The leading name in steam traps.

Yarway Steam Traps

The Industrial Steam Trapping Handbook.

Yarway Industrial Steam Trapping Handbook
Contents
All steam traps and related equipment is governed by an applicable code of construction. ASME,
DIN, B 31.1 and others are mandated by law and code. The end user must use the applicable codewhen designing, constructing or repairing any steam related equipment. This guide book is to be
used as a basic guide and does not address the required Codes for any region. The end user is
responsible to ensure all applicable codes are followed as required in each jurisdiction.

Contents
Chapter 1	Steam trapping, an overview����������������������������������������������������������������������������������������3
Chapter 2	Basics of steam and steam systems���������������������������������������������������������������������������7
Chapter 3	Operating principles of steam traps��������������������������������������������������������������������������14
Chapter 4	Principles of steam trap application�������������������������������������������������������������������������27
Chapter 5	Principles of steam trap installation�������������������������������������������������������������������������39
Chapter 6	Steam trap maintenance and troubleshooting���������������������������������������������������������44
Chapter 7
Condensate return systems���������������������������������������������������������������������������������������56
Appendix A	
How to trap process equipment��������������������������������������������������������������������������������66
Appendix B	Steam trap evaluation methods���������������������������������������������������������������������������������78
Appendix C	Glossary of terms��������������������������������������������������������������������������������������������������������85
Appendix D	Useful tables���������������������������������������������������������������������������������������������������������������87

Copyright © 2017 Emerson. All rights reserved. No part of this publication may be reproduced or distributed inany form or by any means, or stored in a database or retrieval system, without t written permission. Emerson(PVC) provides the information herein in good faith but makes no representation as to its comprehensivenessor accuracy. Individuals using this information in this publication must exercise their independent judgment inevaluating product selection and determining product appropriateness for their particular purpose and system
requirements. PVC makes no representations or warranties, either express or implied, including without
limitation any warranties of merchantability or fitness for a particular purpose with respect to the information
set forth herein or the product(s) to which the information refers. Accordingly, PVC will not be responsiblefor damages (of any kind or nature, including incidental, direct, indirect, or consequential damages) resulting
from the use of or reliance upon this information. Emerson reserves the right to change product designs
and specifications without notice. All registered trademarks are the property of their respective owners.
Printed in the USA.

2

Yarway Industrial steam trapping handbook
Chapter 1 - Steam trapping, an overview
Chapter 1 – Introduction
Steam traps are used wherever steam isused and they are control valves. Their basic
function is to allow condensate to flow, while
preventing the passage of steam until it hasgiven up its heat by condensing back to water.
There are literally millions of steam traps inuse worldwide.
Steam trap users range from laundries andtailor shops (with a few traps) to huge refineries
and chemical complexes (with 10,000 to
15,000 units). Paper mills, textile plants, steel
mills and food processors are all large usersof steam and steam traps. Colleges, hospitals,
prisons, government agencies, and similarlarge building complexes with central steam
heating systems are also users of steam traps.
This wide range of users creates an equallywide range of steam trap applications. In turnthis wide variety of applications is matched bya seemingly bewildering array of steam trap
types and sizes.
Energy costs lead to new awareness becauseof costs and environmental requirements
In recent years, user interest in steam traps
has closely paralleled the increases inenergy costs. This interest has been born ofnecessity. The high fuel costs associated withmalfunctioning traps, and the low level ofattention generally paid to their proper use,
have simply become economically too painful toignore. The malfunctioning traps waste energy,
which in turn increases the requirement
to produce steam and may contribute toenvironmental issues.
A few of the larger and more sophisticatedtrap users have developed test and evaluation
programs to determine the kinds of traps
that perform best in their plants. They
have experimented with various types fromdifferent manufacturers. Organizationalchanges have created the job of Energy
Conservation Officer, and his function invariably
has led him to study the subject of steam
traps. As a result, the skills necessary for
diagnosing inefficient steam systems, andprescribing appropriate cures, have improved.

Figure 1.1
Figure 1.1 shows an ultrasonic steam leakdetector and an infrared heat loss sensor.
Both are used increasingly in efforts to detect
energy losses. Identifying malfunctioning andmisapplied steam traps is now recognized
not only as an important task, but also oneof greater complexity than initially perceived.
Services of consultants and service companies
specializing in the proper maintenance ofsteam traps have become increasingly popular.
No universal steam trap
With all of this attention and inquiry, manyusers have become aware that there is nouniversal trap or single trapping technology for
all their needs. Appreciation has developed forthe fact that many criteria must be consideredin selecting a steam trap for a particularapplication. Different trap types will be selectedor preferred according to the importance a user
assigns to various criteria.
The objective of this book is to provide an
up-to-date reference for trap users whose
requirements may range widely. Its intent
is to clarify and simplify the basics relating
to steam trap selection, sizing, installationand maintenance without ignoring thesubtleties and nuances of interest to themore knowledgeable reader.
While all steam traps have the same basic
objective, pass condensate but trap steam,(they are also expected to pass air and othernoncondensible gases without loss of steam),
there is a wide range of design approaches toachieving this objective. Traps come in a varietyof shapes and sizes. Some weigh less than apound while others will exceed two hundred
pounds. Some are intended for small copper
tubing while others will be used with three inch
steel pipe. Some may be used at pressuresexceeding 2,500 psi while others may actually
see vacuum service. Some are designed todrain several pounds of condensate an hourwhile others are expected to pass tens of
thousands of pounds of condensate an hour.

Detector PM 321
Processor PM 310

Software

Photo shows system manufactured by Miyawaki
that combines testing of the trap with data
storage and reporting3

Yarway Industrial steam trapping handbook
Chapter 1 - Steam trapping, an overview
Trap preferences vary
While steam is the same around the world,
there are interesting preferences for one typeof trap over another in different countries.
This tends to reinforce the conclusionthat despite the universality of the laws ofthermodynamics, the problem of selecting
a correct steam trap has no single correct
answer. All major industrial countries havetheir own steam trap manufacturers serving
local markets. Increasingly, they are trying toexport their more successful models. This has
had the beneficial result of increasing user
options. It also has increased the user’s needto understand fully the limitations and thebenefits of those options. Emerson is a global
supplier for steam traps, many other types
and vendors are available for similar duty andservices. The references in this book include
Emerson products and other similar brands forillustration purposes.
Trap selection criteria
Steam traps are analogous to motor vehicles
in that each has a single underlying purpose
but is available in a wide variety of models andoptions. Selecting the correct model depends
on user needs and preferences. In selecting
the right trap a user must think hard about
the priority of his needs. While efficiency andreliability may seem obvious requirements,
other criteria (such as responsiveness tochanging pressures and condensate flow rates,
installation flexibility, ease of maintenanceand troubleshooting) are more judgmental.

Nevertheless, they can significantly reduce thecosts of operating an efficient steam system.
Increasingly, users are recognizing all steam
traps have the same objective: pass condensate
but trap steam the difference between
purchased cost, installed cost, and life-cycle
cost. When all of these issues are considered,steam trap selection becomes a matter
requiring thoughtful evaluation. At the least, awrong selection means a savings opportunity
missed; – at the worst, it can mean a costly
disruption of production.
Cost considerations
Steam traps, like all other pieces of mechanicalequipment, will fail in time. They may fail closed
thereby restricting flow, or they may fail open,
freely passing steam. It is difficult to appreciate
fully the cost consequences of malfunctioning
steam traps in a large plant without going
through some basic arithmetic. Consider aplant with 6,000 traps and a reasonably The
answer is that he probably doesn’t really know
it is happening. If each failed trap had highvisibility, it would be a different story. But withtraps discharging into a closed return system
the same telltale plumes of vapor, that quickly
identify the leaking valve packing or flanged
joint, are missing. Because frequently they failto create a clearly visible problem, traps simply
don’t receive the attention they deserve.

Figure 1.2
All steam traps have the same objective: pass condensate but trap steam
Water

Steam

4

Yarway Industrial steam trapping handbook
Chapter 1 - Steam trapping, an overview
Process and protection traps
Industrial steam traps can be divided into two
major groups: (1) traps designed for allows theconservative assumption that at least 10% havefailed in the open position and are “blowing
through,” wasting steam. Six hundred traps,
losing 20 pounds of steam per hour per unit,
for twenty-four hours, are losing 288 thousand
pounds of steam per day. While steam
generating costs vary from plant to plant (andare revised annually) an estimate of $5.00 per
thousand pounds is very conservative. In thisexample, that equals $1,440 per day for a rateof $525,600 per year.
∙ 6,000 traps x 10% = 600 failed traps∙ 600 failed traps x 20 lb/hr x 24 hr/day =288,000 lb/day∙ 288,000 lb/day x $5.00/1,000 lb = $1,440/day∙ $1,440/day x 365 day/year = $525,600/year
These are all conservative numbers.
Nor is it necessary to have several thousandtraps to have the potential for very large steam
and dollar losses. Several failed large capacity
traps can also be the source of costly steam
losses.
The costs resulting from traps that have failed
in the closed position are not considered in
the preceding example. They are much moredifficult to quantify but they are no less real.
These costs result from reduced productivity or
product quality and higher rates of equipment
damage due to corrosion, water hammer orfreeze ups.

Why would any plant manager allow his steam
traps to waste this amount of steam? This
example does not include any calculation to
the amount of pollution generated during the
production of the steam in the first place. A
good review of the pay back process will include
environmental issues as well as the direct costof steam.

Yarway Model 741

Typical process trap application
Steam traps are used in draining processequipment such as tire presses, drying rolls,
air heaters and heat exchangers (often referred
to as process traps); (2) traps designed fordraining steam mains or tracing systems.
The latter serve a protection function and aresometimes referred to as protection traps.
Protection service, such as steam main drips
and tracer heating, is by a wide margin themost common trap application and makes up
the majority of the 6,000 units referred to in theearlier example. They generally see very lightcondensate loads, often less than 50 pounds
per hour. Process traps are generally designed
for condensate loads of several hundred
pounds per hour to several thousand pounds
per hour.

5

Yarway Industrial steam trapping handbook
Chapter 1 - Steam trapping, an overview
Summary
Frequently underestimated as a significant
contributor to efficient plant operation,
steam traps are increasingly recognized asa small piece of equipment with a large rolein optimizing plant efficiency and reduced
environmental costs.
Designed to release condensate and air fromsteam systems without allowing the passage
of steam, they are a small automatic selfactuated valve. They come in a wide range ofsizes and models because they must meet awide range of pressures and condensate loadconditions. Users also tend to have different
preferences for the kind of performance they
expect from a trap.
Steam traps that have failed in service
are seldom highly visible unless they aredischarging directly to the atmosphere.

Because of this, they generally receive
inadequate maintenance attention. The direct
cost consequences of this inattention, whenmeasured in terms of unnecessary fuelconsumption, can be startlingly high.
The indirect cost consequences, in terms oflost production or damaged equipment, canalso be significant although they are lesseasily quantified and frequently not properly
assigned to a faulty steam trap installation.
Any successful effort to control these costs
must be based on a solid foundation ofcertain basic factual information about steam,condensate, how steam traps work, and therequirements of the systems into which they
are installed.

Figure 1.3
Typical process trap application
Steam in
Hot process
fluid

Trap

Cool process
fluid

Condensate out

Figure 1.4
Yarway drip traps protect equipment and piping against damage that can result if condensate
is not drained
Steam from boiler

Trap

Trap

Trap
Turbo generator

6

Yarway Industrial steam trapping handbook
Chapter 2 - Basics of steam and steam systems
Chapter 2 – Introduction
Generating steam is not an end in itself.
Steam is generated as a convenient way oftransferring energy (heat and pressure) fromone place to another. Its uses can be forheating, drying, cooking, curing or spinninga turbine – to name a few. It is the special
properties of steam and water, and their easy
availability, that make them so widely selected
for this energy transferring role.
A review of some fundamentals concerning
steam and condensate can be helpful. Whenwater is heated, its temperature continues torise up to the boiling point. Continued heating
does not raise the temperature of the water
but causes it to boil into steam having thesame temperature as the liquid.
If water is heated in a closed vessel, thereaction is different in an important way.
Once boiling starts and with the heating
continued, several things occur; the pressurein the vessel increases and the temperature ofboth the water and the steam also increases.
This means that water has a new andhigher boiling point as pressures increase.

For instance, at 100 psi water boils at 338°F
instead of the familiar 212°F at atmosphericpressure. If heating continues after all thewater has been evaporated, the temperatureand pressure of the steam continues toincrease and the steam is then calledsuperheated steam.
If the heating is discontinued, a process isstarted that is just the reverse of that describedabove. As the vessel cools, the pressure also
decreases. Initially, no condensation takes
place as the steam gives up that portion of theheat it acquired after all the water in the vessel
evaporated. After all the total heat of steam at
atmospheric pressure the superheat has been
given up, however, water starts to condenseon the vessel walls. Continued cooling results
in a decreasing pressure and the formationof more condensate. Ultimately all the steam
will condense into water and the temperatureand pressure will return to that which existed
before the heating process started.

Figure 2.1
Steam and condensate system
Steam mainAirheaterTrap

Highpressure
steam

Heat
exchanger

Trap
BoilerJacketedkettleTrap

End ofmain trap

Tracer traps
Drip
trap
Condensate returnFlash tank7

Yarway Industrial steam trapping handbook
Chapter 2 - Basics of steam and steam systems{

Figure 2.2
Total heat of steam at atmospheric pressure

Total heatof steam(1150 BTU)
1 pound water
evaporated
into steam at
atmosphericpressure

Latent heat ofvaporization

970 BTU

Sensible heatof water

180 BTU

A more realistic situation is that of a steam
generator or boiler with its heat and pressure
energy being transferred by a piping system toequipment that is performing a useful task. As
the steam gives up its heat in the equipment,
condensate is formed. The condensate can thenreturn to the boiler for reheating and the cycle
is repeated. Figure 2.1 shows such a system.
Basic definitions
Some basic definitions are really essential toa full understanding of the steam generating
cycle and the proper use of steam traps in an
efficient steam-using system:• British thermal unit (BTU): the quantity ofheat required to raise one pound of water
1 degree Fahrenheit.
• Sensible heat: heat that produces atemperature rise in a body such as water.
• Latent heat of vaporization: heat that
produces a change of state without a change
in temperature, such as changing water
into steam.
• Saturated steam or dry saturated steam:steam at the temperature of the water fromwhich it was evaporated.
• Wet steam: typically, steam is not dry but
contains fine water droplets resulting fromthe boiling process. The significance is thatwet steam has a lower heat content thandry saturated steam.

{{Heat required to convert
1 pound of water at 211°F to
1 pound of steam at 212°F

Heat required to raise 1 poundof water from 32°F to 212°F• Saturated water: water at the same
temperature as the steam with which it isin contact.
• Superheat: heat added to dry saturated
steam.
Additional concepts• Total heat of steam: the total BTU content
of steam, including sensible heat of water,
latent heat of vaporization and superheat(if any).
	This concept is shown in Figure 2.2 forsteam at atmospheric pressure.
	The conclusion that can be drawn from
Figure 2.2 is that there is more than fivetimes the heat in one pound of steam at
212°F than in one pound of water at the same
temperature. This means that for efficientheating with steam, condensate must be
removed quickly. The presence of condensate
acts to reduce the surface area exposed
to steam with its much greater BTU (heat)
content.
	The total heat of saturated steam at anypressure is the sum of latent and sensible
heat and is shown in Figure 2.3.
Higher pressures mean higher temperaturesand faster heat transfer. But it is worth notingthat higher pressures mean less latent heatof steam. More steam must be condensed at
higher pressures, to transfer a given numberof BTUs, than is the case at lower pressures.

8Yarway Industrial steam trapping handbook
Chapter 2 - Basics of steam and steam systems• Discharge temperature of steam traps:
The temperature of discharging condensate
measured at the steam trap’s inlet. Also,
sometimes referred to as the temperature
at which a steam trap starts to open.

• The saturation curve: graphic representationof the pressure and temperature at whichsaturated steam and water exist.
	As pressures increase in a boiler, so does theboiling point of water. Figure 2.4 shows how
the boiling point increases from 212°F at 0 psi
to 489°F at 600 psi. This curve is called theSaturation Curve. At temperatures above thecurve, steam is in a superheated condition.
At temperatures along the curve bothsteam and condensate are in the saturated
condition. At temperatures below the curve,
condensate is in the subcooled condition; i.e.
its temperature is below that of saturated
steam and water at that pressure.

Understanding the physical phenomena
represented by the saturation curve is essential
to understanding why in certain applications
some types of steam traps are preferredover others. Most steam traps are unable toperform well over the entire range of pressure
and temperature conditions represented in
Figure 2.4. For example, some traps will work
well at higher pressures but will be unable toshut-off the flow of steam at lower pressures.

Figure 2.3
Total heat of steam at pressures of 0 to 100 psi
Total heat of steam(L and S)

1200

Alternatively, some that shut-off steam atlower pressures are unable to open sufficiently
to allow a full flow of condensate at higher
pressures. Also, many applications requirea steam trap that will discharge condensate
very quickly after it forms to obtain maximum
heating efficiency for the equipment it isserving. This condensate will be very close to
steam temperature perhaps only 3 or 4 degrees
below that of steam. In other applications, theheat in the condensate as well as the heatin the steam can be used. In these cases thesteam trap is not expected to open until thecondensate is 30 or 40 degrees below thatof steam.
Steam traps that open and close attemperatures just a few degrees below
steam temperature are often referred to as“hot” traps. Those that discharge condensate
significantly subcooled below steam
temperature are called “cool” traps, eventhough they may be operating at temperatures
much higher than 212°F. The requirements of
the application determine which type of trap ismost suitable.

1100
1000

BTUs per pound of steam

900

Latent heat (L) available
at various pressures

800
700
600
500
400
Sensible heat (S) available
at various pressures

300
200

Sensible heat at
atmospheric pressures

100
0

10

20

30

40

50

60

70

80

90

100

Figure 2.4
Saturation curve
500
Area of superheated steam
400

Boiling point of water(temperature of saturated
steam and saturated waterat various pressures

300

Area of subcooled water or condensate
200

0

100

200

300

400

500

600

9

Yarway Industrial steam trapping handbook
Chapter 2 - Basics of steam and steam systems
Figure 2.5 shows graphically the concepts
described above. One type of trap (represented
by the Trap A curve) opens quickly to discharge
condensate when its temperature has dropped
only a few degrees below that of steam. Its
discharge temperature is said to parallel thesaturation curve because it opens to discharge
condensate the same few degrees below
steam temperature over a wide range of
steam pressures.
In contrast, the number of degrees thatcondensate must cool below steam
temperature before a different type of trap
(represented by the Trap B curve) will open,
varies significantly at different pressures. In
this example, condensate must cool a relatively
large number of degrees below that of steam
before it will open at pressures above 300 psi.
As steam pressures drop below 300 psi, thenumber of degrees condensate must cool
before the trap will open is progressively
reduced until at 25 psi the trap is open
continuously (unable to close), discharging
both steam and condensate.

• Steam tables: listings of the heat content
of steam in BTUs and its volume in ft3·lb at
various pressures and temperatures.
The properties of saturated steam are mostfrequently summarized in steam tables,some of which are very extensive. Figure 2.6
shows this form in a very abbreviated listing.
Appendix D provides more complete but still
abbreviated tables.
Steam tables are essential for calculating
the amount of steam to do a certain heatingjob. When the amount of steam required is
known, so is the amount of condensate thatwill be produced and, in turn, the size of
steam trap that is required. Chapter 4, Steamtrap application, discusses in greater detailthe calculations necessary in estimatingcondensate loads.
Flash steam: steam that results whensaturated water or condensate is discharged
to a lower pressure. When saturated water orcondensate is released to a lower pressure, its
boiling point is instantaneously reduced. Someof the condensate will boil or flash into steam.
This is steam that could not exist at the higher
pressure.

Figure 2.5
Discharge temperature characteristics of two different types of steam traps
500
Saturation curve(Boiling point of waterat various pressures)

Temperature °F

400

300
Trap A
Discharge temperature of a steam trapthat can parallel the saturation curve
200

100

0

Trap B
Discharge temperature of a steam trap that is unable toparallel the saturation curve. Note that in this example,
this trap will be unable to close at pressures below 25 psi

100

200

300

400

500

600

Pressure, psig
10

Yarway Industrial steam trapping handbook
Chapter 2 - Basics of steam and steam systems
While the brief explanation of flash steam
given above is accurate, the significance of thesubject for both steam systems and steam
trapping justifies more discussion. Here areseveral practical reasons for this:
1.	The individual that expects to know thedifference between a trap that is operating
properly and one that is not must know thedifference between flash steam and live
steam.
2.	 Flash steam created unexpectedly ina poorly planned steam system cansignificantly reduce the efficiency ofthat system. It can also (under extreme
conditions) cause malfunction of certain
types of steam traps.
3.	 Flash steam in a properly designed steam
system is an important element in using
steam efficiently at successively reducedpressures for a series of different jobs.
By way of example, consider a steam trap
draining a piece of equipment operating
at 100 psi. Steam flows to the equipment
and condenses as it gives up its heat. It isthen that the steam trap should open, todrain the condensate, and reclose before
live steam escapes. But the temperature ofcondensate at 100 psi is 338°F and, if it drains
directly to atmospheric pressure, the lawsof thermodynamics require it to achieve its
atmospheric boiling point instantly and become
212°F. This is accomplished by some of thecondensate flashing into steam also at 212°F.
This discharge from the outlet of the trap thenis a combination of hot condensate and flash
steam and is typical of a properly functioning
steam trap.

Flash steam problems
Confusion over flash steam starts with anindividual, who is looking at a trap that isdischarging to atmosphere, and who thenattempts to decide if the steam coming fromthat trap is really live steam that has leaked
through (a faulty trap) or if it is flash steam, thenormal result of hot condensate boiling upon
release to a lower pressure (a healthy trap).
Both experience and judgment are needed
to make a correct assessment. Chapter 6,
Steam trap maintenance and troubleshooting,discusses this problem more fully.
Flash steam can create problems in thepiping systems used to return condensate to
the boiler. Condensate return systems thathave not been properly designed to accept thevolume of flash steam they actually experience
will perform poorly. Flash steam expands tomany times the volume that it had as water.
Saturated water at 15 psi will have about
1600 times the volume when it flashes to steam
at atmospheric pressure. This expansion
process can so pressurize condensate returnsystems that proper drainage of the steam
heated equipment, and performance of certain
types of steam traps, are impaired. Connecting
additional equipment to an already existing
condensate return system is frequently thecause of excessive back pressures.

Figure 2.6
Steam table (see Appendix C for expanded table)
Heat in BTUs per lb
Pressure
psig
0
25
50
100
200
300
400
600

Temperature
°F
212
267
298
338
388
422
448
489

Sensible
180
236
267
309
362
399
428
475

Latent
970
934
912
881
837
805
776
728

Total
1150
1170
1179
1190
1199
1204
1204
1203

Specific volume ofsaturated vapor
ft3·lb
27.0
10.5
6.7
3.9
2.1
1.5
1.1
0.75
11

Yarway Industrial steam trapping handbook
Chapter 2 - Basics of steam and steam systems
Flash steam as a valuable resource
Flash steam in a properly designed cascading
return system allows for the efficient use of
steam doing several different heating tasks
at successively reduced steam pressures.
Table (Figure 2.7) shows the percent of flash
steam formed when condensate is discharged
from a higher to lower pressure. For example,
7% of condensate discharged from a 100 psi
system to a 30 psi system will be converted to
flash steam. Tables such as these are usedin designing condensate return tanks andsystems.
Factors affecting steam systems
Up to this point emphasis has been focusedon matters relating to the heat content ofsteam and water. However, there are some
additional considerations associated withsteam systems that have special significancefor the steam trap user and designer alike.

While these are common problems, theiradverse effects can be minimized by goodplanning and equipment selection. These
problems include:• Water hammer: condensate will always
collect in the low points of a steam system
unless special effort is made to drain it away
or to eliminate the low point. Figure 2.8
shows a sagging steam main that has
allowed condensate to accumulate.
	Steam flowing in the main, often at
surprisingly high speeds (90 miles perhour is not unusual), will pick up slugs ofcondensate and slam them into valves,elbows, steam traps or other such equipmentwith devastating affect. Steam trap designers
seek to create robust products that willwithstand water hammer. Steam trap users
are best advised to correct water hammer at
its source by following good piping practice.

Figure 2.7
Percent of flash steam formed
Initial steampressure
psig
25
50
75
100
125
150
175
200
225
250
300
350
400
450
500
550
600

Sat.
temperature
°F
267
298
320
338
353
366
377
388
397
406
422
436
448
459
470
480
489

Flash-tank pressure*, psig
0
5.7
9.0
11.3
13.3
14.8
16.8
17.4
18.7
19.7
20.7
22.4
24.0
25.5
26.8
28.2
29.2
30.2

5
4.1
7.4
10.8
11.7
13.4
14.8
16.0
17.5
18.2
19.2
21.0
22.7
24.2
25.3
26.7
27.8
28.8

10
3.0
6.2
8.6
10.6
12.2
13.7
15.0
16.2
17.0
18.2
20.0
21.6
23.0
24.4
25.7
27.0
28.0

20
1.0
4.3
6.7
8.7
10.3
11.8
13.0
14.4
15.4
16.4
18.2
20.0
21.5
22.7
24.0
25.3
26.4

30
0.0
2.6
5.0
7.0
8.7
10.2
11.6
12.8
13.8
15.0
16.7
18.4
20.0
21.2
22.6
23.7
25.0

40
0.0
1.0
3.7
5.7
7.4
8.8
10.0
11.5
12.4
13.6
15.5
17.0
18.7
20.0
21.4
22.3
23.6

50
0.0
0.0
2.5
4.6
6.3
7.8
9.0
10.4
11.4
12.5
14.4
16.0
17.7
19.0
20.4
21.6
22.7

75
0.0
0.0
0.0
2.2
3.8
5.4
6.7
8.0
9.0
10.0
11.0
13.8
15.6
16.8
18.2
19.5
20.5

100
0.0
0.0
0.0
0.0
1.7
2.3
4.6
6.0
7.0
8.2
10.0
12.0
13.5
15.0
16.4
17.5
18.7

125
0.0
0.0
0.0
0.0
0.0
1.6
3.0
4.4
5.4
6.6
8.5
10.4
12.0
13.4
14.6
16.0
17.3

150
0.0
0.0
0.0
0.0
0.0
0.0
1.5
2.8
3.8
5.0
7.0
8.9
10.5
12.0
13.4
14.7
16.0

* The vessel used to receive high pressure condensate, and flash steam which can be used at lower pressures
for additional heating, is called a flash tank.

Figure 2.8
Water hammer can result from accumulation of condensate in a sagging steam main

12

Yarway Industrial steam trapping handbook
Chapter 2 - Basics of steam and steam systems• Air: boilers and steam systems are full of
air prior to startup. An especially importantpart of getting any steam system operating
efficiently is the removal of air from it. Air isa poor conductor of heat, and mixtures of airand steam have less heat content than steam
alone at the same pressure. Both of thesefactors have an especially adverse affect onheat transfer rates. Air is eliminated fromthe steam system by thermostatic air ventsand by steam traps. Some traps are much
more effective air eliminators than others,
a subject which is discussed in greater
detail in Chapter 3, Operating principles
of steam traps.
• Gases: carbon dioxide and oxygen are bothpresent in steam systems. Free oxygenis a normal constituent of water but it isprincipally the boiling process that volatilizes
the carbonates in water to produce carbon
dioxide. Both· gases foster corrosion. An
important function of a steam trap is to assist
in the purging of these noncondensable gases
from the steam system.
• Corrosion: all steam systems and theirassociated components suffer from theeffects of corrosion. Corrosion attacks boiler
tubes, steam mains, heat exchangers, valve
components and fittings such as steam
traps. Over time all these items succumb.
The primary defense is a carefully monitored
and maintained boiler feedwater treatment
system that controls the gases (oxygen andcarbon dioxide) which promote corrosion.
Carbon dioxide by itself is not corrosive, but
it can combine with free hydrogen to form
carbonic acid which is corrosive. A principal
reason stainless steel is used extensively insteam traps is to resist the effect of corrosion
and prolong the life of the trap.
• Dirt: the trash and accumulated debris
in a newly piped steam system must be
seen to be believed. In older systems dirt,
corrosion products, and sealants fromthe maintenance repair of a leaky joint,
continue to plague such components as
small valves, instruments and steam traps.

These devices with their small clearances andvulnerable seating surfaces are especiallysusceptible to dirt related failures. Dirt which
prevents the free movement of internal partsor which gets caught between the valve andseat sealing surfaces leading to erosion
damage is a major source of problems.
With good reason, the knowledgeable user
places a pipeline strainer upstream of eachsteam trap.

Yarway Model 151

Summary
A basic knowledge of the properties of steam
and the problems of steam systems is an
essential foundation to a good understandingof steam trapping.
Concepts such as the significantly greater
heat content of steam over condensate (at thesame temperature) and the predictable affectof pressure changes on steam and condensate
formation (as shown by the saturation curve)
are important. It is when these principles are
violated that steam heating and steam trapping
problems develop.
Flash steam is useful when properly directed
and a problem when it is not. In addition, it
is confusing to the field technician checking
steam trap performance. Here, experience isthe best teacher.
All steam systems must deal with problemsof corrosion, air and gas venting, dirt (usuallycorrosion products) and water hammer. Steamtraps are both a victim of these problems aswell as potential solution contributors – it isknowledge of good practice that will decide
whether they are part of the problem or part ofthe solution.
Emerson’s goal in writing this book is to informthe engineer on useful tools and tips to using
steam traps correctly.

13

Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
Chapter 3 – Introduction
Steam traps are an important element of any
steam system. They are expected to perform
a vital function with an absolute minimum ofattention. If properly selected, sized, installed
and maintained, traps can provide many yearsof trouble-free service. A clear understandingof their working principles with their inherent
advantages and limitations will greatly simplify
the processes of selecting a proper trap,
solving system problems and diagnosing
trap malfunctions.
Definition
A steam trap can be defined as a self-contained
valve which automatically drains condensate
and discharges air and noncondensible gases
from a steam-containing pipe or vessel. It
remains closed in the presence of steam. In
some designs, however, it will allow steam
to flow at a controlled or adjusted rate.
While this statement defines the basic functionsof a steam trap, it should be understood thatthe device must be capable of operating atpressures ranging from a vacuum to 4500 psi
and pass condensate loads ranging fromzero (under superheated conditions) to ashigh as 100,000 lb/hr for certain processequipment. Actual installations vary as well.
Some traps will see service at constantpressure and condensate load. Others willneed to accommodate variations in pressure
and condensate load and may be installed insystems that are shut down frequently. Clearly,
no single device can serve all needs. A variety
of types, sizes and configurations is necessary
to satisfy all conditions.

Yarway Model 711UCF2Basic steam trap types
Over the years, three basic trap types have
evolved and have been classified according
to their mode of operation. Certain types oftraps may combine two working principles
in their operation. Within the scope of thisbook, however, the predominant condensate
discharge principle shall designate the trap
type. The three types are:
• Thermodynamic traps: traps that are
actuated by the principles of thermodynamics
and fluid dynamics.
• Mechanical traps: traps that are actuated bya float, responding to changes in condensate
level.
• Thermostatic traps: traps that are actuatedby temperature sensitive devices, responding
to changes in condensate temperature.
Thermodynamic traps
Thermodynamic traps are phase detectors inthat they can discriminate between liquids andgases. But they do not discriminate between
steam and air or other noncondensible
gases. Therefore they have a reduced ability
to bleed-off those gases. Minute amounts ofsteam may also be passed. The thermodynamic
working principle is simple and, with only one
moving part, these small devices are rugged.
There are three basic types of thermodynamic
traps. They differ from one another by theconfiguration of the valve they use to open
and close a port. Each is well adapted to aparticular set of service conditions.

14

Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
1.	Disc traps: disc traps utilize the heat energy
in hot condensate and the kinetic energy insteam to open and close a valve disc. They
are phase detectors, sensing the difference
between liquid and gas or vapor.
During initial startup, pressure created bycold condensate pushes the valve disc off theseating surface. This uncovers the inlet andoutlet ports, allowing discharge. As condensate
reaches the inlet port (a restriction), it
experiences a decrease in pressure and anincrease in velocity (in accordance with thelaws of fluid dynamics). If the condensate isvery close to steam temperature, the lower
pressure will cause it to flash into steam (inaccordance with the laws of thermodynamics).
The resulting high velocity flow beneath thedisc, with its attendant localized pressure
reduction under the disc, causes it to snap
shut. Flow through the trap then stops until thepressure in the chamber over the disc decays
sufficiently to allow the inlet pressure to force
the disc off its seat. Condensate then flows
through the trap until once again it reaches
such a velocity and lowering of pressure thatflashing occurs and the disc can snap shut.
This cycle continuously repeats itself the disc
opening to allow the flow of condensate, andclosing on high velocity flash steam.

