Specifications and Tolerances for

Reference Standards and

Field Standards

Weights and Measures

105-4

February 2010

Specifications and Tolerances for Liquefied

Petroleum Gas and Anhydrous Ammonia Liquid

Volumetric Provers

NIST Handbook
Specifications and Tolerances 

for Reference Standards and 

Field Standards Weights and Measures 

Specifications and Tolerances for Liquefied Petroleum Gas 

and Anhydrous Ammonia Liquid Volumetric Provers 

Editor: 

L. F. Eason (Contract) 

Georgia L. Harris 

Val R. Miller 

Carol Hockert, Chief 

Weights and Measures Division 

National Institute of Standards and Technology 

Gaithersburg, MD 20899-2600

U. S. Department of Commerce 

Gary Locke, Secretary 

National Institute of 

Standards and Technology 

Patrick D. Gallagher, Director 

105-4 NIST 

Handbook

February 2010 

Supersedes 1997 Edition 
Certain commercial entities, equipment, or materials may be identified in this document in order to 

describe an experimental procedure or concept adequately. Such identification is not intended to imply 

recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended 

to imply that the entities, materials, or equipment are necessarily the best available for the purpose. 

National Institute of Standards and Technology Handbook 105-4, 2010 Edition 

Natl. Inst. Stand. Technol. Handb. 105-4, 2010 Ed., 39 pages (February 2010) 

CODEN: NIHAE2 

WASHINGTON: 2010
Preface

The 2010 revision of Handbook 105-4 includes the following changes since it was first published 

in 1997: 

 No retroactive requirements were added to the document. However, any existing bleed 

lines on pressurized volumetric field standards should be removed and plugged. 

 The definitions have changed. Liquefied Petroleum Gas (LPG) and anhydrous ammonia 

provers are pressurized volumetric field standards. A number of references and defined 

terms have been expanded. 

 Specific references have been listed to regulatory and safety requirements for the design 

of individual components of LPG and anhydrous ammonia provers that are beyond the 

scope of this document. 

 Series 300 stainless steel is listed as the preferred material due to its corrosion resistance 

and lower maintenance requirements. 

 References to “pressure relief” valves and “hydrostatic relief” valves have been 

corrected. 

 Clear coated aluminum is now allowed for the scale plate material but all markings must 

be permanent (allows silk screen). 

 A non-accredited volumetric field standard manufacturer must make it clear that 

calibration is required before use for Weights and Measures applications. 

 Scale plate graduations must be no smaller in height than 2 mm (approximately 0.1 in). 

 The total span of graduations on pressurized volumetric field standards has been 

standardized to be at least 4 % of the nominal volume. 

 The reflex sight gauge now has to be integral to the neck (upper and lower) of the prover. 

This change eliminates temperature gradients between the liquid in the sight gauge and 

the liquid in the body of the prover. 

 Liquid bleed lines are no longer allowed due to the safety and environmental concerns 

about venting LPG and anhydrous ammonia to the atmosphere. 

 The level condition of pressurized volumetric field standards will be determined by using 

levels to plumb the neck. The levels on pressurized volumetric field standards will be 

adjusted to agree with this level condition. 

 The tolerances for pressurized volumetric field standards have been changed to ± 0.2 % 

of the nominal capacity. All points on the neck scale must be within this tolerance for the 

entire volume (not the neck volume). An additional neck uniformity tolerance of two (2) 

scale divisions from the nominal/zero to any point on the scale also applies. 

 Values in the two tables have been updated. 

 The drawings for the figures have been updated. 

iii NIST Handbook 105-4 
 An optional evaluation checklist has been added to provide a reference for uniform 

evaluation of pressurized volumetric field standards. 

NOTE: Regarding Units of Measure: 

The SI unit of volume is the cubic decimeter (dm3

) or the cubic centimeter (cm3). The Twelfth 

General (International) Conference on Weights and Measures redefined the litre [herein spelled 

liter] as a "special name for the cubic decimeter," but agreed to permit the continuance of the 

terms liter (L) and milliliter (mL), except in association with measurements of the highest 

precision. The commercial measurement system in the United States continues to use gallons 

and cubic inches for practical applications and manufacturers in this industry continue to use 

U.S. Customary dimensions. Since commercial applications in the United States use units other 

than SI or other accepted metric units, this document references common units in current use. 

Acknowledgment 

The first several drafts of this Handbook were written by James Clifford, metrologist with the 

State of Oregon. The 1997 edition was updated with assistance of Karl Herken (KS). This 2010 

edition was finalized through a working group consisting of those who provided comments on 

draft versions, compilation and draft responses of all comments by Michelle Foncannon, with the 

final review and editing effort led by L.F. Eason. Special acknowledgment is given to Emil 

Hazarian, metrologist with the U.S. Navy, Measurement Science Department for preparing 

updated drawings and schematic diagrams. Thanks are also given to numerous metrologists (of 

both state and industry laboratories) for their technical review of several drafts. 

*Trade names used in this Handbook do not imply recommendation or endorsement by the 

National Institute of Standards and Technology (NIST). 

iv NIST Handbook 105-4 
Table of Contents

Preface ...........................................................................................................................iii 

NOTE: Regarding Units of Measure: ........................................................................................... iv 

Acknowledgment ........................................................................................................................... iv 

Introduction ............................................................................................................................ 1

1 Scope................................................................................................................... 1 

1.1 “Field Standard” Classification....................................................................................... 1 

1.2 Retroactivity.................................................................................................................... 2 

1.3 Future Designs................................................................................................................ 2 

1.4 Safety Considerations..................................................................................................... 2 

2 Reference Documents......................................................................................... 3 

2.1 American National Standards Institute (ANSI).............................................................. 3 

2.2 American Petroleum Institute (API)............................................................................... 3 

2.3 American Society for Mechanical Engineers (ASME)................................................... 3 

2.4 American Society for Testing and Materials (ASTM) ................................................... 3 

2.5 International Organization of Legal Metrology (OIML)................................................ 4 

2.6 International Society of Automation (ISA)..................................................................... 4 

2.7 National Fire Protection Association (NFPA)................................................................ 4 

2.8

......................................................................................................... 4 

National Institute of Standards and Technology (NIST), Weights and Measures 

Division (WMD)

2.9 Underwriters Laboratories (UL) ..................................................................................... 4 

2.10 US Department of Labor, Occupational Safety and Health Administration (OSHA).... 5 

3 Terminology........................................................................................................ 5 

4 Specifications...................................................................................................... 6 

4.1 Physical Size ................................................................................................................... 6 

4.1.1 Size Declaration.................................................................................................. 6 

4.1.2 Size Limitations.................................................................................................. 6 

4.2 Reference Temperature and Pressure.............................................................................. 6 

4.3 Identification Markings................................................................................................... 7 

4.3.1 Placement............................................................................................................ 7 

4.3.2 Identification Plate Content ................................................................................ 7 

4.3.3 Limitations on use............................................................................................... 7 

4.3.4 Material and Cross Contamination Safety.......................................................... 8 

4.4 Metal Construction Materials ......................................................................................... 8 

4.4.1 ASME Pressure Vessel Requirements................................................................ 8 

4.4.2 Pressurized Provers for Testing LP Gas Meters................................................. 8 

4.4.3 Pressurized Provers for Testing Anhydrous Ammonia Meters.......................... 8 

4.4.4 Associated Pressurized Hardware....................................................................... 8 

4.4.5 Associated Non-Pressurized Hardware .............................................................. 9 

4.4.6 Other Materials................................................................................................... 9 

4.5 ............................................................................................................................... Body . 9

4.5.1 Pressure Vessel Compliance............................................................................... 9 

4.5.2 Shape................................................................................................................... 9 

4.5.3 Support Structure ................................................................................................ 9 

4.6 Upper and Lower Necks................................................................................................. 9 

4.6.1 Design ............................................................................................................... 10 

v NIST Handbook 105-4 
4.6.2 Drain Plug......................................................................................................... 10 

4.7 Sight Gauges................................................................................................................. 10 

4.7.1 Upper Sight Gauge............................................................................................ 10 

4.7.2 Lower Sight Gauge ........................................................................................... 10 

4.7.3 Sight Gauge Mounting Plate............................................................................. 10 

4.8 Scale Plates................................................................................................................... 10 

4.8.1 Material............................................................................................................. 10 

4.8.2 Mounting........................................................................................................... 11 

4.8.3 Adjustment........................................................................................................ 11 

4.8.4 Sealing .............................................................................................................. 11 

4.8.5 Scale Markings ................................................................................................. 12 

4.8.6 Graduation Lines............................................................................................... 12 

4.8.7 Scale Plate Units............................................................................................... 13 

4.8.8 Dual Scale Calibration...................................................................................... 13 

4.8.9 Span of Graduations.......................................................................................... 13 

4.9 Fill and Discharge (Pump Off) Lines and Valves......................................................... 14 

4.10 Bleed Line Not Allowed ............................................................................................... 14 

4.11 Thermometer Wells and Thermometers ....................................................................... 14 

4.11.1 ASME Compliance ........................................................................................... 14 

4.11.2 Position ............................................................................................................. 14 

4.11.3 Design ............................................................................................................... 14 

4.11.4 Installation in Thermometer Wells................................................................... 14 

4.11.5 Electronic Thermometers.................................................................................. 15 

4.11.6 Liquid-in-Glass................................................................................................. 15 

4.11.7 Bi-Metal Dial Face Thermometers................................................................... 15 

4.11.8 Provision for Calibration .................................................................................. 15 

4.11.9 Additional Thermometer Wells........................................................................ 15 

4.12 ....................................................................................................................... 15 Hardware

4.12.1 External Piping Requirements.......................................................................... 15 

4.12.2 Pressure Gauge ................................................................................................. 16 

4.12.3 Pressure Relief Valve........................................................................................ 16 

4.12.4 Hydrostatic Relief Valves................................................................................. 16 

4.12.5 Excess Flow Valves and Back Check Valves................................................... 16 

4.12.6 Vapor Pressure Equalization............................................................................. 16 

4.13 ........................................................................................................................ 17 Leveling

4.13.1 Leveling Jacks................................................................................................... 17 

4.13.2 Establishment of Level Condition .................................................................... 17 

4.14 ............................................................................................................................ 17 Levels

