy. 

 (b) A flame flicker detector is a photoelectric flame detector with means to prevent response to 

visible light unless the observed light is modulated at a frequency characteristic of the flicker of a flame. 

 (c) An infrared detector is a device with a sensing element that is responsive to radiant energy 

outside the range of human vision. 

 (d) An ultraviolet detector is a device with a sensing element that is responsive to radiant 

energy outside the range of human vision. 

b. Signaling systems. One of the major advantages of using a remote multiplexing system for fire 

detection is the ease of adding alarm detectors without the requirement of long conduit and multiple cable 

runs throughout the plant. The early warning fire detection system may be a Class A proprietary 

protective signaling system that meets the requirements of NFPA 72, National Fire Alarm Code. Class A 

fire detection means a fire alarm can be received and displayed at the central alarm station in the 

abnormal presence of a single break of a single ground fault in any signaling circuit. A Class B system 

does not include this emergency operating feature. 

31-3. Fire suppression systems 

Many types of fire suppression or extinguishing systems are available. Due to environmental impact, 

Halon 1301 fire suppression systems are no longer permitted. Water spray provides cooling action, CO2

reduces the oxygen concentration, isolation removes the fuel from the fire, and dry chemicals disrupt the 

unrestrained chemical chain reaction needed for combustion. However, not all extinguishing agents are 

equally effective and cost efficient in certain types of fires. Water used on electrical control equipment 

and terminal cabinets can cause damage by shorting. CO2 is not cost effective in large volume areas, and 

the area is not immediately habitable after application. Another factor to consider is whether the 

suppression system should be activated by automatic or manual means. The consequences of a false trip 

of an automatic system can be as bad as a fire in that operations personnel may deactivate the system to 

preclude further trips. 

a. Water systems. Protecting facilities from fire frequently requires the installation of a sprinkler 

system. Equipment consisting of overhead piping and attached sprinklers connected to an automatic 

water supply protects defined spaces and a variety of hazards. There are four major types of sprinkler 

systems: wet pipe, dry pipe, deluge, and pre-action. 

 (1) The wet pipe system is the simplest and most common. The wet pipe system utilizes a waterfilled piping system connected to a water supply and is equipped with sprinklers having fixed temperature 

elements which each open individually when exposed to a high temperature due to a fire. The areas 

where wet pipe sprinkler systems will be used are heated shops, garages, warehouses, laboratories, 

offices, record rooms, locker rooms, lunch rooms, and toilets. 
TM 5-692-2 

31-3 

 (2) The dry pipe type of system has heat operated sprinklers attached to a piping system containing 

air under pressure. When a sprinkler head operates, the air pressure is reduced, a “dry pipe” valve is 

opened by water pressure, and water flows to any opened sprinkler heads. 

 (3) The deluge type of system consists of open-type sprinkler heads attached to a network of dry 

(not water-filled) piping which is automatically controlled by a fully supervised fire detection system 

which also serves as a fire alarm system. When a fire is detected, an automatic deluge valve is tripped 

open, admitting water to the system to discharge through all of the sprinkler heads. The system may be 

subdivided into separately controlled headers, depending on the area to be covered and the number of 

sprinkler heads required. The usual pressure required at the sprinkler heads is about 175 psi and the 

piping should be properly sized accordingly. Water spray deluge sprinkler systems are provided where 

required in open areas and areas requiring the protection of the piping from freezing. Water deluge 

systems are provided for outdoor transformers, when the transformers are installed on or adjacent to the 

structure to help prevent the spread of fire and to limit damage to the structure and other close-by 

transformers and equipment. 

 (4) The pre-action type of system is similar to the above water spray deluge system, except that it 

contains closed type sprinkler heads which only discharge water through those sprinklers whose fixed 

temperature elements have been opened by the heat from a fire. 

 b. Carbon dioxide. This type of system usually consists of a truck filled low pressure refrigerated 

liquid carbon dioxide storage tank with temperature sensing controls to permit the automatic injection of 

permanently piped carbon dioxide into areas to be protected. The system usually includes warning alarms 

to alert personnel whenever carbon dioxide is being injected into an actuated area. Carbon dioxide 

extinguishing systems of this total flooding type will be utilized to extinguish coal bunker fires and for 

electrical hazard areas such as in battery rooms, electrical relay rooms, switchgear rooms, computer 

rooms, and within electrical cabinets. 

c. Foam extinguishing systems. Foam fire extinguishing systems utilize a foam producing solution 

which is distributed by pipes equipped with spray nozzles or a fuel tank foam entry chamber for 

discharging the foam and spreading it over the area to be protected. It is principally used to form a 

coherent floating blanket over flammable and combustible liquids which extinguish (or prevent) a fire by 

excluding air and cooling the fuel. The foam is usually generated by mixing proportionate amounts of 

three percent double strength, low expansion standard foam concentrate using either a suitably arranged 

induction device with (or without) a foam storage-proportioning tank to mix the foam concentrate with a 

water stream from a fire water header. A tank foam chamber or open sprinklers aspirate the air to form 

the foam to blanket the area to be protected. The deluge water entry valve to the system may be manually 

or automatically opened. Foam systems will be installed in power plants to protect fuel oil areas, 

lubricating oil systems, and hydrogen seal oil systems. 