Disc traps are most frequently used in lightcondensate load applications and are known
as “hot” traps – i.e., quickly discharging very
hot condensate immediately after it forms.

Yarway Model 721

Advantages• Failure mode, gradually, predictably
open over time.
• Simple construction.
• Small size and light weight.
• Can be mounted in any position.
• Rugged, withstands water hammer.
• Self draining, not damaged by freezing.
• Function not impaired by superheat.
• Versatile, suitable for wide pressure range.
• Condensate discharge temperature closely
follows the saturation curve.
• Performance is easily checked in field.
Disadvantages• Marginal air handling capability.
• Excessive back pressure in return systems
can prevent trap from closing.
• Life is reduced significantly as pressures
move above 300 psi.
• High discharge noise level.
• Dirt particles can increase cycle ratecausing wear.

Figure 3.1
Disc trap
Flash vapor
closes valve discSeating surface

Valve discLiquid condensate
and flash out

Steam and
condensate in
Inlet port

Outlet port

15

Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
2.	Piston traps: piston traps utilize the heat
energy in hot condensate, and the kinetic
energy in steam, to open and close a valve.
Like disc traps, they are phase detectors
sensing the difference between a liquidand gas or vapor.
During initial startup, pressure created by thecold condensate lifts the piston valve, allowing
discharge of condensate. During this phase,the control chamber pressure is low because
the second or control orifice, can discharge
more condensate than can be supplied tothe control chamber through the first orifice.
When the temperature of the discharging
condensate is very close to steam temperature(i.e., saturation temperature), the condensate,experiencing the lower pressure of the control
chamber, will change into flash steam (inaccordance with the laws of thermodynamics).
This flashing of the condensate in the control
chamber chokes the flow through the control
orifice, causing an increase in control chamberpressure. This increased pressure, acting
on a larger effective area of the piston valve
than the inlet pressure, causes it to snap
shut – preventing steam flow through thetrap. When cooler condensate reaches thetrap, causing the control chamber pressure todrop, flashing ceases and the trap re-opens torepeat the cycle.
The control orifice provides a continuous
discharge which is helpful in passing air orother non-condensable gases during startup.

Figure 3.2
Piston trap

The piston valve remains closed in thepresence of steam because the pressure on topof the piston acts on a larger effective area than
the inlet pressure under it. Steam loss throughthe control orifice is minimal.
Introduced in the 1930’s the piston trap was
the first thermodynamic trap. It is a “hot” trap,
providing excellent service in high pressure
applications.
Advantages• Suitable for high pressure.
• Can be mounted in any position.
• Good response to changing condensate loadconditions.
• Rugged, withstands water hammer.
• Self-draining, not damaged by freezing.
• Function not impaired by superheat.
• Good air handling capability.
• Primary failure mode-open.
• Small size and light weight.
Disadvantages• Excessive back pressure in return systems
can prevent trap from closing.
• Condensate discharge temperature follows
the saturation curve over a limited range.
• Difficult to field check because of continuous
control flow discharge.

Flash vapor closes
piston valve

Control chamber
Piston valve
Second orifice(control orifice)Steam and
condensate in

Liquid condensate
and flash out

16

Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
3. Lever traps: lever traps are a variationof the thermodynamic piston trap. They
operate on the same principle as piston
traps but with a lever action rather thana reciprocating piston action.
When the lever is closed, there is a limited
flow through the annulus between the inlet
valve and its seat (first orifice) which thenenters the control chamber and flows out
through the second or control orifice. Incoming
condensate pushes the lever upward with atilting motion and full flow goes under it andout the discharge port. Condensate flowing
past the inlet seat (a restriction) experiences apressure drop (in accordance with the laws of
fluid dynamics) and it will flash into steam (inaccordance with the laws of thermodynamics)
when the condensate temperature is very close
to steam temperature (saturation temperature).
The localized lower pressure under the lever(created by the high velocity flow of flash steam)causes the lever and inlet valve to snap shut.
This prevents steam flow through the trap.
When condensate with its cooler temperature
again reaches the trap, it will reopen, repeating
the cycle.

Figure 3.3
Lever trap

The control orifice has a continuous discharge
which is helpful in passing air and othernoncondensible gases during startup. Steamloss through the control orifice is minimal.
Lever traps are designed for applications
having especially large condensate loads andthat benefit from the very rapid discharge of
condensate after its formation.
Advantages• Suitable for high pressure applications.
• Good response to changing condensate
load conditions.
• Rugged, withstands water hammer.
• Not damaged by freezing.
• Function not impaired by superheat.
• Good air handling capability.
• Small, compact, easy to install and service.
Disadvantages• Excessive back pressure in return systems
can prevent trap from closing.
• Difficult to field check due to continuous
control flow discharge.
• Can only be mounted in one position.

Upper chamberControl orifice

Lever valve

Liquid condensate
and flash out

Steam and
condensate in

Inlet valve

Outlet orifice17

Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
Mechanical traps
Mechanical traps are density detectors andtherefore also have difficulties venting air
and noncondensible gases. Mechanical traps
employ either an open or a closed float toactuate a valve. Closed float mechanical traps
usually employ a secondary thermostatic air
vent which allows the trap to discharge air
rapidly. The air vent, of course, is an extra
component which can fail open, causing theloss of steam, or fail closed and prevent thetrap from discharging condensate. Closed float
traps are usually large in physical size. This,
combined with a float that is fragile to externalpressure, and the continuous presence ofcondensate within the trap, make this device
unsuitable for high pressure applications
or installations where water hammer orfreeze-ups can be expected.
On the positive side, these devices respond tochanges in condensate level only, independentof temperature or pressure. They respondrapidly to changing loads. Condensate
discharge temperatures follow closely thesaturation curve and they have a modulating(rather than an on-off) type of discharge.

They are extremely energy efficient.
Open float mechanical traps share many
characteristics with closed float traps. One
major difference, of course, is the open float
as found in an inverted bucket trap. The open
float is no longer a weak point, because it
cannot be collapsed by excessive pressure.
Venting is usually accomplished by means ofa small vent hole in the top of the bucket. Thisis a compromise, as the efficiency of the trap
is affected by the sizes of the vent. The larger
the vent the better the air handling, but at theexpense of higher steam losses. A smaller venthas the opposite effect. The end result is a trapthat is relatively efficient, but which does notremove air rapidly during startup conditions.
It discharges near steam temperature with anon-off action and the discharge temperature
follows the saturation curve. All mechanicaltraps are position-sensitive and can beinstalled only in their intended orientation.

18

Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
1. Closed float traps: although it is one of theoldest on the market, the closed float trap
is still in widespread use. The opening andclosing of the valve is caused by changes of
the condensate level within the trap shell.
When the trap is empty, the weight of the float
closes the valve. As condensate enters the trap,
the float rises and opens the valve, allowing
condensate to be discharged. The float isdesigned to provide sufficient force to overcome
the differential pressure across the valve. Theinternal float and valve configuration is suchthat the condensate level is always above thevalve, thus creating a continuous water seal
at its seat. Actual construction varies widely
depending upon the manufacturer. While mostdesigns employ a linkage-pivot system, one
particular design uses no linkage at all andrelies on a free floating ball to achieve thedesired action.
An inherent disadvantage of a simple
float trap is that it cannot discharge air ornoncondensible gases. It is therefore necessary
to install an auxiliary thermostatically activatedair vent. For this reason, these traps are known
as float and thermostatic or F and T traps.

Advantages• Unaffected by sudden or wide pressurechanges.
• Responds very quickly to condensate loadchanges.
• Continuous discharge.
• Condensate discharge temperature closely
follows the saturation curve.
• Function is not impaired by high backpressures.
• Energy efficient.
• Simple construction.
Disadvantages• Relatively large and heavy.
• Float easily damaged by water hammer.
• Does not withstand freezing.
• Can be mounted only in one position.
• Suitable only for relatively low pressures.
• Requires auxiliary air vent which is anadditional source of failure.
• Primary failure mode is closed.
• Not self-draining.

Figure 3.5
Float and thermostatic trap
Thermostatic air vent
Body
Cover

Valve seat

Float

19

Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
2. Inverted bucket traps: inverted bucket
traps are members of the mechanical trap
family, using an open “inverted bucket” asa float. The trapping principle utilizes thedifference in density between steam andwater.
The construction of the trap is such that thetrap inlet leads into the bottom and open endof the inverted bucket. Discharge is through anoutlet valve above the inverted bucket.
Steam entering the inverted and submerged
bucket, causes it to float and close the outlet
valve, preventing discharge of steam. Steam in
the bucket both condenses and leaks throughthe vent, allowing the bucket to sink and open
the valve to discharge condensate. The weightof the bucket must be sufficient to overcome
the closing force created by the differential
pressure across the valve. Inverted bucket
traps discharge condensate intermittently
very near saturation temperature.
Any air or noncondensible gases entering
the trap will also cause the bucket to float
and the valve to close. Since they cannot
condense as steam does, those gases
will cause the trap to remain closed.

In order to overcome this problem, the bucket
has a hole to vent air and steam. The size of
this vent hole has to be relatively small toprevent excessive loss of steam in addition
to the air.
While most inverted bucket traps utilize alinkage system to obtain their desired action,
one particular design uses no linkage at all anduses a free-floating open spherically-shaped
float in its design execution.
Advantages• Simple construction.
• Rugged.
• Condensate discharge temperature closely
follows the saturation curve.
• Reliable.
Disadvantages• Marginal air handling during startup.
• Not self-draining; subject to freeze-ups.
• Not suitable when superheat is present.
• Can lose prime, and is not self-priming.
• Can be mounted only in a single position.
• Failure mode is unpredictable (open or
closed).

Figure 3.6
Inverted bucket trap

20

Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
3.	Open bucket trap: open bucket traps are
rarely used today. As with other mechanicaltraps, they utilize the difference in density
between steam and water.
When condensate first enters the trap, it fills
the trap body and causes the bucket to riseand close the valve at the top of the trap. If
entrapped air is removed, condensate willcontinue to enter the trap, finally spilling over
into the bucket. This causes it to sink and open
the valve allowing discharge of condensate.
When steam arrives, it pushes the condensate
out of the bucket through the syphon tube,
which in turn refloats the bucket and closes
the valve. As the steam in the trap condenses,
additional condensate enters the trap and thecycle is repeated.
This type of trap requires an auxiliary
thermostatically activated air vent, similar tothat used in the float and thermostatic trap.

Advantages• Simple construction.
• Reliable.
• Condensate discharge temperature closely
follows the saturation curve.
• Function not impaired by high back pressure.
• Fast response to changing condensate loads.
Disadvantages• Not self-draining; subject to freeze-ups.
• Not suitable when superheat is present.
• Can lose prime, not self-priming.
• Can be mounted only in a single position.
• Requires auxiliary air vent which is anadditional source of failure.
• Suitable only for relatively low pressures.
• Relatively large and heavy.

Figure 3.7
Open bucket trap

Valve
Seat

Liquid condensate
and flash outA

Air vent

Steam and
condensate in

Steam space

Condensate level

Syphon tube

Open bucket
21

Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
Thermostatic traps
Thermostatic traps respond to changes intemperature and therefore discriminate very
well between steam and cooler noncondensible
gases. They can rapidly purge air from asystem, especially on a cold startup, andcan be installed in various positions. Most
frequently, actuation is by means of a bimetallic
element or a bellowslike capsule filled with avaporizing liquid.
Bimetallic actuated devices are characterized
by their high resistance to damage fromfreeze-ups, water hammer and superheat. They
are relatively small in size and lend themselves
to high pressure designs. The condensate
discharge temperature, however, does notfollow the saturation curve very well, and thebimetallic elements are subject to corrosion
with some reduction in closing force over time.

Bellows actuated traps, on the other hand,discharge condensate at a temperature which
follows the saturation curve. The weak pointis the bellows itself which can be damaged bysuperheat, water hammer or freeze-ups.
Thermostatic traps respond slowly to changing
conditions even though the cause is usually
misunderstood. It is not the heat sensitiveelement that is slow to respond. Rather it is theheat energy in the condensate inside the trap,
which is slow to dissipate, that causes the timedelay. Insulating thermostatic traps reduces
their responsiveness even more. Mounting thetrap at the end of a cooling leg in an area where
air can circulate improves responsivenessand is the basis for installation instructions
recommending a cooling leg at least threefeet in length.

Figure 3.8
Cross-sectioned bimetallic actuated trap;
a simple thermostatic

Figure 3.9
Yarway Model 151

Yarway Model SP80

Yarway Model 151A

22

Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
1. Bimetallic: bimetallic steam traps utilize
the sensible heat in the condensate inconjunction with line pressure to open
and close a valve mechanism.
The valve and seat system is usually arranged
to produce a “flow under the seat” condition.
Supply pressure, in other words, tends toopen the valve. The bimetallic elements arein the form of small discs and are arranged
to produce a closing force with increasing
temperature. This closing force is in opposition
to the opening force created by the supply
pressure. Some bimetallic traps use a single
leaf element rather than the stacked discelements shown in Figure 3.10.
The traps are generally factory-adjusted so thatat saturated steam conditions, the temperature
created force of the bimetallic elements
prevails, closing the valve and preventing lossof steam. As the temperature of the condensate
cools, the line pressure becomes the dominant
force, causing the valve to open and allowing
the discharge of condensate. Back pressure ina closed return system provides an additional
closing force resulting in a lower opening
temperature than the same trap discharging
to atmosphere. The discharge temperature,
therefore, is affected by back pressure.
A design problem for bimetallic traps is createdby the non-linearity of the saturation curve.

Shaping and stacking techniques of thebimetallic elements have made it possible forthese traps to have a discharge temperaturethat approximates the saturation curve. This
has expanded the useful pressure range ofbimetallic traps without adjustment.
The modern bimetallic trap has manytechnical and practical advantages.
Advantages• Rugged.
• Energy efficient.
• Self-draining.
• Resistant to freeze damage.
• Withstands water hammer.
• Capable of discharge temperatureadjustment.
• Can be mounted in several positions.
• Primary failure mode-open.
Disadvantages• Dirt particles can prevent tight valve closing.
• Condensate discharge temperatures do notfollow the saturation curve closely.
• Difficult to field check when operating in athrottling mode.
• Condensate discharge temperature is madelower as back pressure increases.
• Relatively slow response to changing
condensate loads.
• Bimetallic elements are relatively
susceptible to corrosion.

Figure 3.10
Bimetallic trap

23

Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
2. Bellows traps: bellows traps arethermostatic traps that respond to changes
in the temperature and pressure of thesteam supply to open and close a valve.
The valve actuator is a capsule or bellows
filled with a vaporizing liquid, and having
both a fixed and a free moving end, it opens
or closes the valve in response to internalpressure changes. The most frequently
used actuating element is a corrugatedbellows. Single-diaphragm capsules arealso used but provide a correspondingly
shorter stroke.

After such a rupture, the bellows will return to
its natural free length which can be designed sothat the trap will be in either an open or closed
condition.

This simple operating principle provides
many desirable operating characteristics. For
example, the number of degrees below steam
temperature at which the trap will open canbe varied so the trap provides either a “hot” or“cold” discharge. Also the normal failure mode
(open or closed) can be changed.
The characteristics of the actuating system
can be affected by the liquid fill and natural
free length of the actuator. The principles canbest be explained by considering a bellows,
even though they apply equally well to single
diaphragm capsules.
The Yarway bellows traps have been improvedin design, construction and materials tominimize their inherent disadvantages. Today
they play an important role in steam trap
application.

Low boiling point liquids, such as alcohols or
ether, are frequently used in bellows but havethe disadvantage that their saturation curve
does not exactly correspond to that of steam.
As a result steam traps having such a bellows
will discharge condensate having different
levels of subcooling over a wide pressure
range.

Concepts defined• Natural free length: length of the bellows
assembly before it is sealed.
• Assembled free length: length of thebellows assembly after it is sealed, in its
cold (contracted) condition.
In the most common arrangement, the bellows
is located upstream of the valve and thus
senses upstream conditions. Flow direction isover the seat tending to close the valve. Duringcold startup, the bellows is contracted, allowing
condensate and air to be discharged. As thetemperature of the flowing medium rises,
the bellows also gets hot, the liquid inside itvaporizes and expands (strokes) the bellows
to close the valve. Failure of this type of trap
generally refers to the rupture of the bellows.

• Fail open design: this definition implies thatthe natural free length must contract thebellows away from the seat. To make thisarrangement functional, the bellows mustbe filled with a liquid having a boiling point
lower that of water, because for the bellows
to expand, the internal pressure must be
higher than the external steam pressure.

Disadvantages• Bellows elements tend to be failure prone,especially when subjected to water hammer.
• Difficult to field check when operating in athrottling mode.
• Generally not suited for high pressure
applications.
• Limited superheat capability.
• Short stroke diaphragm design susceptible
to dirt initiated failures.

• Fail closed design: this definition implies
that the bellows remain expanded upon
rupture. This can be accomplished by
evacuating the bellows initially to obtain acontracted assembled free length. During
normal operation when the bellows is hot,the pressure inside the bellows will approach
the steam supply pressure, causing it to
expand. Evacuated bellows are usually filledwith water. The inherent advantage is that thecondensate discharge temperature of traps
having such a bellows will closely follow thesteam saturation curve.
Advantages• Excellent air handling capability.
• Energy efficient.
• Self-draining.
• Various condensate discharge temperatures
available depending on bellows design.
• Condensate discharge temperature follows
the saturation curve.
• Can be mounted in several positions.
• Simple construction.
• Small size and weight.

Figure 3.11
Bellows trap

Steam and/or
hot condensate
depending on trap

FLOW

Steam and
condensate in24

Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
3. Liquid or solid expansion trap (wax
capsule type): liquid or solid expansion
traps are finding limited application today.
The opening and closing of these traps is afunction of temperature and balanced return
spring forces. Elevated temperatures cause an
expansion of the thermostatic element whichcloses the valve, while low temperatures cause
a contraction of the element, aided by the
spring, which results in opening the valve.
Traditionally, the thermostatic actuator has
been in the form of a metal rod, having ahigh thermal coefficient of expansion, oran elastic metallic capsule (bellows) filledwith a liquid which expands when heated. In
recent years design innovation has introduceda small diaphragm actuator filled with a
wax-like substance which expands rapidly at apreselected temperature. This has significantly
reduced trap size and increased the speedof response relative to the more traditional
design. Figure 3.12 shows the working internals
typical of a newer wax capsule expansion trap.
Regardless of design variations, these traps
have one characteristic in common. The
temperature of the condensate they discharge
remains constant at a predetermined point
and is not a function of steam supply pressure.

All other steam trap types have a condensate
discharge temperature that increases withsteam supply pressure.
In general, these constant discharge
temperature traps respond slowly to changes
in temperature and should only be specified
where subcooled discharge with resultant
condensate back-up is desired.
Advantages• Rugged.
• Good air handling capability.
• Resistant to freeze damage.
• Withstands water hammer.
• Can be mounted in any position.
• Self-draining.
• Primary failure mode is open.
Disadvantages• Dirt particles can prevent tight close.
• Requires substantial subcooling.
• Difficult to field check.
• Slow response to changing condensate loads.
• Actuator damaged by exposure to hightemperature.

Figure 3.12
Wax capsule trap
Adjustment mechanism

Thermostatic element
Over temperature spring
Return spring

Seat

Valve plug

25

Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
Orifice traps
Orifice traps are seldom used because of theirinherent limitations in application range. This
device consists of one or more successive
orifices. Where two or more orifices are used,condensate passes through a number ofsuccessive chambers where flashing occurs.
This, in turn, creates a restricting or choking
effect and allows the use of larger and lessdirt sensitive orifices for a given condensate
capacity. In some design executions, theseorifices are adjustable valves.
Advantages• No moving parts.
• Suitable for high pressure application.
• Rugged, withstands water hammer.
• Not damaged by freezing.
• Function not impaired by superheat.
• Can be mounted in any position.

Summary

Disadvantages• Orifice size must be carefully selected foreach installation.
• Cannot respond to varying condensate loads.
• Inefficient if oversized.
• Dirt particles readily impair performance.
• Difficult to field check because of continuous
discharge.
• In the absence of condensate, the trap
passes live steam.
A steam trap designer’s comments
Most engineering solutions are a compromise
in one form or another and steam traps are no
exception. The end result is usually a practicalbalance between operating characteristics,
utility and cost.
In the preceding discussion, inherent
advantages and disadvantages associated withthe various trap technologies are presented
with very few qualifications. However over
the years, engineers have been ingenious infinding ways to diminish many of the inherent
shortcomings while enhancing many of theadvantages. The result has been an extensionof the utility of all the various steam trap types.

Figure 3.13
Fixed orifice trap

The influence of standards settingorganizations
In recent years, voluntary standards-settingorganizations have become increasinglyinterested in steam trap design, testingand performance. Responsible steam trap
designers and manufacturers are guided
in their activities by the work of theseorganizations. The American National
Standards Institute’s ANSI/FCI Std. 69-1 andANSI/ASME PTC 39.1 are two standards that
presently relate to steam traps in the UnitedStates. The former is broadly concerned withthe design and safety of steam traps while thelatter is specifically focused on the issues ofmeasuring a trap’s condensate capacity andsteam losses.

Steam traps are automatic valves that open in
the presence of condensate and close in thepresence of steam. They should also be able
to pass air without passing steam, althoughsome types compromise on this point. Typicallythey employ one of three basic operating
principles – thermostatic, thermodynamic ormechanical – to open or close a valve. Eachprinciple has certain inherent advantages anddisadvantages that makes traps of its typemore suitable for certain applications than theothers. Some trap types combine two principles
in an effort to improve overall performance.
A basic understanding of how each type oftrap works greatly strengthens the ability toselect the optimum trap for each application.
It is also essential knowledge when attempting
diagnostic troubleshooting of steam traps or
steam trapping systems.

Steam, flash, or liquid inintermediate chamber

Steam and/or
condensate andflashing vapor out

Steam and
condensate inFirst orificeSecond orifice26

Yarway Industrial steam trapping handbook
Chapter 4 - Principles of steam trap application
Chapter 4 – Introduction
The actual procedure of matching a steam trap
to the needs of the application is to performthe “sizing” first and the “selection” second.
Basic definitions of sizing and selection arepresented in that sequence. However, to have amore complete background and understandingof the situation, the Application Universe is
first discussed in some detail, followed by adiscussion on the Selection Process, and thenthe Basic Sizing Steps. You are also referredto Appendix A for more detailed profiles on
specific applications.
Steam trap application is the process ofmatching a steam trap to the needs of a steam
system and its associated equipment.
This involves a two-step process:1. Sizing it correctly
2. Selecting a suitable type of steam trap
These steps are described in detail in thischapter. However, it must be emphasized that
two additional steps are required to assure
successful steam trapping results. Chapter 5
discusses the elements that are importantto the proper installation of a steam trap andChapter 6 describes the key to long-term
success – proper maintenance.
Sizing and selection of the correct trap fora given application can be complicated bya number of variables, but there are some
guiding principles that can make for a logicalselection process. They will be discussed inthis chapter. Some simplifying rules of thumb,which can be helpful when quick decisions
must be made, will also be presented.
Basic definitions• Steam trap sizing: this is the process ofchoosing a trap which has the capabilities tomeet the operating conditions of pressure,temperature and condensate drainage rate
for a given application.
	Steam trap sizing has been mistakenly limited
by many to matching the end connection sizeof a trap to the particular pipe size being used
to drain a piece of steam heated equipment.
Sizing in its correct sense is matching thesteam condensing rate (in pounds per hour)of a piece of equipment (at its particularpressure and temperature conditions) to therated condensate discharge capabilities of asuitable steam trap.
	Trap manufacturers are prepared tomake sizing calculations to determine
condensate loads in support of their selling
efforts. Small plants having only a few
stream traps tend to rely heavily on thetrap manufacturer for sizing guidance.

Engineering contractors and large plants
using many steam traps generally make theirown sizing calculations. Examples of several
sizing calculations are shown later in thischapter.
• Steam trap selection: this is primarily theprocess of choosing the type of trap, from oneof the major trap technologies (mechanical,
thermostatic, thermodynamic) that will
provide the combination of performance
characteristics most closely matching theneeds of both plant and equipment.
	Selection secondarily includes making
judgments about the usefulness of certain
accessories and features which are included
in some trap designs, as well as making
judgments about the advantages of choosing
to do business with one trap manufacturer in
preference to another.
Trap application universe
It is possible to classify steam trap applications
in a number of different ways. This bookaddresses itself to the field of indus­trial steam
trapping in contrast to the steam trapping
associated with the low pressure (below 15 psi)
heating, ventilating and air conditioning field.
There is some overlap, of course, but industry
has tended to recognize these two majorclassifications of users.
Industrial steam trapping applications arethemselves typically divided into two majorclassifications:Protection service• Steam main drip: drainage of the condensate
that normally forms in the pipes delivering
steam from a boiler to a specific point of use.
This helps prevent damaging water hammer
and promotes the delivery of dryer steam toplant equipment.
• Steam tracing: drainage of the condensate
that normally forms in the small steamlines or steam jackets used to heat valves,
field instruments, and the liquids in larger
pipelines during freezing conditions or when
product temperatures must be maintained at
specified levels.
Process service• Steam using equipment: drainage of thecondensate that normally forms when steam
is used to heat liquids, gases or solids.
These various classifications of steam traps
are presented in the simplified matrix shown in
Figure 4.1.

27

Yarway Industrial steam trapping handbook
Chapter 4 - Principles of steam trap application
Figure 4.1
Industrial steam trapping universe
Service
Protection

Process

Characteristics of service
Small, steady condensate loads
infrequent shutdowns lower
pressures (tracing) and higher
pressures steam main drips.

Application
Steam main drips.

Steam heats air/gas indirectly througha metal wall.
Steam heats a solid or slurry indirectly

Description
Drainage of condensate from pipes used to transfer steam froma boiler to its point of use.
Drainage of the condensate that normally forms in the small steamlines used to heat valves, field instruments, and the liquids in larger
pipelines during freezing conditions. Or when product temperatures
must be maintained above specified levels.
Shell and tube heat exchangers.
Submerged coils.
Jacketed kettles.
Plain or finned coils.
Unit heaters or air blast coils.
Rotating cylinders for paper or textiles.

Larger and fluctuating condensate
loads. Frequent startups arecommon, good air handlingrequired.

Steam heats a liquid indirectly througha metal wall.

through a metal wall to dry, cure or form.
Steam heats a solid through direct contact
to dry, clean or sterilize.

Plattens or presses for plastics; particle board and similar materials.
Autoclave.
Sterilizer.

Steam tracing.

Figure 4.2
Industrial trapping applications universe

Steam pressuresLow
15 psi-100 psi
Medium100 psi-300 psi
High
300 psi-600 psi
Very HighOver 600 psi

Low
0 to 100 lb/hr
Tracing and drip

Condensate load
MediumHeavy
100 lb/hr to 1,000 lb/hr
1,000 lb/hr to 10,000 lb/hr
Process applications

Tracing and drip

Process applications

Drip

Process applications

Very heavy
over 10,000 lb/hr

Drip

An alternative way of looking at the steam
trap application universe is by classificationsof steam pressure and condensate load.
Figure 4.2 shows the ranges of pressure andload most commonly encountered in different
applications. By its very nature such a matrix
tends to be arbitrary, but it does show thegeneral picture.
If the number of traps in the industrial world
were summarized by steam pressure andcondensate load, and listed in the appropriate
quadrant of the matrix, the largest numbers
by far would be in the low pressure, lowcondensate load quadrant. The numbers would
rapidly decrease as the loads and pressure
increase.
Since no single trap design or principle ofoperation is suitable for use across such awide range of pressures and condensate
loads, preparation of a matrix similar to
Figure 4.2 is sometimes used as a technique
to assist a large plant in standardizing on thesmallest variety of traps for its use. Chapter 6,
Maintenance, describes further the process ofestablishing plant standards.

The steam trap selection process
The steam trap selection process starts witha description of a plant’s need. Unfortunately,
simply stating that need in terms of equipment
to be served – such as a soup kettle, tire
vulcanizing press, or an air heater – is notadequate. While it is important information,
it is not sufficient to assure that all therequirements of a specific installation will be
met in a satisfactory manner.
Selecting a trap, like selecting an automobile,
requires an indication of user preference withrespect to a rather large number of criteria.
Fuel economy versus performance, comfort
and safety versus cost, latest style versus anestablished model with proven reliability arefamiliar car selecting choices. While the factorsthat are evaluated in selecting a steam trap
are not nearly as familiar, they are no lessimportant in making a successful decision.
They can be classified into several levels ofimportance. Such a list can then be used asa basis for assuring that all the significant
requirements of a particular application
are considered. Figure 4.3 summarizes andclassifies the most significant steam trap
selection criteria.

28

Yarway Industrial steam trapping handbook
Chapter 4 - Principles of steam trap application
Figure 4.3
Steam trap selection criteriaFirst level criteria• Safety• Efficiency• Service life

Second level criteria• Ease of checking• Sensitivity to back pressure• Resistance to freeze damage• Dirt sensitivity• Installation versatility• Air venting• Responsiveness to changing loads• Resistance to shock vibration and water hammer• Predominant failure mode
• Discharge mode
• Condensate discharge temperature relative
to saturation curve• Magnitude of condensate subcooling• Ease of maintenance• Supplementing accessories or features
Third level criteria• Product availability• Post-sales service• Warranty• Price

It is important to understand fully the
implications of the selection criteria
summarized in Figure 4.3 if a systematic
selection process is to be successful. The
importance assigned to those criteria listed
as affecting overall utility will vary from plant
to plant and from application to application –and properly so. Conditions vary from plant toplant and application to application. Equallyimportant – perhaps most important –management philosophies vary. All want highsystem efficiencies and low maintenancecosts, but their views vary as to the best way
to achieve these objectives. The significant
point is that it is the weight or value assignedby the user to the differing criteria that will
shape the decision as to whether a mechanical,
thermostatic or thermodynamic trap will beselected for a particular application.
A more detailed discussion of the steam trap
selection criteria listed in Figure 4.3 is provided
below:• Safety: product safety results when a good
design is well manufactured and properlyused. In the United States, the American
National Standards Institute (ANSI) describes
for the manufacturer both design and testing
standards that relate to factors affecting
product safety. Manufacturers can describe
installation and maintenance practices theyknow to be successful, but safety in the plant
ultimately rests with the user.

Satisfy primary requirements
These criteria are least subject to compromise.
All trap types (mechanical, thermostatic,
thermodynamic) are capable of providing excellent
performance in a range of applications whenproperly sized and installed.
Affect overall utility
These criteria relate to a steam trap’s overall
utility. The differences between mechanical,
thermodynamic and thermostatic trap designs are
significant. Each trap type has its strengths andweaknesses. These second level criteria are ofparticular interest to the user who is looking beyond“first cost” and who makes an evaluation based on“installed” or “life cycle” costs.

Commercial considerations
These are the commercial criteria that lead to theselection of one supplier over another.

• Service life: a long lasting steam trap is
obviously desirable. Regardless of design,
however, every steam trap’s life is shortened
as steam pressures and temperatures
increase. Hot condensate is a particularly
difficult liquid to handle. It can be both
corrosive and erosive and, under certain
conditions, it can cause cavitation. It can
destroy valves and seating faces in a matterof days in extreme circumstances. The
frequency with which a trap must open andshut also obviously influences its life span.
Opposing these destructive forces are thedesigner’s skills, hardened materials andthe level of special concern a plant has forselecting and sizing traps suitable for theconditions they will experience.
• Efficiency: the most efficient steam trap is
one that has failed in the closed position
because it wastes no steam. Obviously
efficiency can not properly be considered
without reference to how a trap performs its
other functions. Claims that one trap type ismore efficient than another are as difficult
to support as they are to refute. Given acalorimeter test in a laboratory, virtually
every major trap type can achieve efficiencies
of or close to 100%. In fact, the differencesin efficiency between traps will often be
unmeasurable because they are less than theaccuracies of the testing equipment.