4.14.1 Position ............................................................................................................. 17 

4.14.2 Level Sensitivity ............................................................................................... 18 

4.14.3 Bulls Eye Bubble Levels................................................................................... 18 

4.14.4 Adjustment........................................................................................................ 18 

4.14.5 Auxiliary Levels ............................................................................................... 18 

4.15 Workmanship, Finish, and Appearance ........................................................................ 18 

4.15.1 Air Entrapment ................................................................................................. 18 

4.15.2 Finished Quality................................................................................................ 18 

vi NIST Handbook 105-4 
vii NIST Handbook 105-4 

4.15.3 Required Assemblies ........................................................................................ 18 

4.15.4 Thread Connector Lubricant............................................................................. 19 

4.15.5 Valve Operation................................................................................................ 19 

4.15.6 Metal Joints....................................................................................................... 19 

4.15.7 Exterior Coatings.............................................................................................. 19 

4.16 Other Requirements...................................................................................................... 19 

4.16.1 Return Pump ..................................................................................................... 19 

4.16.2 ................................................................................................................. 19 Hoses

4.16.3 Protective Caps................................................................................................. 19 

4.16.4 Electrical Requirements.................................................................................... 19 

4.16.5 Braking System................................................................................................. 20 

4.16.6 Labeling and Placarding ................................................................................... 20 

5 Tolerances (Maximum Permissible Errors)...................................................... 20 

5.1 Capacity Tolerance ....................................................................................................... 20 

5.2 Neck Tolerance ............................................................................................................. 20 

5.2.1 Neck Calibration Tolerance .............................................................................. 20 

5.2.2 Neck Uniformity Tolerance .............................................................................. 20 

6 Verification Requirements................................................................................ 21 

6.1 Legal Requirements...................................................................................................... 21 

6.2 Traceability ................................................................................................................... 21 

6.3 Calibration Reports....................................................................................................... 21 

6.4 Initial and Periodic Verification.................................................................................... 21 

7 Test Methods and References........................................................................... 21 

7.1 NIST IR 7383 Selected Volume Procedures, SOP 21 .................................................. 22 

8 Uncertainties..................................................................................................... 22 

8.1 Legal Applications........................................................................................................ 22 

8.2 Sources of Variation ..................................................................................................... 22 

8.2.1 Accuracy ........................................................................................................... 22 

8.2.2 Repeatability ..................................................................................................... 23 

Table 1.

.......................................................................................................................... 24 

Metric specifications and tolerances for pressurized volumetric field standards

Table 2.

........................................................................................................... 24 

Customary specifications and tolerances for pressurized volumetric field 

standards

Appendix 1.

........................................................................................... 25 

Optional LPG and Anhydrous Ammonia Pressurized Volumetric Field 

Standards Checklist

Figure 1.

.......................................................................................... 27 

Schematic Drawing of a LPG and Anhydrous Ammonia Prover and Associated 

Hardware/Plumbing

Figure 2. Schematic Drawing of Gauge Plates (Top and Bottom)................................... 28 

Figure 3. 100 Gal retention plate (schematic).................................................................. 29 

Figure 4. Schematic for use of prover in meter verification ............................................ 30 

References .......................................................................................................................... 31 
viii NIST Handbook 105-4 

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1 NIST Handbook 105-4 

SPECIFICATIONS AND TOLERANCES 

FOR REFERENCE STANDARDS AND FIELD STANDARD 

WEIGHTS AND MEASURES 

4. Specifications and Tolerances for 

Liquefied Petroleum Gas and Anhydrous Ammonia 

Pressurized Volumetric Field Standards 

These specifications and tolerances are recommended as minimum requirements for standards 

used by State and local weights and measures officials and others in the regulatory verification of 

meters used in quantity determination of pressurized liquid commodities. Other users may find 

this handbook helpful in the design of volumetric standards for measuring pressurized liquid 

commodities, but the requirements should not be considered mandatory for special applications 

outside of the scope of regulatory weights and measures. 

Key words: back check valve; excess flow valve; hydrostatic relief valve; pressure vessels; 

pressure relief valve; pressurized volumetric field standards; provers; specifications; vapor 

return; volumetric specifications and tolerances; weights and measures. 

Introduction

Pressurized volumetric field standards (pressurized provers) are used primarily to test 

commercial pressurized liquid measuring devices for compliance with commercial requirements. 

Use of these field standards at all appropriate levels of manufacture, distribution, and weights 

and measures inspection will help promote accuracy and uniformity in commerce. The breadth 

of topics in this handbook is intended to provide information for manufacturers, calibration staff, 

weights and measures officials, and other end users. References are provided when additional 

information may be useful to the reader. 

1 Scope

1.1 “Field Standard” Classification 

These specifications and tolerances are limited to pressurized, graduated neck type volumetric 

field standard provers. The field standards covered by this publication are intended to be used 

by weights and measures officials. Manufacturers and distributors of liquefied gases, service 

maintenance personnel, research and testing laboratories, and others concerned with volume 

measurements of pressurized liquids may find these specifications and tolerances useful. Use of 

these standards at all appropriate levels of manufacture, distribution, and weights and measures 

inspection will help promote accuracy and uniformity in commerce. 

The terms “pressurized volumetric field standard”, “pressurized prover”, and “prover” as used 

in this publication refer to all sizes in general. The pressurized provers referenced here are those 

whose volume is established between a graduated bottom zero and the nominal volume point on 

the graduated neck scale, when pressurized to 689.4757 kPa (100 pounds per square inch, 
gauge, or “psig”). The unit psig will be used hereafter to reflect the pressures in common usage 

in the United States. 

In some cases larger or special purpose pressurized provers may be required which are outside 

of the scope of this publication. For example, a large truck or trailer mounted pressurized 

volumetric field standard may be transported in a horizontal position and raised to vertical for 

use. Larger volumetric field standards may be built based on design considerations within this 

document, but they are not specifically covered. Additional performance, structural integrity, 

stability, and safety issues applicable to these larger standards, though outside of the scope of 

this handbook, must be considered. 

1.2 Retroactivity

These specifications are not intended to make obsolete those field standards fabricated to meet 

prior specifications. All new pressurized volumetric field standards (provers) placed in service 

after March 1, 2010, must meet these requirements prior to certification for regulatory Weights 

and Measures (legal metrology) use. 

Pressurized volumetric field standards fabricated to meet prior specifications may be used as 

long as they 1) comply with applicable ASME and NFPA requirements, 2) maintain the current 

tolerances, 3) meet the calibration repeatability requirement of 0.02 % of nominal volume, and 

4) their performance is adequate to meet NIST Handbook 44 fundamental considerations 

(i.e., the correction plus the measurement uncertainty does not exceed one third of the tolerance 

for the device being tested). 

1.3 Future Designs

These specifications are not intended to limit innovation made possible by advances in 

technology or changes in the commercial field devices they are used to test. All design revisions 

should be evaluated by NIST for accuracy, repeatability, and suitability for the task. Approved 

design revisions may be included in future revisions of this document. 

1.4 Safety Considerations

This documentary standard involves hazardous materials, operations, and equipment and does 

not purport to address the safety problems associated with its use. It is the responsibility of the 

user of this standard to establish appropriate safety and health practices and determine the 

applicability of regulatory limitations prior to use. Specific safety information is documented in 

the American Petroleum Institute (API) references. 

Although these specifications include pressurized volumetric field standards for liquefied 

petroleum gas (LPG) and anhydrous ammonia, these products cannot be interchanged in the use 

of the standard. Cross contamination of either product would create additional safety hazards to 

the inspector and user of the products. 

Commercial volume measuring devices tested with these field standards are typically used to 

measure quantities of LPG, anhydrous ammonia, and other pressurized liquids in sealed systems. 

These liquids are known hazardous materials and hazardous wastes if spilled/released. The user 

is encouraged to obtain Material Safety Data Sheets (MSDS) from the manufacturer of any 

2 NIST Handbook 105-4 
product encountered. Federal and local safety and disposal regulations concerning hazardous 

materials encountered should be reviewed by the user. 

Ethyl Mercaptan (Ethanethiol) is added to LPG to make it easier to detect in case of a leak. It 

has a very strong odor that is detectable in very small concentrations. Anhydrous ammonia also 

has a very pungent odor. It is very caustic and hazardous. Therefore, field standards should be 

purged of product and the interior be thoroughly flushed with water prior to being submitted for 

test. These calibrations should be conducted in a well ventilated area. 

This handbook does not address possible emissions from field standards during their use in the 

testing of hydrocarbons or ammonia. Please note that venting propane within city limits is 

usually prohibited by law. 

2 Reference Documents

Specifications in this handbook are based in part upon information contained in publications 

from various standards and safety organizations. Due to the hazardous nature of the products 

being measured, there are safety regulations and references for all major components of LPG 

and anhydrous ammonia pressurized volumetric field standards. The following is a list of 

reference documents pertaining to LPG and anhydrous ammonia regulations and safety 

engineering. These documents detail requirements for each component of liquefied petroleum 

gas and anhydrous ammonia pressurized volumetric field standards. This handbook is intended 

to be in compliance with the requirements of these documents. However, if a conflict is found 

between this handbook and the current version of the references cited below, the requirements 

of the cited regulatory agency supersede the requirements of this document. Any conflicts found 

should be brought to the attention of the NIST, Weights and Measures Division to be included 

in future revisions of this document. 

2.1 American National Standards Institute (ANSI)i

2.1.1 ANSI/ISA RP12.06.01, Recommended Practice for Wiring Methods for Hazardous 

(Classified) Locations Instrumentation Part 1: Intrinsic Safety.

2.2 American Petroleum Institute (API)ii

2.2.1 Manual of Petroleum Measurement Standards, Chapter 11.2.4, Temperature Correction 

for the Volume of NGL and LPG Tables 23E, 24E, 53E, 54E, 59E, 60E. 

2.2.2 Manual of Petroleum Measurement Standards, Chapter 14.8, Liquefied Petroleum Gas 

Measurement. 

2.3 American Society for Mechanical Engineers (ASME)iii

2.3.1 ASME International Boiler and Pressure Vessel Code, Section VIII, Pressure Vessels.

2.4 American Society for Testing and Materials (ASTM)iv

2.4.1 ASTM D1250 - 07 Standard Guide for Use of the Petroleum Measurement Tables. 

2.4.2 Table 24, Volume Reduction to 60 °F. 

2.4.2.1 Table 24B, Generalized Products, Correction of Volume to 60 °F against Relative 

Density 60/60 °F. 