d. Portable fire extinguishers. Portable hand held CO2 fire extinguishers should be provided and 

located throughout the facility in accordance with the NFPA. The use of dry chemical fire extinguishers 

is not recommended, primarily due to cleanup problems. 
TM 5-692-2 

A-1 

APPENDIX A 

REFERENCES 

Required Publications 

Government Publications

Department of Defense: 

 MIL-HDBK-419A 

 Grounding, Bonding, and Shielding for Electronic Equipment and Facilities (Cited in paragraph 28-3c) 

 MIL-STD-882 

 System Safety Program Requirements (Cited in paragraph 2-2c(1) 

 MIL-STD-1472 

Human Engineering Design Criteria for Military System, Equipment, and Facilities (Cited in paragraph 

2-2b) 

 MIL-F-16884J 

 Fuel, Naval Distillate (Cited in paragraph 10-3k) 

Department of Army:

 TM 5-692-1 

Maintenance of Mechanical and Electrical Equipment at C4ISR Facilities, Recommended Maintenance 

Practices (Cited in paragraph 1-1) 

Code of Federal Regulations:

 Department of Transportation – Title 49 

 Code of Federal Regulations. Oct 1974 (Cited in paragraph 29-3i) 

Other Government Documents: 

Federal Specification A-A-52557 

 Fuel Oil, Diesel; For Posts, Camps and Stations (Cited in paragraph 10-3k) 

Non-Government Publications

American Society of Mechanical Engineers (ASME): 

345 East 47th Street, New York, NY 10017 

 ASME Boiler and Pressure Vessel Codes (Cited in paragraph 16-2i)

 ASME B31.1 

 Power Piping (1998) (Cited in paragraph 18-2d) 
TM 5-692-2 

A-2 

 ASME B31.3 

 Process Piping (1999) (Cited in paragraph 11-2h) 

ASME B36.10M 

 Welded and Seamless Wrought Steel Pipe (1996) (Cited in paragraph 11-2h(2)) 

American Society for Testing and Materials (ASTM):

100 Barr Harbor Drive, West Conshohocken, PA 19428-2959 

 ASTM A 53 

Standard Specification for Pipe, Steel, Black and Hot-Dipped, Zinc-Coated, Welded and Seamless 

(1999) (Cited in paragraphs 11-2h(2), 16-2k, 17-2e(2)(d) and 20-2h) 

 ASTM A 105 

Standard Specification for Carbon Steel Forgings for Piping Applications (1998) (Cited in paragraph 

11-2h(1)) 

 ASTM A 106 

Standard Specification for Seamless Carbon Steel Pipe for High-Temperature Service (1999) (Cited in 

paragraphs 11-2h(2) and 14-4j) 

 ASTM A 216 

Standard Specification for Steel Castings, Carbon, Suitable for Fusion Welding, for High-Temperature 

Service (1998) (Cited in paragraph 11-2h(1)) 

American Waterworks Association (AWWA): 

6666 West Quincy Avenue, Denver, CO 80235 

 AWWA C104 

Cement-Mortar Lining for Ductile-Iron Pipe and Fittings for Water (1995) (Cited in paragraph 17- 

2c(2)(e)) 

Institute of Electrical and Electronic Engineers (IEEE): 

445 Hoes Lane, P. O. Box 1331, Piscataway, NJ 08855-1331 

 IEEE C57.12.80 

 Standard Terminology for Power and Distribution Transformers (1992) (Cited in paragraph 3-2a(3)) 

 IEEE C37.2 

Standard Electrical Power System Device Function Numbers and Contact Designations (1996) (Cited in 

paragraph 6-2g) 

 IEEE C37.90 

Standard for Relays and Relay Systems Associated with Electric Power Apparatus (1994) (Cited in 

paragraph 6-2f(3)) 

 IEEE 142 

IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems (1991) 

(Cited in paragraph 27-4d) 
TM 5-692-2 

A-3 

National Association of Corrosion Engineers 

1440 South Creek Drive, Houston, TX 77084 

 NACE RP0169 

Control of External Corrosion on Underground or Submerged Metallic Piping Systems (1996) (Cited in 

paragraph 29-3g) 

National Electrical Manufacturers Association (NEMA) 

412 River Rd., Tewksbury, MA 01876 

 Standard 250 

 Electrical Electronic Enclosure Classifications (Cited in paragraph 3-2a(4) 

National Fire Protection Association (NFPA)

One Batterymarch Park, P. O. Box 9101, Quincy, MA 02269-9101 

 NFPA 30 

 Flammable and Combustible Liquid Code (1996) (Cited in paragraph 11-2b) 

 NFPA 70 

 National Electrical Code (Cited in paragraph 27-3c) 