29

Yarway Industrial steam trapping handbook
Chapter 4 - Principles of steam trap application
If there is one trap type that is theoreticallysuperior from the standpoint of efficiency,
it is probably the thermostatic because its
opening temperature can be below steam
temperature. As a consequence, it can bemade to back up sufficient condensate thatsteam is unable to reach the trap and passthrough it in normal service. This condensate
backup, however, is not always desirable
because it may adversely affect the efficiencyof the system. Thermal efficiency of thesteam system in which a steam trap isinstalled is more important to the user thanthe efficiency of the steam trap. A steam
trap may be very efficient but if it backs
condensate into a heat exchanger – thereby
reducing system efficiency – it is unsuitedfor this particular application. The same trap
backing up condensate in certain tracing
applications can be contributing to systemefficiency by utilizing the sensible heat in thecondensate. Clearly, steam trap efficiency isvery important, but overall system efficiency
is even more important, and steam trap
selection should be made with this fact
in mind.
• Ease of checking: considering the difficulties
inherent in detecting whether a steam
trap is performing properly (see Chapter 6“Maintenance”), it is surprising moreconsideration isn’t given to this criterion. A
trap that has a crisp open-close cycle canquickly be judged to be healthy with a simple
listening device. Traps that modulate or havea slower and softer open-close cycle often
leave the steam trap checker uncertain about
their condition. “Is it capable of shutting off
tightly?” is the nagging question. As a group,
traps that normally provide modulating
control such as the float and thermostatic orthe bimetallic thermostatic are more difficult
to check than other trap types.
• Sensitivity to back pressure: traps
discharging into closed condensate returnsystems will experience varying amountsof back pressure, depending on the returnsystem’s design and the number andcondition of other traps discharging into
it. Most bimetallic traps will discharge
condensate at progressively cooler
temperatures as they experience increasing
back pressures. Thermodynamic traps tend
to decline in efficiency as back pressuresexceed 50% of the inlet pressure.

• Resistance to freeze damage: steamlines shut down for maintenance or by
accident, or condensate return lines
reduced to very slow or sluggish flow
because of dirt or accumulated scale, areall subject to freezing in cold weather.
The degree of concern by plant managers fordamage to equipment and lost production isquite different between the Gulf Coast andCanada for obvious reasons. Some steam
traps are inherently more susceptible todamage by freezing than others by virtue of
their design and materials of construction.
Cast iron body bucket and float traps are
not popular for use out of doors in cold
climates because they require an internal
water reservoir which makes them especiallyvulnerable to freezing problems. In addition,
the piping configuration used for theirinstallation often makes system drainage
difficult. By contrast, bimetallic thermostaticand thermodynamic traps are free of thisproblem.
• Dirt sensitivity: all steam traps can be put
out of commission by pipeline scale, pipe
joint sealants, oxide build-up or similar formsof contamination. Typically, dirt is caught
between a trap’s valve and seat. This prevents
tight shut-off, allows steam leakage and very
quickly causes permanent erosion damage
to these sealing faces. Some thermostatic,
thermodynamic and bucket traps will havetheir smaller passage or vent holes closed byoxide build-up. Knowledgeable engineers will
carefully consider the relative susceptibilityof various trap types to contamination bydirt before selecting a trap for their plant.
• Installation versatility: some steam
trap models (such as thermostatic orthermodynamic types), can be installedsuccessfully in either a horizontal orvertical line. This simplifies the inventory,
storekeeping and installation problems of
the plant. Mechanical traps do not easily
lend themselves to this flexibility of use, thus
often creating the need for specific models
for installation into either horizontal orvertical lines.

30

Yarway Industrial steam trapping handbook
Chapter 4 - Principles of steam trap application• Air venting: in startup situations, air must be
vented from pipe lines and equipment before
steam can enter it. The faster it is vented,
the more quickly equipment is brought up
to temperature. Some steam traps – suchas thermostatic types – pass air very quickly
under these conditions, while thermodynamic
disc traps and bucket traps release air much
more slowly. If equipment is started andshutdown frequently, as in many processapplications, good air venting is an especially
important consideration in determining thetype of trap to be installed.
Installations which operate around the clock
for months at a time are less concerned withthis special startup capability, but they stillrequire the ability to pass non-condensable
gases such as carbon dioxide (CO2) that may
accumulate in a condensate return system.
• Responsiveness to changing loads: not all
trap types accommodate themselves quickly
to the changing condensate loads typicalof process applications. Mechanical andthermodynamic traps are very responsive,
but thermostatic traps must first cool slightly
before they can open wider to pass a greater
amount of condensate. An adequate “coolingleg” is required in front of thermostatic traps
to assure good system efficiency.
• Resistance to shock, vibration and water
hammer: despite the system designer’s
best efforts, all steam systems tend to
experience some level of vibration, shock, orwater hammer. Startups, pressure changes
or changing loads, are the periods thatgenerally are the hardest on equipment suchas steam traps. Not all traps, however, areequally vulnerable to damage from thesecauses. Thermodynamic traps and bimetallic
thermostatic traps are generally very rugged.
The bellows in thermostatic traps and theclosed float in some mechanical traps are
fragile and damage-prone. These damage
producing conditions are most frequently
seen in process applications.
• Predominant failure mode: all traps are
susceptible to failing closed when plugged
with dirt. But, apart from this special case,some types of trap normally fail in the open
position while others will typically fail inthe closed position. Thermodynamic traps
and bimetallic traps fail open when they
are worn out. Bucket traps tend to have an
unpredictable failure mode as they can fail inthe open position with a loss of prime, or they
can fail closed if the bucket vent becomesclogged or the trap experiences pressure
differentials above that allowable for the
trap’s orifice size. Bellows thermostatic traps
will fail either open or closed depending on
the design of the bellows if the bellows isdamaged.

	Opinions differ concerning the desirabilityof one failure mode over the other. A trap
“failed closed” is not losing steam. On theother hand, a trap however wasteful, that has
failed open, maintains condensate drainage
and therefore has not interfered or disrupted
the process. In general, it would seem that
preserving the process is the higher need anda trap that fails open is more desirable than
one that fails closed.
• Discharge mode (cyclic or modulating
and continuous): does a trap that has adistinct open and shut cycle provide inherent
advantages or disadvantages relative to
one that has a continuous and modulating
discharge? The cycling thermodynamic discand bucket traps are easier to check forproper performance, and perhaps better atpassing dirt particles. On the other hand, thecontinuous draining float trap is especially
responsive to rapidly changing condensate
loads and it does not contribute to pressure
surges in the return system. The judgment as
to which is the superior trap depends on therelative value that the plant operator assigns
to these various characteristics.
• Condensate discharge temperature relative
to the saturation curve: the temperatureof condensate immediately in front of asteam trap at the moment it opens is called
the condensate discharge temperature.
Of course the trap is expected to close
after the accumulated condensate has
been drained and before live steam canbe discharged. In general, it is desirable
that this opening and closing cycle takeplace at temperatures very close to thatof saturated steam. As the temperature ofsaturated steam varies with its respective
steam pressure (see steam saturation curve,
Figure 2.5), it is very desirable that a trap
be able to accommodate these changing
conditions. A trap that does this well issaid to “follow or parallel the saturation
curve” and is a more versatile device andmore easily applied than one that does not.
Mechanical, some bellows thermostatic,
and most thermodynamic traps follow thesaturation curve closely. Bimetallic traps
can be designed to “follow the saturation
curve” approximately, but they do not provide
the same range of performance that can be
expected with the other trap types.

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Yarway Industrial steam trapping handbook
Chapter 4 - Principles of steam trap application• Magnitude of condensate subcooling: theterms “subcooling” and “suppression” referto the temperature difference between
that of condensate at the moment thetrap starts to open and the temperature ofsaturated steam (at the same pressure).
For example, a trap operating at 100 psi(steam saturation temperature 338°F) anddesigned for 10 degrees subcooling will
not start to open until the temperature ofcondensate at the trap drops to 328°F. A
trap with little subcooling or suppression
will discharge condensate within two or
three degrees of steam temperature, while
a trap with a large amount of subcoolingwill discharge condensate at temperatures
30°F or more below steam temperature.
Under most circumstances it is desirable todischarge condensate as soon as it forms
as this helps in the achievement of steady
temperature control. This fact leads to thegeneral desirability of a “hot” trap i.e., onewith only two or three degrees of subcoolingor suppression. Because hot traps discharge
condensate almost as soon as it arrives,
they are rapidly responsive to changing
condensate loads. Condensate is not heldback until it cools 20°F or 30°F before thetrap opens, as is the case with some of themore slowly responding trap types.
	There are a number of applications in thearea of tracing where the heat in highly
subcooled condensate is adequate forthe warming job to be done. Under these
conditions a “cool” trap will tend to improveoverall system efficiency provided the system
has been specifically designed to achieve
this objective. It is the requirement of theequipment being served by the steam trapthat will establish whether one level ofsubcooling is more desirable than another.
• Ease of maintenance: all steam traps fail intime. it is a matter of management philosophy
whether they are repaired or scrapped andreplaced. While steam traps are available
in both repairable models and throw-away
versions, the longer economic view favors
repairability. This preference has encouraged
several manufacturers to design traps thatsignificantly simplify the maintenance task.
• Supplementing accessories or features:
steam traps may be purchased with a varietyof features that increase their life or utility.

Strainers integral to the trap body protect
the trap mechanism from dirt and simplify
field installations. Integral blowdown valvesclean the strainer and help with system
troubleshooting. Integral check valvesprovide system protection, sight glasses
aid in verifying proper trap performance,
temperature adjusting capability is available
with some bimetallic traps and auxiliary
thermostatic air vents can be added to certain
bucket traps to improve their air handlingcapability. Each option requires evaluation
based on its merits and the needs of theapplication and installation.
The steam trap sizing process
Regardless of whether a mechanical,
thermostatic or thermodynamic trap is selected
for a particular application, its satisfactory
performance will depend on it being sizedproperly for the pressures, temperaturesand condensate loads it will experience.
For instance:• Pressure and temperature: safety is
obviously the first consideration. No trap
should be used unless its pressure andtemperature rating equals or exceeds thatof the system into which it will be installed.
Mechanical traps, such as bucket or float
traps, frequently have a maximum operatingpressure that is well below its maximum
design pressure rating. The trap’s utility iscorrespondingly restricted to the smaller
rating. These important design and operating
limitations of pressure and temperature aremarked on a trap’s body or nameplate.
• Capacity: the basic objective of the sizing
process is to select a steam trap that will
have a suitable capacity for passing thecondensate created by the particular pieceof equipment being drained. Selecting a
trap with too small a capacity will cause thebackup of condensate, effectively reducing
the area of steam exposed heat transfer
surface. This reduces total system efficiency
and increases freezing and water hammer
risks. Selecting a trap with too large acapacity, or “oversizing,” not only involves
buying a larger and more costly trap thannecessary, but tends to result in traps that do
not close well and have a shorter than normal
service life. In turn when they fail, they arelarge wasters of steam.

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Yarway Industrial steam trapping handbook
Chapter 4 - Principles of steam trap application

The basic sizing steps – in detail
In order actually to perform steam trap sizing
calculations, more information is required.
A detailed description of the sizing steps is
given below:• Step 1:	Determine the pressure
conditions at the trap.
Pressure at the inlet of the trap will often beconsiderably less than that generated at theboiler. Pressure reducing valves, cascading
systems, line losses and condensing rates all
work to reduce pressure in the system before
the trap. While it is always important to know
the inlet pressure a trap will experience, itis especially true in sizing mechanical types
such as bucket or float traps. Their operating
principle requires the weight of the bucket or
float to open their valve. Should differential
pressures be above the rating of the trap, it will
fail in the closed position.
Pressure at the outlet of the trap will range
from below atmospheric to near inlet pressuresdepending on the design of the condensate
collection system and the performance ofother equipment connected to it. The effect ofback pressure on a trap’s performance is an
important selection criterion. For example,
excessive back pressures upset the normalpressure temperature balance of most
bimetallic traps; the increased closing force
results in increased condensate back-up andincreased condensate subcooling. As backpressures increase beyond design limits,
thermodynamic traps will remain in the
open position.

Figure 4.4
Steam trap capacity changes

20
0°
Fw
ate
r

The basic sizing steps• Step 1:	Determine the inlet and outletpressure conditions of the trap.
• Step 2:
Calculate the condensate load
produced by the equipment being
drained.
• Step 3:	Select a suitable safety load factor.
• Step 4:	Solve the equation:(condensate load) x (safety loadfactor) = desired trap capacity.
• Step 5:
Choose trap from manufacturer’s
catalog with appropriate pressure
and capacity ratings.

Discharge capacity

Factors that affect a steam trap’s capacity
A trap’s capacity to pass condensate is basicallydetermined by three factors: (1) orifice or seatsize; (2) pressure differential between the inlet
and outlet ends; (3) temperature of condensate.
Because these factors are variables, a
trap’s capacity can properly be stated only
if the differential pressure and condensate
temperatures are also stated. The manner inwhich these factors variously influence a trap’s
capacity is described below:• Orifice or seat size: this has been carefully
established by the trap designer with certain
applications in mind. In the mechanical andthermodynamic trap, this orifice is fixedin size. In thermostatic traps (especiallybimetallics), the net orifice area effectively
varies in size as temperature changes slowly
move the valve into or out of the seat.
• Differential pressure: it seems obvious thatthe amount of flow through an orifice will
depend on the difference in pressure between
its inlet and outlet. Less obvious (especiallyin very large industrial complexes with milesof steam lines) is what these pressures arein many steam trap applications. In such
installations, there are many operating
reasons why line pressures will vary. Traps
discharging immediately to atmospherehave only the inlet pressure in doubt. Traps
discharging into closed condensate returnsystems have the added uncertainty of
the level of back pressure in that system.
The significance of these uncertainties isthat properly sizing a steam trap for suchconditions is made more difficult.
• Condensate temperature: the curves in
Figure 4.4 graphically show how much thecapacity of a steam trap can vary simply
because of changes in the temperature ofcondensate coming to it. It can be seen thatfor a given pressure, the discharge capacityof a trap will increase as the condensate
temperature decreases below that ofsteam temperature. A steam trap understartup conditions, discharging 200°F water,
can have four times more capacity thanwhen discharging condensate near steam
temperature (say, at 340°F).

ow
bel
0°F
3
ter
Wa

am
ste

p.
tem

mp.
m te
stea
t
a
er
Wat

0
Pressure

33

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C=

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Yarway Industrial steam trapping
handbook
Q x (T2 – T1)
Page 55
C=
Chapter 4 - Principles of steam trap application 4
C=• Step 2:

Calculate the condensate load tobe handled – process traps
Various formulas are used to calculatecondensate loads depending on the nature of
the application. Some are technically moreaccurate than others because theyPage
employ55
fewer assumptions about the operating
Page 56
conditions but, in general, most provide
Page 55
acceptable approximations. There are four
broad classifications of heating equipment
discussed on the following pages:
1. Steam heats a liquid indirectly througha metallic wall
Typical examples: cooking coils, storage tanks,
Page 57
jacketed kettles, stills
Page 56
The following simple formulas are generally
satisfactory for quickly estimating condensate
Page 56
loads when heating water or a petroleum
product:
Water being heated:C=

Q x (T2 – T1)

Page 58
Q x 2(T2 – T1)
Page 57
C petroleum=A
being heated:
Q x 2(T2 – Tproduct
1)C=
4 –T )Q x (T
Page 57
2
1
C=
Q x4500 x S g x Sh x (T2 – T1)
C=When:
Q x 500 x SHgfgx Sh x (T2 – T1)
C = = condensate
load in lb/hr
H fgwater being heated in gal/min
Q = quantity ofQ x 500 x S g x Sh x (T2 – T1)
H

Substituting intofgthe preceding equation resultsin the following:

Q x (T2 – T1)
C = 25 x 500
x .93 x .47 x (225 – 65)
2C=912
Q xx (T(T2 –– TT1))
Q
2
1
C
=
C
=
958
lb/hr
C = SCFM
24 x (T2 – T1)
C=
QQxx(T500– xT1S) 900
2. Steam
air or a gas indirectly through2heatsg x Sh x (T2 – T1)
C
=
x
D
x
C metallic= SCFM
awall
4v Sh x (T2 – T1) x 60
C=
H fg
Plain or finned heatingcoils and unit spaceH
Q x are500commonx S g xfgShexamples
x (T2 – T1)
heatersC=
H
The following formulaprovides a quick and25 x 500 x .93fgx .47 x (225 – 65)
approximate
condensateC= 970 x (w1 basis– w2 ) for+ westimating
1 x (T2 – T1)
C = for this type912
loads
of equipment.
Hfgx x.47
t x (225 – 65)
25 x 500 x .93
C = SCFM x (T2 – T1)
C = w x S x (T – T912h
2 9001)
C=
x
t
H T)
SCFM
fgxx(T
SCFM
D2v –x formula
S1h x (T2 –will
T1) provide
x 60
A =moredetailed
a moreCC=
900
accurate estimate
H of condensate load:
fg

[

]

SCFM
x Shxx(T(T2 2––TT1)(1.1)
Lp x wx pDxv .121) x 60H
H fgx t970 x (w1 – wfg– T1)2 ) + w1 x (T+2[(.5)(C
Where:C=2)]
Hfg x loadtC
= condensate
in lb/hr
970(w– w )T+a)wor– T1) heated
L xx Aantity
x1Uxgasx(TI2f being
p x1 (Tpof2– air
CSCFM	=
C = w px Su
h x (T2 – T1) 3
C2 =in standard
HHfgfg x ftt /min
fg x t H of gas in lb/ft3 (0.75 air)Dv
= density
w x Sh x (T2 – T1)
Sh== s pecific heat of gas being heatedC
x t H x (T – T )(1.1)
fgBTU/lb/°Fw
LLp xinwppxx.12.12 x (T22 – T1 1)(1.1)
CT1 == =pixnitialC
temperatureof gas being heated11
HHfg xx tt
CC1 =

[
[
[

]
]

in degreesfg
L x w x .12 x (T2 – T1of
+ [.5C+)(1.1)[(.5)(CQ =25quantityof petroleum
heatedgas
being
2 ] heatedx 500 x .93
x .47 x (225being– 65) Page
58 in
2)]
CT12= =pfinalp temperature
Page 59
C = gal/min
Q x (Tin2 degrees– T1)H x t
C = L x A x (T fg
x 500temperature
x .93912
x .47 x (225
– 65) being heated
Taof)xxvaporization
U x I–f 40) x 1.1
T1 =25initialof liquid
p=2latentpx–.12x p10.79heat(338+ [(.5)(C2in)] BTU/lb
C=
CH21 fg= 100
Page 58
SCFM
x (T2 – T912)
in degrees
900
=
c

onstant
thatassumesa typical
Hfg
1
881 x 149
C=
(T –temperatureT)
2 – T1) heat, density, latent heat andT2 =Q fxinalof liquid being
in C = QLx x(TspecificPage heated55
p Ap x (Tp – Ta) x U x If
C = SCFM2x (T12 –900
T1)
C
=
4
+ [8.95]
a conversion of minutes
to hours
degrees2
2
C = SCFM
Hfg
x Dv x900
Sh x (T2 – T1) x 60
60=
minutesinanhour
C = Q x (T – T )wp xx S.12
x
(T–
T)(1.1)
Lpx x500
Q
x
S
x
(T
–
T
)
g
h2
21
1
CC1 == 338 – 40 = 1.49
2 x D1 x HAdetailed
formulais appropriate whenfg
C more= SCFMt=v Sh x (T2 – T1) x 60
xtC
= liquids
4200HHafgfgsolid
3. Steam heats
or a slurry indirectly
otherareHbeing heated:
Lp x wp x .12 x (T2 – T1)(1.1)+ [.5C ]fg
a metallic wall
Cthrough2
Q x 500 x S g x Sh x (T2 – T1)
1=
Page
59
xt
C = 970 x (w1 – w2 ) + w1 x (T2 – T1)
Clothing presses,Hfg
cylinderdriers for textiles or
H fg
25and
x 500
xT.47
xU(225– 65) are typicalC=x x(T.93
x If–plastics
paper
presses
for
pxA
p x–
a) xx (338xpplaten
10.79
.12
40)
x 1.1
+ [.5C
Hfg) x+tw x (T – T )C= L1002]970 x (w1 – w
C
=
1
2
1
2
1 Page 59
2The
formula shown
When:
L912below is suitable forC=
881 x 149x t in lb/hr Page 60
x Sh x (T2 –HTfgload
estimating the condensate loads associatedC w= condensate
1)
SCFM
x10.79(T2 –xT.12
C = 25 x 500
100xx1.178
40)
x–1.1
x .93 x .47 x (225 – 65)
1) x– (338
=
C
100
x
(338
40) x–3The
x+ (1
.85)
[8.95]
with
this
type
of
equipment.
constantQ=
quantityofliquidbeing
heatedingal/minC=
C = w x S fgx x(Tt H– T )Page 56
C21 =
900
h
2 912
1
881881
xof149970 is the latent heatvaporization at
Sg= = specific gravity of heated liquidCH
338 – 40 = 1.49
fg x t heat
atmosphericsteam tables,
Sh =specific
v x Sh x (T(reference
2 – T1) x+60
[8.95]
t == SCFM x Dpressure
SCFM
x (T2 – T1)of liquid being heated in
C
200It His included because the drying
C = British
Appendix“C”).
per pound per
Lp x wp Thermal
x .12 x (T2Units– T1)(1.1)
fg
C1 = degree (BTU/lb/°F)
900
process
definition
338 by– 40= 1.49 requires that the moisture
H
t
L
x
w
x
.12
x
(T
–
T
)(1.1)t=p x pheat
Dv x fg
Sofh xvaporization(T2 2 – T1 1) x 60in BTU/lb
in the product
Hfg= =SCFM
latentCC
200be evaporated.
1=+ [(.5)(C2)]Lx
Ax
500 = c onstant,Hforconverting
gallonsperxtHpp (Tp – Ta) x U x If
fgfg
CC2 == 970 x (w1 – w2 ) + w1 x (T2 – T1)
minute to pounds per+ hour[(.5)(C )]
L

[
[

C2 =

[
[

]
]

Lp x Ap x (Tp – Ta) x U x If

2Page 60
Page
57
Hfg– T )the
Example:determinecondensate
load
L
x
A
x
(T
x
U
x
I
p x (w
p –wp ) +a w x (T f – T )C2 = 970
1
2
1
2
1
in
that
resultsfromheating
C =pounds/hour
HHfg x t
Page 60fg
a liquid with a specificgravity of .93 and awxp(Txof.12x )(BTU/lb/°F)(T2 – T1)(1.1) from 65°F to
Lxp Sxheat
specific
.47
w
–
T
C1 =
h
2
1
C
= at the225°F
per minute.
t –gallons
Hfgof
xrate
.12
x x(T25
Lp x wxtHp2 T1)(1.1)
fg
CAssumea steam pressureof 50 psi. The1=+ [.5C2]x tused to convert
Hfgbe
constant 500 may
gallons
per minute to pounds per hour.
The+ [.5C] 58
Page
2 latent
L
x
w
x
.12
x
(T
–
T
)(1.1)p
1 – 40) x 1.1
100psteamx 10.79.12psix2(338= ofCatx50
is foundin the steam
Cheat
1=
Hfg881
xDtxto149
tables100
in xAppendixbe
BTU/lb.
10.79 x .12 x (338912
– 40)
x 1.1

C1 =

[
[

] ]
]

+ [(.5)(C2)]+ [8.95]
881 x 149

Lp x Ap x (Tp – Ta) x U x If + [8.95]– 40 = 1.49
C2 = 338t=Hfg
338 – 40200= 1.49
t=
200

]

]
]

H xt
Lp x Ap x (Tp –fgTa) x U x If
CWhen:= 100 x 1.178 x (338 – 40) x 3 x (1 – .85)
C22 = w x Sh x (T2 –LT1)
C = = condensate load in lb/hr
881
tH
fg xweight
w1 100= initialof –productdried (lb)
x 1.178x (33840) x 3 xbeing(1 – .85)
Cw
2 2= = final weight of product being dried (lb)
881 of product in degrees
T1 = initial temperature
Lp x wp x .12 x (T2 – T1)(1.1)
temperature of product in degrees
CT12= = final
Hfgofxvaporizationt
Hfg = latent heatin BTU/lb+ [(.5)(Ct = time required for drying(hr) 2)]

[

C2 =

]

Lp x Ap x (Tp – Ta) x U x If
Hfg

34

C1 =

Lp x wp x .12 x (T2 – T1)(1.1)
Hfg x t+ [.5C ]

e 55

e 56

e 57

e 58

ge
e 5955

ge 56

e 60

ge 57

ge 58

C=

Q x (T2 – T1)

C=

Q x 500 x S g x Sh x (T2 – T1)

C=

4

SCFM x Dv x Sh x (T2 – T1) x 60
Hfg

H fg
Yarway Industrial
steam trapping
handbook
970 x (w1 – w2 ) + w1 x (T2 – T1)
C=
Chapter 4 - Principles of steam trap application
Hfg x t25 x 500 x .93 x .47 x (225 – 65) Page 57

C=

912

4. Steam heats a solid through direct contact
SCFM x (T2 – T1)
This
done in a sterilizer or aC
= is most frequently
900 an “autoclave”
steel chamber called
SCFM x Dvformulax Sh x (Tmay) xused60 for
The following
2 – T1beC=
estimating condensate
loads when this typeHfg
Pageof equipment is being used. It should
be 55
Page
Page 58
55
remembered that the surrounding equipment
will also create a large condensate load at
970 x (w1 – w2 ) + w1 x (T2 – T1)
startup.
The same equation may be used toC=
Hfg x testimate this load.

C=

w x Sh x (T2 – T1)
fg x t H

When:
C = condensate load in lb/hr
Lp x wp x .12 x (T2 – T1)(1.1)
Page 59of material heated in lb
Cw1 = = weight
56
Page
56
Hfg xoft material being
Sh = specific heat
heated+ [(.5)(C2)]in BTU/lb/°F
T1 = initial temperature of material being
Lheatedx A x in(Tpdegrees– Ta) x U°F
x If
C2 = p p
T2 = final temperatureof material being
Hfg
heated in degrees °F
Hfg = latent heat of vaporization in BTU/lb
t = Lt ime
reach
final
of 57
wto
– Ttemperature
Page
pxx(T
p x .121)(1.1)) x (T2heated
C1 = Qmaterial
2 – T1being
in
hr
Page
57
C=

[

]

Hfg x t2[.5Ccondensate• StepQ 2x continued:
 alculate +the2]
(T2 – T1) C
C=
load to be handled
–60
Page
4
100 x 10.79 x .12protection
x (338 – 40)traps
x 1.1

[

]

C1 =
Q x 500 x S x Sh x (T2 – T1)
C = main dripg881
x 149
Steam
H servicefg+ [8.95]
In each of the preceding conditions,the 58Page
58
objective has been to heat a liquid, Page
air, gas
338
–
40
=
1.49
or
steam
25 xother
500 xproduct.
.93 x .47 The
x (225– 65) is being
t =someC=
condensed
to200serve a useful purpose. In
912

considering condensate formation in steam
mains,
the reverse
SCFM
x (T2 – T1IS) true. Every effort is made= L x A xthe
toCminimize–900Ta) x U x ofIf condensate as itpp (Tp formation
Cis
condensate
forms because
2 =wasted heat. The
SCFM x Dv Lx Sh thex (T2wall– T1of) x the60 pipe and its
ofCheat= loss throughHfg – 40)
100 x 1.178
x (338x 3 x traps(1 – .85)
surrounding
insulation.
Steamin steam
C2 =Page 59
main drip service are filling a need Page
common59 to881
every steam system, regardless of the purpose
for whichgenerated.
970 xthe(w1steam– w2 ) is+ wbeing
1 x (T2 – T1)
C=
Standard
formulasexistforcalculating
Hfg x tcondensate loads during warming or startup
w x Shfor
x (Tsteamconditions
2 – T1) mains and also for steadyC=running conditions.
xtH
fg

Steam main warming load

C1 =

[

Lp x wp x .12 x (T2 – T1)(1.1)
Hfg x t]wp = weight of pipe in lb/ft.12 = specific heat of steel in BTU/lb/°F
L x wp x .12 x (T2 – Tof1)(1.1)
T1 = initial
pipe in degrees
C = p temperature
T21 = final temperature
Hfg x t of pipe in degrees –use steam saturation temperature (°F)

+ [.5C2][

C1 = 100 x 10.79 x .12 x (338 – 40) x 1.1
881 x 149
+ [8.95]t=

338 – 40 = 1.49
200

w x Sh x (T2 – T1)

x t H of vaporization in BTU/lb
Hfg = latentfgheatt = time for warm up in hr
Q x (T2 – T1to) accommodate warming
1.1
C ==Qc onstantLx p2(Tx2w– pTx1).12 x (T2 – T1)(1.1)
CC = of insulation
1[

2
Q x (T – T )Hfg x t

]

2
1
Steam
load + [(.5)(C2)]C = Q mainx (T2 –runningT1)

4
4
LQpxx500
Ap xx (TU2x–IfT1)
S pg –x TSah) xx (TCC2 == Q x 500
x S g x Sh x (T2 – T1)
Hfg
C=
fg
H fg
C=

When:
C2 = condensate
wp x .12
x (TLpxx500
25.93load.472in–x Tlb/hr
(225
– 65)
1)(1.1)= lengthLCC
p1 == 25x 500ofx pipe
.93 x in
.47ftx (225 – 65)
912
x
t
H
ACp == external areafg of pipe in ft2
912
Tp =SCFM
temperature
pipe in degrees+ [.5C2]°F
x (T2 – Tof1)= ambientx (Ttemperature
T1)
TC
in degrees °F
a =SCFM
2 –900C=
U	 = h100
eatxtransfer
coefficientof steel
10.79900x .12x (338 – 40)
x 1.1 in
C1 = SCFM
x Dv2/°F.
x Sh Ax (TBTU/hr/ft
value
isfrequently
2 – Tof1) x3 60
C = SCFM x Dv x S881
x x(T149– T1) x 60
hpipe
2in
Hfg
still air.
C = used for steel
Hfg equal to +1[8.95]
If = insulation factor
minus
insulation efficiency
338x–(w40=– 1.49Hfg = 970
latentheatwof )vaporization+ w x (T – Tin) BTU/lb

[

]

1
2
1
2
1
Ct == 970 x (w200) + w x (T2 – T1)
1–w
H2fg x t 1
C=
Example: determine
Hfg xthet warming and runningloadswforof 4” schedule 40 steel pipe whenx S100’h x (T2 – T1)
C = wfrom) ) x U x I temperature atraisedLpxxSAh px40°F
x(T(T2 –to–T1Tsaturationaf
fg x t Hp
CC2 ==psi. Assume
100awarm-uprate of 200°F/hr,
x
t
H
fg
L

a heat transfer co-efficient for steel of 3 andinsulation
85%x efficiency.
specific
100 xxof
1.178(338 – 40) xThe
3 x (1– .85) heat ofp wp x .12 x (T2 – T1)(1.1)
C2 = is LL.12.
xw
x .12 ofx (T4”2 –pipe
T1)(1.1)
steel
Weightper foot is 10.79
1
p
p
C1 =
Hfg x 881
t area in square feetpoundsand its external
H xt[(.5)(C2)] D). The
is 1.178 (referencefgtables in +Appendix+ [(.5)(C )]latent heat of steam (881 BTU/lb) at2 100 psi is
L x Apsteamx (Tp – Ta) x Uin
x If
found
C = Linp thex A x (T – tables
T ) x U x IAppendix D.

[[]]

Lp x Ap x (Tp – Ta) x U x If
Hfg
Hfg load (example)
Steam main warming
C22 =L x w x .12 x (T – T )(1.1)
C1 = Lp x wp x .12 x (T2 – T1)(1.1)
C1 = p p H x t2 1
fg
Hfg x t+ [.5C2]+ [.5C2][[

C1 = 100 xx 10.79 x .12 x (338 – 40) x 1.1.12 x (338 – 40) x 1.1
C1 = 100 10.79 x881
x 149
881 x 149
+ [8.95]+ [8.95]
C1 = 41.3 lb/hr
338 – 40 = 1.49
t = 338 – 40 = 1.49 hr
200
t=
200

]]

Steam main running load (example)+ [(.5)(CPage2)] 60Page 60
When:
Lp x Ap x (Tp – Ta) x U x If
C1 == condensate
load in lb/hr
2
Hfg in ft
Lp = length of pipe

ge 59

C=

]

Lp x Ap x (Tp – Ta) x U x If
C2 = Lp x Ap x (Tp – Ta) x U x If
L
C2 =L
100 x 1.178 x (338 – 40) x 3 x (1 – .85)
C2 = 100 x 1.178 x (338 – 40) x 3 x (1 – .85)
C2 =
881
881

C2 = 17.9 lb/hr
Appendix A provides tables that may be used
for making estimates of the condensate loadcreated in insulated steel pipe at various
operating pressures.