3 NIST Handbook 105-4 
2.4.3 Table 34, Reduction of Volume to 60 °F against S.G. 60/60 °F for Light Petroleum 

Gases. 

2.5 International Organization of Legal Metrology (OIML)v

2.5.1 International Recommendation, OIML R 117-1, Edition 2007 (E), Dynamic measuring 

systems for liquids other than water, Part 1: Metrological and technical requirements. 

2.6 International Society of Automation (ISA)vi

2.6.1 See ANSI/ISA RP12.06.01 referenced under ANSI above. 

2.7 National Fire Protection Association (NFPA)vii

2.7.1 NFPA 54, National Fuel Gas Code. 

2.7.2 NFPA 58, Liquefied Petroleum Gas Code. 

2.7.3 NFPA 58HB, LP-Gas Code Handbook. 

2.7.4 NFPA 70, National Electrical Code. 

2.8 National Institute of Standards and Technology (NIST), Weights and Measures 

Division (WMD)viii

2.8.1 Handbook 44, Specifications, Tolerances, and Other Technical Requirements for 

Weighing and Measuring Devices, see current edition, published annually. 

2.8.2 NISTIR 7383, Selected Procedures for Volumetric Calibrations, 2007. 

2.9 Underwriters Laboratories (UL)ix

2.9.1 UL Standard 21, LP-Gas Hose. 

2.9.2 UL Standard 25, Meters for Flammable and Combustible Liquids and LP-Gas. 

2.9.3 UL Standard 51, Power-Operated Pumps for Anhydrous Ammonia and LP-Gas. 

2.9.4 UL Standard 125, Valves for Anhydrous Ammonia and LP-Gas (Other Than Safety 

Relief). 

2.9.5 UL Standard 132, Safety Relief Valves for Anhydrous Ammonia and LP-Gas. 

2.9.6 UL Standard 331, Strainers for Flammable Fluids and Anhydrous Ammonia. 

2.9.7 UL Standard 495, Power-Operated Dispensing Devices for LP-Gas. 

2.9.8 UL Standard 565, Liquid-Level Gauges and Indicators for Anhydrous Ammonia and LPGas. 

2.9.9 UL Standard 567, Emergency Breakaway Fittings, Swivel Connectors and PipeConnection Fittings for Petroleum Products and LP-Gas. 

2.9.10 UL Standard 569, Pigtails and Flexible Hose Connectors for LP-Gas. 

2.9.11 UL Standard 644, UL Standard for Safety for Container Assemblies for LP-Gas. 

2.9.12 UL Standard 1203, Explosion-Proof and Dust-Ignition Electrical Equipment for Use in 

Hazardous (Classified) Locations. 

4 NIST Handbook 105-4 
2.9.13 UL Standard 2061, Adapters and Cylinder Connection Devices for Portable LP-Gas 

Cylinder Assemblies. 

2.9.14 UL Standard 60079, Electrical Apparatus for Explosive Gas Atmospheres. 

2.10 US Department of Labor, Occupational Safety and Health Administration (OSHA)x

2.10.1 29 CFR, Part 1910 Occupational Safety and Health Standards, Subpart H - Hazardous 

Materials. 

2.10.1.1 Standard 1910.101 - Compressed gases (general requirements). 

2.10.1.2 Standard 1910.110 - Storage and handling of liquefied petroleum gases. 

2.10.1.3 Standard 1910.111 - Storage and handling of anhydrous ammonia.

3 Terminology 

Anhydrous Ammonia. A relatively pure, very caustic and hazardous, form of ammonia, 

synthesized from nitrogen and hydrogen, combined at high temperatures and pressures in the 

presence of a catalytic agent. It is used primarily as a fertilizer or a refrigerant, It will react 

rapidly with copper, brass, zinc and many alloys, especially those containing copper. It boils at 

atmospheric pressure at −33.3 °C (−27.9 °F). Anhydrous Ammonia will contaminate LPG. 

Back check valve. A valve designed to automatically prevent liquid or vapor from flowing in the 

wrong direction.

Capacity, nominal. The nominal capacity of a volumetric field standard is the volume used to 

designate the prover (e.g., 100 gal LPG prover). The nominal volume is defined between the 

nominal mark on the graduated upper neck gauge and the lower zero mark on a lower neck 

gauge on an LPG/anhydrous ammonia prover. 

Cubical coefficient of thermal expansion. Three dimensional expansion or contraction of a 

material due to temperature change, expressed °C−1

 or °F−1 (/°C or /°F). 

Excess-Flow Valve (also called excess-flow check valve). A device designed to close, reducing, 

or stopping the flow when the liquid or vapor passing through it exceeds a prescribed flow rate 

as determined by pressure differential. This is a safety device primarily designed to cut off flow 

in case of a ruptured line or hose. 

Hydrostatic Relief Valve. A pressure relief valve designed to protect liquid-filled piping from 

excessive pressure and possible rupture. 

Liquefied Petroleum Gas (LPG). Means a mixture of normally gaseous hydrocarbons, 

predominantly propane, or butane, or both, that has been liquefied by compression, cooling, or 

both to facilitate storage, transportation, and handling. 

Plumb. The condition of being perpendicular to a horizontal plane, vertical. 

Pressure Gauge. A calibrated test device capable of sensing and indicating from 0 psig to 

300 psig in 5 pounds per square inch increments (as applied to this specification). 

Pressure Relief Valve. A pressure relief valve designed to protect piping that is not in contact 

with liquid (i.e., a vapor return line) from excessive pressure and possible rupture. 

5 NIST Handbook 105-4 
Pressurized Prover. A mounted volumetric field standard (truck, trailer, or stationary) built to 

ASME Pressure Vessel Code specifications designed to test liquefied propane gas, anhydrous 

ammonia, or other liquids in a closed system at the pressure needed to maintain a liquid state at 

ambient temperatures. 

Reference temperature. The temperature at which the pressurized volumetric field standard is 

intended to deliver its nominal capacity. 

Reflex Sight Gauge. A liquid level gauge, designed in such a way as to cause the liquid level to 

disrupt the refraction of light, causing the liquid within the gauge to appear black. 

Sight Flow Indicator. A fitting with windows, for visually observing the flow through a pipe, 

that may or may not be equipped with a mechanical flow indicator. 

Standard. In a physical realization or representation of a unit of measure, which in the context 

of this handbook, a standard may mean a laboratory standard or a field standard.

Tolerance. Maximum permissible error: extreme value of measurement error, with respect to a 

known reference quantity value, permitted by specifications or regulations for a given 

measurement, measuring instrument, or measuring system. 

4 Specifications 

4.1 Physical Size 

4.1.1 Size Declaration 

The nominal volumes of pressurized volumetric field standards (pressurized provers) are 

represented by the nominal volume lines located on their upper scale plates. Recommended 

metric sizes are shown in Table 1 and U.S. Customary (inch-pound) sizes are shown in Table 2 

at the end of this document. Nominal volumes in each system are ideally selected in multiples of 

1, 2, and 5 (liters or gallons) to facilitate calibration. However, a prover may be built to any size 

to meet specific needs. Non-standard size volumetric field standards that comply with all other 

requirements shall be considered to be in full compliance with this standard.

4.1.2 Size Limitations

The largest pressurized volumetric field standard described in this document is 2000 L (500 gal). 

Truck or trailer mounted provers must meet legal weight and width regulations. This will 

typically limit the maximum size of pressurized volumetric field standards (pressurized provers) 

intended for portable operation. Pressure vessel design limitations along with practical and 

available calibration methods will typically limit the size of stationary provers. Exceptions to 

these size limitations may be made for special applications if proper engineering and safety 

considerations are followed, but these special application provers are outside the scope of this 

document. 

4.2 Reference Temperature and Pressure

The following reference conditions shall be applied to pressurized volumetric field standards 

(pressurized provers) when calibrated to deliver a volume equal to its nominal capacity of 60 °F 

(15.56 °C) and 100 psig. International standards typically reference petroleum products to 

15 °C. Temperature and pressure measurements shall meet the accuracy requirements of the 

6 NIST Handbook 105-4 
procedure chosen and be traceable to national standards. The uncertainty of the calibration must 

be adequate to meet NIST Handbook 44 fundamental considerations (correction plus uncertainty 

does not exceed one third of the tolerance for the device being tested). During use of 

pressurized volumetric field standards all measurement indications must be corrected to the 

reference temperature and pressure for correct application of meter tolerances. 

4.3 Identification Markings 

4.3.1 Placement 

Identification information shall be engraved, embossed, or otherwise permanently placed on a 

stainless steel plate. The stainless steel plate must meet the requirements and be attached in 

accordance with National Fire Protection Association (NFPA) 58, Liquefied Petroleum Gas 

Code. All lettering shall be permanent, durable, weather resistant, impervious to the liquids the 

volumetric field standard is intended to measure, and if not engraved or embossed, of a 

contrasting color to that of the background of the data plate. This information (however placed) 

should be either laminated or coated with a clear protective coating to preserve its legibility 

indefinitely. 

4.3.2 Identification Plate Content 

Each identification plate shall be attached in a conspicuous place on the standard and shall bear 

the following information: 

4.3.2.1 Nominal capacity; 

4.3.2.2 Reference temperature for calibration; 

4.3.2.3 Name and address of manufacturer; 

4.3.2.4 Model number; 

4.3.2.5 Non-repetitive serial or identification number; 

4.3.2.6 Material identification; 

4.3.2.7 Cubical coefficient of thermal expansion of material; 

4.3.2.8 Drain time after cessation of main flow or the total drain time; 

4.3.2.9 Proof of ASME certification; 

4.3.2.10 Maximum allowable working pressure; 

4.3.2.11 Date and pressure to which hydrostatically tested; and 

4.3.2.12 Inside diameters of upper and lower necks. 

4.3.3 Limitations on use 

Any limitations on use shall be clearly and permanently marked on any volumetric field standard 

intended to measure accurately only: 

4.3.3.1 Products having particular properties (i.e., anhydrous ammonia will contaminate LP gas); 

4.3.3.2 Under specific installation or operating conditions; or 

4.3.3.3 When used in conjunction with specific accessory equipment. 

7 NIST Handbook 105-4 
4.3.4 Material and Cross Contamination Safety 

Care shall be taken to ensure that the materials used for the volumetric field standards, or any 

subsequent contamination of such materials, do not create a safety hazard. 