 NFPA 72 

 National Fire Alarm Code (1999) (Cited in paragraph 31-2b) 

 NFPA 780 

Standard for Installation of Lightning Protection Systems (1997) (Cited in paragraphs 28-3, 28-3c, 28- 

3d and 28-3h) 

Underwriters Laboratories, Inc. (UL) 

333 Pfingsten Road, Northbrook, IL 60062-2096 

 UL 555S 

 Smoke Dampers Fourth Edition (1999) (Cited in paragraph 19-2m(4)) 

 UL 96 

Lightning Protection Components, Fourth Edition (2000) (Cited in paragraph 28-3c) 

 UL 96A 

Installation Requirements for Lightning Protection Systems, Tenth Edition (1998) (Cited in paragraph 

28-3c) 

Related Publications

Department of the Army 

TM5-691 Utility System Design Requirements for Command, Control, Computer, Intelligence, 

Surveillance, and Reconnaissance (C4ISR) Facilities 
TM 5-692-2 

G-1 

GLOSSARY 

____________________________________________________________ 

Abbreviations 

A 

Ampere 

AC 

Alternating Current 

ADP 

Automated Data Processing 

Ah 

Ampere-hour 

ANSI 

American National Standards Institute 

ASME 

American Society of Mechanical Engineers 

ASTM 

American Society for Testing and Materials 

AWG 

American Wire Gage 

AWWA 

American Waterworks Association 

BTU 

British Thermal Unit 

C4ISR 

Command, Control, Communications, Computer, Intelligence, Surveillance, and Reconnaissance 

C

Centigrade 

CBR 

Chemical, Biological, and Radiological 

cm

Centimeter 

CI 

Cast Iron 
TM 5-692-2

G-2 

CP 

Cathodic Protection 

CPU 

Central Processing Unit 

d

day/days/daily 

DC 

Direct Current 

DOD 

Department of Defense 

EM 

Electromagnetic 

EMC 

Electromagnetic Compatibility 

EMCS 

Energy Management Control Systems 

EMF 

Electromotive Force 

EMI 

Electromagnetic Interference 

EMP 

Electromagnetic Pulse 

EPA 

Environmental Protection Agency 

ESS 

Electronic Security Systems 

F 

Fahrenheit 

FID 

Field Interface Device 

HAD 

Heat Actuator Detector 

HEMP 

High Altitude Electromagnetic Pulse 
TM 5-692-2 

G-3 

HFE 

Human Factors Engineering 

HPM 

High Power Microwave 

hr

hour/hours/hourly 

HVAC 

Heating, Ventilating, and Air Conditioning 

HVAC&R 

Heating, Ventilating, Air Conditioning & Refrigeration 

Hz 

Hertz 

IEEE 

Institute of Electrical and Electronics Engineers 

IDS 

Intrusion Detection System 

IGBT 

Insulated Gate Bipolar Transistor 

K 

Thousand 

kg

Kilogram 

km

Kilo Meter 

kVA

Kilo Volt Amperes 

kW

Kilo Watts 

LAN 

Local Area Network 

LC 

Line-commutated (inverter) 

NACE 

National Association of Corrosion Engineers 
TM 5-692-2

G-4 

NEC 

National Electrical Code 

NFPA 

National Fire Protection Association 

NPDES 

National Pollutant Discharge Elimination System 

O&M 

Operations and Maintenance 

ppm

Parts Per Million 

psig

Pounds Per Square Inch, Gage 

PVC 

Polyvinyl Chloride 

PWM 

Pulse Width Modulated 

R/A 

Reliability/Availability 

RAM 

Reliability, Availability, and Maintainability 

RF 

Radio Frequency 

RFI 

Radio Frequency Interference 

RMG 

Roesel Motor Generator 

RMS 

Root Mean Square 

s

Second 

SCADA 

Supervisory Control and Data Acquisition 

SCR 

Silicon Controlled Rectifier 
TM 5-692-2 

G-5 

SE 

Systems Engineering 

SF6

Sulfur Hexafoluoride 

THD 

Total Harmonic Distortion 

TIMA 

Thermal Insulation Manufacturers Association 

TM 

Technical Manual 

UL 

Underwriters Laboratories 

UPS 

Uninterruptible Power Supply 

UWB 

Ultra Wide Band 

VAR 

Volt-Ampere Reactive 
TM 5-692-2 

The proponent agency of this publication is the Chief of Engineers, United States Army. 

Users are invited to send comments and suggested improvements on DA Form 2028 

(Recommended Changes to Publications and Blank Forms) directly to HQUSACE, (ATTN: 

CEMP-OS-P), Washington, DC 20314. 

 

Distribution: 

To be distributed in accordance with Initial Distribution Number (IDN) 344719, requirements 

for non-equipment TM 5-692-2. 

By Order of the Secretary of the Army: 

PETER J. SCHOOMAKER 

General, United States Army 

Official: Chief of Staff

SANDRA R. RILEY 

Administrative Assistant to the 

Secretary of the Army
 PIN: 078975-000