35Yarway Industrial steam trapping handbook
Chapter 4 - Principles of steam trap application
Figure 4.5
Typical tracer condensate loads in lb/hr/100 ft of pipe and product temperature between 100°F
and 200°F, stream pressure 100 psig.

Ambient temp. °F
-20
20
60

4
4-8
3-9
2-7

8
8-14
5-15
3-12

Product pipe size, in
12
16
10-19
14-25
7-20
9-26
4-16
5-22

20
17-31
11-32
6-27

24
20-37
13-38
7-32

Assume wind velocity of 0 mph, insulation efficiency 85% and no heat transfer cement

Steam tracing service
Supplemental heat is often provided to protect
piped fluids from freezing or becoming so
viscose that handling becomes difficult or
impossible. Valves, controls and instruments
also are commonly “traced” to assure cold
weather does not prevent their satisfactory
performance. The principles involved in
calculating the condensate loads for tracer
lines are similar to those associated withcalculating the running loads of steam mains.
Experience shows these loads to be very small,as can be seen in Figure 4.5.
• Step 3:	Select a suitable safety load factor
The safety load factor is a number. It isbased on the judgment of an individual withexperience in steam trapping and is usedin trap sizing calculations to compensate
for the lack of exact knowledge about thecondensate load a trap will actually experience.

Estimates of condensing rates in the heatexchange equipment are rough approximations
at best. Pressure and condensate temperature
estimates are often significantly in error
because of unexpected or uncontrollable
system variances or fluctuations.
It is human nature to err on the side of
selecting overly conservative safety loadfactors. It is unfortunate that the problems
resulting from oversizing take longer tobecome visible than those from undersizing.

Technically the safety load factor may be defined as:
Safety load factor =Rated capacity of steam trap
Calculated condensate load of application

36

Yarway Industrial steam trapping handbook
Chapter 4 - Principles of steam trap application
Figure 4.6
Typical relationships between the heating function being performed by the steam, the type ofequipment being used, the system characteristics and a reasonable safety load factor. Reviewing
such a matrix can help form the judgment necessary to select a suitable safety load factor.
Equipment being drained

Function
Heating liquid

Type
Batch stills, shell and tube
heaters, tank coils, vats
Tilting kettle, shipboard tankHeating air

Unit heaters, pipe coilradiators, process air heaters

Drying or curing

Platen, chest type ironer
Cylinder dryer, paper machine
Autoclave sterilizer

Transfer steam
Main drip
to point of use
Provide auxiliary
Tracingheating to controls
and process piping

Significant
characteristic
Gravity drainage

Safety load factor
Pressure
Constant
Variablepressurepressure
2
3

Syphon or lift drainage

3

4

Ambient air above
freezing
Ambient air below
freezing
Gravity drainage
Syphon drainage
Normal warm up

2

3

3

4

3
5
3

-

Fast warm up
Small condensate load

5
1*

-

Small condensate load

1*-

* Theory would suggest that a safety load factor of (1) is bad practice. However, experience establishes that
trap manufacturers seldom design a steam trap for these light load services with a suitably small seat orificebecause it is so easily blocked with dirt or oxides in normal service.

• Step 4:	Solve the equation
Condensate load (lb/hr) x Safety load factor =Desired trap capacity (lb/hr)
The product of the calculated condensate load
and the estimated safety factor is the trap
capacity that forms the basis for choosing
a correctly sized trap.
• Step 5:

Choose a trap from the
manufacturer’s catalog
Manufacturers generally provide their sizing
capacity data in graphic form indicating thepressure and condensate temperature atwhich the rated capacity is stated to exist. As
an example, Figure 4.7 shows capacity curves
typical of a bimetallic trap having medium toheavy capacity.
Temperatures may sometimes be statedas “near steam temperature” or “within
10 degrees of saturation temperature.”

These generalizations result from the fact thatobtaining very accurate data is difficult evenin a well equipped laboratory because of the
difficulty in providing sufficient amounts ofcondensate at constant temperature. “Coldwater” ratings are sometimes stated because
they are easiest to obtain and because theygive an indication of a trap’s capacity during
a startup situation.
Choose a trap with a capacity close to
the calculated capacity for the pressure
conditions and, of course, the proper sizedend connections. Remember that while thecalculated load can be carried out to thesecond decimal place, it is at best a roughapproximation and that unexpected systemvariables may upset an otherwise good
selection.

37

Yarway Industrial steam trapping handbook
Chapter 4 - Principles of steam trap application
Yarway Model 40

Figure 4.7
Steam trap capacity
Differential, pressure, bar
0.1

0.2

0.3

0.5

1

2

3

5

10

20

30
5000

10,000
9,000
8,000
7,000
6,000
5,000
4,000

3000

d
Col

3,000

°F
, 70
ter
wa

2000

Discharge, lb/hr

700

1,000
900
800
700
600
500
400

500

re
mperatuteam te, near s
te
a
s
n
e
d
Hot con300
200

Discharge, kg/hr

1000

2,000

300
100

200

70
50

100
80

30

60
1

2

3

4 5 6 7 8 9 102030 40 50 60

80 100200

300 400 500 600

Differential, pressure, psi

Summary
Steam trap application is the process of first,
sizing it to meet the specific condensate
drainage requirements of a particular pieceof equipment, and second, selecting a typeof steam trap.
• Steam trap sizing is the process of matching
the condensate drainage requirements of aparticular piece of equipment with a steam
trap’s condensate handling capacity at thepressure and temperature conditions towhich it will be exposed.
Standard formulas exist to calculate thecondensate loads that process traps will
experience when serving any of the following
four classes of equipment:• Heats a liquid indirectly through a metal wall.
• Heats air or a gas indirectly through a metalwall.
• Heats a solid or slurry indirectly through ametal wall.
• Heats a solid through direct contact.
Condensate loads experienced by protection
traps in tracer and steam main drip service
can also be calculated by the use of standard
formulas. These loads are generally quite smalland experience has shown that trap oversizing
is a common problem.
Calculated condensate loads for process
traps are normally increased by a safety loadfactor to compensate for system unknowns.

Guidelines exist to aid in the selection of safetyload factors. In general, the more that is
known about the conditions associated with anapplication, the smaller will be the size of thefactor.
• Steam trap selection is the process ofevaluating the relative advantages anddisadvantages associated with each of
the basic trap technologies (thermostatic,
thermodynamic and mechanical), andmatching them with the needs or criteriaof the plant in which they will be used.
These needs, or selection criteria, create
a surprisingly long list:• Safety• Efficiency• Service life
• Ease of checking• Sensitivity to back pressure• Resistance to freeze damage• Dirt sensitivity• Installation versatility• Air venting• Responsiveness to changing loads• Resistance to shock, vibration and water
hammer• Predominant failure mode
• Discharge mode
• Condensate discharge temperature relative
to saturation curve• Magnitude of condensate subcooling• Ease of maintenance• Supplementing accessories or features• Commercial considerations
Selection of a thermostatic, thermodynamic
or a mechanical type trap for a particularservice will necessarily depend on the criteria
considered most important for satisfactory
plant operation, as each trap technology has
its unique advantages and disadvantages.

38

Yarway Industrial steam trapping handbook
Chapter 5 - Principles of steam trap installation
Chapter 5 – Introduction
A steam trap that fails to perform as expected
is not necessarily faulty. Often “trap problems”
are directly traceable to “piping systemproblems.” There are general piping system
practices that must be followed if certain basic
steam trapping problems are to be avoided.
While some pieces of heat exchange equipment
have rather special piping requirements toachieve good trap performance, most do not.
This chapter addresses the generalized rules
for good piping practice and proper steam trap
installation. Recommendations for trapping
specific pieces of equipment are describedin Appendix A.
A review of the problems affecting steam
trap performance“Good practice” evolves as knowledge isgained about the cause of problems and thetechniques that are developed to avoid theirrepetition in the future. As background toa consideration of steam trap installation
principles, it is helpful to review the mostcommon problems associated with trap
performance:
Problems:• Water hammer
Comment: slugs of water hurtling through apiping system not only damage steam traps,
but also other valuable equipment including
the piping system itself. Good piping practices
promote good drainage and prevent theaccumulation of water that makes water
hammer possible.
• Freeze-ups
Comment: a shutdown in freezing conditionsof a system that drains poorly, for whateverreason, is an invitation to trouble. In
extremely cold conditions, poorly insulatedcondensate return systems can freeze. Evenif equipment is not damaged by ice, seldom
the case, startups become extremely tedious
because ice blockages prevent the circulationof steam necessary to bring the system up totemperature. Valuable production time is lost.

Yarway Model 515• DirtComment: by their nature, steam traps
generally have small passages that are
subject to obstruction. Corrosion products
and pipeline trash are the usual culprits. A
clogged steam trap means trouble because
it is no longer able to protect or drain theequipment it was meant to serve. Dirt pockets
and strainers help to protect the trap.
• Air binding
Comment: at startup time, steam systems
can be full of air. Some mechanical andthermodynamic traps have difficulty
differentiating between steam and air. Whensuch traps restrict the proper venting of
air and delay the heating up of the system,
they are considered to be “air binding.”
Thermostatic air vents and thermostatic traps
are commonly used to improve air venting.
• Steam binding
Comment: certain applications, piping
configurations and steam trap types tend
to create conditions in which steam at thetrap keeps it closed, thereby preventing
condensate which has formed upstreamof the trap from being drained.
• Back pressure
Comment: small levels of back pressure
typical of a properly designed condensate
return system are not generally a problem.
It is the elevated levels of back pressure
found in the inadequate return system thatcreates drainage problems.
• Corrosion
Comment: corrosion is best controlled
by proper boiler water treatment but any
piping arrangements that interfere withgood drainage increases the potential for
corrosion problems.

39

Yarway Industrial steam trapping handbook
Chapter 5 - Principles of steam trap installation
The steam trap station – some basics
Figure 5.1 shows a typical steam trap
installation in a closed condensate returnsystem.
Several of its features will apply to any
installation, specifically:• Strainers with blowdown valves: dirt isthe enemy and unless a steam trap has
an integral strainer, as many now do, itshould have a strainer installed immediately
upstream. The blowdown valve which permits
easy cleaning of the strainer screen often
sees service as a useful diagnostic tool whena system or piece of equipment is slow toheat up.
• Test “T”: regular verification that a steam
trap is functioning properly is common
practice in all well maintained plants.
Chapter 6, Steam trap maintenance, has asection on steam trap checking that describes
the usefulness of a test “T” for verifying
proper performance of a trap discharging into
a closed return system.
• Isolation valves: isolation valves arenecessary to permit the inevitable repair or
replacement that all steam traps ultimately
require. They are also required when using
the test “T”. Valves should be fully ported –such as ball or gate valves – to minimizepressure drops that cause condensate
flashing or raise back pressures.

Steam trap location – the inlet piping andoutlet piping
Steam traps should be installed one or two feetbelow the outlet of the equipment being servedwith the inlet piping sloping towards the trap tofacilitate gravity drainage. A drip or dirt leg thatis the same size pipe as the equipment drain
connection will help provide clean condensate
and also serve as a condensate collecting
reservoir. Pipe and fittings ahead of the trap
should be equal to or one size larger than thetrap to reduce the potential for the formation offlow interrupting flash steam. Discharge piping
should be amply sized to accommodate flash
steam and minimize back pressure. For shortdischarge lines, use pipe equal to trap size; forlonger lines use one pipe size larger.
When it is not possible to install a trap below
the low point of the equipment being drained, alift fitting or water seal is necessary. This may
take the form of either a “U” shaped lift fitting
or a small pipe or tube within the larger coil(see Figure 5.2).
Without such an arrangement, steam is able
to reach the trap and keep it closed (steam
binding) before the coils have been adequately
drained. The trap should be located below thehigh point of the loop going over the side of thetank. A check valve is installed just ahead of
the trap to prevent back flow into the coil.

Figure 5.1
A typical steam trap installation

Overhead return line

Branch line
Valve
Steam
equipment

Steam main
Drip trap

Dirt
pocketStrainer andblowdown valve

Strainer

Trap

Union
Tee

Check
valve

Blowdown
valve
Return line

Figure 5.2
A lift fitting application
Steam line

To returnSwing check
valve

ProcessliquidSlope

Small pipe

Steam

Large coil

To returnCondensate

40

Yarway Industrial steam trapping handbook
Chapter 5 - Principles of steam trap installation
The steam distribution system drainage andtrapping
Good drainage of steam mains and branchlines is mandatory. A piping system that sags
or otherwise allows pockets of condensate toform, creates the conditions that cause water
hammer and its associated damage. Suchsystems when shut down in freezing climates
experience additional problems because of
unwanted ice formation. All natural drainage
points arid low points in a steam line or main
require a steam trap and, in fact, steam
main drip service is the most common trap
application. Where long pipe runs exist without
natural drainage points, they need to be createdin the form of drip pockets at intervals of
approximately 300 feet. Drip pockets should be
the same diameter as the main or branch line
as this helps prevent condensate from being
carried past the pocket by high velocity steam.
Drip pockets and drip traps should be placed
upstream of temperature control, pressure
reducing, and stop valves to prevent damage
and assure dry steam supply to equipment.
Drip traps are also required at expansion
joints and loops and the terminal ends ofsteam mains.
The steam main itself should have a slopeof about one inch in twenty feet to facilitate
condensate drainage by gravity.

Steam supply lines should always be tapped off
the top of the steam main. This helps deliver
dry steam to the equipment (see Figure 5.1).
Steam separators
Separators perform a job that steam traps
cannot do. Steam traps drain condensate
that has collected at a drainage point. Steamseparators (or steam dryers) remove water
droplets that are entrained in the steam
flow. They are installed in the steam main
immediately down-stream of the boiler, toimprove the quality of steam going into the
distribution system, or immediately ahead ofequipment that requires especially dry steam.
Steam separators, in turn, are drained by asteam trap.
The condensate return system
The primary purpose of a condensate returnsystem is to save the expense of continually
upgrading water to a quality suitable for goodboiler performance and to recover heat energy
still in the condensate, thus improving overallsystem efficiency. In addition, condensate
return systems afford the opportunity to use
flash steam in progressively lower pressure
heating systems. Condensate return is
discussed in detail in Chapter 7.

While the benefits of a return systemsignificantly outweigh the problems associatedwith it, such a system does allow theformation of a back pressure against whichsteam traps must discharge. Back pressure
at moderate levels is not a problem but at
levels of 50% or more of inlet pressure, it canadversely affect the performance of bimetallic
and thermodynamic traps. The discharge
temperature of bimetallic traps become
extremely suppressed, creating significant
condensate backup. Thermodynamic traps
become less efficient i.e., begin to pass steam.
The significance of these comments is simply
to establish that piping factors which increase
the back pressure against which a trap must
discharge, also increase the potential for
unexpected trapping problems.
A common cause of excessively elevated backpressures in a return system is the plant
expansion that increased the number of steam
traps discharging into the system without also
having increased its size to accommodate theadditional flash steam.

Figure 5.3
A condensate return system showing the collection and use of low pressure flash steam
Low pressure flash steam

High pressure
condensate from traps

Drip traps
H-P flashtank

Atmospheric ventLow pressure
condensate
from traps
Condensate
pump
Carefully size andselect condensate
pumps and controls

To boiler-feed system

Atmosphericreceiver

Condensate pump41

Yarway Industrial steam trapping handbook
Chapter 5 - Principles of steam trap installation
Condensate lifting
When the condensate discharged from a steam
trap must be raised to a collecting manifold
or header, it is necessary to assure that thedischarge pressure at the trap is sufficient toovercome the vertical lift plus the pressurein the overhead return line. If this is not thecase, reverse flow will take place. Every footof elevation following a trap will add ½ psi
to the back pressure the trap experiences.
It is important to assure in these applications
that total back pressure does not exceed theallowable limits of the particular type of trap
selected. Figure 5.4 shows an example of thearithmetic used in estimating back pressure
when a trap is discharging to an overhead
return line. Note that pipe, valves and fittingpressure losses will also contribute to the backpressure.
In the example shown, a check valve is installedat the bottom of the riser. This is to prevent
backflow into the heating coils and encouraging
corrosion when the system is shut down. Checkvalves tend to leak over time and hence, inthis example, would be effective only during
relatively brief periods.
Pumping traps
The installation shown in Figure 5.4 isrepresentative of many situations in whichcondensate is raised to an overhead return
main by pressure in the discharge line. There
are occasions when this type of drainage
arrangement is not considered especiallysatisfactory. An alternative approach employs
a device called a “pumping” trap. This has
the advantage of allowing a number of traps
to drain condensate by gravity to a sump
before being raised to the return main.

Water hammer potential is reduced and quicker
plant startups are possible when pumping
traps are used. Pumping traps also can lift
condensate from a condenser or turbine drainthat may be operating at vacuum conditions.
The principle of a pumping trap is that ofa closed receiver fed and drained throughcheck valves. It contains a float that rises
until it opens a valve admitting steam thatpressurizes the receiver. This, in turn, forces
the accumulated condensate out of the receiverto an elevated return system. The falling float
closes the valve admitting steam and opens an
atmospheric vent. Condensate can now flow
again by gravity into the unpressurized receiver
until the float again rises sufficiently to repeat
the pressurizing cycle.
Auxiliary air vents
Air in a heating system significantly reduces its
efficiency. Air is a very poor conductor of heat
and air filming on pipes and heat exchanger
tubes reduces the heat transfer rate throughtheir metal walls. Also, steam mixed with air
contains fewer BTUs at a given pressure thansteam alone. It is the function of a steam trap
to aid in venting air from a steam system,
but auxiliary thermostatic air vents are often
required. Open to cooler air and closed tohotter steam, they greatly speed up the air
purging process. When frequent startups
and shutdowns are the rule, rapid air purging
is a significant factor. Thermostatic traps
are often favored for their good air handlingcharacteristics on startup. Figure 5.5 shows
schematically a typical autoclave installation
with auxiliary air venting.

Figure 5.4
Estimating back pressure when discharging to an overhead return
Steam in

5 psi
condensate
returnControl
valve

6 ft

Swing
check
valve
Trap

Sufficient length toprevent coil corrosion
and/or freezing½ psi per footcreates 3 psi

Pipe flooded withcondensate

3 psi + 5 psi = 8 psi
Total back pressure

Dirt pocket

42

Yarway Industrial steam trapping handbook
Chapter 5 - Principles of steam trap installation
Vacuum breakers
When a closed and pressurized steam system
is allowed to cool down, it is not just thetemperature that drops. The pressure in thesystem will decay to a vacuum unless somemechanism permits the entrance of air, thus
allowing the system to achieve atmosphericpressure. Such a mechanism is called avacuum breaker. It is essentially a check valve,closed to internal pressure, but open whenthat internal pressure becomes less thanatmospheric. Figure 5.6 shows schematicallythe installation of a vacuum breaker on an air
heating coil.
If the upper shut-off valve is closed while theheating unit is in operation, condensate will
not be able to drain out of the unit.
As it cools, it is possible for condensate thathas drained, into the return system earlier,to be drawn back into the unit unless a vacuum
breaker functions to permit air to enter thesystem.
Summary
Performance problems with steam traps
are often directly traceable to the piping
arrangements used to install them. Experience
continues to justify the wisdom of knowing andfollowing good piping practice.

Figure 5.5
Auxiliary air vents are often helpful in purging
air from large steam spaces at startup

Ideally, condensate should be able to drain
freely to (and from) a steam trap by gravity.
Line restrictions which may produce elevatedback pressures or lead to condensate flashing,should be avoided. Such restrictions may result
from the use of undersized valving or excessive
pipeline size reductions. When condensate
must be raised to reach a trap or an elevatedreturn main, care should be exercised so thatsteam binding or excessive back pressures
do not occur.
Steam traps should be installed so that
performance checks and maintenance activities
can be easily performed. Properly sizedstrainers with a suitable blowdown valve arean easily justified steam trap protection device.
Air vents, vacuum breakers and check valves
may be required to solve specific drainage orflow problems which otherwise would adversely
affect a steam trap’s performance.
The removal of condensate from a steam
system cannot be considered as anafterthought. The absence of problems
associated with water hammer, corrosion, dirt
and freeze-ups has been the result of carefulplanning and conscious effort to avoid theroot causes of these problems.

Yarway Model 71I

Figure 5.6
A vacuum breaker aids in the drainage of condensate when a steam system is shut down

Vacuum breaker

Steam inSteam line

VB

Auxiliary
air vent
A
Air heating coil

A Air vent

AutoclaveAir

Min. as recommended
by coil mfgr. up to 3 ft formodulating steam andfreezing air temperature

Trap

Condensate return43

Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
Chapter 6 – Introduction
Steam traps must be selected, sized andinstalled carefully if good system efficiencies
are to be achieved. By themselves, however,these factors will not assure an efficientsystem. In the long run, regular maintenance ofthe selected traps will be the significant factor
in system efficiency because in time all steam
traps fail. In spite of the certainty of failure andthe high cost consequences that can result,really good trap maintenance programs seemto be the exception rather than the rule. Thismay be because traps are relatively inexpensive
devices and it may be wrongly considered thatthey perform a relatively inconsequential task.
The equipment that traps protect is often
large and expensive. Its damage or reduced
productivity can be very costly. When a steam
trap fails in the closed position, condensate willback up into a heat exchanger. This can spoil
the product at the worst or simply reduce heatexchanger utility at the best. A trap that has
failed closed in other circumstances, such as ina freezing environment, can readily lead to lines
blocked or broken by ice.
Alternatively, when a steam trap fails in its open
position, it usually damages nothing. It simply
allows steam to flow through a system at muchhigher rates than is necessary for the heating
job to be performed.
It reduces system efficiency in the samemanner as any other steam leak. While it isgenerally considered more desirable for a
trap to fail in the open rather than the closed
position, either can have significant adverse
cost consequences.
The very high cost of generating steam, andthen failing to use it properly, is beginningto gain the attention of plant managers.
Also, recognition is developing that a goodsteam trap maintenance program is nota questionable expense but a source ofsignificant cost savings both in fuel costs
and in higher equipment utilization. Any plant
seriously interested in reducing its energy
costs must develop a systematic approachto maintaining its steam traps in proper
operating condition:
Maintenance programs
Maintenance programs will necessarily differ
among plants having five, five hundred or
fifteen thousand steam traps. Nevertheless,their objective will be fundamentally the same.
In larger plants having one thousand or more
traps, individuals with the full-time assignmentof checking and reporting the performance ofsteam traps are increasingly common. Smaller
plants may not have a full-time specialist, butsome are attempting to have an individual
who is especially knowledgeable about
steam traps and steam-trapping practice.

Regardless of the size of the plant; a common
problem exists for every steam trap user: thedifficulty of determining if a trap is working
properly. While sometimes it is a relatively easy
matter, frequently it is difficult, speculative
and uncertain. Specialized equipment exists to
help the steam trap checker and a great deal
has been written listing logical progressionsof questions and tests to establish if a trap isperforming properly for its given conditions.
However, conclusive answers to some of thesequestions are frequently not easy to supply.
To date a good bit of experience, judgment andart are still necessary to identify malfunctioning
traps – especially if they are discharging into a
closed return system.

• Numbering and tagging every trap location
is essential for a successful maintenanceprogram. The written records of the conditionof each trap at the time of inspection are
also essential so that inspection frequencies
can be logically established. These records
also provide opportunities for a wide rangeof performance analyses and comparisons
between trap types should there be evidence
that additional cost savings can be obtainedby seeking absolutely optimum performance.

The essentials of a successful maintenanceprogram
Successful maintenance programs of thelarger users of steam traps tend to have certain
common elements. A review of these elements
can be useful to maintenance managers in
the plants having small as well as large trap
populations. They are:
• A committed member of Plant Management
who understands the high financial
payback associated with an efficient andwell-maintained steam trapping system.
• A valid cost analysis developed over ameaningful period of time which has shown
the dollar savings in energy costs associatedwith a specialized pilot maintenance programfor steam traps. Often initiated in a single
portion of the plant, these pilot programs,
allow product produced to be correlatedwith steam consumed both before andafter the start of a specialized steam trap
maintenance activity.
• A full time steam traps maintenance crew,
including a diagnostic specialist, in addition to
the personnel who repair or replace defective
traps.
• A set of steam trapping standards which
recommend a correct piping configurationand trap type for the various trap applicationsin the plant. Efforts generally have been
made to standardize on as few trap types
as practical.
• A complete, but easily kept, set ofmaintenance records including simple
maps identifying the location of every trap
in each area of the plant. Survey sheets are
employed that list (1) an identifying number
for every trap location in a given area; (2) theequipment being drained; (3) the operatingpressure; (4) the trap type suitable for theapplication; (5) and a place to record trap
condition at the time of a survey.

44

Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
The importance of trapping standards
When experience has shown that therequirements of a certain application are wellsatisfied by a specific type of trap and piping
configuration, it makes sense to establish atrapping standard that will apply to all similar
applications. When this standardizing process
is expanded to cover all trap applications ina plant, it produces important benefits. The
steam trap maintenance activity is greatly
simplified. The variety of traps in use is reduced
and their proper performance becomes better
understood by maintenance personnel. Traps
that have reached the end of their normal
service life are repaired. Misapplied traps
are more easily recognized and are replaced,rather than mistakenly reinstalled. Repeatedly,
the experience of steam trap users who makethe effort to standardize their steam trapping
practices is an improvement in system
reliability and efficiency.
Establishing trapping standards
A plant that has become convinced it canbenefit from the establishment of steam
trapping standards may be tempted to simply
adopt standards which have been successfully
used elsewhere. This is probably unwise. A
chemical plant, a refinery, a papermill or a foodprocessing plant reasonably can be expected tohave different trapping standards. The mannerin which these plants operate will be different
and their exposure to freezing weather canvary – both factors will strongly influence thestandards that should be adopted. While good
piping and installation practices are the same,
regardless of industry or climate, the specifictrapping requirements of individual plants
should be recognized.

Getting started with trapping standards
The initiation and development of trapping
standards for an organization may occur in awide variety of ways, but ultimately someone
has to wrestle with some basic questions.
Typically:
1.	 How should steam trap applications beclassified so that standardization canreasonably take place?
2.	 What are the most important criteria bywhich steam trap performance should
be judged?
Classification of steam trap applications
Steam trap applications are classified in atleast two major ways:
1.	Type of equipment being drained. For
example; steam mains, drying cylinders,heat exchangers, storage tanks, vulcanizingpresses, tracing lines.
2.	By generic conditions as defined bypressure and condensate load. These canbe represented by a simple matrix suchas Figure 6.1 or one that is more refined,
Figure 4.2.
If the operating conditions – i.e., pressure andcondensate loads – are quite uniform for eachof the specific types of equipment in a plant,
then classification by equipment being served
may be quite suitable. Often this is not the case;as there may be steam mains at 100 psi andothers at, say 500 psi, or small heat exchangers
having condensate loads of 1000 psi whileothers approach 10,000 psi. Differences ofthese magnitudes almost inevitably lead todifferent standards recommendations. Genericclassification of operating conditions by its very
nature tends to be more widely applicable.
Sometimes it is portrayed in a graphic manneras shown in Figure 6.2.

Figure 6.1
Matrix format that can be helpful in establishing plant-wide steam trap standards.
Each quadrant block should reference the preferred type of trap for the stated conditions.

Diff. pres.
Below 100 psi
Between 100 and 300 psi
Between 300 and 600 psi

Below 100 lb/hr

Load
Between 100 and1000 lb/hr

Between 1000 and
10,000 lb/hr

45

Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
Trap evaluation criteria
A list of the criteria useful in evaluating thesuitability of a steam trap for a particularapplication can be quite long. Chapter 4'Principles of steam trap application' discusses
these criteria at length and Figure 4.3 showssuch a list. Selecting a steam trap type(thermostatic, thermodynamic or mechanical)
as the standard for a particular application
in a plant requires making decisions about
the inherent advantages and disadvantages
associated with each type. Chapter 3 'Operating
principles of steam traps' describes theseadvantages and disadvantages. Obviously, thedecision to standardize on a particular trap typefor a certain application should be made withgreat care and after evaluation of all relevant
factors because, by definition and intent, astandard will be used over and over again.
Steam trap checking
Regardless of the care that has been spent inclassifying a plant’s steam trap installations,and the thoroughness with which various
types of traps have been evaluated and thecare with which plant standards have been
prepared, there will ultimately be the needto judge whether the installed traps areworking properly or whether they require
repair or replacement. This is not a job for
the untrained and inexperienced.

Certain gross failures are of course readily
detectable. A cold steam trap is obviously notworking although it remains to be determined
whether the trap has failed mechanically,or whether accumulated dirt and scale has
choked flow through the trap, or whether it has
been inadvertently valved out of service as aresult of some unrelated maintenance activity.
Traps that are visibly leaking steam at joints orseals have clearly failed. Traps conspicuously
blowing large amounts of vapor from their
exposed discharge side probably have failed,
but it is at this point that a level of uncertainty
begins to develop. Most properly operating
traps will have “flash steam” associated with
their discharge. In addition, the amount ofvapor and the pattern of discharge (continuousor cyclic) of a properly operating trap are
significantly influenced by normal operating
variables such as pressure and condensate
load. Uncertainty increases in a dramatic
fashion with attempts to assess a trap’s
performance when it is discharging into a
closed return system and it is not possible tosee its discharge pattern.
Despite these areas of uncertainty, learning to
identify grossly failed steam traps can proceedwith a reasonable level of confidence. However,
it is the ability to identify that a trap has started
to fail and is beginning to pass more steam
than is acceptable (but has yet to reveal itself
as a grossly failed trap) that elevates steam
trap checking to a task for a skilled andknowledgeable individual.

Figure 6.2
Example of a graphic format that can be helpful in establishing plant-wide steam-trap standards.
Equipment having operating conditions defined by one of the reference areas should be able toutilize successfully a given trap type and installation layout.
10,000
Reference D

Condensate load lb/hr

1,500

1,000
Reference C
150

100
Reference A

Reference B

50

10
0

100

200

300

400

500

600

Pressure, psi (trap inlet, minus trap outlet)

46

Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
A basic rule (with no exceptions)
It is essential that anyone assigned the
responsibility of checking steam traps
understand the principles of operation of thevarious types of devices to be checked.
It is no more realistic to attempt to diagnose
the performance of a steam trap without
first knowing its principle of operation than it
would be to diagnose the performance of aninternal combustion engine without knowing
the difference between a diesel, turbine, orgasoline engine.
Chapter 3 'Operating principles of steam
traps' describes how each of the various
trap technologies work. Thermostatic traps(bimetallic, filled bellows, diaphragm capsuleand constant temperature-capsule) all
have different performance characteristics.
Thermodynamic traps (disc, piston, lever) havedifferent performance characteristics between
themselves and also from the thermostatic
models. Mechanical traps (bucket and float)
have performance characteristics that differ
from each other and yet are similar to some ofthe other trap types.
In summary, it is essential to know the
principles of operation of a trap before
attempting to check its performance. It isalso important to be aware of a complicating
factor: the “usual” performance characteristic
associated with some trap types can be alteredsignificantly under certain operating conditions.
This phenomenon is generally associated withvery high or low condensate loads (relative
to the trap’s capacity) or with very high or
low pressure differentials across the trap
(relative to its pressure rating).
Fundamentals concerning trap failures• Most types of traps will fail open so that theyleak steam. Some types of traps fail closed sothat they pass neither condensate nor steam,and some types of traps will fail unpredictably
in either an open or closed mode.
• All types of steam traps can appear to havefailed because of some shortcoming or
problem in the system in which they are
installed. While this fact must always be kept
in mind it does not become a significant issue
unless the steam system has been neglected.
• The most common failure for all types ofsteam traps is erosion of the seat and valve
sealing faces. This keeps the trap fromclosing tightly. Once a small leak starts ina pressurized steam system, it becomes alarge and expensive leak in a short time.

	Seat and valve leakage generally resultsfrom pipeline dirt becoming caught between
their mating surfaces. Small manufacturing
imperfections relating to surface finishes orproper alignment can also shorten trap life.
• Pipeline dirt, oxides, scale and pipe joint
sealants are the enemy of all types of steam
traps. Some trap types are more forgiving
than others, but all have their limits. A trap
which has the appearance of having failed
closed because of dirt can often be restored
to useful service with a simple cleaning.
	A trap leaking steam because of dirt between
the valve and seat probably should be
replaced or repaired with new components.
The likelihood of permanent damage having
occurred because of the dirt is high.
• The life expectancy of a trap is largely related
to the pressure at which it must operate.
In general – the higher the pressure, theshorter the life.
Fundamentals concerning trap checking
techniques
Checking a steam trap is the process ofobserving its performance and comparing itwith the performance characteristics that one
has learned are typical for a healthy trap of thesame type. If the performances are similar,
the trap may be judged to be O.K. If there aredifferences, it can be concluded that either thetrap is faulty or the system in which the trap isinstalled has a problem.
There are three basic techniques used inobserving the performance characteristics ofa steam trap. They are:• Sight: visually observe the discharge pattern.
• Sound: listen to the functioning of the valve
mechanism and the flow of fluid throughthe seat.
• Temperature: determine the trap’s
temperature.
Each of the checking techniques has its
limitations and seldom can a conclusive opinion
be reached on the basis of a single type ofobservation. Experienced steam trap checkers
invariably try to use all three techniques. Somewill use more expensive checking equipment
than others in this checking process, but
the quality of their results does not seemto vary much.