NOTE: A pressurized volumetric field standard prover must be properly labeled and placarded 

according to Department of Transportation (DOT) operational rules, NFPA 58, and other 

regulatory requirements. Local laws and regulations vary between jurisdictions. It is incumbent 

upon the user of a pressurized volumetric field standard prover to be aware of and comply with 

local laws and regulations regarding the labeling and placarding of pressurized volumetric field 

standard used to test hazardous materials. 

4.3.4.1 Product Labeling 

The user shall appropriately label a pressurized volumetric field standard in a conspicuous place 

according to the product it will be used to test. Labeling shall include “Anhydrous Ammonia 

Only”, “LPG Only”, or other similar identification of the specific type of pressurized liquid the 

standard will be used to test. 

4.3.4.2 Multiple Products 

If the standard is to be used for multiple products, all products that may be tested must be labeled 

with additional labeling detailing the method of purging or cleaning required between different 

products. 

4.4 Metal Construction Materials 

4.4.1 ASME Pressure Vessel Requirements 

A pressurized volumetric field standard shall meet the requirements of Section VIII, Pressure 

Vessels of the American Society for Mechanical Engineers (ASME), International Boiler and 

Pressure Vessel Code. 

4.4.2 Pressurized Provers for Testing LP Gas Meters 

A pressurized volumetric field standard used to test LPG meters shall be constructed of either 

300 series stainless steel (preferred) or low carbon steel. Construction must comply with all 

ASME pressure vessel requirements. Three hundred series stainless steel is more resistant to 

corrosion of the interior walls of the vessel and is the strongly preferred material. Corrosion of 

low carbon steel will cause the bottom sight gauge to become dirty and difficult to read. Since 

the sight gauges on pressurized volumetric field standards are not readily accessible for cleaning 

and a sight glass cannot be reused after removal, frequent replacement of sight gauges (and 

recalibration) is required. Corrosion will also eventually weaken the vessel. 

4.4.3 Pressurized Provers for Testing Anhydrous Ammonia Meters 

Due to the corrosive nature of anhydrous ammonia, a pressurized volumetric field standard used 

to test anhydrous ammonia meters shall be constructed of 300-series stainless steel. 

4.4.4 Associated Pressurized Hardware 

Piping, valves, fittings, handles and other associated hardware that is subjected to pressure may 

be constructed of other materials provided, they are compatible with the product tested and meet 

all applicable American Society for Mechanical Engineers (ASME) requirements. In addition, 

all pressurized hardware and fittings must meet National Fire Protection Association (NFPA), 

8 NIST Handbook 105-4 
Underwriters Laboratories (UL), and US Department of Labor, Occupational Safety and Health 

Administration (OSHA) safety requirements, and any other regulatory requirements, including 

those requiring periodic maintenance, requalification, or replacement. 

4.4.5 Associated Non-Pressurized Hardware 

Brackets, fittings, handles and other associated hardware that is not subjected to pressure may 

be constructed of other materials provided they are durable and are suitable for their intended 

purpose. These materials must also meet all applicable regulatory and safety requirements. 

4.4.6 Other Materials 

These specifications are not intended to preclude the use of other suitable materials, provided 

such materials conform to all ASME pressure vessel requirements, associated agency regulatory 

and safety requirements, and the applicable parts of these specifications. The material shall be 

of sufficient strength, shall be thermally stable, and not have an unduly high coefficient of 

thermal expansion, which would render it unsuitable for field use. All applicable physical 

properties' data must be accurately documented for the material chosen. Interested parties are 

urged to submit proposed designs to the National Institute of Standards and Technology (NIST), 

Weights and Measures Division (WMD) for evaluation before fabrication is begun. 

NOTE: These pressurized volumetric field standards are ASME containers. They do not meet 

the definition of a DOT container for DOT maintenance requirements. Therefore, periodic 

hydrostatic testing is typically not required. However, if local regulatory authorities do require 

a pressurized volumetric field standard to be hydrostatically tested, the standard should be 

recalibrated after testing since the hydrostatic test will expand the vessel slightly. 

4.5 Body

4.5.1 Pressure Vessel Compliance 

A pressurized volumetric field standard shall comply with all applicable requirements of Section 

VIII, Pressure Vessels of the American Society for Mechanical Engineers (ASME) International 

Boiler and Pressure Vessel Code. A LPG prover shall have a maximum allowable working 

pressure (MAWP) of 250 psig. An anhydrous ammonia prover shall have a maximum allowable 

working pressure (MAWP) of 300 psig. 

4.5.2 Shape 

Any cross section taken in a plane perpendicular to the vertical axis shall be circular, and the 

shape shall ensure complete emptying and draining. The volume of a prover shall be 

established without the use of fillers, adjusting plugs, or cavities of any kind. 

4.5.3 Support Structure 

The support structure of the pressurized volumetric field standard, consisting of legs and 

framework shall be attached to reinforcement plates on the body of the prover. The attachment 

method of the support structure shall not contribute to prover deformation when routinely 

transported on a trailer or when fully loaded. 

4.6 Upper and Lower Necks

Upper and lower neck maximum diameter requirements are given in tables 1 and 2 for different 

nominal volumes. Additional specifications are listed below. 

9 NIST Handbook 105-4 
4.6.1 Design 

The upper and lower neck shall be seamless pipe, smooth inside, and specially inspected and 

selected for uniformity in the circular cross section. The upper and lower neck axes shall be 

perpendicular to a level horizontal plane. 

4.6.2 Drain Plug 

The lower neck shall be provided with a threaded plug to facilitate cleaning for calibration and 

completely drain the prover after calibration. The bottom should have a slight slope to facilitate 

drainage of prover through the drain plug. 

4.7 Sight Gauges

A pressurized volumetric field standard shall be equipped with two liquid level gauges of the 

reflex type mounted as an integral part of the upper and lower neck. The liquid level gauges and 

retaining plates shall meet the requirements of UL Standard 565, Liquid-Level Gauges and 

Indicators for Anhydrous Ammonia and LP-Gas and all applicable ASME requirements. 

4.7.1 Upper Sight Gauge 

The sight gauge shall be capable of displaying a volume not less than 4 % of the prover nominal 

volume. 

NOTE: Available sight gauges can display more than 4 % of the prover nominal volume. This 

design extends the application of the prover for the user. 

4.7.2 Lower Sight Gauge 

A pressurized volumetric field standard shall have a bottom zeroing capability (also called wet 

zero). The wet zero shall have a similar type liquid level gauge as the top neck adequate for 

establishing the zero set-point. To facilitate the ability to see and stop the liquid drain in time to 

set the zero, the lower sight gauge assembly shall display a minimum length of 10 cm 

(approximately 6 in) of liquid level in the lower neck. 

4.7.3 Sight Gauge Mounting Plate

The width of the opening in the sight gauge mounting plates (upper and lower) shall be at least 

12.7 mm (0.5 in) to allow for a clear view of the liquid level in the sight gauge. 

NOTE: The sight gauge and mounting plate must meet the requirements of Section VIII, 

Pressure Vessels, of the ASME, International Boiler and Pressure Vessel Code. If an opening of 

12.7 mm (0.5 in) or larger is not approved for a specific application, an approved sight gauge and 

mounting plate with the widest allowed opening shall be used. Regardless of the width of the 

opening, the scale plates shall not extend past the bevel of the retaining plate opening by more 

than 1 mm (approximately 0.04 in) to allow the best possible view of the liquid level. 

4.8 Scale Plates

4.8.1 Material 

The scale plate shall be rigid and resistant to corrosion and discoloration (i.e., anodized 

aluminum, clear coated aluminum, or stainless steel). 

10 NIST Handbook 105-4 
4.8.2 Mounting 

There shall be a sufficient number of scale brackets (minimum of two per scale plate) to hold 

the plate firmly. These brackets will be independent of the sight gauge retaining plate bolts. 

The scale plates shall be securely attached to the brackets and be provided with a means for 

sealing. 

4.8.2.1 Location 

The scale plates shall be mounted on the sight gauge mounting plate, parallel to the face of the 

reflex liquid level gauge. 

4.8.2.2 Parallax 

To minimize the effects of parallax, the graduated edge of the scale plates shall be bent in toward 

the sight gauge in conformation with the angle of the mounting plate bevel. When viewed from 

directly in front of the sight gauge, the graduated edge(s) of the scale plate(s) shall be within 

± 1 mm (approximately ± 0.04 in) of the line of view along the perpendicular edge of the 

mounting plate for the sight gauge. 

4.8.2.3 Maximum liquid level visibility 

In order to allow the best possible view of the liquid level, the scale plates shall not extend past 

the bevel of the retaining plate opening. 

4.8.3 Adjustment 

4.8.3.1 Top scale plate(s) 

Movement of the top scale plate(s) of a pressurized volumetric field standard prover shall be 

used to adjust the volume of the prover. Adjustment or removal of the upper scale plate(s) shall 

not require loosening, removal, or any other manipulation of the sight gauge retaining plate bolts. 

4.8.3.2 Incremental adjustment 

Where the design of the scale adjustment provides for movement of the scale by increments only, 

the maximum increment shall be no larger than 25 % of the smallest scale division. 

4.8.3.3 Lower scale plate(s) 

The lower scale plate(s) of a pressurized volumetric field standard prover shall be fixed in 

position with provision for sealing. Removal of the lower scale plate(s) shall not require 

loosening, removal, or any other manipulation of the sight gauge retaining plate bolts. 

4.8.4 Sealing 

All adjustments shall be provided with a means for sealing which will prevent movement or play. 

Removal or movement of any adjusting mechanism or scale plates (top and bottom) shall not be 

possible without breaking the seal. Any gauge movement or play in the adjustment mechanism 

or scale plates after tightening or sealing the adjustment mechanism shall be less than 25 % of 

the smallest scale division. 