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Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
Sight
Watching the discharge pattern of a steam
trap is probably the most reliable method ofdetermining whether it is working properly.
Unfortunately, many traps discharge into closed
condensate return systems without test “T”sand the discharge pattern is not visible. Under
these conditions trap performance appraisal islimited to sound and temperature monitoring.
The fundamental limitation to observing thedischarge pattern of a steam trap in order
to assess its health is that hot condensate
discharging to atmosphere flashes into steam.
The observer then has to decide whether the
clouds of vapor being witnessed are the resultof leaking steam or the normally expectedflash steam. An experienced eye begins
to distinguish the lazier action and white
appearance of flash steam from the moretransparent jet-like discharge of live steam thatcan be seen right at the trap’s outlet. The bestclues come with watching a steam trap thathas a normal crisp off/on cycle, such as a discor bucket trap. If the discharge vapor has any
velocity during the closed period of the trap’s
cycle, it can be reasonably assumed that it isleaking steam and should be replaced.
While most thermostatic traps can have a cyclic
mode discharge, it tends to be slower and lessdefinite than either the disc or bucket types.
Thermostatic traps, especially bimetallic traps,
can also have a continuous discharge pattern.
Float traps that are designed for continuous
modulating drainage are harder to diagnose,
especially in the early stages of failure.
Steam trap manufacturers recommend, andmany users routinely install, a test “tee”
and valving arrangement that will permit
witnessing a trap’s discharge pattern in anotherwise closed condensate return system.
The initial extra cost of this type of installationis handsomely repaid by the surer knowledge it
produces concerning steam trapping efficiency.
Sound
Listening to the sound of a steam trap
functioning with the bit of a long handledscrewdriver (held against the trap andits handle pressed against an ear)can provide important information as
to whether it is doing its job properly.

Because of the high background noise that
often surrounds a steam trap, the screwdriveror industrial stethoscope is giving way to theultrasonic listening device with earphones.
These help to screen out the normal
ambient background noise and permit more
precise identification of a noise pattern in an
individual trap.
The weakness of these devices, which is notovercome with the more expensive models, isthat to hear a noise pattern is not necessarily
the same thing as understanding what itmeans. Listening to a trap which is designed
to have an open and closed cycle action canquickly reveal if the trap is operating in thismanner. It can also reveal if there is any
significant leakage past the valve when it is in
its closed position. But the value of listening tofloat traps or thermostatic traps operating ina modulating mode in an effort to determine
if they are leaking steam is questionable. The
noise patterns generated in the trap can beheard relatively easily. The problem is in themind of the listener – “What do they mean?”Temperature
Every individual who checks steam trap
performance employs some sort oftemperature sensing means. A wet finger(obviously dangerous), a squirt bottle, asurface-contacting pyrometer, or an infrared
sensor all have the same initial objective: Is
this trap hot? If not, it can be deduced that little
or nothing is flowing through it and the trap
is not performing one of its major functions –draining condensate. This does not necessarilymean that the trap has failed. It first must be
determined if some obstruction either up or
downstream of the trap has blocked flow in thepipe. Once that issue is resolved, it is logicalto proceed with steps investigating the trap
for blockage by pipeline dirt or failure of its
internal mechanism.
When it has been determined that a steam
trap is hot, the next question is whether it isas hot as it should be. Steam traps designed
to discharge condensate very close to steam
temperature such as disc, bucket or float traps
will have a surface temperature about 5 to 10%
below the temperature of steam in the system.
Figure 6.3 shows typical pipeline surface
temperatures.

Figure 6.3
Pipe surface temperature vs. steam pressures
Steam pressure(psig)
15
50
100
150
200
450

Steam temperature
(°F)
250
298
338
366
388
460

Pipe surface temperature range(°F)
238 - 225
283 - 268
321 - 304
348 - 329
369 - 349
437 - 414
48

Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
Figure 6.4
Live steam and flash steam

Figure 6.5
Steam trap checking decision tree

Equipment• Temperature measuring• Sound detection• Safety glasses

Knowledge• Of basic system• Of trap operation

Any trap tobe checked

Is it hot?

Thermodynamic• Disc• Piston• Lever

Yes

No

What type of trap?

Is the system shut-off, blockedwith air or dirt?

Thermostatic• Bellows• Bimetal• Diaphragm• Constant temp.
(wax cap)

Mechanical• Bucket• Floatthermostatic

Yes

No

Correct
problemMaybefaulty trap

Proceed to section describing specific trap type49

Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
Unfortunately, it does not follow that if
temperatures are observed in this range thatthe trap is healthy. It only means it is doing half
its job properly, i.e., draining hot condensate. It
is difficult to determine by temperature alone
if a trap is leaking steam when it is designed
to operate at close to steam temperatures. If
measured temperatures are much below the
expected range, the trap can be suspected ofbacking up more condensate than normal.
Traps designed to discharge condensate at
temperatures well below that of steam, suchas some of the thermostatic types simply
reverse the generalities described above.
If they measure hotter than expected; they
probably have failed and are leaking steam.
If the temperatures are well below the steam
temperatures in the system, these traps may
be judged to be backing up condensates as
they have been designed to do.
In general, there will be a significant differencein temperatures between that observed
upstream of a trap and that observed
downstream. These temperatures will bedirectly related to the pressure in the system atthe point of measurement. If the temperatures
measured up and downstream of a trap are thesame, it can only be deduced that the pressure
on either side of the trap is the same. As thisis an abnormal condition, it can be concluded
that a system problem exists that may or may
not be caused by a faulty trap discharging into
a common return. More analysis is necessary.

In attempting to answer these basic questions,
it is assumed that visual, temperature andlistening techniques will all be used. It isalso assumed that the individuals doing thechecking will have certain basic backgroundinformation about:
1.	The system in which the trap is installed.
Specifically,• The approximate pressure upstream anddownstream of the trap.
• That the overall system is stable neither
starting up nor being shut down; the trap
application and its general characteristics.
2.	The basic operating principle of the trap
and whether it can be expected to:• Discharge condensate within about
10° of steam temperature as mostthermodynamic and mechanical traps
do or at much larger suppression
temperatures as is characteristic ofsome of the thermostatic traps.
•H ave a distinct off-on cycle typicalof a thermodynamic (disc type) andmechanical (bucket) or have a modulatingor continuous flow typical of a mechanical(float) and some thermostatic traps which
tend to throttle flow.
Figure 6.5 outlines the first major branchesof the steam trap checking decision tree.
Successive branches associated with eachtrap type are presented on subsequent pages.

The trap checking decision tree
There is a logical progression of steps leading
to the decision that determines whether
an installed steam trap is healthy enoughto continue in service or whether it should
be repaired or replaced. Because of themultiplicity of variables and the increasingly
wide variety of trap types, this decision tree canbe enormous. Outlined below is a progressionof basic questions which illustrates only the
major branches of the tree. It is suitable asa troubleshooting starting point and entirely
adequate for identifying the vast majority offailed traps.

50

Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
Checking thermodynamic traps (disc, piston and lever traps)
Disc traps – mechanical failure mode
• Disc traps fail in the open position. Seating surfaces wear and erode to the point they can nolonger shut tightly.
Hot disc trap

Cold disc trap

Using listening device or by witnessing
discharge, determine number of open/close
cycles per minute.
1.	Disc traps may cycle up to 50 times aminute without wasting steam. The higher
the cycle rate, the closer the trap is to theend of its useful life. Cycles in excess of 1asecond indicate a worn out trap unless it
is experiencing an exceptionally high backpressure. It is advisable to consider repair
or replacement of the trap when it cycles
20 to 30 cycles per minute. The trap should
open and close crisply with no leakage inthe closed mode.
2.	 If cycling cannot be detected with a listening
device and discharge is not visible, close
downstream block valve to condensate
return system and open test tee. If trap:a. s tarts to cycle normally, it may be
assumed that elevated back pressure in
the condensate return system has caused
trap to fail open; seek and correct causeof system problem.
b. f ails to cycle and blows steam andcondensate continuously, it can beconcluded internal parts have failed;repair or replace trap.

If it has been established that the system is
not the cause of the trap being cold:
1.	Open strainer blow-down valve in front oftrap to purge it of dirt or air. If trap fails
to start normal function, then
2.	 Close block valves and disassemble trap
to clean passages. If inspection reveals
damaged intervals, repair or replace
the trap.

Yarway Model 741

51

Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
Checking thermodynamic traps (disc, piston and lever traps)
Piston and lever trap – mechanical failure mode
• Piston and lever traps fail in the open position. Seating surfaces wear and erode so that trap
can no longer close tightly.
Hot piston or lever trap

Cold piston or lever trap

Follow same procedure described for checking
disc traps. Note that these traps are designedwith a control flow orifice. This small orifice
will constantly discharge condensate between
normal full open cycles of the main valve. If
control flow discharge appears excessive,
inspect trap valve seat for wear.

Follow same procedure described for checking
disc traps. Note that these traps have good
air handling characteristics and are notsusceptible to air binding.

Yarway Model PB40

Checking thermostatic traps (bellows, bimetallic, diaphragm and wax capsule)
Bellows trap – mechanical failure modes• Many bellows traps fail closed due to a ruptured bellows that allows the valve to be pressedclosed against the seat. Some trap manufacturers provide a bellows that allows the valve to
move to an open position if the bellows ruptures.
• Bellows traps can also fail open due to wear and erosion of the valve and seat or extreme
bellows distortion that prevents valve from contacting seat.
Hot bellows trap

Cold bellows trap

Confirm that seat and valve are momentarily
capable of being shut, and that bellows is“alive” by:1.	Partially opening strainer blow-down valve
in front of trap to drain condensate from line
and expose trap to dry steam.
2.	 Witness shut-off of trap discharge bymeans of downstream test tee.
3.	 Failure to see tight shut-off confirms
trap needs repair or replacement.
Using a listening device or temperature
sensor can assist in confirming that bellows
is “alive” and cycling if test tee is not available
to witness trap’s response to dry steam.
If cycling is not evident, it may be induced
momentarily by shutting off upstream block
valve for a minute or two to artificially backup
condensate. Releasing condensate will cause
trap to open briefly, before closing again, thus
demonstrating that bellows is “alive.”
Listening devices can occasionally detectsteam leakage if seat and valve are sufficiently
worn to prevent tight shut-off. If tight shut-off isstill doubtful, close block valves, disassemble
trap and inspect bellows and seat for erosion.

If it has been established that the system
is pressurized and is not the cause of trap
being cold:
1.	 Close block valves and disassemble trap toinspect it for failed bellows or need to clean
flow passages of dirt.
2.	Repair or replace trap if bellows is ruptured
or spongy.

52

Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
Checking thermostatic traps (bellows, bimetallic, diaphragm and wax capsule)
Bimetallic trap – mechanical failure modes• Most bimetal traps fail in the open position because bimetal elements tend to fatigue in a steam
environment and lose their ability to close valve tightly.
• Erosion of seat and valve results from trap’s failure to close tightly due either to dirt or
weakened bimetals.
Hot bimetal trap

Cold bimetal trap

Follow same procedure described for checking
performance of hot bellows trap.

If it has been established that system ispressurized and is not the cause of trap
being cold:
1.	 Close block valves and disassemble trap
to inspect it for dirt or other obstruction.
Repair or replace trap if internals appear
damaged.

Diaphragm capsule trap – mechanical failure modes• Diaphragm capsule traps are relatively new, with less field experience than that associated withbellows or bimetallic types. They are designed to fail in an open condition should diaphragmcrack and its liquid fill be lost.
Hot diaphragm trap

Cold diaphragm trap

Follow same procedure described for checking
performance of hot bellows traps.
Cycling of diaphragm trap is slower and lessdistinctive than is typical of bellows trap.
Several minutes may be required for a closed
trap to open to discharge condensate.
If tight shut-off is impossible, trap should
be repaired or replaced.

If it has been established that system ispressurized and is not the cause of trap
being cold:
1.	 Close block valves and disassemble trap
to clean dirt from flow passages (small
passages and condensate flows make thistrap more susceptible to dirt accumulation
than other trap types).

53

Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
Constant temperature wax capsule trap – mechanical failure modes
The use of a temperature sensitive wax-filled capsule to open and close a trap is a relatively newtechnique. These traps discharge condensate at a single predetermined temperature which may
be adjusted. They are designed to fail in the open position should the capsule lose its fill.
Hot constant temperature trap

Cold constant temperature trap

Follow the procedure described for checking
performance of bellows traps.
Objective is to establish that trap can shut-off
tightly. Once closed, it may require several
minutes to open. If trap is unable to shut-off
tightly, repair or replace it.

If it has been established that the system
is pressurized and is not the cause of trap
being cold:
1.	 Close block valves and disassemble trap
to inspect it for dirt or other obstruction.

Checking mechanical traps (bucket, float and thermostatic)
Bucket trap – mechanical failure modes• Bucket traps tend to fail in the open position. The “prime,” necessary to float the bucket andclose the valve, can be evaporated so that the trap cannot shut off. The valve and seat also wear
and become eroded over time so that they can no longer shut off tightly. Bucket traps can also
fail in the closed position. If the bucket vent hole becomes clogged, air can keep the trap closed.
Higher than expected steam pressures also may prevent the bucket from opening the trap.
Hot bucket trap

Cold bucket trap

Using a listening device or by witnessing
discharge pattern, determine if trap is cycling,
thus confirming free movement of bucket.
1.	 If cycling is visible, verify valve and seatcondition by observing tight shut-off whentrap is in closed portion of its cycle.
2.	 If cycling is not visible, close upstream block
valve for several minutes. This will allow
condensate to accumulate in front of the
trap. Opening the block valve will enable
condensate to reprime trap or induce
temporary cycling if line conditions are
causing trap to operate in its less typicalmodulating mode.
3.	Trap should be repaired or replaced
if cycling cannot be induced or if tightshut-off is not visible.

If it has been established that the system ispressurized and is not the cause of the trap
being cold:
1.	 Verify that line pressure does not exceed
trap’s rated pressure. Such a condition willcause trap to remain in the closed position.
If over-pressurization is not the problem, close
block valves and disassemble trap so thatinternal parts can be inspected. Dirt and oxides
may need to be cleaned from bucket air venthole. When air cannot be removed, bucket will
float, holding valve closed.

54

Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
Checking mechanical traps (bucket, float and thermostatic)
Float and thermostatic trap – mechanical failure modes• Float and thermostatic traps can fail in either a closed or an open position. They fail closed if thefloat is ruptured by water hammer and can no longer rise to open the valve. They also fail closed
if the thermostatic element fails and air cannot be vented from trap.
They fail open when the main valve and seat or thermostatic air vent valve and seat are worn oreroded so that they leak steam.
Hot float and thermostatic trap

Cold float and thermostatic trap

Because trap is designed to drain condensate
continuously, verification that valve and seat oftrap and air vent are not leaking steam is very
difficult unless leakage is very large.
1.	Examine trap discharge pattern for evidenceof excessive vapor – i.e., steam leakage.
2.	 If possible, drain condensate throughstrainer blowdown vent in front of trap to
determine if both trap and air vent valve
can close tightly in the presence of dry
steam. Tight shut-off establishes thattrap’s condition is good. Failure to shut-off
tightly indicates that trap needs repair or
replacement.

If it has been established that the system
is pressurized and is not the cause of trap
being cold:
1.	 Verify that system pressure does not exceed
rated pressure of trap. This can prevent
float from opening valve.
2.	 Close block valves and disassemble trap
to examine internal parts for damage
especially thermostatic air vent. Also
inspect for flow obstructions.

Summary
The subject of steam trap maintenance is bestsummarized by three key points:
1.	 Careful selection and sizing of a suitablesteam trap type is important, but regular
maintenance is essential to the efficientand reliable steam system.
2.	Taking the time to establish steam trapping
standards for a plant repays its initialcosts year after year because it simplifies
steam trap checking and the maintenanceprogram.

3.	Regardless of plant size, steam trap
maintenance should be recognized as a
specialized activity requiring specialized
knowledge and experience on the part ofthose expected to do the job. The costsof doing this job well are trivial whencompared to the costs of doing it poorly.

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Yarway Industrial steam trapping handbook
Chapter 7 - Condensate return systems
Chapter 7 – Introduction
Today, an estimated 75% of installed steam
traps discharge into closed condensate
return systems, compared to less than 50%
a few years ago. Energy saving reasons forthis increased usage are covered in the brief
description of such systems in Chapter 5; thediscussion there also emphasizes that thesesystems have the potential for creating trapping
problems.
In general, traps discharging into condensate
return lines have much higher failure rates
than those discharging to atmosphere. Designof return piping can contribute to such failuresand hence warrants serious attention.
Designing return piping
Proper design of return lines is a complicatedtask. Correct pipe length and diameter are
difficult to predict, so a method is given here
to provide a first estimate. (It also can be used
to estimate the impact of various line sizes on
system pressures).
The Yarway method of estimating return line
size differs from other published methods ina number of ways. These differences and theassumptions involved are as follows:
1.	The condensate is assumed to be ahomogeneous mixture of liquid andvapor as it is discharged from the steam
trap, and while it is traveling through thereturn piping.
2.	The mixture is assumed to be at constanttemperature; therefore, there is nocondensation of vapor or cooling of liquid.
This results in an estimate of larger
pipe size.
3.	At the lower initial steam pressures,
velocities of the liquid/vapor mixture arelimited to lower values; in general, thisproduces lower velocities with larger
proportions of liquid. Some methods
assume a constant return line velocity forthe mixture in the range of 3,000 fpm to
7,000 fpm. Such velocities are relatively
high and can produce erosion of the pipe,
especially where there’s a very small
percentage of flash and a large proportionof liquid.

4.	The velocity profile for a typical turbulent
situation is used. This further limits
velocities and pressure drops.
5.	The installed steam trap capacity, notcondensate load, is considered an
important factor.
6.	A guide for fractional loads from manifolded
traps is provided.
When condensate return line sizing is
inadequate, it is due to one or more of thefollowing reasons:• The lines are receiving discharge from agreater number of sources than originallyplanned. This may be due to plant expansions
or energy conservation programs.
• Lines carrying steam at varying pressures
are discharging into a common return line.
• The steam traps are oversized and/or
misapplied.
• The return line design, initially, wasunder-sized or marginal, or the piping
installation was inadequate.
Whatever the conditions leading to theinadequacy of return lines, the results are
overpressurization of the return system,
venting of excessive amounts of vapor to theatmosphere, vapor binding of condensate
pumps, noise, and unsatisfactory steam trap
operation. All of these shorten trap life, impede
drainage, promote freeze-ups, and increase
maintenance time as well as cost.
Guidelines for system components
Yarway has developed guidelines for thedesign or use of the various components
of a condensate return system. They aresummarized in the following paragraphs andmore broadly applicable considerations are
given in the next section.
Steam main: the main, which carries steam
from the boiler to headers or other distributionlines, should be of sufficient size to handle flowin the existing plant plus any additional flows
required by plant extensions or additions. In
this way, the heat user will have steam at the
expected (design) pressure and temperature.
The main should be well drained of condensate
and vented free of air and noncondensibles.

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Yarway Industrial steam trapping handbook
Chapter 7 - Condensate return systems
Steam header or distribution line: carrying
steam from the main to the heat user, this line
should be sized adequately for the flow raterequired so that it does not impose a severepressure drop. It may have a control valve andshould then be connected to the top of thesteam main; the installation should include“drip” traps to protect the control valve andassure moisture-free steam to the heat user.
The important point to remember for the steam
header or the main is to be sure they provide
steam at the conditions anticipated.
Heat user: tracing lines, unit heaters, heatexchangers, and process equipment are
typical examples of heat users. Each shouldhave an adequate “pocket” or hot well tocollect condensate. When provision is madefor condensate collection, consideration
should be given to guidelines for other processequipment - such as those for pumps that drain
a vessel for entrance loss and separation of
steam bubbles from liquid condensate.
Fittings: to handle condensate that forms at
saturation temperature, fittings from the heatuser to the steam trap should be full bore.
Requirements are similar to those for theprevention of “pre-flash” at control valves.
Maximum possible pressure at the steam trap
inlet should be assured. Trap size should be
reduced only at the trap outlet.

Steam trap: traps should be selected forspecific applications. Design of the application
should be taken into account, as well as theoperating pressure and temperature ranges
especially if the heat user has a control valve on
the steam supply. Variations in condensate load
should also be considered.
The steam trap should not be selected on thebasis of pipe size and should not be oversized.
On process equipment, a trap may be judged
oversized if it has a safety load factor (SLF)of 10:1 or more.
To provide gravity drainage to the trap, it should
be installed below the equipment. It should
also be installed for ease of checking andmaintenance.
Trap discharge line: oversized piping rarely
creates problems; the line should never be
undersized. It should be adequate to handle
flashing condensate. All traps discharging
near saturation temperature, or wherecondensate temperature is above saturation
temperature for the return line pressure, will
form flash vapor. The trap manufacturer’s
recommendation should be followed and theline sized for the instantaneous discharge
rate of the trap.
If used, check valves should be suitable for theoperating conditions; this requirement shouldbe verified with the check valve manufacturer.

If present, lift of the discharge line to thereturn line should be accounted for (a lift of 2
feet adds approximately 1 psi to the pressure
at the steam trap outlet). The discharge line
should enter the return line on the top and not
be directly opposite any other discharge line
(see Figure 7.2 c and 7.2 d).
General design considerations
In the design of condensate return systems,
there are some general considerations which
can affect sizing of more than one component.
Also, some of these pertain to problems thatcan come from undersized and overloaded
systems.
Steam traps: the instantaneous discharge rateof the trap can contribute to overloading of the
return line. If the trap is of the “fail open” type,the amount of steam it can put into the line
must be allowed for.
Because traps differ in operating principles,some may tend to get “hot” when discharging
into high pressure. This can cause accelerated
wear of such traps as well as overloading orover-pressuring of the return line. Risk ofsteam loss also increases. Further, some typesof traps tend to back up condensate if returnpressures are elevated.

Figure 7.1
From steam
drip stations

Drip trap collecting
manifold - size basedon 25-50% of installed
trap flow rate

From tracer
collecting manifold

From tracers
Tracer collecting
header – size basedon sum of flows fromindividual manifolds
Tracer trap collecting
manifold – size basedon 25-50% of installed
trap flow rate

From process

Ma
in r
etu
rn
Size based on 100%of installed trap
flow rate

From processes

Process collecting manifold.
Size based on 75-100% of
installed trap flow rate

57

Yarway Industrial steam trapping handbook
Chapter 7 - Condensate return systems
Condensate load: when the steam trap issized, the smallest possible SLF should be
used. Variations in ambient conditions must be
checked out as to having a significant influence
on condensate load, steam pressures, orcondensate lines. Winter, for example, tends
to result in lower steam pressures and higher
return pressures. Sizing of the system may
also be significantly affected by startup loads.
Piping: because it is very likely that the piping
will have to serve some future plant expansion,
it is best to provide for such growth in the initialdesign.
Allowances should be made for possible
damage to piping. One cause is high velocity
liquid that can result in erosion. Also, there
can be excessive noise and/or cavitation
damage. Corrosion is a frequent problem and isspecifically important if erosion is also present.
Deposition of “dirt” reduces pipe bore and thus
is a problem.
Collection headers: a separate return line may
be advisable for each steam header pressure.
This prevents discharge of a high pressure
system from interfering with drainage andproper operation of a lower pressure system.
Collection vessel (or receiver tank): a vesselof sufficient size (volume) should be used, with
the quantity of flash vapor taken into account.
Its location should permit gravity flow from thereturn line into it.
If pumps are used to drain the liquid fromthe tank, there must be adequate NPSH
(net positive suction head) on the pumps forthe liquid temperature involved. Pumped
liquid should be figured to be at saturation
temperature for the pressure in the vessel.
Vents and reliefs should be added, as needed
and required by appropriate codes andstandards. Also, transient loads should beallowed for; these include start ups, bypasses,
and failed traps that may blow into the system.
Overloaded receivers result in venting ofexcessive flash vapor and loss of energy. If the
return is to a condenser, excessive coolingwater is used.
If the collecting vessel is over-pressurized,
liquid temperature can be too high for theselected condensate pump. This can result invapor binding of the pump and damage to thepump itself.

Insulation: insulation of the return system
helps conserve energy, but it maintains highflashing fluid temperatures that can make fluid
handling difficult. Fluid handling problems,
however, are overcome by proper regard for thenature of hot condensate and proper selectionof components.
Safety: settings and size of relief valves andvents should be reviewed, especially if thesemust relieve a flashing liquid. As mentioned
previously, transient situations – such as start
up loads, open bypasses and blowing traps –should be allowed for.
Return line installation
1.	 For gravity flow, the line should slope
toward the receiver (see Figure 7.7 a).
Preferably, the slope should be constant;risers and pockets that produce shock andwater hammer should be avoided.
2.	 With eccentric reducers, to accommodate
larger pipe for larger loads, expansion
should be on the bottom of the pipe(see Figure 7.7 b).
3.	Discharge lines should be into the top of
return lines so that they discharge into
the vapor space and thus reduce noise(see Figure 7.7 c).
4.	Discharge lines should be staggered tominimize noise, high local back pressure,and potentials for erosion (see Figure 7.7 d).
5.	 If heat using equipment must be gravity
drained, the trap discharge line and thereturn line must be below the drainage pointof the heat user. The return line should be atleast two or three feet below the heat user
outlet. Care should be taken with regard topossible freezing situations.
6.	Alignment and support should be adequate
for the main return line. Anchors arenormally required. The code for power
piping, ANSI B31.1, should be referred to.
Consideration must be given to the weightof pipe itself, fittings, flanges, valves,
insulation, and the fluid itself. The fluid
should be assumed as being all liquidbecause hydrostatic testing is probably
needed.

Figure 7.2
a. Slope toward receiver
Flow
Slope
b. Expand on bottom
Slope

Flow

Eccentric
reducersc. Discharge in top
Trap discharge line
Return line
flow

d. Discharge not opposite
Flow

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Yarway Industrial steam trapping handbook
Chapter 7 - Condensate return systems
Other potential factors – such as wind, snow,
ice, shock, seismic effects, vibration, andthermal stresses – need to be included in
the considerations.
Estimating return line size and maximum load
Figure 7.3 is a nomograph that can be used
for estimating the return line I.D. and also
maximum load (condensate rate) that a given
return line can handle. There are three basic
elements involved in such estimates; theseare defined by the equation:
W = (Factor X) (Factor Y)When:
W = maximum discharge rate (catalog ratingsin lb/hr) of all steam traps discharging into
the return line, multiplied by a percentagethat depends upon the trap application(25 to 50% for drips and tracings and
75 to 100% for process)Alternately, for a given return line,
W = maximum carrying capacity in lb/hr offlashing condensate for all steam traps
in the system
X = flash factor for various steam trap inlet
pressures, P1, and flash tank pressures,
P2, in psig (see Figure 7.3)
Y = pipe factor for various return line I.D.’s
in inches and equivalent pipe lengths, Le,
in feet (see Figure 7.3)

Included in factor X are considerations fora limiting pressure drop, percent of vapor
formed, and the average density of thetwo-phase mixture (the latter is assumed
homogeneous). Included in factor Y is a pipe
friction factor for complete turbulent flow; thisfactor is based upon Figure 20 in the hydraulicinstitute pipe friction manual for steel pipe.
Sizing flash and receiver tanks
There are certain characteristics of acondensate return system that can affect how
flash and receiver tanks are applied. These will
be considered before the matter of tank sizing
is covered.
Condensate and flash vapor should be piped
into the top of the receiver. If the liquidcondensate is returned, but no attempt is madeto use the flash vapor, the receiver can bevented from the top to atmosphere.
An unvented receiver is satisfactory as longas the heat in the flash vapor can be absorbed
in the receiver while the condensate is being
pumped back to the boiler feed tank. If the flash
enters the closed receiver faster than it can beabsorbed, however, pressure in the receiverand return lines can interfere with performanceof the system steam traps. Appropriate safety
and relief valves are necessary.

In a flash condensate recovery system, a
helpful and sometimes indispensable adjunctto the receiver is a flash tank that operates
at some pressure above atmospheric. The
flash condensate and its liquid are directed
into the flash tank either through a top inlet or
centrifugally through a side inlet near the top.
Figure 7.5 illustrates these connections as well
as steam and water outlets.

Figure 7.5
Condensate and flash steam recovery system
High pressure
condensate from traps

Low pressure flash steam

Drip traps
H-P flashtank

Atmospheric ventLow pressure
condensate
from traps
Condensate
pump

Carefully size andselect condensate
pumps and controls

AtmosphericreceiverTo boiler-feed system
Condensate pump59

Yarway Industrial steam trapping handbook
Chapter 7 - Condensate return systems
Table 1
Maximum ratings, centrifugal and top-inlet tanks, 1,000 lb/hr of flash steam
Flash tank pressure psig
Tank no.
1
Centrifugal flash tanks
2
1.5
3
3.2
4
6.0
5
16.0
6
27.0
Top-inlet flash tanks
2
3
4

1.1
2.2
4.3

2

5

10

20

30

40

50

1.6
3.4
6.1
17.0
29.0

1.8
3.9
7.1
20.0
34.0

2.3
4.9
8.8
24.0
42.0

3.0
6.4
12.0
32.0
58.0

3.9
8.5
15.0
41.0
73.0

4.8
10.0
18.0
49.0
89.0

5.5
7.5
9.5 13.0 17.0
12.0 16.3 20.0 27.7 35.0
21.0 27.0 34.0 50.0 66.0
58.0 79.0 100.0 142.0 184.0
105.0 142.0 180.0 254.0 329.0

1.1
2.5
4.6

1.3
2.9
5.2

1.7
3.5
6.5

2.2
4.9
8.7

2.8
6.1
10.8

3.4
7.4
12.0

4.0
8.7
15.0

Dimensions of commercial flash tanks

5.5
11.8
20.0

100

6.9
14.8
25.0

150

10.0
21.4
36.0

200

13.0
25.4
46.0

Tank
height, in

Overallheight, in

Inlet-pipe
size, inCentrifugal flash tanks
2
24
3
36
4
48
5
60
6
72

56
62
67
78
89

65
72
77
88
99

2
3
4
6
8

3
4
6
8
10

1½
2
4
5
6

Top-inlet flash tanks
2
24
3
36
4
48

56
62
67

65½
71½
76½

3
4
6

3
4
6

1½
2
4

Tank no.

Outsidedia., in75

Outlet-pipe
Steam
Water

Rule-of-thumb sizing method: one method by which a flash tank can be sized is based on theassumption that the lb/hr of steam that can be flashed per square foot of water surface is threetimes the absolute pressure inside the tank would be:
Ws/A = 3 (P2)
Where:A	 = water surface in square feet
P2 = flash tank pressure in psia
Ws = lb/hr of flash vapor (steam)60

Yarway Industrial steam trapping handbook
Chapter 7 - Condensate return systems
Table 2
Percent of flash steam formed
Initial steamSat.
pressuretemperature
psig
°F
25
267
50
298
75
320
100
338
125
353
150
366
175
377
200
388
225
397
250
406
300
422
350
436
400
448
450
459
500
470
550
480
600
489
Total heat of flash steam, BTU/lb

Flash-tank pressure, psig
0
5.7
9.0
11.3
13.3
14.8
16.8
17.4
18.7
19.7
20.7
22.4
24.0
25.5
26.8
28.2
29.2
30.2

5
4.1
7.4
10.8
11.7
13.4
14.8
16.0
17.5
18.2
19.2
21.0
22.7
24.2
25.3
26.7
27.8
28.8

10
3.0
6.2
8.6
10.6
12.2
13.7
15.0
16.2
17.0
18.2
20.0
21.6
23.0
24.4
25.7
27.0
28.0

20
1.0
4.3
6.7
8.7
10.3
11.8
13.0
14.4
15.4
16.4
18.2
20.0
21.5
22.7
24.0
25.3
26.4

30
2.6
5.0
7.0
8.7
10.2
11.6
12.8
13.8
15.0
16.7
18.4
20.0
21.2
22.6
23.7
25.0

40
1.0
3.7
5.7
7.4
8.8
10.0
11.5
12.4
13.6
15.5
17.0
18.7
20.0
21.4
22.6
23.6

50
2.5
4.6
6.3
7.8
9.0
10.4
11.4
12.5
14.4
16.0
17.7
19.0
20.4
21.6
22.7

75
2.2
3.8
5.4
6.7
8.0
9.0
10.0
11.0
13.8
15.6
16.8
18.2
19.5
20.5

100
1.7
2.3
4.6
6.0
7.0
8.2
10.0
12.0
13.5
15.0
16.4
17.5
18.7

125
1.6
3.0
4.4
5.4
6.6
8.5
10.4
12.0
13.4
14.6
16.0
17.3

150
1.5
2.8
3.8
5.0
7.0
8.9
10.5
12.0
13.4
14.7
16.0

1150.01156.01160.01167.01172.01176.01179.01185.01189.01193.01195.0

970.0

960.0

952.0

939.0

929.0

919.0

912.0

895.0

881.0

868.0

857.0

180.0

196.0

208.0

227.0

243.0

257.0

267.0

290.0

309.0

324.0

338.0

212.0

228.0

240.0

259.0

274.0

287.0

296.0

320.0

338.0

353.0

366.0

26.8

20.0

16.3

11.9

9.4

7.8

6.6

4.9

3.9

3.2

2.7

Latent heat of evaporation, BTU/lb
Heat of liquid, BTU/lb
Saturated water temperature, °F
Volume of flash steam, ft·lb

For horizontal tanks, this rule works satisfactorily and is often used. It usually oversizes the tankbecause it does not take into account the large steaming surface area of the condensate as it
flows through the return lines to the flash tank.
Example:Assume the inlet pressure to the traps is 100 psig and the receiver pressure is 30 psig.
Also assume a total discharge of 10,000 lb/hr.
Solution:
1.	 From Table 2 determine that the flash is 7%.
2.	Multiply total load by 7% 10,000 lb/hr x .07 = 700 lb/hr flash
3.	 Convert receiver pressure 30 psig to absolute pressure 30 + 15 = 45 psia
4.	Solve the equation
Ws/A	 = (P2)700/A	 = 3 (45)	A	
= 5.185 ft2
A horizontal tank with 1½ foot I.D. and 3½ foot internal length would provide sufficient area
(Ph x 3½ = 5.25 ft2)

L = 3½’

D = 1½’

61

Yarway Industrial steam trapping handbook
Chapter 7 - Condensate return systems
Experience method: because it is difficult
to arrive at an accurate figure for the total
steaming surface in a condensate system, flash
tank sizing is frequently based on experience.
This method will be discussed with reference toTable 1. The first table develops the dimensions
as well as the design of the tank; Figure 7.6
illustrates the height dimensions and identifies
the several inlets and outlets.
Table 2 tabulates percentages of flash
vapor formed at various values of flash-tankpressures and initial steam pressures. Its use
is discussed later.
Table 1 gives separate ratings for (a) centrifugal
flash tanks and (b) top-inlet tanks. Size for size,
ratings for top inlet tanks are approximately
70% of those for centrifugal inlet tanks. In thecentrifugal type, the condensate spirals aroundthe inside of the tank as it falls to the bottom;
the longer path provides more time andsurface for steam flashing.
Separation of vapor from liquid in the tankis important. This is frequently improved byinsertion of a screen or “demister.”
When the type and size of the flash tankare being chosen, it should be born in mind
that, if operating pressure is increased, thepermissible velocity of flash steam entering
the tank should be lowered. This prevents
condensate from being carried over into thelow pressure steam line.
Ratings in Table 1 have been worked out
to avoid the carrying over of condensate. In
addition, the steam outlet line should be amply
sized because its diameter bears directly on theexit velocity and, of course, on the possibility ofcondensate being carried over.
Sizing a vented receiver: Table 2 can also be
used when the size of a vented condenser isbeing selected (a flash tank not being included).
This table gives the amount of flash vapor
formed for various combinations of trap inlet
and tank pressures.
If Table 2 is used in the selection of a vented
receiver, the tank pressure should be assumed
to be less than 5 psig, because the flash
condensate will flow freely to the atmosphere.
The amount of flash will actually be less thanthat for the maximum tank rating if the receiver
is sized similarly to the tank.

In an existing installation, if the condensate
pressure (and temperature) in the receiver ishigh enough to cause flashing and cavitationin the receiver pump, the difficulty can bealleviated temporarily by an increase in
the size of the steam outlet or the vent. An
alternate solution is to install a flash tankahead of the receiver.
Example of calculating tank size(including flash vapor and its heat content)
As an example, in an industrial plant, there
are 50 steam traps of several different
sizes, discharging a total of 95,000 lb/hr ofcondensate from equipment operating at
150 psig. The condensate flows to a vented
receiver that operates at 5 psig.
The first questions to be considered are:“How much flash vapor is formed if thecondensate is discharged very near to steam
temperature?” And “How much heat isavailable in the flash steam?”
To determine the amount of flash vapor formed,
150 psig is located in the left-hand column ofTable 2 and lined up with the vertical column
for a flash-tank pressure of 5 psig. This gives
a figure of 14.8% for the amount of condensate
that forms flash vapor. The quantity of flash
vapor is thus 95,000 x 0.148 or 14,060 lb/hr.
To determine how much heat is available
in this vapor, the latent heat of evaporation
at 5 psig (at the vented receiver) is figured
at 960 BTU/lb. The flash vapor thus
provides nearly 13,500 million BTU/hr(14,060 x 960 = 13,497,600).
If this heat energy were used to heat waterfrom 40°F to 140°F (a 100°F rise) and thewater heater had an overall efficiency of
85%, 114,730 lb/hr of water would be heated(13,500,000 x 0.85 x 1/100 = 114,730). That isnearly 230 gpm. In addition, the condensate
from the water heater could still be returned
to an atmospheric pressure receiver and usedagain in the boiler.
Now the question can be considered: Whatsize and type of flash tank would be selected
and what would be its dimensions?

62

Yarway Industrial steam trapping handbook
Chapter 7 - Condensate return systems
From the above calculations, it is assumed thatthe 14,060 lb/hr of flash steam is available at
5 psig for heating equipment. In Table 1 the
5 psig value for flash tank pressure is locatedin the horizontal line of figures across thetable. The vertical column under this figure
gives the maximum ratings of flash tanks forthis pressure (note that these are given inthousands of lb/hr so that 1.8, for example,
means 1,800).
For the available 14,060 lb/hr of steam
flow, a no. 5 tank with a maximum rating of
20,000 lb/hr (20.0 in the table) would be theproper size. The tank would have to be acentrifugal-inlet type because no standard
top-inlet type shown in the table has sufficient
capacity.
The lower part of the table gives the dimensionsof the tank. The no. 5 centrifugal tank has
a 60” diameter, an overall height of 88” anda 78”. tank height. It has a 6” condensate inlet,
an 8” steam outlet, and a 5” liquid outlet at thebottom. (These dimensions and connections
are identified in Figure 7.6).
Flash tank sizing – alternate method
Another means of estimating the size of a flash
tank and its associated piping is shown in the
nomograph of Figure 7.7. The graph is enteredfrom the left at given values of flow in lb/hr. As
explained in the example below, the percent
flash vapor table (Table 2) is used to determine
the quantities of flash vapor, liquid, or total of
the two, in lb/hr. All three of these flows areused in the estimation of dimensions.
The graph is entered at the proper flow value
and pertinent tank dimensions are obtained
at intersections with curves A through E.

As illustrated in Figure 7.7, the dimensions, ininches, are:A	 = t ank height, based on total liquid andflash flowB	 = t ank I.D., based on total liquid andflash flow
C = c ondensate inlet I.D. based on totalliquid and flash flowD	 = f lash outlet I.D., based only on flash
portion of arriving condensate. To assure
adequate size, no allowance is made forcondensation of flash.
E	 = liquid outlet I.D., based on liquid portion ofarriving condensate; no allowance is madefor vapor condensation
Example: condensate to be collected is
30,000 lb/hr. Nominal steam pressure is
150 psig Atmospheric pressure is to be
maintained in tank.
Solution:
1.	 With reference to the table for percent flash
vapor (Table 2), 150 psig to atmosphere
gives 16.8% flash formed.
2.	 30,000 lb/hr x 0.168 = 5,040 lb/hot flash
vapor.
3.	 30,000 – 5,040 = 24,960 lb/hr of liquid.
4.	On Figure 7.7, at 30,000 lb/hr, for total liquidand flash flow, dimensions for A, B, and C
are determined as 47 in, 21 in and 7 + in,
respectively.
5.	On Figure 7.7, at 5,040 lb/hot flash only,
dimension D for the flash outlet I.D. isdetermined as 7 in.
6.	On Figure 7.7, at 24,960 lb/hr of liquid only,
dimension E for the bottom liquid outlet J.D.
is determined as 2 in.
7.	As a last step, applicable codes, standards,
and the like should be consulted for final
design of the tank, walls, supports, vents,
reliefs, etc.

Figure 7.6
Sizing top or centrifugal inlet tank

Top inlet

Centrifugal inlet

Blowdown inlet

Tank height
Overall height

Steam outlet

Water outlet

63

Yarway Industrial steam trapping handbook
Chapter 7 - Condensate return systems
Design factors that save money
In the disposition of flash condensate, money
can be saved and operating headaches avoided,
if the following suggestions are heeded during
the design of the condensate return system:
1.	The return line should be sized to carry the
flash vapor as well as the liquid condensate.
Undersized lines cause high back pressuresat the traps; this reduces their effectiveness.
2.	All steam equipment in the process
should be analyzed to determine: (a)which units provide a continuous supplyof high temperature and high-pressure
condensate that can be used, and (b) what
equipment can operate on low-pressure
flash condensate. Some equipment may
be operating on boiler steam that is being
reduced. Present operating pressures andtemperatures of this equipment should
be checked; they may be higher thannecessary.
3.	 For each case, the economies of using flash
condensate should be checked out. Thiskind of saving, which goes on from year toyear, should be balanced against the costof installing the flash-condensate recovery
system.
4.	The pipeline that carries the flash vapor
should be sized to lessen pressure
drop between the flash tank and the
low-pressure steam equipment. Also,
money can be saved if the flash tank andpipeline are insulated. Further, condensate
return lines should be insulated so thatthe maximum amount of flash steam isrecovered. If the flash L-P heating pipeline
is long, drip traps should be installed.
5.	The flash tank (and the receiver tank, if
it is not vented) should be constructed inaccordance with the ASME unfired pressure
vessel code. Local codes, insurancecompany requirements, and plant standards
should be checked. The role of applicable
codes and standards cannot be minimized.
ANSI B31.1 code for power piping contains
specific requirements; for example,
Para. 102.2.5(c).

6.	Types of traps already in use should bechecked. Some types discharge condensate
near steam temperature; others requirethat the condensate cool considerably
before they open and discharge. The former
types produce more flash condensate andreturn the most heat. Some types of traps
discharge subcooled condensate and thelatent heat is lost to ambient if the systemdoes not accommodate backup.
7.	A systematic plan for using flash
condensate can save heat, cut fuel costs,
and improve process efficiency. For thebest results, however, the whole systemand each of its parts should be carefully
analyzed.
8.	The condensate pump must handle very hot
liquid. The pump, controls, and associatedpiping should be carefully selected toassure proper operation. Under adverse
conditions, the pump could “vapor bind” orcavitate. When this occurs, the liquid will not
be removed from the flash tank or receiver.
These vessels will then accumulate liquidand possibly over-pressurize.
In addition to reducing the effectiveness of
the return system, over-pressurization can
result in a safety hazard.
9.	A frequent solution to over-pressurizedtanks and systems is to drain them tosewer or grade. For vessels under these
conditions, relief or safety valves should beconsidered. Again, applicable codes andstandards for valve sizing, selection, andinstallation should be consulted.
	All design consideration of the condensate
system must include a full review of ASME
code and section 8 piping code. Applicable
codes and engineering calculations are
required for any condensate systems. This
guide is not intended to discuss any specific
ASME code requirements and each users
must satisfy all code requirements prior
to installation of any condensate system.

64

Yarway Industrial steam trapping handbook
Chapter 7 - Condensate return systems
Figure 7.7
8
6
5
4
3
2

'E'
bas
ed
on
liqu
id o
nly

100,000
8
6
5
4
Step 4

3

Step 6

'C'
bas
ed
on
tot
al l
iqu
id a
nd
fla
sh
flo
w

2

10,0008
Step 5

6
5
4

1,000
8
6
5
4
3

'A' b
ased
on

'D'
'B'
bas
bas
ed
ed
on
on
fla
tot
sh
al l
onl
iqu
y
id a
nd
flas
h fl
ow

Flow, lb/hr2

tota
l liqu
id an
d fla
sh fl
ow

3

2

100
1

2
'E'

3

4

5

6 7 8 9 10
'D' 'C'

20
'B'

30

40

50 60

100

'A'

Dimension, NPS

65

Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
Appendix A
Listed below, alphabetically, are over 90 typical pieces of process equipment. They are identified
by type and class (number and letter). To obtain a trap type recommendation, with appropriate
installation tips, match the type and class designation to comparable reference on one of thefollowing pages.
Equipment 	Type Class

Equipment 	Type Class

Acid vat................................................ 1	A,C
Air blast coil........................................ 2	B
Air dryer............................................... 2	B
Air heater............................................. 2	B
Air preheater....................................... 2	BAsphalt tank........................................ 1	A
Autoclave............................................. 4	A
Batch dryer.......................................... 2	B
Bayonet heater.................................... 1	A
Belt press............................................ 3	A
Bleach tank......................................... 1	A,C
Blender................................................ 1	A
Brew kettle.......................................... 1	B
Cabinet dryer....................................... 2	A,B
Calender.............................................. 3	A
Candy kettle........................................ 1	B
Chamber dryer.................................... 2	B
Chamber, reaction.............................. 4	A
Cheese kettle...................................... 1	B
Confectioners’ kettle.......................... 1	B
Continuous dryer................................ 2	A,B
Conveyor dryer.................................... 2	A,B
Cooking coil......................................... 1	A
Cooking kettle..................................... 1	B
Cooking kettle, tilting.......................... 1
C
Cooking tank....................................... 1	B
Cooking vat.......................................... 1	B
Cylinder dryer...................................... 3	B
Cylinder, jacketed............................... 3	B
Double drum dryer............................. 3	B
Drum dryer.......................................... 3	B
Drum, dyeing....................................... 1	A,C
Dry can................................................. 3	B
Dry kiln................................................ 2	A,B
Drying roll............................................ 3	B
Drying room........................................ 2	A,B
Drying table......................................... 3	A
Dye vat................................................. 1	A,C
Dyeing bath.......................................... 1	A,C
Dyeing drum........................................ 1	A,C
Dyer, package...................................... 1	A,C
Evaporator........................................... 1	B
Feed water heater............................... 1	A
Festoon dryer...................................... 2	B
Fin type heater.................................... 2	A
Fourdrinier.......................................... 3	A
Fuel oil preheater............................... 1	A
Greenhouse coil.................................. 2	A

Heat exchanger................................... 1	A
Heating coil-air blast fin type............. 2	B
Heating kettle...................................... 1	B
Hot break tank.................................... 1	A,C
Hot plate.............................................. 3	A
Kiers..................................................... 1	A
Liquid heater....................................... 1	A
Milk dryer............................................ 3	A
Mixer.................................................... 1	A
Molding press platen.......................... 3	A
Package dryer..................................... 1	A
Paper dryer......................................... 3	B
Percolator............................................ 1	B
Phono-record platen.......................... 3	A
Pipe coil, circulating air...................... 2	B
Pipe coil, still air................................. 2	A
Platens, press..................................... 3 	A
Plywood platen.................................... 3 	A
Preheater, fuel oil............................... 1	A
Preheating tank.................................. 1	A
Plating tank......................................... 1	A,C
Pressure cooker................................. 4	A,B
Process kettle..................................... 1	B
Pulp dryer............................................ 3	B
Reaction chamber............................... 4	A
Reheater.............................................. 1	A
Retort................................................... 4	B
Rotary dryer......................................... 3	B
Shell and tube heat exchanger.......... 1	A
Sterilizer.............................................. 4	A
Storage tank coil................................. 1	A
Storage water heater.......................... 1	A
Stretch dryer....................................... 3	A
Submerged coil................................... 1	A
Suction heater..................................... 1	A
Sugar dryer.......................................... 2	B
Tank coil.............................................. 1	A
Tank car coil........................................ 1	A
Tire mold press................................... 3	A
Tray dryer............................................ 2	A,B
Tunnel dryer........................................ 2	A,B
Unit heater........................................... 2	B
Vat........................................................ 1	A,C
Veneer platen/press........................... 3	B
Vulcanizer............................................ 3	A
Water still............................................ 1	A
Water heater, storage......................... 1	A
Water heater, instant.......................... 1	B

66

Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
Equipment Type 1, Class A

Steam

Storage tank

Tank car

Steam

Steam heats a liquid indirectly througha metal wall
Typical equipment:• Asphalt tank
• Reheaters• Suction heaters• Bayonet heaters• Storage tank
• Tank car

Activity: coils used to heat liquids (often very
viscous) in large weather exposed equipment
frequently in remote locations. Several coils
may be employed due to the large surface
area of containers.
Steam pressures: will range from 5 to 125 psiwith 40-75 psi being most typical. Generally
constant pressure but occasionally will be
modulated by pressure control valve.
Condensate loads: wide ranges in final
temperature of material being heated and inambient temperatures results in especiallylarge range of loads. Startup loads are typicallyvery heavy with seasonal weather variation
having a significant influence.
Drainage to trap: gravity drainage is thenormal condition.

Discharge from trap: generally to open drain.
Condensate return systems are often missing
due to distance from power house and low
pressures.
Ambient conditions: vary as widely as weather
conditions themselves – arctic to equatorial
desert.
Air venting: prompt venting of air is desirable
when frequent startups and rapid heating
requirements are the norm.
Shock, vibration and water hammer: may bepresent during startup.
Dirt and corrosion: corrosion of coils can leadto contamination of steam system by material
being heated.
Recommended traps
Desired characteristics: rugged, fail open,
self-draining with good air handling
Installation tips:
Strainer with suitable blow-down valve
should be placed ahead of trap. A suitable
drop or collecting leg (2’-3’) is desirable forbimetallic trap.

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Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
Equipment Type 1, Class B

Steam

Cooking oil

Hot process
fluid

Steam
Cool process
fluid
Full size pipe
Shell and tube heater

Steam heats a liquid indirectly througha metal wall
Typical equipment: • Acid or bleach tanks• Feedwater heaters• Plating tanks• Brew kettles• Fuel oil preheaters• Storage water heaters• Dye vats
• Kettle coils• Water heater, instant• Evaporators• Mixer or blenders
Activity: coils or jackets are used in tanks orvats for heating liquids in either batch or thecontinuous flow typical of shell and tube typeheaters. Equipment is generally protected fromthe weather and of a size that one heating coil
is most typical.
Steam pressures: will range from 15 to 150 psi
with 40-75 psi most frequent. Some equipment
may see pressure up to 600 psi. Pressures may
be constant, but often modulated by pressure
control valve.
Condensate loads: heavy startup loads,
followed by smaller and steadier running loads
are to be expected, but without the extremeswings of weather-exposed equipment.
Drainage to trap: gravity drainage is thenormal condition.

Discharge from trap: generally to closed
return with nominal pressures. Also overhead
lift to elevated condensate header or return.
Ambient conditions: protection from weather
may be partial or complete and equipment
tends to experience smaller temperatureswings.
Air venting: proper venting is important.
Equipment is often run on regular daily
or weekly schedules. Tendency is for total
shutdown of equipment following completionof run or batch. Lack of adequate venting cancause condensate to be drawn back into heatexchange coils.
Shock, vibration and water hammer:
improperly drained coils lead to shock andvibration during startup.
Dirt and corrosion: problems are aggravatedby poor drainage and frequent shut downs.
Recommended traps
Desired characteristics: rugged, fail open,
good air handling, rapid response rate, anddischarge condensate at close to steam
temperatures.
Installation tips: strainer with suitable
blowdown valve should be placed aheadof trap. A vertical drop leg ahead of trap isalso recommended.

68Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
Equipment Type 1, Class C

Steam

Submerged
coil

A Air ventJacketed kettle

Lift fitting(see Figure 5.2)

Steam heats a liquid indirectly througha metal wall
Typical equipment:

Air vent

Steam• Cooking kettle, tilting• Candy kettle• Embossed coils• Tanks with elevateddischarge

Activity: liquids or materials are heatedor cooked in jacketed kettles or tanks withsubmerged coils. All require raising discharge
to the trap.
Steam pressures: generally 5 to 125 psi withmost frequently experienced pressures in the
middle of this range.
Condensate loads: startup loads heaviest withrunning loads lighter.
Drainage to trap: condensate is passed to trap
through use of a lift fitting that creates a water
seal or reaches trap through syphon tube incase of tilting kettle.

Syphon on
tilting kettle

Ambient conditions: equipment is generally
protected from the weather and unlikely to see
extreme temperatures (either) hot or cold.
Air venting: frequent startup and the need toget equipment hot quickly requires a good air
venting.
Shock, vibration and water hammer: may bepresent during startup.
Dirt and corrosion: poor drainage and frequent
startups increases potential for corrosion.
Recommended traps
Desired characteristics: resistant to steam
binding, rapid response, discharge condensate
at close to steam temperatures, rugged, failopen, resistant to water hammer and shock.
Installation tips: auxiliary air vents are helpful.
Lift leg or syphon should be a smaller pipe size
than trap to reduce tendency for steam binding.

Discharge from trap: may be either to an open
drain or a closed pressurized return.

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Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
Equipment Type 2, Class A
A

Auxiliary
air vent

Steam

Slope
Slope pipe
coils

Steam heats air/gas indirectly through ametal wall
Typical equipment: • Dry kiln (without fans)• Drying room
• Greenhouse coil
Activity: space heating or drying of materials in
enclosed equipment with natural air circulation.
Fans or blowers are not employed.
Steam pressures: typically 5 to 50 psi withfluctuation occurring during startups. Normallyconstant pressure without control valves.
Condensate loads: will vary widely dependingon the size of the exposed surface area of thecoils. Loads will be heaviest at startup andrather steady thereafter.
Drainage to trap: gravity drainage is importantwith amply sized collecting leg required toprevent condensate backup into coils.
Discharge from trap: gravity to closed return,low pressure to vacuum.

Ambient conditions: generally protected fromweather because installation is inside building
or structure. Seasonal changes can expose
shut-down system to freezing conditions.
Air venting: important to assure fast startups.
Shock, vibration and water hammer: on
startup hot condensate, flowing into improperly
drained coils or return system, can createshock and vibration.
Dirt and corrosion: may be heavy due toseasonal use, long shut-downs possibly inflooded conditions.
Recommended traps
Desired characteristics: rugged, good air
handling, medium response rate, corrosion
resistant.
Installation tips: provide collecting leg andstrainer with suitable blowdown valve aheadof trap.

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Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
Equipment Type 2, Class B

Steam

Steam in

Vacuumbreaker

VB
Air heating coilUnitheater
AirA

Air vent
Min. as recommended
by coil mfgr. up to
3 ft for modulating
steam and freezing
air temperature

Condensate return

Steam heats air/gas indirectly through ametal wall
Typical equipment: • Chamber dryer• Pipe coils (circulating air)
• Conveyor dryer• Air preheater• Dry kiln (with fan)
• Unit heater• Fin coil
Activity: forced circulation of air over or
through coils for space heating. Also the drying
or heating of materials in either open or closed
containers or chambers with air circulation
created by fans or blowers.
Steam pressures: generally 25 to 150 psi with
50-75 psi most common. Pressures can vary
greatly due to cyclic off-on action, the changing
of dampers and mix of makeup air. Sudden
drafts of freezing outside air can lower coilsteam pressure to below atmospheric.
Condensate loads: vary greatly due to variety ofcontrols and changing inlet air temperatures.
Coils in series will have highest loads on first
coil with decreasing loads on successive coils.
High loads and low pressures will occur when
fan starts and cold air is blown over coils.
Drainage to trap: must be by gravity with asufficiently large collecting leg to momentarily
store condensate until trap can open anddischarge.
Discharge from trap: generally, discharge isto a closed return system.

Ambient conditions: freezing is a major
concern when cold outside air can be drawn
into system. Dry kilns and heaters in hot areas
may expose traps to such high temperaturethat some traps are adversely affected.
Air venting: very important to assure rapid
startup. vacuum breakers are recommended
to facilitate coil drainage on shut-down.
Shock, vibration and water hammer: often
from return lines on startup or improperly
trapped steam supply. Can also occur due toinadequate drainage from coils resulting fromchanges in load, pressures or the sagging
of coils.
Dirt and corrosion: corrosion can be asignificant problem if coils are manufacturedof dissimilar materials.
Recommended traps
Desired characteristics: rugged, fast
responding, hot discharge, fail open,
self-draining good air handling when subject
to frequent startups.
Installation tips: trap should be well below
unit (2 ft to 3 ft) with amply sized collection
leg. Air vents on larger equipment to aid
in startup. Vacuum breakers help assurecomplete drainage of coils on shut-down. Thisis especially important if freezing temperatures
are possible. Strainers with blow-down valves
and test “T” reduce maintenance and simplify
trap troubleshooting.

71

Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
Equipment Type 3, Class A
Always below trap outlet
PlatenSteam in

Flexible
metallic hose

Typical - eachtrap station A Air ventCollecting
manifold

Platen press

Steam heats a solid or slurry indirectly througha metal wall
Typical equipment: • Belt press• Molding press• Tire mold press• Drying table• Plywood press• Vulcanizing equipment
Activity: molding, bonding, curing, drying
and vulcanizing materials such as plastics,
rubber, particle board, and similar substances.
Generally a “finished” form is being developed
using platens or steam heated molds.
Steam pressures: generally in the range of
50 to 150 psi. Batch operation associated withplatens and vulcanizing presses can produce
wide changes in pressures.
Condensate loads: are quite variable. Platensand presses have cyclic loads that are very highduring warming and then much lower when
maintaining temperatures. Some platens havecold water introduced to arrest or control thetime temperature cycle.
Drainage to trap: typically drainage to the trap
is by gravity.
Discharge from trap: most frequently to aclosed return system.

Air venting: an important consideration forthis class of equipment due to the frequencyof startups.
Shock, vibration and water hammer: usuallycomes from return systems or improperly
trapped steam supply. Rapid formation ofcondensate slugs produce shocks as willcold water injection into molds.
Dirt and corrosion: are significant factors,
especially in platens with air venting. Frequent
shut-downs encourages corrosion.
Recommended traps
Desired characteristics: rugged, having hot
discharge and fast response. Good air handlingdue to frequent startup of equipment. Failuremode should be “open.”
Installation tips: mount trap below platen’slowest (open or closed) position. Flexible hoses
should be carefully selected for materials
and proper bore diameter to assure easydrainage. They should be connected to provide
positive head to the trap when it is stationary
and downstream of hose. It is preferred thatthe trap be mounted on and below the platen
outlet. A suitable flexible hose should beconnected to the trap outlet and the drain
header. The connection at the drain header
should always be below the trap outlet,
whether the platen is open or closed.

Ambient conditions: processing is generallyindoors. Temperatures are frequently hot due
to heat from equipment.

72

Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
Equipment Type 3, Class B

Steam

Syphon drained apparatus
Steam(Trap arrangements typicalfor cylinder ironer)

Cylinder dryer

Steam heats a solid or slurry indirectly througha metal wall

Discharge from trap: discharge is generally
to a closed condensate return system.

Typical equipment:

Ambient conditions: generally hot due to heatfrom the equipment.

• Calender• Paper dryer• Drum dryer• Dry can• Pulp dryer• Fourdrinier• Rotary dryer

Activity: continuous drying of materials is being
performed by exposure to the heated surfacesof rotating cylinders or drums. Commonly usedin the manufacture of felt, asbestos, rubber,
textiles, paper and other sheet or fibrousmaterials, including foods and slurries ofchemicals.
Steam pressures: generally in the rangeof 75-150 psi. Once warm up is complete,pressures are reasonably constant.
Condensate loads: high startup loads andmoderate running loads are typical. Whenmany dryers are in series, the first several
have highest loads and those toward theend have progressively smaller loads.

Air venting: an important requirement during
startup when drums or cylinders contain large
amounts of air.
Shock, vibration and water hammer: usually
come from return systems or improperly
trapped steam supply. Faulty or broken
syphons can produce shocks.
Dirt and corrosion: can be a significant factor
and is related to frequency of startups.
Recommended traps
Desired characteristics: rugged, having hot
discharge and fast response. Ability to handle
flash steam by means of small bleed passage
is a necessity. Failure mode should be “open”.
Installation tips: mount trap below cylinder.
If flexible hose is used, care should be taken
to assure it has an adequate bore and liner,materials suitable for steam service.

Drainage to trap: syphon drainage is standardpractice. Condensate moving up the syphon
from the outer rim to the center of the drum
is subject to reheating and flashing-steam
binding of trap is common problem.

73

Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
Equipment Type 4, Class A

Steam
A

Auxiliary
air vent
A

Dressing
sterilizer

Autoclave

Steam heats a solid directly
Typical equipment:• Reaction chamber• Retort• Pressure cooker

Activity: heating a material or producing achemical reaction in an enclosed pressure
vessel, by direct exposure to live steam.
Condensate forms on product surfaces.
Steam pressures: range from 15 to 150 psi
with 15 to 50 being most typical. Whenthe process is temperature controlled,
steam temperatures can vary. On startup,
pressures may be unexpectedly low.
Condensate loads: can be very large on startup
and quite low after temperature is reached.
Drainage to trap: must be gravity drainage
with trap well below equipment.
Discharge from trap: good condensate
drainage after the trap is especially importantin preventing contamination due to flooding.
Ambient conditions: equipment is usually ina building and may be subject to generally hot
conditions.

Air venting: very important consideration due
to potentially large volumes involved. Separate
air vents are frequently used.
Shock, vibration and water hammer: shock
may be generated in the return system andas a result of condensate forming in slugs.
Dirt and corrosion: may be a problem because
condensate can be contaminated fromcontact with material being heated. Becauseof frequent startups and exposure to air,corrosion problems can be expected.
Recommended traps
Desired characteristics: fail open and self
draining desirable. Hot discharge and fast
response with good air handling a must.
Good dirt handling especially required insome applications.
Installation tips: place strainer (extra large
where contamination is heavy) with blowdown
valve ahead of trap and position for frequent
servicing. Good drainage after trap is
especially important with outdoor installations
where freeze-up can be a problem. Bellows
thermostatic trap mounted in vertical-up
position is a good auxiliary air vent.

74

Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
How to trap steam mains

Recommended drip
pocket diameter andlengthActivity: removal of condensate from steam
mains to protect steam equipment, prevent
water hammer and maintain steam quality
between boiler and point of use.
Steam pressures: generally constant withsome seasonal variation. Typical industrial
pressures 100-600 psi. Utilities, pulp and paper,and chemical plants frequently higher.
Condensate loads: usually small and constant,
10 to 50 lb/hr per trap station except during
startup when loads can be quite heavy. Larger
at ends of mains especially if earlier trapping
has been inadequate.
Drainage to trap: most commonly by gravity
with trap below steam main. Occasionallypiping in trenches will require lift fitting froma collector when trap is above main.
Discharge from trap: commonly to closed andpressurized return systems but also to open
atmospheric drains.
Ambient conditions: vary widely. Range fromunderground tunnels to outdoor exposure to
Arctic winters. Freezing is the most common
concern.

Air venting: need is minimal because startups
are infrequent. Some pipelines will have
manual valves as air vents at startup.
Shock, vibration and water hammer:
generally result from inadequate drainage of
condensate Moving at high velocity. Excessive
warm-up rates can produce thermal shocks
in return system. Also, negative pipe pitch andinn properly located drip traps will produce
problems.
Dirt and corrosion: no unusual problems
beyond the oxides and dirt particles typicalof any steam system.
Recommended traps
Desired characteristics: fail open, self
draining, install in any position. Tolerant ofsuperheat. Capability of operating over wide
pressure ranges aids standardization.
Installation tips: use of a standard pipeline“T” in main provides a drainage pocket so thatcondensate can get to a trap. An extension to“T” is sometimes used to increase its storage
volume. Strainers with blowdown valve and test“T” are recommended in addition to standard
block valves for maintenance and checking.