4.8.4.1 Manufacturer’s seals on new volumetric field standards 

A manufacturer that is not accredited by an Accreditation Body that is a signatory to the 

International laboratory Accreditation Cooperation (ILAC) mutual recognition agreement (for 

the appropriate scope of volume calibration), shall not seal a new volumetric field standard 

unless a tag attached to the seal (or a label obscuring the view of the sight gauge) clearly states 

11 NIST Handbook 105-4 
that calibration is required before the measure can be used for Weights and Measures 

applications. 

4.8.5 Scale Markings 

The graduation lines, numbers, and other inscriptions on the scale plate shall be permanent, 

durable, weather resistant, impervious to the liquids the volumetric field standard is intended to 

measure, and of a contrasting color to that of the gauge plate. All letters and numbers on a scale 

plate shall be legible and of adequate size, in no event smaller in height than 2 mm 

(approximately 0.1 in). 

4.8.5.1 Nominal volume and units indication 

Scale plates shall be clearly marked with the nominal volume of the standard and the 

identification of the unit of measurement used on the scale plate. Proper abbreviations may be 

used for the unit of measurement (i.e., gal, cu in, in3, L, mL, etc.). 

4.8.5.2 Nominal volume line 

The nominal volume or zero lines on all top neck scale plates shall extend across the entire 

width of the scale plate (except as allowed for dual unit scale plates) and shall be clearly 

identified with the nominal volume of the volumetric field standard. 

4.8.5.3 Bottom zero line 

The bottom zero scale plate on of a pressurized volumetric field standard prover shall have a 

line extending across the entire width of the scale plate. This line shall be clearly marked as the 

“zero” or “0” line. 

4.8.5.4 Additional marking 

The intended method of use, either “To Contain” or “To Deliver” shall also be clearly marked 

on the top scale plate. LPG and Anhydrous Ammonia provers are typically used “To Deliver.”

4.8.6 Graduation Lines 

4.8.6.1 Graduation line length - Major divisions 

Convenient major (numbered) graduation lines, consistent with the measurement system used, 

shall meet with the maximum value requirements listed in tables 1 and 2. Major graduations 

shall be numbered to indicate the volume and shall be twice the length of any subdivision lines. 

Major divisions shall be at least 6 mm (approximately 0.236 in) in length. 

4.8.6.2 Graduation line length – Subdivisions 

Any subdivision graduation lines shall be at least 3 mm (approximately 0.118 in) in length. 

4.8.6.3 Graduation line width 

Graduation lines shall be of uniform width and not more than 0.6 mm (approximately 0.024 in) 

or less than 0.4 mm (approximately 0.016 in) wide. 

4.8.6.4 Line position 

All graduation lines shall extend to the edge of the scale plate nearest to the sight gauge. 

12 NIST Handbook 105-4 
4.8.6.5 Graduation line spacing 

The minimum distance between the center of any adjacent graduations lines shall be 1.6 mm 

(approximately 1/16 in or 0.0625 in) and the lines shall be evenly spaced. 

4.8.7 Scale Plate Units 

The basic scale on metric standards shall be milliliters. The basic scale on U.S. Customary 

standards shall be decimal gallons (0.1 gal). Maximum graduation volumes are listed in Table 1 

(metric) and Table 2 (U.S. Customary). Subdivision graduations (if present) shall be either one 

half (1/2), one fourth (1/4), one fifth (1/5), or one tenth (1/10) of the volume of the major 

divisions. 

4.8.7.1 Additional bottom scale plate graduations 

Additional graduations are allowed for the convenience of the user in the evaluation of wet 

down characteristics of the vessel. If present, these graduations will be clearly differentiated 

from the zero line and clearly identified. If present, it is recommended that the bottom scale 

plate major graduations be 50 mL (0.01 gal) and minor divisions (subdivisions) 25 mL 

(0.005 gal), consistent with the measurement system used. 

4.8.7.2 Dual unit scale plates 

A volumetric field standard graduated in multiple (dual) units, shall have each nominal capacity 

mark clearly identified. The units of measure will also be clearly identified for each scale. 

4.8.7.3 Dual units - Two scale plates 

If two scale plates are used with dual unit scales, each shall be capable of being adjusted and 

sealed independently. Both shall be adjusted as close to nominal as possible during calibration. 

4.8.7.4 Dual units - Single scale plate 

A single piece dual unit scale plate is acceptable as long as the units are clearly defined, the two 

scales are clearly separated, the conversion between units across the scale plate is accurate, and 

each scale unit is clearly identified. 

4.8.7.5 Lack of confusion 

Additional care must be taken in the design of any dual scale plate(s) to ensure there is no 

confusion between units. 

4.8.8 Dual Scale Calibration 

A calibration report for a volumetric field standard with dual units must include calibration 

values for both scale plates. If the secondary scale was adjusted based on conversion of the 

units of the primary scale, it must be clear which scale was adjusted based on the calibration and 

which was adjusted based on the mathematical conversion (e.g., a 25 gal calibration with 

nominal zero adjusted to 25.0 gal and a 95 L nominal mark adjusted to coincide with the 

+ 0.096 gal indication on the U.S. Customary scale plate based on the calculated conversion that 

95 L is approximately 25.096 gal). 

4.8.9 Span of Graduations 

The graduated section of the scale plate shall cover at least 4 % of the nominal volume of the 

prover. The scales shall be graduated both above and below the nominal capacity graduation by 

13 NIST Handbook 105-4 
an amount not less than 1.5 % of the nominal volume of the pressurized volumetric field 

standard prover. 

NOTE: If a sight gauge is used that allows viewing of more than the minimum required, 

graduations should span the entire sight gauge. If 1.5 % of the volume is above the nominal 

value, 2.5 % must be below the nominal value to equal 4 %. 

4.9 Fill and Discharge (Pump Off) Lines and Valves 

Two fast acting shut off valves specifically designed for LPG and/or anhydrous ammonia must 

be positioned at the bottom of the lower neck of the pressurized volumetric field standard, below 

the bottom zero level, to allow filling and draining of the prover. These valves must be protected 

with appropriate excess flow and/or back check valves. These valves must comply with UL 

Standard 125, Valves for Anhydrous Ammonia and LP-Gas (Other Than Safety Relief) and any 

other applicable safety standards. 

4.10 Bleed Line Not Allowed 

A bleed line attached to the bottom fill valve or to the piping between the bottom fill valve and 

the prover body to facilitate the adjustment of the zero level is no longer allowed. The discharge 

pump and valve shall be used for the final adjustment of the bottom zero level. 

NOTE: Bleed lines present both safety and environmental hazards associated with venting LP 

gas to the atmosphere. Any existing bleed line should be removed and the opening plugged with 

an appropriate ASME schedule 80 plug. Appropriate sealant tape or joint compound must be 

used to ensure the plug is leak free. 

4.11 Thermometer Wells and Thermometers 

4.11.1 ASME Compliance 

All thermometer wells shall comply with the requirements of the ASME International Boiler and 

Pressure Vessel Code, Section VIII, Pressure Vessels. 

4.11.2 Position 

A thermometer well shall be installed on the main vessel of the pressurized volumetric field 

standard. It shall be located so that the inserted thermometer or digital thermometer display can 

easily be read by the operator when reading the prover meniscus. 

4.11.3 Design 

A well shall extend at least 20 cm (8 in) into the prover at a downward angle of at least 

15 degrees from the horizontal plane to allow a temperature conducting liquid to be poured into 

the well. It will protrude 5 cm (2 in) out of the prover and will be filled with an adequate amount 

of temperature conducting liquid to cover the sensitive portion of the thermometer of 

temperature probe that is used. The thermometer well should be located so that its lower 

(closed) end is at the approximate center of the vertical cross section of the prover. 

4.11.4 Installation in Thermometer Wells 

Regardless of type, all thermometers must be installed in an appropriate thermometer well. 

14 NIST Handbook 105-4 
4.11.5 Electronic Thermometers 

Any electronic thermometer must be intrinsically safe. Any electronic temperature probe, 

wiring, and associated digital display must meet the requirements of ANSI/ISA RP12.06.01, 

Recommended Practice for Wiring Methods for Hazardous (Classified) Locations 

Instrumentation Part 1: Intrinsic Safety and all other safety requirements applicable to 

electronics in flammable atmospheres. 

4.11.6 Liquid-in-Glass 

A thermometer well designed for liquid-in-glass type thermometers shall be sized to receive an 

armored liquid-in-glass thermometer. It shall be provided with a removable cap connected to the 

prover body by a security chain. 

SAFETY NOTE: Mercury is extremely toxic. If mercury thermometers are used, care should be 

taken to prevent breakage (e.g., armored cases). Mercury spill kits should be available at all 

times when these thermometers are in use. Mercury thermometers (of any type) should not be 

used with anhydrous ammonia. Some states have restricted the use of mercury thermometers, so 

the local jurisdiction should be contacted to determine whether thermometers containing mercury 

may be used. 

4.11.7 Bi-Metal Dial Face Thermometers 

Mechanical, bi-metal strip, dial face type thermometers may be used if they meet the accuracy 

and stability requirements of applicable meter calibration procedures (i.e., NIST Handbook 112, 

Examination Procedure Outlines for Commercial Weighing and Measuring Devices, A Manual 

for Weights and Measures Officials) and prover calibration procedures (NIST IR 7383 Selected 

Volume Procedures, SOP 21, Recommended Standard Operating Procedure for Calibration of 

LPG Provers). If used, these thermometers must be installed in an appropriate thermometer well. 

4.11.8 Provision for Calibration 

Any thermometer or temperature probe that is installed must be easily removable for periodic 

calibration or replacement if damaged. Temperature measurements shall be accurate to the level 

required by the applicable device testing requirements and traceable to naturally occurring 

intrinsic or national standards covering their range of use. 

4.11.9 Additional Thermometer Wells 

For larger prover volumes than identified in this handbook, more than one thermometer well 

should be spaced at two or three points in the upper, middle, and lower portions of the prover 

body. They should be placed at points equally spaced around the circumference of the prover. 

They should be positioned so that they can be easily read and averaged by the operator. An 

intrinsically safe system composed of multiple electronic probes attached to a single 

multichannel digital display is ideal for this application. 