75

Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
How to estimate steam main condensate loads
Condensate load, C1(Warming up)
lb/hr per 100 ft of pipe

Nominal pipe size
in
1
1½
2
3
4
6
8
10
12
14
16
18
20
24

10
14
22
30
60
93
166
250
315
337
416
478
536
605
721

100
16
25
35
69
99
185
277
352
419
461
532
596
673
802

Operating steam pressure, psi
200
300
400
17
19
19
27
30
32
38
40
46
74
78
81
107
113
126
198
208
220
298
313
329
375
395
415
448
472
495
493
519
545
578
592
628
638
670
703
719
757
793
857
900
945

600
20
36
48
92
131
239
357
449
541
591
681
763
860
1024

1000
26
42
57
108
154
280
414
521
623
686
789
884
997
1189

600
13
19
24
35
45
66
87
108
128
141
161
181
202
242

1000
13
26
33
49
63
93
121
151
179
197
225
253
280
337

Assumed conditions:Warm-up rate, 400°F	Extra strong pipe
Ambient, 0 deg. °F
Wind, 0 MPH
Insulation 85% eff.
10% additional load for warming insulation
50% of running load

Condensate load, C2(Normal)lb/hr per 100 ft of pipe
Nominal pipe size
in
1
1½
2
3
4
6
8
10
12
14
16
18
20
24

10
3
4
5
8
10
15
20
25
30
33
38
43
48
57

100
5
8
10
15
19
29
38
47
56
62
70
79
88
106

Operating steam pressure, psi
200
300
400
7
9
10
11
13
15
13
16
19
20
24
28
26
31
36
38
46
53
50
60
69
62
75
87
74
89
103
81
98
113
93
112
129
105
126
145
116
140
161
140
168
194

Assumed conditions:Ambient. 0 deg. °F: insulation efficient. Saturated steam, zero (0) wind velocity; pipe surface
temperatures same as steam temperature.
Note: ambient temperature, wind and rain can influence loads.
Comments:• Increasing ambient temperature from 0°F to 100°F will decrease condensate load
approximately 30%.
• Increasing wind velocity from 0 mph to 15 mph will increase condensate load
approximately 225%.

76

Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
How to trap steam tracers

TracerSteam

Tracer
Steam

Process pipeline

Activity:• Maintaining the temperature of processmaterial such as asphalt, sulfur, wax or otherchemicals to aid in handling by preventing
congealing, solidification or separation.
• Prevent water lines, safety showers, pumps,
valves, etc. from freeze-ups.
• Maintain uniform temperatures in andaround instruments.
Steam pressures: typically 75-400 psi when
tracing process materials, but 15-150 psi morecommon in freeze protection applications.
Below 40 psi, condensate return problems
increase in closed system when pressure
differentials are not adequate for gooddrainage.
Condensate loads: low (0-40 lb/hr) andrelatively steady, varying with seasonalchanges. Long tracing runs, poor insulation,
submerged lines can produce higher loads.
Drainage to trap: most frequently by gravity,
but lift drainage can be experienced when
tracing occurs below grade in trenches.
Discharge from trap: by gravity to open drainsor closed returns-some pressurized andelevated.

Control valve

Air venting: of limited importance when
tracing process materials because of
infrequent startups. If startups are frequent
during seasonal changes, freeze protection
systems may have modest air venting needs.
Shock, vibration and water hammer:a minimal problem.
Dirt and corrosion: generally modest in tracingof process lines. Dirt can be a problem in freeze
protection systems due to corrosion products
in seasonally activated lines and light sluggish
condensate flows.
Recommended traps
Desired characteristics: fail open, selfdraining, small and lightweight as frequently
trap is not well supported. Easy checking is
helpful as many traps are installed.
Installation tips: when possible, locate traps
close together using condensate return
manifold. This also simplifies maintenanceand trap checking. Provide strainers, test “T”
and suitable block valves. Assure adequate
pressure differential across trap for gooddrainage when discharging to a closed andelevated return system.

Ambient conditions: freezing is the mainconcern. Most tracing is exposed to theweather but is also used in unheated buildings.

77

Yarway Industrial steam trapping handbook
Appendix B - Steam trap evaluation methods
Appendix B – Introduction
This section is intended for those particularlyinterested in the laboratory testing technology
of steam traps. It recommends test methods
and procedures for use in making comparativeevaluations of steam traps.
Steam trap checking is the process ofdetermining in the field, whether or not a trap isfunctioning properly. (Refer to Chapter 6, Steamtrap maintenance and troubleshooting). Steamtrap evaluation is the practice of quantifying
specific performance characteristics andthen making judgments about the trap’s
suitability for various types of service. Thisrequires the controlled conditions and precise
measurements of a qualified laboratory.
Evaluation criteria
Selecting the performance-related criteriathat should be evaluated requires a thoroughknowledge of the specific needs of differing
steam trap applications. For example, process
traps and protection traps serve different needs
and should be evaluated accordingly. Fiveimportant evaluation criteria can properly belisted in different relative orders of importance,
depending on the intended service of the trap
being evaluated.
Protection (drip and tracer) traps
1.	Steam loss
2.	Back pressure limit
3.	Predominant failure mode
4.	Capacity
5.	Air handling on startup
Process traps
1.	Capacity
2.	Air handling on startup
3.	Predominant failure mode
4.	Back pressure limit
5.	Steam loss
While the relative significance of these various
criteria can be debated, it should be clear thatan evaluation program should be tailored to
specific application needs.
Criteria definitions• Steam loss: the amount of saturated steam
discharged during successive condensate
removal operations expressed in pounds perhour. A measure of trap efficiency.

• Capacity: the amount of condensate thatcan be discharged continuously from a
trap in a given period of time and under
specific conditions or pressure differential
and condensate temperature expressed inpounds per hour.
• Back pressure limit: back pressure limit is
the maximum amount of back pressure thatcan be applied to the discharge side of thetrap without causing malfunction. (A decreasein discharge capacity with increasing backpressure is normal and not considereda malfunction). Back pressure limits are
expressed as the ratio of back pressure tosupply pressure (in absolute units) expressed
as a percent.
• Failure mode: the manner in which a trap ismost likely to malfunction. It can be either
open or closed, depending on the specificdesign.
• Air handling on startup: the capabilityof steam trap to vent air and other noncondensable gases during cold startup
conditions. At the present time there is no
generally recognized expression for this term.
In its testing programs, Yarway Corporation
expresses air handling capability in termsof actual cubic feet per hour passed under
specific conditions of inlet and differential
pressures.
Evaluation philosophy
In order to obtain meaningful results, traps
should be tested under controlled conditions
that are typical of actual field installations.
A minimum of three (3) identical traps isrecommended for testing. This avoids basingconclusions on a single unit that may not be
representative of the model being evaluated,
due to manufacturing or other variations.
Well established trap manufacturers usually
publish reliable technical information.
Unfortunately, the test conditions used are notalways clearly stated, making valid competitive
comparisons difficult, if not impossible.
Published catalog information should be usedwith caution when employed for this purpose.
Evaluative judgments are improved
when comparisons between trap types(thermodynamic, mechanical and thermostatic)
are made in addition to the comparisons
between traps of a common technology.

78

Yarway Industrial steam trapping handbook
Appendix B - Steam trap evaluation methods
Yarway corporation standard test conditions
Yarway corporation has established its own test
conditions for use when making comparativeevaluations of all types of traps:
1.	Steam loss
• Protection traps: 100 psi supply, nominal
condensate load 10 lb/hr• Process traps: 100 psi supply, nominal
condensate load at 10% of statedcondensate capacity at the same
operating pressure.
2. Capacity-all traps• 100 psi supply.
• Traps that discharge near saturated
conditions should be tested within 5°F
of saturation temperature.
• Subcooled traps, usually thermostatic
types, have a capacity that varies with theamount of condensate subcooling. These
traps should be tested using different
levels of condensate subcooling so that
their relationship between subcoolingand capacity can be properly established.
3. Back pressure limit-all traps• 100 psi supply, condensate loads sameas steam loss test.
4.	Air handling• 100 psi supply, condensate loads sameas steam loss test.
5. Characteristics such as failure modeor freeze resistance can generally beevaluated satisfactorily from publisheddata and technical analysis.

Steam loss – test method
Condensate discharge is collected from a
trap operating under specific and constantconditions. Heat balance calculations
determine the amount of steam discharged
with the condensate. The test is referred
to as a calorimeter test. Constant andcontrolled conditions for the duration of
the test are required to obtain meaningful
results. Atmospheric conditions such as
ambient temperature must remain constantand error-causing influences such as drafts
must be avoided.
Figure B.2 shows a typical calorimeter testingarrangement. Figure B.3 is a data sheet
showing the type of information required andheat balance calculations used in determining
steam loss. It has been completed using test
data representative of a properly performing
thermodynamic disc trap.
A note of caution: there are practical limits
to the accuracy that can be achieved inthis steam loss test. The applicable code
(ANSI PTC 39.1) states: “The average result
from three consecutive tests must agree within
10 percent or 1 pound per hour, whichever isgreater”. Obviously energy efficiency judgments
concerning steam traps can not properly bebased on differences that are smaller than
the accuracy of the test itself.

Figure B.2
Typical test arrangement for steam loss tests
Valve5
Cooling water in

Valve
1

Temp.
T1
in

Steam in

Ps
Heat exchanger
Valve
2

Condensate drain
device trap

TL

Temp. out

Supplypress.
Ts
Supply
temp.

Valve
4
Valve
3

Test
trap

Vacuumbreaker
Slope
Agitator

To drain
Cooling water out
To drain

Vented coveror plastic
balls

Wc

Calorimeter
tank

TFE

Scale

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Yarway Industrial steam trapping handbook
Appendix B - Steam trap evaluation methods
Test procedure
Start with all valves closed and tank empty(reference Figure B.2).
1.	Open valves 1, 2 and 3 to permit trap
draining steam inlet line and test trap
to operate at test pressure Ps.
2.	During warm-up, weigh and record
weight of empty calorimeter tank Wt, andrecord steam pressure Ps and steam
temperature Ts.
3.	Open valves 5 and 6 to allow flow of coolingwater through heat exchanger to create
desired condensate load on test device.
Allow system to come to equilibrium.
4.	 Fill calorimeter tank with enough water
having a temperature T1 at least 15°F below
ambient temperature Ta to obtain a test runof reasonable duration. Weight and record
water temperature T1 and weight of waterplus calorimeter tank, TL.
5.	Rapidly close valve 3 and open valve 4. Start
timing interval when valve 4 is open. (Use of
a 3-way valve is recommended to facilitate
rapid closing and opening).
6.	Agitate the water in the calorimeter tankas necessary to ensure uniform watertemperature.
7.	 When the temperature of the water in thecalorimeter tank is as many degrees above
ambient as the initial temperature was
below, rapidly close valve 4 and open valve 3,
simultaneously recording the elapsed time,then the final water temperature T2 , andweight of water plus calorimeter tank, W2.
8.	Enter data in the calorimeter test data
sheet and calculate steam loss. Refer tosteam tables Appendix D for enthalpy values(i.e., sensible heat of liquid and latent heatof evaporation) required by data sheet.
For reference, calorimeter test guidelines
are published in the ANSI/ASME PTC 39.1
performance test code for condensate removal
devices by the American Society of MechanicalEngineers, United Engineering Center, 345 East
47th Street, New York, N.Y. 10017

Discharge capacity – test method
Condensate discharge capacity of steam traps
varies with each type and make. Interest is
directed to two distinct flow rates: (1) cold
condensate capacity for startups; and (2) hot
condensate capacity that will be available in
the actual installation.
For on-off type traps that discharge nearsteam temperature, usually thermodynamic
and mechanical traps, the discharge capacity
is primarily a function of differential pressure
and is proportional to the square root ofdifferential pressure. (For estimating purposes,
the steam temperature discharge capacity isapproximately ⅓ of the cold water capacity
due to the choking effects of flash steam
and changes in liquid density.)
For certain modulating traps (usually bimetallic
thermostatic type traps), the discharge capacity
is a function of both differential pressure
and temperature. The discharge capacity
will increase with increasing amounts ofcondensate subcooling until the maximum
capacity is reached. Capacity data for a
modulating type trap must reference bothtemperature and pressure.
Typical condensate capacity discharge curves
are presented in Figures B.4 and B.5. theirdifferent form results from the different
operating principles of the traps being tested.

80

Yarway Industrial steam trapping handbook
Appendix B - Steam trap evaluation methods
Figure B.3
Yarway calorimeter test data
Yarway calorimeter test data
Trap type:Age and service:
Data recorded by:PPa

Yarway 720 A
1 year, 150 psi drip
D. Kalix

Log #:
Date:
Test station:
Trap number:1
Run number:
1
100.00Size: ½”

Nominal steam test pressure (psig)

Barometric pressure (psia) 1 in. Hg. = .4914 psia
Inlet steam pressure (psia)
Inlet steam temperature (°F)
Enthalpy of saturated liquid at Ts (BTU/Ibm)
Latent heat of evaporation at Ts (BTU/Ibm)
Weight of container (Ibm)
Equiv. water weight of container = *Wc x .225 (Ibm)
Weight of initial water + container (Ibm)
Ambient temperature (°F)
Initial temperature of water (°F)
Enthalpy of water initially at T1 (BTU/Ibm)
Weight of final water plus container (Ibm)
Final temperature of water and condensate (°F)
Enthalpy of water finally at T2 (BTU/Ibm)
Time of test (seconds)
Weight added to scale = W2 – W1 (Ibm)
Initial total enthalpy = (W1 – Wc+ We)Hf1= (W1 – 12.75)Hf1 (BTU)
Final total enthalpy = (W2 – Wc + We)Hf2
E2= (W2 – 12.75)Hf2 (BTU)
E2 – E1 BTU provided by discharge (lbm/hr)
Es
Discharge enthalpy of saturated water = Hfs x ØW
Total discharge = ØW x 3600/Øt (lbm/hr)
Steam loss = WL = (E2 – E1) – Es x 3600 (lbm/hr)
Hfgs
Øt
Ps
Ts
Hfs
Hfgs
Wc
We
W1
Ta
T1
Hf1
W2
T2
Hf2
Øt
ØW
E1

Cycles/minute:
Back pressure limit:
Discharge temperature (°F):

0973
18 May 1983
5
1
1
2
3
100.00100.0015.00
115.00338.00309.10880.60
15.45
2.70
40.70
70.00
59.10
27.16
42.95
81.00
49.02
596.002.25
759.0015.00
115.00338.00309.10880.60
15.45
2.70
40.70
69.00
60.50
28.56
45.95
78.00
46.02
560.002.10
888.0015.00
115.00338.00309.10880.60
15.45
2.70
40.70
68.00
58.80
26.86
43.20
78.00
46.02
512.001.95
766.001480.00

1528.00

1401.00

721.00695.0013.60
0.20

640.00649.0013.50-

635.00603.00
13.70
0.30

5.00
336.003.00
336.004.00
337.00

Notes
Back pressure limit test not performed* Excludes weight of nipples and valve

81

Yarway Industrial steam trapping handbook
Appendix B - Steam trap evaluation methods
Figure B.4
Condensate capacity near steam temperature (typical for on-off type traps)
0.1

0.2

0.3

0.5

1

2

3

5

10

20

30

5000

10,000
9,000
8,000
7,000
6,000
5,000

3000
2000

4,000

Req. trap flow rate, lb/hr

3,000
1000

2,000

700
500

1,000
900
800
700
600
500

300
200

400
300

100

200

70
50

100
90
80
70
60
50

30

1

2

3

4

5 6 7 8 9 102030

40 50 60 80100 200300

400 500 600

Trap inlet pressure, psi

Figure B.5
Condensate capacity vs discharge temperature (typical for subcooled thermostatic traps)
Trap flow rate kg/hr

Saturation
temperature

50

100

200

300

400

25

50

50

100

75

150
50 psi

100 psi

200 psi

300 psi

200
0

200

400

600

800

Subcooling °C

Subcooling °F

0

100

1000

Trap flow rate lb/hr

82

Yarway Industrial steam trapping handbook
Appendix B - Steam trap evaluation methods
Discharge capacity test procedure(dynamic weight method)
Start with all valves closed (reference
Figure B.6).
1.	Open valves 1 and 2 and fill accumulator
tank to desired level. Close valve 1.
2.	Open valve 3 and heat water in accumulator
tank to desired temperature. Close valves 2
and 3 and open valve 4.
3.	 Fill barrel approximately half full of cold
water. The end of the discharge pipe should
be under water in the weigh tank. Balancescale lever arm, then add an appropriate
weight to allow time for opening andclosing valves.
4.	Open valves 5 and 6 to heat pipe and test
trap.
5.	 When thermal equilibrium is reached,close valve 6 and open valve 7.
6.	 When scale lever arm is balanced, starttiming and add an appropriate weight tothe yoke corresponding to the number ofpounds of condensate to be collected. Thisshould be less than the amount necessary
to cause boiling of the water in theweigh tank.
7.	 When scale lever arm is again balanced,
stop timing and close valve 5.

8.	Observe and record the following data:a.	Elapsed timeb.	Ambient temperature Ta (°F)
c.	Barometric pressure, Pa (psia)d.	Steam pressure and temperature,Ps (psig) and Ts (°F)
e.	Weight of condensate plus barrel atstart and finish, We (lb)f.	 Initial and final values of the following:(i)	Temperature differential (T5 – Tcl °F)(ii) Inlet pressure, P1 (psig)(iii)	Back pressure, P2 (psig)
9.	 Calculate capacity in lb/hr.
Discharge capacity test guidelines are
published in ANSI/ASME PTC 39.1 performance
test code for condensate removal devices.
Back pressure – test method
At the present time there is no generally
accepted standard procedure for performingback pressure tests. Experience has shown thatback pressure limitations can be determinedeasily by installing a trap into a test rig having
controlled inlet conditions, and with an outlet
connected to a receiving tank, whose pressure
can be regulated, to simulate a closed returnsystem. Either steam or air may be used topressurize the tank. Assure its pressure rating
is adequate for the test. This test is usually
performed on thermodynamic traps.

Figure B.6
Typical arrangement for discharge capacity testing (dynamic weight method)
Safetyvalve

Vent

Supplypress
Ps

Pressure
reducing
valve

Valve
2
Valve
4

Ts

Valve
1
Cold water
Accumulator
Note 2
Press
Gauge
P1
glass
Tc

Steam
supplyCirculation

Valve
3
Injector line

Valve
5

Press
P2

Valve
7 Slope

Test trap

Valve
6

Temp.
condensate

Scale
Open pit

Vacuumbreaker
BarrelNotes
1.	The piping from the accumulator to the test
device shall be of the same diameter as theinlet connection on the test device. The inlet tothe piping from the accumulator shall be in theform of a well rounded entrance.
2.	The distance between the sensors and the test
device shall not exceed 20 internal pipe diameters.

83

Yarway Industrial steam trapping handbook
Appendix B - Steam trap evaluation methods
Test procedure (for trap closing limit)
1.	 Confirm normal operation of the trapwith a suitable listening device.
2.	Gradually increase the back pressure insteps of 5 psi, waiting approximately threeminutes after each adjustment to allow thetrap time to stabilize itself. Listen for the
opening and closing action.
3.	 When the trap stays open and stops
functioning, the back pressure limit has
been reached.
4.	 Confirm the limit by repeating the test 2
or 3 times.
Test procedure (for discharge temperature
reduction)
In a similar manner the effects of backpressure on discharge temperature can beestablished. Depending on the type and makeof trap, 40°F to 120°F reductions in discharge
temperature can result when subjecting it toback pressures up to 80%.
1.	 Install the trap (usually a bimetallic
thermostatic trap) in the same system.
Provision to measure the inlet temperatureof the trap is required.
2.	Allow 3 to 5 minutes for the trap tostabilize itself before recording the inlet
temperature.

3.	 Increase back pressure in 5 psi increments.
Allow sufficient time for the trap tostabilize its operations and the record inlet
temperature.
Repeat the process over the desired backpressure testing range in order to establish
a complete profile of discharge temperature
reduction.
Note: in evaluating the effects of backpressure on a steam trap, it is important thatthe condensate flow not exceed the trap’s
capacity for the pressures involved.
“Flooding” of the trap will give erroneous
results.
Air handling capability – test method
Currently there is no generally recognized
test standard for evaluating a steam trap’s air
handling capability. Yarway Corporation has
developed a simple and reliable method forcomparing the relative air handling capabilities
of various types of traps. Figure B.7 is aschematic representation of its air handling test
arrangement. The test requires the installationof a trap in a steam line and allowing it
sufficient time to heat up and stabilize its
performance. Then a known volume of air is
injected (under supply pressure conditions)
into the supply line ahead of the trap.

The time required to discharge the air is thenmeasured. By comparing the times required
to remove the air, it is possible to rank various
types of traps according to their relative air
handling capability.
Test procedure
1.	Allow temperatures of test trap and rig towarm up by opening V-1, V-2, V-3 and V-4.
Normal steam pressure 100 psig, (338°F).
2.	After temperatures have stabilized,
blowdown air cylinder by closing V-2, V-3
and opening V-5 and A-1. Blowdown until an
air temperature of 200°F is attained at T2.
3.	 Close V-4 and V-5 and pressurize the air
cylinder to 90 psig.
4.	Open V-4 and V-2.
5.	 If using a recorder to measure temperature
at T1 start the recorder.
6.	Shut V-1 and immediately open V-3. If using
a timer, start the timer.
7.	Stop the timer when the inlet temperature
at T1 returns to normal operating
temperature.

Figure B.7
Steam trap air handling capability – test rig
Steam supply
V-2
T1

Pressure

V-1

Test trap

V-3

Drain
Pressure

V-6 (Drain)

Regulator

A-1

Air supply

Air cylinder

T2 Thermocouple

V-4

V-5 (Drain)

84

Yarway Industrial steam trapping handbook
Appendix C - Glossary of terms
Appendix C
Air binding: the process of a steam trap closing
due to the presence of air rather than steam.
This slows down the discharge of condensate
and the ability of a steam system to reach its
desired temperature (reference Chapter 5).

Flash steam: steam that results whensaturated water or condensate is discharged
to a lower pressure. It is steam that could
not exist at a higher pressure (reference
Chapter 2).

Blow-down valve: a valve used when
blowing pipeline dirt or scale from a strainer
screen or boiler drum (reference Chapter 5,
Figure 5.1).

Flash tank: a vessel or tank where flash steamis accumulated for subsequent use (reference
Chapter 5, Figure 5.3).

British Thermal Unit (BTU): The quantity ofheat required to raise one pound of water
one (1) degree fahrenheit (reference Chapter 2).
Capacity: the maximum amount of condensate
that can be discharged by a steam trapat specific conditions of temperature andpressure differential (between its inlet andoutlet)-capacity is measured in pounds perhour (reference Chapter 4).

Latent heat of vaporization: heat that
produces a change of state without a change
in temperature, such as changing water
into steam-sometimes referred to simply
as “latentheat” (reference Chapter 2).
Modulate: the partial opening and closing of asteam trap, thereby regulating the discharge
flow of condensate. Modulation is in contrast
to a full open/full closed mode of operation.

Condensate: the result of steam changing
from vapor to a liquid.

psia: pounds per square inch absolute-a
measure of pressure including atmosphericpressure (about 14.69 psi).

Cycle: the opening and closing action of asteam trap that allows it to pass condensate
and then stop the passage of steam.

psig: pounds per square inch gage – a measureof pressure excluding atmospheric pressure(about 14.69 psi).

Dirt pocket: a length of pipe in the dischargeline of steam heated equipment that allows thecollection (by gravity) of pipeline scale and dirt
(reference Figure 5.1).

Safety load factor: a factor, by which thecalculated condensate load is multiplied, todetermine the capacity a trap should possess
to properly serve its selected application. The
safety load factor is used to accommodate
system variables and uncertainties affecting
the condensate flow rate (reference Chapter 4).

Discharge temperature: the temperatureof condensate (measured at a steam trap’s
inlet) while it is being discharged. Sometimes
referred to as the temperature at which asteam trap starts to open (reference Chapter 2
and Chapter 4).
Efficiency: see also ASME power test code
ANSI PTC39.1.
Enthalpy: the energy content of a fluid,
including both heat and mechanical energy,
BTU/lb-see Sensible, latent heat, and totalheat of steam.

Sizing: the process of matching the condensate
drainage requirements of an application
to a steam trap having a suitable capacity(reference Chapter 4).
Saturated condensate: condensate that has
a temperature equal to that of the steam withwhich it is in contact (reference Chapter 2).
Saturated steam: steam that has atemperature equal to that of the condensate
with which it is in contact (reference Chapter 2).

85

Yarway Industrial steam trapping handbook
Appendix C - Glossary of terms
Saturation curve: graphic representation of
the boiling point of water at various pressures(the pressure and temperature at whichsaturated steam and condensate exist)(reference Chapter 2).
Saturation temperature: the temperature atwhich saturated steam and condensate exist(reference Chapter 2, Figure 2.3).
Sensible heat: heat that produces atemperature rise in a body (such as water)(reference Chapter 2).
Steam:• Dry: steam having no water droplets
suspended in it (reference Chapter 2).
• Live: “live steam” is an expression commonlyused to describe steam that is still able to
do useful work-in contrast to flash steam
at atmospheric pressure.
• Wet: steam having fine water droplets
suspended in it, and as a result, having
a lower heat content than dry steam(reference Chapter 2).
• Total heat of: the sum of BTUs per pound ofboth the sensible heat (of condensate) andthe latent heat (of vaporization) (reference
Chapter 2).
Steam binding: the process of steam keeping
a steam trap closed and thereby preventing
the discharge of condensate that has formed
upstream of the trap. This condition results
when the condensate discharge line to a steam
trap is subjected to sufficient heating that thecondensate in it is changed back into steam,
thereby blocking the flow of condensate to
the trap (reference Chapter 5).
Steam separator: a device that removes
entrained water droplets from steam flow(reference Chapter 5).
Steam tables: tables that list the propertiesof steam and condensate at various pressuresand temperatures (reference Chapter 2).
Steam tracing: the use of steam to: (1) heator maintain the temperature of a process
liquid in a pipeline, (2) prevent water lines andrelated equipment from winter freeze-ups,and (3) provide uniform temperature in andaround instruments so as to help maintaintheir calibration (reference Appendix A-11).

Steam trap: a self-contained valve which
automatically drains condensate anddischarges air and non-condensible gases
from a steam-containing pipe or vessel(reference Chapter 3).
• Cool: a steam trap that discharges
condensate at temperatures significantly
below saturation temperature is referred
to as a “cool trap” even though it may be at
a temperature well above 212°F (reference
Chapter 4).
• Hot: a steam trap that discharges condensate
at temperatures up to 10 degrees below
saturation temperature (reference Chapter 4).
• Process: a steam trap that discharges
condensate from equipment used in theheating or production of some productas distinct from a “protection service”
application.
• Protection: a steam trap that discharges
condensate from an application such asa steam main (to protect it from water
hammer) or from a tracer application
providing protection from freezing.
Steam trap standard: a preferred type of
steam trap and piping configuration forremoving condensate from each designatedpiece of equipment in a steam system.
Superheat: heat that is added to dry saturated
steam.
Subcooling: the temperature difference
between that of steam and the condensate
being discharged by a steam trap. This
subcooling or suppression will be at least
2 or 3 degrees and sometimes much more.
Certain applications benefit from steam
traps that discharge condensate with a small
amount of subcooling, while others will benefit
from a large amount of subcooling.
Suppression: (see “Subcooling”).
Water hammer: the shock created whenaccumulated condensate is swept down apipeline at high velocities and is slammed into
valves, elbows, steam traps, or other fittings.

86

Yarway Industrial steam trapping handbook
Appendix D - Useful tables
Appendix D – Contents
Conversion factors�����������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������87
Temperature conversion tables��������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������88
Steam tables (abbreviated)���������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������90
Sensible heat of liquid�����������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������91
Properties of pipe������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������92
Heat transfer coefficients����������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 93
Specific heats�������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������95
Standard piping symbols�������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������97

Conversion factors
Length1 in = 25.4 mm
1 mm = .03937 in
1 ft = 30.48 em
1 m = 3.28083 ft
1 micron = .001 mm
Area
1 in2 = 6.4516 cm2
1 ft2 = 929.03 cm2
1 cm2 = 0.155 in2
1 cm2 = 0.0010764 ft2
Volume1 in3 = 16.387 cm3
1 ft3 = 1728 in3
1 ft3 = 7.4805 U.S. gal
1 ft3 = 6.229 British gal
1 ft3 = 28.317 liters
1 U.S. gal = 0.1337 ft3
1 U.S. gal = 231 in3
1 U.S. gal = 3.785 liters
1 British gal = 1.20094 U.S. gal
1 British gal = 277.3 in3
1 British gal = 4.546 liters
1 liter = 61.023 in3
1 liter = 0.03531 ft3
1 liter = 0.2642 U.S. gal
Velocity
1 ft per sec = 30.48 cm per sec
1 cm per sec = .032808 ft per sec

Weight1 ounce av = 28.35 g
1 lb av = 453.59 g
1 gram = 0.03527 oz av
1 kg = 2.205 lb av
1 ft3 of water = 62.425 lb
1 U.S. gal of water = 8.33 lb
1 in3 of water = 0.0361 lb
1 British gal of water = 10.04 lb
1 ft3 of air at 60°F and 1 atm = 0.0764 lb
Flow
1 ft3 per sec = 448.83 gal per min
1 ft3 per sec = 1699.3 liters per min
1 U.S. gal per min = 0.002228 ft3 per sec
1 U.S. gal per min = 0.06308 liters per sec
1 cm3 per sec = 0.0021186 ft3 per min
Density
1 lb per ft3 = 16.018 kg per m3
1 lb per ft3 = .0005787 lb per in3
1 kg per m3 = 0.06243 lb per ft3
1 g per cm3 = 0.03613 lb per in3
Energy1 BTU = 777.97 ft·lb
1 erg = 9.4805 x 10-11 BTU
1 erg = 7.3756 x 10-6 ft·lb
1 kilowatt hour = 2.655 x 106 ft·lb
1 kilowatt hour = 1.3410 hp hr
1 kg calorie = 3.968 BTU

Pressure
1 in of water = 0.03613 lb per in2
1 in of water = 0.07355 in of Hg
1 ft of water = 0.4335 lb per in2
1 ft of water = 0.88265 in of Hg
1 in of mercury = 0.49116 lb per in2
1 in of mercury = 13.596 in of water
1 in of mercury = 1.13299 ft of water
1 atmosphere = 14.696 lb per in2
1 atmosphere = 760 mm of Hg
1 atmosphere = 29.921 in of Hg
1 atmosphere = 33.899 ft of water
1 lb per in2 = 27.70 in of water
1 lb per in2 = 2.036 in of Hg
1 lb per in2 = .0703066 kg per cm2
1 kg per cm2 = 14.223 lb per in2
1 dyne per cm2 = .0000145 lb per in2
1 micron = .00001943 lb per in2Power
1 horsepower = 33,000 ft·lb per min
1 horsepower = 550 ft·lb per sec
1 horsepower = 2,546.5 BTU per hr
1 horsepower = 745.7 watts
1 watt = 0.00134 horsepower
1 watt = 44.26 ft·lb per min
Viscosity
1 Centipoise = .000672 lb per ft sec
1 Centistoke = .00001076 ft2 per sec

Temperature
Temperature Fahrenheit (F) = 9/5 Celsius (C) + 32 = 9/4 R + 32
Temperature Celsius (C) = 5/9 Fahrenheit (F) – 32 = 5/4 R
Temperature Reaumur (R) = 4/9 Fahrenheit (F) – 32 = 4/5 C
Absolute temperature Celsius or Kelvin (K) = Degrees C + 273.16
Absolute temperature Fahrenheit or Rankine (R) = Degrees F + 459.69
Heat transfer
1 BTU per ft2 = .2712 g cal per cm2
1 g calorie per cm2 = 3.687 BTU per ft2
1 BTU per hr per ft2 per °F = 4.88 kg cal per hr per m2 per °C
1 kg cal per hr per m2 per °C = .205 BTU per hr per ft2 per °F
1 Boiler horsepower = 33479 BTU per hr87

Yarway Industrial steam trapping handbook
Appendix D - Useful tables
Temperature conversion tables
C-273.15
-268
-262
-257
-251
-246
-240
-234
-229
-223
-218
-212
-207
-201
-196
-190
-184
-179
-173
-169
-168
-162
-157
-151
-146
-140
-134
-129
-123
-118
-112
-107
-101
95.6
-90.0
-84.4
-78.9
-73.3
-67.8
-62.2
-56.7
-51.1
-45.6
-40.0
-34.4
-28.9
-23.3
-17.8

*
-459.67
-450
-440
430
-420
-410
-400
-390
-380
-370
-360
-350
-340
-330
-320
-310
-300
-290
-280
-273
-270
-260
-250
-240
-230
-220
-210
-200
-190
-180
-170
-160
-150
-140
-130
-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0

F
-459.4
-454
-436
-418
-400
-382
-364
-346
-328
-310
-292
-274
-256
-238
-220
-202
-184
-166
-148
-130
-112
-94
-76
-58
-40
-22
-4
14
32

C
-17.2
-16.7
-16.1
-15.6
-15.0
-14.4
-13.9
-13.3
-12.8
-12.2
-11.7
-11.1
-10.6
-10.0
-9.4
-8.9
-8.3
-7.8
-7.2
-6.7
-6.1
-5.6
-5.0
-4.4
-3.9
-3.3
-2.8
-2.2
-1.7
-1.1
-0.6
0.0
0.6
1.1
1.7
2.2
2.8
3.3
3.9
4.4
5.0
5.6
6.1
6.7
7.2
7.8
8.3
8.9
9.4
10.0

Fahrenheit and Celsius (Centigrade)
*
F
C
*
F
C
1
33.8 10.6
51 123.8
432
35.6 11.1
52 125.6
49
3
37.4 11.7
53 127.4
54
4
39.2 12.2
54 129.2
60
541.0 12.8
55 131.0
66
642.8 13.3
56 112.8
717
44.6 13.9
57 134.6
77
8
46.4 14.4
58 136.4
82
948.2 15.0
59 138.2
88
1050.0 15.6
60 140.0
93
1151.8 16.1
61 141.8
99
12
53.6 16.7
62 143.6
13
55.4 17.2
63 145.4
14
57.2 17.8
64 147.2
1559.0 18.3
65 149.0
1660.8 18.9
66 150.8 100
1762.6 19.4
67 152.6
18
64.4 20.0
68 154.4
19
66.2 20.6
69 156.2
20
68.0 21.1
70 158.0
21
69.8 21.7
71 159.8
2271.6 22.2
72 161.6 104
2373.4 22.8
73 163.4 110
2472.5 23.3
74 165.2 116
25
77.0 23.9
75 167.0 121
2678.8 24.4
76 168.8 1272780.6 25.0
77 170.6 132
28
82.4 25.6
78 172.4 13829
84.2 26.1
79 174.9 14330
86.0 26.7
80 176.0 149
3187.8 27.2
81 177.8 154
31
89.6 27.8
82 179.6 160
33
91.4 28.3
83 181.4 166
34
93.2 28.9
84 183.2 1713595.0 29.4
85 185.0 177
36
96.8 30.0
86 186.8 182
3798.6 30.6
87 188.6 188
38 100.4 31.1
88 190.4 193
39 102.2 31.7
89 192.2 199
40 104.0 32.2
90 194.0 204
41 105.8 32.8
91 195.8 210
42 107.6 33.3
92 197.6 216
43 109.4 33.9
93 199.4 221
44 111.2 34.4
94 201.2 227
45 113.0 35.0
95 203.0 232
46 114.8 35.6
96 204.8 238
47 116.6 36.1
97 206.6 243
48 118.4 36.7
98 208.4 249
49 120.2 37.2
99 210.2 254
50 122.0 37.8 100 212.0 260

Interpolation values
*
110
120
130
140
150
160
170
180
190
200
210
212
220
230
240
250
260
270
280
290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
460
470
480
490
500

F
230
248
266
284
302
320
338
356
374
392
410
413
428
446
464
482
500
518
536
554
572
590
608
626
644
662
680
698
716
734
752
770
788
806
824
842
860
878
896
914
932

C
266
271
277
282
288
293
299
304
310
316
321
327
332
338
343
349
354
360
366
371
377
382
388
393
399
404
410
416
421
427
432
438
443
449
454
460
466
471
477
482
488
493
499
504
510
516
521
527
532
538

*
510
520
530
540
550
560
570
580
590
600
610
620
630
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
800
810
820
830
840
850
860
870
880
890
900
910
920
930
940
950
960
970
980
990
1000

F
950
968
986
1004
1022
1040
1058
1076
1094
1112
1130
1148
1166
1184
1202
1220
1238
1256
1274
1292
1310
1328
1346
1364
1382
1400
1418
1436
1454
1472
1490
1508
1526
1544
1562
1580
1598
1616
1634
1652
1670
1688
1706
1724
1742
1760
1778
1796
1814
1832

C
0.56
1.11
1.67
2.22
2.78

*
1
2
3
4
5

F
1.8
3.6
5.4
7.2
9.0

C
3.33
3.89
4.44
5.00
5.56

*
6
7
8
9
10

F
10.8
12.6
14.4
16.2
18.0

* In the center column, find the temperature to be converted. The equivalent temperature is in the left column,
if converting to Celsius, and in the right column, if converting to Fahrenheit.