4.12 Hardware

4.12.1 External Piping Requirements 

Piping shall be ASME Schedule 80 and all fittings and valves shall comply with National Fire 

Protection Association (NFPA) 58, Liquefied Petroleum Gas Code. Provers intended for use 

with anhydrous ammonia shall have series 300 stainless steel valves, fittings, and piping 

throughout. 

15 NIST Handbook 105-4 
4.12.2 Pressure Gauge 

Provers shall be equipped with a calibrated pressure gauge piped to the vapor portion of the 

upper neck capable of reading 300 psig, with 5 pound per square inch or smaller graduations and 

mounted so that it is readable when the operator is reading the liquid meniscus level in the upper 

sight gauge of the prover. When practical, a liquid filled gauge is preferred. This pressure gauge 

shall be equipped with an appropriate shutoff valve between the gauge and the pressure vessel. 

4.12.3 Pressure Relief Valve

At the top of the upper neck, there shall be a pressure relief valve (set at 250 psig for LPG and 

300 psig for anhydrous ammonia) to protect the vessel. The type, placement, and maintenance of 

these valves must comply with UL Standard 132, Safety Relief Valves for Anhydrous Ammonia 

and LP-Gas and any other applicable safety standards. 

4.12.3.1 Safety collar 

The top of the neck shall have a collar designed to protect the pressure relief valve from 

accidental damage while allowing for complete drainage of water. 

4.12.3.2 Pressure relief valve cover 

In addition to a protective collar, the pressure relief valve shall have a cover that will prevent 

water from collecting that could freeze and plug the valve. The cover must protect the relief 

valve from water without interfering with the pressure relief function of the valve. 

4.12.4 Hydrostatic Relief Valves 

All portions of the plumbing containing liquid, or capable of trapping liquid (i.e., located 

between two valves), shall be equipped with an adequate hydrostatic pressure relief valve. These 

valves shall have a cover to prevent the accumulation of moisture that could freeze and block the 

valve, preventing the proper operation of the valves. Likewise, valve covers must not be tight 

enough to interfere with the proper operation of the valves. The type, placement, and 

maintenance of these valves must comply with UL Standard 132, Safety Relief Valves for 

Anhydrous Ammonia and LP-Gas and any other applicable safety standards. 

4.12.5 Excess Flow Valves and Back Check Valves 

All pipe and hose attachments to the vessel shall comply with National Fire Protection 

Association (NFPA) 58, Liquefied Petroleum Gas Code. Where applicable, piping and hoses 

must be fitted with excess flow valves that will limit the escape of product if a pipe fails or a 

hose ruptures. Where appropriate (i.e., on the inlet line), back check valves may be used in lieu 

of excess flow valves. 

4.12.6 Vapor Pressure Equalization

4.12.6.1 Vapor return line (hose) 

Prover shall be equipped with a vapor return line (hose) at least 6 m (20 ft) in length with an 

excess flow valve where the hose attaches to the neck of the pressurized volumetric field 

standard. It must have an appropriate (UL Standard 125) shutoff valve at end that attaches to 

the vapor return line on the tank of the truck or meter being tested. The vapor line connector 

shall either have a bleeder valve or be of the self bleeding type to relieve pressure when the 

shutoff valve is closed before disconnecting. 

16 NIST Handbook 105-4 
4.12.6.2 Diameter 

The vapor return line inside diameter shall be at least one-half the inside diameter of the liquid 

supply line. 

NOTE: Restrictive vapor return lines or other system flow restrictions in addition to creating 

safety hazards, may contribute to proving errors. 

4.13 Leveling 

A prover not permanently installed shall have adequate provisions for leveling. A truck or 

trailer mounted prover shall be equipped with a minimum of three, and preferably four, leveling 

jacks to safely maintain a level and stable condition when under full liquid load. 

4.13.1 Leveling Jacks 

All leveling jacks shall operate freely and be stable under load. Load rating should be 

determined on the basis of 125 % of the anticipated maximum load including the heaviest 

product to be tested. 

4.13.2 Establishment of Level Condition 

A pressurized volumetric field standard prover shall be leveled by placing a precision machinist 

spirit level vertically against the neck on at least two locations, 90 degrees apart around the 

circumference of the neck and adjusting the orientation of the standard until the neck is as close 

to vertical (plumb or perpendicular to the horizontal plane) as possible. 

This method of determining the level condition (plumbing the neck) shall be used for the 

replacement and adjustment of levels on all mounted volumetric field standards. It shall 

retroactively be used to establish the reference level condition of all volumetric field standards, 

effective January 1, 2011. 

NOTE: Due to the variability in the mounting of the glass level vials, spirit levels are not always 

accurate. A simple test for a vertical (plumb) level is to place the level on a nearly vertical 

surface, note the reading of the bubble in relation to the lines on the vial and then flip the level 

around 180 degrees (left to right) on the same surface. The position of the bubble in relation to 

the lines on the vial (the reading) should be the same. The same test can be applied for the 

horizontal level by placing it on a nearly level horizontal surface and flipping it around 

180 degrees (left to right). In either case, if the positions of the spirit level bubble relative to the 

lines on the vial do not agree, the level should be replaced. 

4.14 Levels 

4.14.1 Position 

All mounted pressurized volumetric field standard provers shall be equipped with two, 

non-spring loaded, adjustable spirit levels that are mounted at right angles to each other, one 

approximately perpendicular, in the horizontal plane, to the sight gauge glass surface, on the 

upper cone or where best visible from a standing position. Each level shall be mounted on a 

sturdy shelf and be equipped with a protective cover. The adjusting and mounting screws shall 

have provisions for sealing. 

17 NIST Handbook 105-4 
4.14.2 Level Sensitivity 

Spirit levels must have adequate sensitivity such that the level bubble will move by at least 0.1 in 

when the prover is out of level in the orientation of the vertical plane passing through the center 

of the sight glass and the center of the neck cylinder (i.e., commonly referred to as “front to 

back”) enough to cause an error of 25 % of the volumetric field standard tolerance (0.0125 % of 

the nominal volume). 

NOTE: Commercially available spirit levels with a specification of 0.1 in bubble offset per 

45 min tilt or better meet this sensitivity requirement. 

4.14.3 Bulls Eye Bubble Levels 

On 200 L (50 gal) or smaller pressurized volumetric field standard provers, a precision “bull'seye” spirit level is permitted in lieu of two spirit levels, if it has sufficient sensitivity to ensure 

proper reading of the liquid level in the standard. Each level shall be mounted on a sturdy shelf 

either near the base of the sight glass or on the rim of upper cone, directly in front of the sight 

gauge assembly. 

NOTE: Commercially available precision “bull's-eye” spirit levels with a specification of 0.1 in 

bubble offset per 45 min tilt or better meet this sensitivity requirement. 

4.14.4 Adjustment 

Spirit levels will be adjusted to indicate as close to center as possible and sealed in position when 

the volumetric field standard is level based on plumbing the neck (described in section 4.12.2). 

Levels permanently attached to a pressurized volumetric field standard prover must be verified 

each time the measure is calibrated. 

4.14.5 Auxiliary Levels 

Vehicle or trailer mounted pressurized volumetric field standards provers may have auxiliary 

levels mounted at a lower plane for operator convenience in adjusting leveling jacks. The 

primary levels on the prover (described above) shall be the reference levels for final leveling of 

the volumetric field standard. The primary levels should be used to set auxiliary levels. 

Auxiliary levels are only to be used for coarse leveling. 

4.15 Workmanship, Finish, and Appearance 

4.15.1 Air Entrapment

Fabrication shall ensure that no pockets, dents, or crevices will be present which may entrap air 

or liquid, or impair the proper filling or draining of the standard. All drainage piping must be 

routed at a level lower than the bottom wet zero, especially in the area preceding valve(s). This 

will prevent an air pocket from forming when the prover is tested in the certifying laboratory. 

4.15.2 Finished Quality 

A field standard, together with its associated valves, piping, gauge, etc., shall be free of slag, 

scale, weld or solder splatter, grit, dirt, dents, interior rust, water or product residue, or any other 

foreign matter before shipment from the factory or before submission for calibration. 

4.15.3 Required Assemblies 

All parts of the gauge assemblies, and all piping and valves that affect the volume of a 

pressurized volumetric field standard shall be fully assembled by the manufacturer or supplier. 

18 NIST Handbook 105-4 
4.15.4 Thread Connector Lubricant 

All threaded connections, including plugs and caps, shall be thoroughly lubricated with a 

suitable non-hardening paste, or pipe joint tape, and shall not leak. All threaded connections 

must be tested while the prover is under pressure using a suitable leak detection method to 

detect leaks. 

4.15.5 Valve Operation 

All valves shall operate freely and positively and shall not leak under normal operating 

pressures. Valves should be placed where the operator finds them to be easily accessible. 

4.15.6 Metal Joints 

All seams shall be filled and smooth to provide a continuous surface to prevent the entrapment 

of air or liquid, and shall not leak. 

4.15.7 Exterior Coatings 

The exterior surface of pressurized volumetric field standards made of low carbon steel shall be 

properly primed and coated with a glossy finish (white) or a color which is reflective and 

prevents any unnecessary heating of the product within the prover. Stainless steel pressurized 

volumetric field standards may also be painted in this way, but the natural stainless steel surface 

is acceptable (and recommended since it reduces the maintenance requirements of the painted 

surface). 

4.16 Other Requirements

Evaluation of the following items is beyond the training and expertise of the typical laboratory 

metrologist. Each is covered by requirements and specifications of other organizations that 

supersede the requirements of this document. They are included for reference by manufacturers 

and as basic guidance to facilitate the detection of gross safety issues related to these systems. 

Calibration and evaluation of a pressurized volumetric field standard to the requirements of this 

handbook do not imply examination and approval of the items included in this section. 

4.16.1 Return Pump 

The pump and piping shall be designed for use in LPG or anhydrous ammonia service and sized 

according to the prover volume to offer reasonable fill and drain times. 

4.16.2 Hoses 

All hoses shall be at least 6 m (20 ft) in length and meet the requirements of NFPA 58. 

4.16.3 Protective Caps 

The ends of all fill, product return, and vapor equalizing lines or hoses on a truck or trailer 

mounted prover shall be supplied with removable caps or mounted male fittings of like size to 

secure and cap hoses when not in use. 