88

Yarway Industrial steam trapping handbook
Appendix D - Useful tables
Temperature conversion tables (continued)
C
543
549
554
560
566
571
577
582
588
593
599
604
610
616
621
627
632
638
643
649
654
660
666
671
677
682
688
693
699
704
710
716
721
727
732
738
743
749
754
760
766
771
777
782
788
793
799
804
810
816

*
1010
1020
1030
1040
1050
1060
1070
1080
1090
1100
1110
1120
1130
1140
1150
1160
1170
1180
1190
1200
1210
1220
1230
1240
1250
1260
1270
1280
1290
1300
1310
1320
1330
1340
1350
1360
1370
1380
1390
1400
1410
1420
1430
1440
1450
1460
1470
1480
1490
1500

F
1850
1868
1886
1904
1922
1940
1958
1976
1994
2012
2030
2048
2066
2084
2102
2120
2138
2156
2174
2192
2210
2228
2246
2264
2282
2300
2318
2336
2354
2372
2390
2408
2426
2444
2462
2480
2498
2516
2534
2552
2570
2588
2606
2624
2642
2660
2678
2696
2714
2732

C
821
827
832
838
843
849
854
860
866
871
877
882
888
893
899
904
910
916
921
927
932
938
943
949
954
960
966
971
977
982
988
993
999
1004
1010
1016
1021
1027
1032
1038
1043
1049
1054
1060
1066
1071
1077
1082
1088
1093

Fahrenheit and Celsius (Centigrade)
*
F
C
*
1510
2750
1099
2010
1520
2768
1104
2020
1530
2786
1110
2030
1540
2804
1116
2040
1550
2822
1121
2050
1560
2840
1127
2060
1570
2858
1132
2070
1580
2876
1138
2080
1590
2894
1143
2090
1600
2912
1149
2100
1610
2930
1154
2110
1620
2948
1160
2120
1630
2966
1166
2130
1640
2984
1171
2140
1650
3002
1177
2150
1660
3020
1182
2160
1670
3038
1188
2170
1680
3056
1193
2180
1690
3074
1199
2190
1700
3092
1204
2200
1710
3110
1210
2210
1720
3128
1216
2220
1730
3146
1221
2230
1740
3164
1227
2240
1750
3182
1232
2250
1760
3200
1238
2260
1770
3218
1243
2270
1780
3236
1249
2280
1790
3254
1254
2290
1800
3272
1260
2300
1810
3290
1266
2310
1820
3308
1271
2320
1830
3326
1277
2330
1840
3344
1282
2340
1850
3362
1288
2350
1860
3380
1293
2360
1870
3398
1299
2370
1880
3416
1304
2380
1890
3434
1310
2390
1900
3452
1316
2400
1910
3470
1321
2410
1920
3488
1327
2420
1930
3506
1332
2430
1940
3524
1338
2440
1950
3542
1343
2450
1960
3560
1349
2460
1970
3578
1354
2470
1980
3596
1360
2480
1990
3614
1366
2490
2000
3632
1371
2500

F
3650
3668
3686
3704
3722
3740
3758
3776
3794
3812
3830
3848
3866
3884
3902
3920
3938
3956
3974
3992
4010
4028
4046
4064
4082
4100
4118
4136
4154
4172
4190
4208
4226
4244
4262
4280
4298
4316
4334
4352
4370
4388
4406
4424
4442
4460
4478
4496
4514
4532

C
1377
1382
1388
1393
1399
1404
1410
1416
1421
1427
1432
1438
1443
1449
1454
1460
1466
1471
1477
1482
1488
1493
1499
1504
1510
1516
1521
1527
1532
1538
1543
1549
1554
1560
1566
1571
1577
1582
1588
1593
1599
1604
1610
1616
1621
1627
1632
1638
1643
1649

*
2510
2520
2530
2540
2550
2560
2570
2580
2590
2600
2610
2620
2630
2640
2650
2660
2670
2680
2690
2700
2710
2720
2730
2740
2750
2760
2770
2780
2790
2800
2810
2820
2830
2840
2850
2860
2870
2880
2890
2900
2910
2920
2930
2940
2950
2960
2970
2980
2990
3000

F
4550
4568
4586
4604
4622
4640
4658
4676
4694
4712
4730
4748
4766
4784
4802
4820
4838
4856
4874
4892
4910
4928
4946
4964
4982
5000
5018
5036
5054
5072
5090
5108
5126
5144
5162
5180
5198
5216
5234
5252
5270
5288
5306
5324
5342
5360
5378
5396
5414
5432

Temperature conversion formulas
Degrees Celsius(formerly Centigrade °C)°C + 273.15 = °K Kelvin(°C x %) + 32 = °F Fahrenheit°C x o/s = °R Reaumur

Degrees Fahrenheit - ° F°F + 459.67 = °Rankine(°F – 32) x % = °C Celsius(°F – 32) x % = °R Reaumur

Degrees Reaumur - °R
°R x % = °C Celsius(°R x %) + = °F Fahrenheit

89

Yarway Industrial steam trapping handbook
Appendix D - Useful tables
Steam tables
Steampressure
psig
28*
26*
24*
22*
20*
18*
16*
14*
12*
10*
8*
6*
4*
2*
0*
1
2
3
4
5
6
7
8
9
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
110
120
125
130
140
150
160
170
180
190

Steam
temperature
°F
101
126
141
152
162
169
176
182
187
192
197
201
205
209
212
216
219
222
224
227
230
232
235
237
240
250
259
267
274
281
287
292
298
303
307
312
316
320
324
328
331
335
338
344
350
353
356
361
366
371
375
380
384

Heat BTU/lb
Sensible
60
93
109
120
130
137
144
150
155
160
165
169
173
177
180
183
187
190
193
195
198
201
203
206
208
218
227
236
243
250
256
262
267
272
277
282
286
290
294
298
302
306
309
316
322
325
328
334
339
344
348
353
358

Latent
1037
1023
1014
1007
1001
997
993
989
986
983
980
977
975
972
970
968
965
964
962
961
959
957
956
954
952
945
940
934
929
924
920
915
912
908
905
901
898
895
892
889
886
883
881
876
871
868
866
861
857
853
849
845
841

Total heatof steam
1105
1116
1122
1127
1131
1134
1137
1139
1141
1143
1145
1146
1148
1149
1150
1151
1152
1154
1155
1156
1157
1158
1159
1160
1160
1163
1167
1170
1172
1174
1176
1177
1179
1180
1182
1183
1184
1185
1186
1187
1188
1189
1190
1192
1193
1193
1194
1195
1196
1197
1197
1198
1199

Specific volume
ft3·lbSaturated steam
339.0
177.0
121.0
92.0
75.0
63.0
55.0
48.0
43.0
39.0
36.0
33.0
31.0
29.0
27.0
25.0
24.0
22.5
21.0
20.0
19.5
18.5
18.0
17.0
16.5
14.0
12.0
10.5
9.5
8.5
8.0
7.0
6.7
6.2
5.8
5.5
5.2
4.9
4.7
4.4
4.2
4.0
3.9
3.6
3.3
3.2
3.1
2.9
2.7
2.6
2.5
2.3
2.2

* Vacuum in Mercury

90

Yarway Industrial steam trapping handbook
Appendix D - Useful tables
Steam tables (continued)
Steampressure
psig
200
220
240
250
260
280
300
350
400
450
500
600
750
1100
1450
1800
2200
2600
3000
3193

Steam
temperature
°F
388
395
403
406
409
416
422
436
448
460
470
489
513
558
593
622
650
675
696
705

Heat BTU/lb
Sensible
362
370
378
381
385
392
399
414
428
441
453
475
503
560
607
650
697
746
805
906

Latent
837
830
823
820
817
811
805
790
776
764
751
728
697
629
565
501
424
334
211
0

Total heatof steam
1199
1200
1201
1201
1202
1203
1204
1204
1204
1205
1204
1203
1200
1189
1172
1151
1121
1080
1016
906

Specific volume
ft3·lbSaturated steam
2.10
2.00
1.80
1.75
1.70
1.60
1.50
1.30
1.10
1.00
0.90
0.75
0.45
0.39
0.29
0.22
0.16
0.12
0.08
0.05

To facilitate steam trap calculations, values are rounded to the values shown.

Superheated steam
Steampressure
psig
200
400
600
1100
2200
3193

Saturated steam
Total heat of
Temperaturesaturated steam°F
BTU/lb
388
1199
448
1204
489
1203
558
1189
650
1121
705
906

Total temperature, °F
400
600
800
1000
Total heat of superheated steam BTU/lb
1207
1322
1425
1529
1306
1416
1523
1289
1408
1517
1235
1384
1502
1323
1467
1250
1432

To facilitate steam trap calculations, values are rounded to the values shown.

Sensible heat of liquid (btu/lb)
Temperature
°F
32
34
36
38
40
42
44
46
48
50
52
54
56
58
60
62
64
66

Sensible heat
(BTU/lb)
0.00
2.02
4.03
6.04
8.05
10.05
12.06
14.06
16.07
18.07
20.07
22.07
24.06
26.06
28.06
30.05
32.05
34.05

Temperature
°F
68
70
72
74
76
78
80
82
84
86
88
90
92
94
96
98
100

Sensible heat
(BTU/lb)
36.04
38.04
40.04
42.03
44.03
46.02
48.02
50.01
52.01
54.00
56.00
57.99
59.99
61.98
63.98
65.97
67.97

91

Yarway Industrial steam trapping handbook
Appendix D - Useful tables
Properties of pipe - Schedule 40 pipe dimensions
Diameters, in

Size
in
⅛
¼
⅜
½
¾
1
1¼
1½
2
2½
3
3½
4
5
6
8
10
12
14
16
18
20
24

External
.405
.540
.675
.840
1.050
1.315
1.660
1.900
2.375
2.875
3.500
4.000
4.500
5.563
6.625
8.625
10.75012.75014.00016.00018.00020.00024.000Internal
.269
.364
.493
.622
.824
1.049
1.380
1.610
2.067
2.469
3.068
3.548
4.026
5.047
6.065
7.981
10.02011.93813.12515.00016.87418.81422.626

Metal
.072
.125
.167
.250
.333
.494
.669
.799
1.075
1.704
2.228
2.680
3.174
4.300
5.561
8.399
11.90015.74018.64024.35030.85036.15050.300Length of pipe per ft2 ofExt. surface
Int. surface
feet
feet
9.431
14.1997.073
10.493
5.658
7.747
4.547
6.141
3.637
4.635
2.904
3.641
2.301
2.767
2.010
2.372
1.608
1.847
1.328
1.547
1.091
1.245
.954
1.076
.848
.948
.686
.756
.576
.629
.442
.478
.355
.381
.299
.318
.272
.280
.238
.254
.212
.226
.191
.203
.159
.169

Metal
.093
.157
.217
.320
.433
.639
.881
1.068
1.477
2.254
3.016
3.678
4.407
6.112
8.300
12.76018.92026.00031.22040.13050.61061.43087.180Length of pipe per ft2 ofExt. surface
Int. surface
feet
feet
9.431
17.7507.073
12.650
5.658
9.030
4.547
7.000
3.637
5.150
2.904
3.995
2.301
2.990
2.010
2.542
1.608
1.970
1.328
1.645
1.091
1.317
.954
1.135
.848
.995
.686
.792
.576
.673
.442
.501
.355
.400
.299
.336
.272
.306
.238
.263
.212
.237
.191
.208
.159
.177

Transverse areas, inNom.
thick., in
.068
.088
.091
.109
.113
.133
.140
.145
.154
.203
.216
.226
.237
.258
.280
.322
.365
.406
.437
.500
.563
.593
.687

External
.129
.229
.358
.554
.866
1.358
2.164
2.835
4.430
6.492
9.621
12.56015.90024.30034.47058.42090.760127.640
153.940201.050254.850
314.150452.400

Internal
.057
.104
.191
.304
.533
.864
1.495
2.036
3.355
4.788
7.393
9.886
12.73020.00028.89050.02078.850111.900
135.300
176.700
224.000
278.000
402.100

Properties of pipe - Schedule 80 pipe dimensions
Diameters, in

Size
in
⅛
¼
⅜
½
¾
1
1¼
1½
2
2½
3
3½
4
5
6
8
10
12
14
16
18
20
24

External
.405
.540
.675
.840
1.050
1.315
1.660
1.900
2.375
2.875
3.500
4.000
4.500
5.563
6.625
8.625
10.75012.75014.00016.00018.00020.00024.000Internal
.215
.302
.423
.546
.742
.957
1.278
1.500
1.939
2.323
2.900
3.364
3.826
4.813
5.761
7.625
9.564
11.37612.50014.31416.12617.93821.564

Transverse areas, inNom.
thick., in
.095
.119
.126
.147
.154
.179
.191
.200
.218
.276
.300
.318
.337
.375
.432
.500
.593
.687
.750
.843
.937
1.031
1.218

External
.129
.229
.358
.554
.866
1.358
2.164
2.835
4.430
6.492
9.621
12.56015.90024.30034.47058.42090.760127.640
153.940201.050254.850
314.150452.400

Internal
.036
.072
.141
.234
.433
.719
1.283
1.767
2.953
4.238
6.605
8.888
11.49718.19426.06745.66371.840101.640
122.720160.920204.240
252.720365.220ft3 per ft ofpipe.00039.00072.00133.00211.00370.00600.01039.01414.02330.03325.05134.06866.08840.13890.20060.35520.54760.77630.935401.22300
1.55500
1.92600
2.79300

ft3 per ft ofpipe.00025.00050.00098.00163.00300.00500.00891.01227.02051.02943.04587.06172.07980.12630.18100.31710.49890.70580.852201.11700
1.41600
1.75500
2.53600

Wt per ft
lb
.244
.424
.567
.850
1.130
1.678
2.272
2.717
3.652
5.793
7.575
9.109
10.79014.61018.97028.55040.48053.60063.00078.000105.000
123.000
171.000

No. thrds per
in of screw
27
18
18
14
14
11½
11½
11½
11½
8
8
8
8
8
8
8
8
-

Wt per ft
lb
.314
.535
.738
1.000
1.470
2.170
3.000
3.650
5.020
7.660
10.30012.50014.90020.80028.60043.40064.40088.600107.000
137.000
171.000
209.000
297.000

No. thrds per
in of screw
27
18
18
14
14
11½
11½
11½
11½
8
8
8
8
8
8
8
8
-

92

Yarway Industrial steam trapping handbook
Appendix D - Useful tables
Overall heat transfer coefficients
The “U” value, or overall heat transfer coefficient, represents the total BTU transmitted in one
hour for each square foot of heat transfer surface at a temperature difference of one degree
Fahrenheit (BTU/hr ft2 °F). “U” values are the arithmetical result of experiments, research, tests,
practice and operations in controlled installations. Most “U” values are given for bare metal heattransfer surface in intimate contact with the product. In general, the “U” value is relatively highwhen a) the temperature of operation is high, b) there is mechanical circulation, c) surfaces aresmooth and clean, and d) the viscosity of the fluid is low. In the table below, two “U” values, thelow and high values normally experienced in general practice, are given for several of the morecommon heat transfer media/product applications.

Overall heat transfer coefficients
Service
Alphabetical
listing
Air
Anodize solution
Asphalt
Brine, salt
Fatty acid (tallow)
MolassesOil, heavy
Oil, medium
Paraffin wax
PhosphatizingFreeconvection
1-2
100-200
18-25
100-175
50-100
20-40
15-40
30-50
25-45
100-200

Saturated steam
Forcedconvection
6-8
150-300
40-60
150-275
125-25060-90
50-90
50-10040-60
150-300

Clamp
on*
2
25-30
7-10
25-30
12-20
10-15
7-10
9-12
10-15
25-30

Free
convection
2-3
50-90
5-9
60-100
15-30
6-10
6-10
6-10
6-10
50-90

Water
Forcedconvection
5-8
100-18010-15
100-150
30-55
10-15
12-25
12-25
30-50
100-180

Clamp
on*
2
18-20
3-5
18-20
6-10
5-8
3-5
5-7
5-8
18-20

solution
Plating solution
Slurry, light
Syrup
Sugar solution
Sulphur, molten
Tar
Water

100-22575-150
20-40
40-80
25-40
15-25
125-225

160-300
140-28070-90
100-200
40-50
40-60
150-300

25-30
20-25
10-15
12-20
10-15
7-10
25-30

50-100
30-90
6-10
15-30
6-10
5-9
70-100100-200
60-160
10-20
30-60
10-15
10-15
100-200

18-20
16-18
5-8
6-10
5-8
3-5
18-20

* All values except as noted by "*" are for immersion or integral installations.
Selection of the “U” value should be on the conservative side and depends on the accuracy of data describing
the actual operating conditions and heat transfer characteristics of the product. “U” value estimates should be
influenced by the following considerations: is the fluid thick or viscous? Will it precipitate or cling to the heattransfer surface? What degree of fouling can be expected during the operating cycle?

Physical properties of gases
Material
Air
Ammonia
Chlorine
Nitrogen
OxygenSulphur dioxide
Water, vapor (STM)

Density
0.075
0.048
0.020
0.073
0.083
0.183
-

Spec. heat at 60°F (BTU/lb °F)
0.24
0.52
0.12
0.25
0.23
0.16
0.45

93

Yarway Industrial steam trapping handbook
Appendix D - Useful tables
Physical properties of liquids and solids
State
L
L
S
S
L
L
L
L
L
S
L
L
L
L
L
L
L
L
L
S
L
S
S
L

Spec. grav.
at 60-70°F
1.05
0.81
2.64
1.30
0.84
1.24
1.19
1.15
0.95
1.20
1.00
1.11
0.81
0.89
0.96
0.86
0.60
1.09
1.26
2.25
1.05
0.90
0.80

Spec. heatat 60°F (BTU/Ib °F)
0.48
0.60
0.23
0.22-0.40
0.41
0.69
0.79
0.39
0.47
0.35 at 105°F
0.63
0.58
0.47
0.43
0.40
0.65
0.53
0.89
0.58
0.20
0.75
0.50
0.70
0.47

Lard
Lead
Leather
Linseed oil
Magnesia 10%
Meat, fresh, avg.
Machine oil
Nickel, rolled
Nitric acid – 95%
Nitric acid – 20%
Olive oil
Paper
Paraffin, solid
Paraffin, melted
Petroleum
Phosphoric acid – 20%
Rubber goods
Sodium hydroxide – 50% caustic soda

S
S
S
L
S
S
L
S
L
L
L
S
S
L
L
L
S
L

0.92
11.36
0.86-1.02
0.93
0.21
0.93
8.66
1.50
1.12
0.93
0.93
0.86-0.91
0.90
0.87
1.11
1.50
1.53

0.64
0.031
0.36
0.44
0.27
0.70
0.40
0.50
0.81
0.47
0.45
0.62
0.69
0.51
0.85
1.0-2.0
0.78

StarchSteel, mild at 70°F
Steel, mild at 160°F
Steel, stainless (300 Series)
Sucrose – 60% sugar syrup
Sucrose – 40% sugar syrup
Sugar, cane and beet
Sulphuric acid – 98%
Sulphuric acid – 60%
Sulphuric acid – 10%
Trichloroethylene
Turpentine, spirits ofVegetables, fresh, avg.
Water, pure, 32°F
Water, sea
Wines, table, avg.
Wool
Zinc

S
S
S
S
L
L
S
L
L
L
L
L
S
L
L
L
S
S

1.53
7.90
8.00
8.00
1.29
1.18
1.66
1.84
1.50
1.14
1.62
0.86
1.00
1.03
1.03
1.32
7.04

0.11
0.16
0.12
0.74
0.66
0.30
0.35
0.52
0.84
0.22
0.42
0.92
1.00
0.94
0.90
0.33
0.10

Material
Acetic acid – 100%
Alcohol – ethyl 95%
Aluminum
Asphalt
BenzeneBrine (CaCl – 25%)
Brine (NaCl – 25%)
Chocolate mixture
Cotton seed oil
Coal tars
Dowtherm a
Ethylene glycol
Fuel oil #1 (Kerosene)
Fuel oil #3 (PS 200)
Fuel oil #6 (Bunker C)
Fatty acid
Gasoline
Glue (2 Pts H20,1 Pt dry glue)
Glycerin
Glass, pyrex
Hydrochloric acid – 10%
Ice
Ice cream
Kerosene

94

Yarway Industrial steam trapping handbook
Appendix D - Useful tablesSpecific heats of foodstuffs

Product
ApplesApricots, fresh
Artichokes
Asparagus
Avocados
BananasBarracudaBass
Beef, carcass
Beef, flank
Beef. loin
Beef, rib
Beef, round
Beef, rumpBeef, corned
Beer
Beets
Blackberries
Blueberries
BrainsBroccoli
Brussels sprouts
ButterButterfish
Cabbage
Candy
Carp
Carrots
Cauliflower
CeleryChard
CheeseCherries. sour
Chicken, squab
Chicken, broilers
Chicken, fryers
Chicken. hensSpecific heat BTU
per lb per °F
Above
Below
freezing
freezing
.87
.42
.88
.43
.87
.42
.94
.45
.72
.37
.80
.40
.80
.40
.82
.41
.68
.48
.56
.32
.66
.35
.67
.36
.74
.38
.62
.34
.63
.34
.89
.90
.43
.87
.42
.87
.42
.84
.41
.92
.44
.88
.43
.65
.34
.77
.39
.94
.45
.93
.82
.41
.91
.44
.93
.44
.94
.45
.93
.44
.65
.88
.43
.80
.40
.77
.39
.74
.38
.65
.35

Product
Chicken, capons
Clams. meat only
Coconut, meat and milk
Coconut. milk only
CodfishCod Roe
Cowpeas, fresh
Cowpeas, dry
Crabs
Crab apples
Cranberries
Cream
CucumberCurrants
Dandelion greens
Dates
Eels
Eggs
Eggplant
EndiveFigs, freshFigs. driedFigs, candied
Flounders
Flour
Frog legs
GarlicGizzards
Goose
Gooseberry
Granadilla
Grapefruit
GrapesGrape juice
GuavasGuinea hen
Haddock

Specific heat BTU
per lb per °F
Above
Below
freezing
freezing
.88
.44
.84
.41
.68
.36
.95
.45
.86
.42
.76
.39
.73
.39
.28
.22
.84
.41
.85
.41
.90
.43
.90
.38
.97
.45
.97
.45
.88
.43
.20
.007
.77
.39
.76
.40
.94
.45
.95
.45
.82
.41
.39
.26
.37
.26
.86
.42
.38
.28
.88
.44
.79
.40
.78
.39
.61
.34
.86
.42
.84
.41
.91
.44
.86
.42
.82
.41
.86
.42
.75
.38
.85
.42

Product
Halibut
Herring, smoked
Horseradish, fresh
Horseradish, preparedIce cream
Kale
Kidneys
Kidney beans, dried
Kohlrabi
Kumquats
Lamb, carcass
Lamb, legLamb, rib cut
Lamb, shoulder
Lard
Leeks
LemonsLemon juice
Lettuce
Lima beans
Limes
Lime juice
Lobsters
Loganberries
Loganberry juice
Milk, cow
Mushrooms, fresh
Mushrooms, dried
Muskmelons
Nectarines
Nuts
Olives, green
OnionsOnions, welsh
Oranges, fresh
Orange juice
Oysters

Specific heat BTU
per lb per °F
Above
Below
freezing
freezing
.80
.40
.71
.37
.79
.40
.88
.43
.74
.45
.89
.43
.81
.40
.28
.23
.92
.44
.85
.41
.73
.38
.71
.37
.61
.34
.67
.35
.54
.31
.91
.44
.91
.44
.92
.44
.96
.45
.73
.38
.89
.43
.93
.44
.82
.41
.86
.42
.91
.44
.94
.47
.93
.44
.30
.23
.94
.45
.86
.42
.28
.24
.80
.40
.90
.43
.91
.44
.90
.43
.89
.43
.84
.41

95

Yarway Industrial steam trapping handbook
Appendix D - Useful tablesSpecific heats of foodstuffs (continued)

Product
Peaches, Georgia
Peaches, N. Carolina
Peaches, Maryland
Peaches, New Jersey
Peach juice, fresh
Pears, Bartlett
Pears, Beurre Bosc
Pears, dried
Peas, young
Peas, medium
Peas, oldPeas, split
Peppers, ripe
PerchPersimmons
Pheasant
Pickerel
Pickles, sweet
Pickles, sour and dill
Pickles, sweet mixed
Pickles, sour mixed
Pig’s feet, pickled
Pike
Pineapple, fresh
Pineapple, sliced
Pineapple juice
Plums
Pomegranate
PompanoPorgy
Pork, baconSpecific heat BTU
per lb per °F
Above
Below
freezing
freezing
.87
.42
.89
.43
.90
.43
.91
.44
.89
.43
.89
.43
.85
.41
.39
.26
.85
.41
.81
.40
.88
.43
.28
.23
.91
.44
.82
.41
.72
.37
.75
.38
.84
.41
.82
.41
.96
.45
.78
.29
.95
.45
.50
.31
.84
.41
.88
.43
.82
.41
.90
.43
.89
.43
.85
.41
.77
.39
.81
.40
.36
.25

Product
Pork, hamPork, loin
Pork shoulder
Pork, spareribs
Pork, smoked ham
Pork, salted
PotatoesPrickly pears
PrunesPumpkin
Quinces
RabbitRadishes
Raisins
Raspberries, black
Raspberries, red
Raspberry juice, black
Reindeer
Rhubarb
Rutabagas
SalmonSapoteSauerkraut
Sausage, beef and pork
Sausage, bockwurst
Sausage, bologna
Sausage, Frankfurt
Sausage, salami
Sardines
ShrimpSpanish mackerel

Specific heat BTU
per lb per °F
Above
Below
freezing
freezing
.62
.34
.66
.35
.59
.33
.62
.34
.65
.35
.31
.24
.82
.41
.91
.43
.81
.40
.92
.44
.88
.43
.76
.39
.95
.45
.39
.26
.85
.41
.89
.43
.91
.44
.73
.37
.96
.45
.91
.44
.71
.37
.73
.37
.93
.44
.56
.32
.71
.37
.71
.37
.69
.36
.45
.28
.77
.39
.83
.41
.73
.39

Product
Strawberries
String beans
Sturgeon, raw
Sugar apple, fresh
Sweet potatoes
Swordfish
Terrapin
Tomatoes
Tomato juice
Tongue, beef
Tongue, calf
Tongue, lambTongue, pork
Tripe, beef
Tripe, pickled
Trout
Tuna
TurkeyTurnips
TurtleVeal, flank
Veal, loin
Veal, rib
Veal, shank
Veal, quarter
VenisonWatercress
Watermelons
Whitefish
Wines
Yams

Specific heat BTU
per lb per °F
Above
Below
freezing
freezing
.95
.45
.91
.44
.83
.41
.79
.39
.75
.38
.80
.40
.80
.40
.95
.45
.95
.45
.74
.38
.79
.40
.76
.38
.74
.39
.83
.41
.89
.43
.82
.41
.76
.39
.67
.35
.93
.44
.84
.41
.65
.35
.75
.38
.73
.37
.77
.39
.74
.38
.78
.39
.95
.45
.94
.45
.76
.39
.90
.78
.39

96

Yarway Industrial steam trapping handbook
Appendix D - Useful tables
Piping symbols
Item

SymbolItem

Bushing

Union

Cap

Valve – Check, angle

Cross

Valve – Check, straight

Elbow – 45°

Valve – Cock

Elbow – 90°

Valve – Diaphragm

Gauge – Pressure

P

Valve – Float

Gauge – Temperature

T

Valve – Gate, angle

SymbolOrifice

Valve – Isolation, gate or ball

Plug – Pipe

Valve – Globe, angle

Pump – Centrifugal

Valve – Globe, straight

Reducer – Concentric

Air Vent

A

Reducer – Eccentric

Vacuum Breaker

VB

Steam Trap

Valve – Quick opening

Strainer

Valve – Safety

Tee

Valve – Solenoid97

Yarway Industrial steam trapping handbook

98Yarway Industrial steam trapping handbook99

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