4.16.4 Electrical Requirements 

4.16.4.1 Electrical wiring

All electrical wiring must be enclosed in appropriate conduit or approved flexible tubing. All 

electrical connections must be explosion proof. All wiring, including low voltage wiring shall 

19 NIST Handbook 105-4 
meet the requirements of NFPA 58, Liquefied Petroleum Gas Code and/or other applicable 

articles of the latest edition of the NFPA 70, National Electrical Code. 

4.16.4.2 Ancillary equipment and instrumentation 

All additional electrical equipment and instrumentation used in conjunction with the pressurized 

volumetric field standard shall be intrinsically safe per the requirements of 

ANSI/ISA RP12.06.01, Recommended Practice for Wiring Methods for Hazardous (Classified) 

Locations Instrumentation Part 1: Intrinsic Safety. 

4.16.5 Braking System 

The truck or trailer mounted prover shall have an adequate braking system to meet all DOT 

requirements and handle the load. 

4.16.6 Labeling and Placarding

A pressurized volumetric field standard prover and any vehicle it is mounted on must be properly 

labeled and placarded according to DOT operational rules, NFPA 58, and other regulatory 

requirements. Local laws and regulations vary between jurisdictions. It is incumbent upon the 

manufacturer and purchaser of a pressurized volumetric field standard prover to be aware of and 

comply with local laws and regulations regarding the transport of hazardous materials. 

5 Tolerances (Maximum Permissible Errors)

5.1 Capacity Tolerance 

For volumetric field standards (test measures and provers) the maximum permissible errors shall 

be ± 0.2 % of the nominal capacity. 

5.2 Neck Tolerance 

5.2.1 Neck Calibration Tolerance 

The requirement in 5.1 Capacity Tolerances, also applies to the scale intervals marked on both 

sides of the scale mark corresponding to the nominal capacity of a volumetric field standard (test 

measure or prover). This means that the volume represented by each scale mark over the entire 

range of the scale plate must be accurate within the maximum permissible error of 0.2 % of the 

nominal capacity. 

5.2.2 Neck Uniformity Tolerance 

The maximum capacity tolerance between the nominal volume line and any other line on the 

scale shall be less than two (2) major scale divisions as listed in Tables 1 and 2. If smaller 

divisions or subdivisions are used, two (2) times the maximum allowed division listed in 

Tables 1 and 2 is the tolerance applied to the neck uniformity. The application of this tolerance 

must allow for the uncertainty of the neck scale calibration measurement. Therefore, in order to 

be rejected, the neck scale capacity error must exceed the value of two divisions plus the 

uncertainty of the neck scale calibration. 

20 NIST Handbook 105-4 
6 Verification Requirements

6.1 Legal Requirements 

The specifications and tolerances specified in Tables 1 and 2 are intended to permit the use of 

the equipment in normal field testing operations as standards having nominal values. Weights 

and measures requirements, including but not limited to, inspection, testing, and sealing by a 

NIST recognized laboratory, shall be followed. 

NOTE: Some States have requirements that are not documented here. 

6.2 Traceability 

Field standards used for legal metrology shall be traceable to national standards by calibration in 

a laboratory recognized by NIST Weights and Measures Division or accredited to 

ISO/IEC 17025 to calibrate in that parameter, range, and scope as specified by local regulations. 

6.3 Calibration Reports 

Acceptable accuracy and traceability to national or international standards shall be documented 

in a calibration report using accepted test methods. A calibration report must be prepared that 

states the calibration method used, the calibration medium (should be water), the nominal 

volume of the prover, the reference temperature, the reference pressure, the volumes at various 

applied pressures, the calibration error on the graduated neck, the expanded uncertainty (k=2; or 

approximately a 95 % confidence interval), the prover serial number, and the date. A pressure 

correction table and a temperature correction table should be provided with the calibration 

report. Additionally, guidance for correct application of the pressure and temperature 

corrections should be provided the user. 

6.4 Initial and Periodic Verification 

Field standards must be verified prior to use and rechecked as often as regulations or 

circumstances require, especially when damage is known or suspected. Pressurized volumetric 

field standard calibration may be established at one year intervals and extended or reduced 

based on historical evidence up to the limit determined by State or local regulations, but should 

not exceed three years due to possible leaking valves or seals which are often difficult to detect 

under field conditions. 

7 Test Methods and References

To ensure the safety of metrologists, improve the accuracy of calibration, and to prevent 

environmental contamination, all pressurized volumetric field standard provers must be cleaned 

and thoroughly flushed with water before bringing inside for calibration. Internal contamination 

may create environmental and safety issues and reduce calibration accuracy. External 

contamination may create environmental pollution hazards. If there is evidence of residual 

contamination, the pressurized volumetric field standard prover should be rejected and removed 

from the building until it can be safely cleaned in a way that is not detrimental to the 

environment. 

To facilitate calibration, it is suggested that all pressurized volumetric field standard prover 

systems be disassembled with excess flow and back check valves removed. These valves may 

interfere with the calibration process by leaking during pressurization. It is important that the 

21 NIST Handbook 105-4 
pressure relief valve be left on the pressurized volumetric field standard prover during 

pressurization for the safety of the metrologists. Disassembly of piping makes it important that 

the final step of calibration is to reassemble the system and check all connections for leaks using 

an appropriate leak detection method while the prover is under pressure. 

7.1 NIST IR 7383 Selected Volume Procedures, SOP 21 

SOP 21, Recommended Standard Operating Procedure for Calibration of LPG Provers. Test 

methods shall comply with those documented in NIST IR 7383, Selected Volume Procedures or 

other nationally or international recognized procedures. 

8 Uncertainties

8.1 Legal Applications

Uncertainties of the calibration must be evaluated according to the ISO Guide to the Expression 

of Uncertainty in Measurements, 1993xi to ensure that the three to one accuracy ratio of NIST 

Handbook 44 is maintained. As of 2009, the acceptance tolerance for liquid petroleum gas and 

anhydrous ammonia measuring devices is 0.6 % of the measured volume. Therefore, the 

expanded uncertainty for calibration of a pressurized volumetric field standard must be less than 

0.2 % of the measured volume. 

NOTE: LP gas and anhydrous ammonia measuring device tolerances should be evaluated at the 

time of use to ensure use of suitable standards, tolerances for standards, and applications. 

8.2 Sources of Variation 

8.2.1 Accuracy 

Accurate measurement demands the use of calibration equipment and standards with accuracy 

traceable to national or international standards and the use of standard procedures. Accurate and 

traceable measurements require the analysis of measurement uncertainty and an evaluation of 

that uncertainty to determine the adequacy for its intended use. In the case of LPG and 

anhydrous ammonia provers used in weights and measures applications, the expanded 

uncertainty for calibration must be less than 0.2 % of the measured volume. Further, the 

correction/error in the standard plus or minus the uncertainty must be less than the tolerance. 

To achieve the required expanded uncertainty, the following estimates demonstrate the required 

standard uncertainties associated with major contributors in the calibration: 

 laboratory standard(s): 0.01 % of the volume of the standard prover per delivery (at 

95 % confidence interval); 

 measurement process: 0.02 % of the volume of the prover under test; 

 neck calibration: 0.05 % of the neck volume (the neck volume is at least 4 % of total 

volume) of the prover under test; and 

 applicable tolerance: 0.2 % of the nominal volume for the prover under test. 

When these factors are combined in a root-sum-square method and multiplied by a k-factor of 

two (95 % confidence interval), it provides an uncertainty of less than 0.2 % of the measured 

volume. If any one of the factors listed is greater than what is noted in the above list, the other 

22 NIST Handbook 105-4 
factors must be reduced to compensate when one desires to maintain the required values for the 

expanded uncertainty. 

E.g., for the previous example, the values are combined as follows: 

)04.0*05.0(02.0)2/01.0(*2 %) 2.0( 2 2 2   Error Prover  Tolerance

To achieve the necessary accuracy, the corrected volume depends on: 

 use of proper temperature corrections; 

 the uncertainty associated with the cubical coefficient of thermal expansion; 

 the accuracy of temperature measurements; 

 correction for the compressibility of water; 

 use of an accurate pressure gauge; 

 a single standard (as few as possible) should be used in the calibration of a pressurized 

volumetric field standard; 

 the use of a proper “wet down” prior to calibration or use; 

 whether gravity drain is used during calibration or whether the volume of water is 

eliminated by pumping; 

 differences in drain between calibration and use for both the standard (reduced drain 

size) and the prover; 

 wetting characteristic differences between water and LPG or anhydrous ammonia; 

 the cleanliness of the prover (sight glass and inner surface) and calibration medium; 

 prover retention characteristics related to inside surface, contamination or corrosion, 

and total drain times; 

 possible air entrapment in the water; and 

 the ability to properly read the meniscus. 

Proper reading of the meniscus must be followed to prevent additional error in the calibration 

and field use (see NIST IR 7383 Selected Volume Procedures, Good Measurement Practice 3). 

If the same pressure gauge is used during calibration and during meter verification, errors due to 

inaccuracy of the pressure gauge should be minimized. 

8.2.2 Repeatability

A pressurized volumetric field standard must be capable of repeating within 0.02 % of the test 

volume during calibration. Repeatability problems may be the direct result of poor prover 

design, material corrosion over time/use, a leak in the valves or seals of the prover, or due to 

contamination and lack of cleanliness, and must be corrected before calibration can be 

completed. 

23 NIST Handbook 105-4 
24 NIST Handbook 105-4 

Table 1. Metric specifications and tolerances for pressurized volumetric field standards 

Size 

Liters 

(L) 

Tolerance 

(mL) 

(± 0.2 %) 

Maximum 

Graduations

(mL) 

Total Neck

Volume on

Scale 

(L) 

Maximum 

Upper Neck 

Inside Diameter 

(in) 

Lower Neck 

Inside Diameter

(in) 

100 200 50 4 5 4 

200 400 100 8 6 4 

500 1000 200 20 12 4 

1000 2000 200 40 12 4 

2000 4000 500 80 18 4 

Table 2. Customary specifications and tolerances for pressurized volumetric field standards

Tolerance* 

(± 0.2 %) Size 

(gal) 

(in3) (gal) 

Maximum

Graduations

(gal) 

Total Neck

Volume on

Scale 

(gal) 

Maximum 

Upper Neck 

Inside Diameter 

(in) 

Lower Neck 

Inside Diameter

(in) 

20 9 0.04 0.01 0.8 6 4 

25 12 0.05 0.01 1 6 4 

50 23 0.1 0.02 2 8 4 

100 46 0.2 0.05 4 12 4 

200 92 0.4 0.1 8 18 4 

300 139 0.6 0.1 12 18 4 

500 231 1 0.1 20 18 4 

*Values are rounded to the nearest appropriate unit and are not exact conversions between units. 

For a capacity intermediate between two capacities listed above, the tolerances and graduations 

prescribed for the lower capacity shall be applied.
Appendix 1. Optional LPG and Anhydrous Ammonia Pressurized Volumetric Field Standards 

Evaluation Form 

Submitted by: Date:

Test Number:

Metrologist:

Model Number:

Serial Number:

Seals intact: Yes/No 

Description: 

Instructions: Evaluate each item. Check either the approved or rejected box. If not applicable or allowed for a special 

application, draw a line through both boxes. Explain all rejections and special application exemptions in the 

comments section. File with calibration documentation.

Requirement HB 105-4 Ref. Evaluation Tips Appd Rej 

Check individual requirements for overall 

approval. Identification 4.3 

Permanent, stainless steel plate, weather & liquid 

resistant, contrasting color? 1 Identification placement 4.3.1 

2 Nominal capacity 4.3.2.1 

3 Reference temperature 4.3.2.2 

4 Manufacturer information 4.3.2.3 Name and address? 

5 Model number 4.3.2.4 

6 Serial number 4.3.2.5 May be combined in serial number if clear 

Material identified? Stainless steel  Lowcarbon steel  Other _________ 7 Material ID 4.3.2.6 

Cubical coefficient of 

expansion 8 4.3.2.7 CCE marked on standard? 

9 Drain time 4.3.2.8 

10 ASME certification 4.3.2.9 Year: 

11 Maximum working pressure 4.3.2.10 Pressure: 

Date and pressure to which 

hydrostatically tested 12 4.3.2.11 Date: _________ Pressure: _________ 

13 ID upper and lower necks 4.3.2.12 Upper: _________ Lower: _________ 

Note any limitations on use: 14 Limitations on Use 4.3.3 

15 Product labeling 4.3.4.1, 4.3.4.2 Labeled LPG  or Anhydrous Ammonia  only? 

ASME code compliance marked? 

16 Construction material 4.4.1, 4.4.2, 4.4.3 LPG: Stainless or low carbon steel? 

Anhydrous Ammonia: Stainless Steel? 

Circular cross section in horizontal plane? 

17 Body and Shape 4.5.1, 4.5.2, 4.5.3 No fillers, adjusting plugs or cavities? 

Shape ensures emptying, support? 

Neck (top) Uniform, seamless, ID ____________ 

17 4.6 Uniform, seamless, ID ____________ Neck (bottom) Drain plug? 

Top: Reflex, clear, unbroken? 

19 Sight gauges 4.7 Scale range ≥ 4 % of nominal capacity? 

Bottom: Wet zero, reflex, clear, unbroken, ≥ 6 in? 

Width of opening at least 1⁄2 inch unobstructed, all 

bolts present and tight 20 Sight gauge mounting plate 4.7.3 

Rigid, corrosion & discoloration resistant? 

21 Scale plate construction 4.8.1, 4.8.2 Top: Mounting, does not obstruct view? 

Bottom: Mounting, does not obstruct view? 

25 NIST Handbook 105-4 
26 NIST Handbook 105-4 

22 Adjustment 4.8.3 Top adjustment, stable, ≤ 25 % scale division? 

23 Sealing 4.8.4 Adequate, no removal/movement of scale plates? 

Permanent and legible? 

Nominal volume & unit abbreviations? 

Nominal & zero lines? Top  Bottom  24 Scale plate markings 4.8.5 

“To Contain”  or “To Deliver”  

Graduation spacing (≥ 1.6 mm) & width? 

25 Scale plate construction 4.8.6 Bottom scale plate – zero line? 

Adequate provisions for sealing? 

Major Divisions? 

Sub divisions? Yes  No  Compliant?

Dual scale? Yes  No  Compliant? 26 Scale plate graduations 

4.8.7 

Table 1 

Table 2 Lack of confusion? 

27 Span of graduations 4.8.9 Percent of nominal (≥ 4 %)? _______ 

28 Fill/discharge line, valves 4.9 Fast acting valves, piping below zero? 

29 Bleed line not allowed 4.10 Should be removed and plugged. 

Number of wells: 

30 Thermometer wells 4.11 

Placement of wells, calibration provision? 

31 External piping 4.12.1 Schedule 80? 

32 Pressure gauge 4.12.2 At least 300 psig x 5 psi? 

33 Pressure relief valve 4.12.3 Safety collar, cover? 

34 Hydrostatic relief valve(s) 4.12.4 All sections of piping that could trap liquid? 

35 Excess flow/back check 

valves 4.12.5 Placement back check on fill, excess flow other 

large openings? 

36 Vapor return line 4.12.6 Length, diameter, excess flow? 

37 Leveling 4.13 Leveling jacks adequate? 

38 Levels 4.14 Adequate, protected, agree w/plumb neck? 

Workmanship, finish, and 

appearance 

4.15 Check individual requirements for overall 

approval. 

39 Air entrapment 4.15.1 No pockets, discharge piping below zero? 

40 Finished quality 4.15.2 Joints leak free and smooth, no residues? 

41 Assembly, leak free, valve 

operation 

4.15.3, 4.15.4, 

4.15.5, 4.15.6 

Everything assembled with pipe thread sealant, 

valves convenient? 

42 Coatings 4.15.7 Exterior paint light color, reflective, and in good 

condition (non-stainless)? 

Other Requirements 4.16 No Approval Implied – Note any gross problems. 

43 Return pump and hoses 4.16.1, 4.16.2 Adequate & appropriate for purpose? 

44 Protective caps 4.16.3 Supplied for all hoses? 

45 Electrical Requirements 4.16.4 No exposed wiring or connections? 

46 Brakes 4.16.5 Note if present. 

47 Labeling and Placarding 4.16.6 Note if present. 

Test methods 7 Examine in preparation for calibration. 

48 Cleanliness 7 No residue, clear sight glass(es)? 

Requirement HB 105-4 Ref. Comments 
1

2

3

4

5

6

7

8

9

10

11

12

6

2 13 14

15

16

17

18

19

20

21

22

1. Pump and motor

2. Hydrostatic relief valve

3. Prover discharge

 line with valve

4. Strainer

5. Discharge valve

6. Excess flow valves

7. Lower neck

8. Prover body

9. Levels

10. Upper neck

11. Vapor return line

12. Collar

13. Pressure gauge

14. Reflex sight gauge and

 scale asembly (top)

15. Thermometer well

16. Reflex sight gauge and

 scale assembly (bottom)

17. Back check valve

18. Prover inlet with

 valve

19. Bypass line

20. Prover leg

 (adjustable)

21. Bypass valve

22. Power cord

Figure 1. Schematic Drawing of a LPG and Anhydrous Ammonia Prover and Associated 

Hardware/Plumbing. 

27 NIST Handbook 105-4 
501

500

502

504

503

505

506

507

508

496

495

497

498

499

494

493

492

LITERS

101

100

102

99

98

TO DELIVER

US GALLONS TO DELIVER

0

Sealing details

Holes in rod Holes in nuts Hole in bolt head

TOP GAUGE PLATES

BOTTOM GAUGE PLATE

Figure 2. Schematic Drawing of Gauge Plates (Top and Bottom). 

28 NIST Handbook 105-4 
1/2"

minimum*

1

2

4

6

1. Prover wall

2. Gauge glass

3. Retaining plate

4. Retaining plate bolt

5. Mounting screw

6. Scale plate

3

5

Figure 3. 100 Gal Retention Plate (schematic). 

*NOTE: Regardless of the width of the opening, the scale plates shall not extend past the bevel 

of the retaining plate opening by more than 1 mm (approximately 0.04 in). Optimally, the scale 

plates should not extend past the bevel at all in order to allow the best possible view of the liquid 

level. 

29 NIST Handbook 105-4 
Figure 4. Schematic for Use of Prover in Meter Verification. 

30 NIST Handbook 105-4 
31 NIST Handbook 105-4 

 

References 

i American National Standards Institute (ANSI), 1819 L Street, NW, Suite 600, Washington, DC 20036, USA. 

WEB Site: http://www.ansi.org/ 

ii American Petroleum Institute (API), 1220 L Street, NW, Washington, DC 20005-4070, USA. 

WEB Site: http://www.api.org/ 

iii American Society for Mechanical Engineers (ASME), Three Park Avenue, New York, NY 10016-5990, USA. 

WEB Site: http://www.asme.org/ 

iv American Society for Testing and Materials (ASTM), 100 Barr Harbor Drive, West Conshohocken, Pennsylvania 

19428-2951, USA. WEB Site: http://www.astm.org/ 

v

 International Organization of Legal Metrology (Organisation Internationale de Métrologie Légale, OIML), 11, rue 

Turgot, F-75009 Paris, France. WEB Site: http://www.oiml.org/ 

vi International Society of Automation (ISA), 67 Alexander Drive, PO Box 12277, Research Triangle Park, NC 

27709, USA. WEB site: http://www.isa.org 

vii National Fire Protection Association (NFPA), 1 Batterymarch Park, Quincy, Massachusetts 02169-7471, USA. 

WEB Site: http://www.nfpa.org/ 

viii National Institute of Standards and Technology (NIST), Weights and Measures Division (WMD), 100 Bureau 

Drive Stop 2600, Gaithersburg, MD 20899-2350, USA. WEB Site: http://ts.nist.gov/WeightsAndMeasures/ 

ix Underwriters Laboratories (UL), 2600 N.W. Lake Road, Camas, WA 98607-8542, USA. WEB Site: 

http://www.ul.com/ 

x

 US Department of Labor, Occupational Safety and Health Administration (OSHA), 200 Constitution Avenue, NW, 

Washington, D.C. 20210-0002, USA. WEB Site: http://osha.gov/ 

xi International Organization for Standardization (ISO), 1, ch. de la Voie-Creuse, Case postale 56, CH-1211 Geneva 

20, Switzerland. WEB Site: http://www.iso.org/