Xylem Bell & Gossett Hoffman Speciality Series User manual

Hoffman Specialty®
Steam Traps
HS-203C
ENGINEERING DATA MANUAL
• Application
• Selection
• Installation
• Piping Diagrams

Contents
3
Introduction
Steam Trap Functional Requirements 4
Operation, Advantages, Disadvantages
and Primary Applications 5
Chapter 1
Selection Guide Chart 10
4-Step Method for Sizing 11
Helpful Hints, Formulas and Conversion Factors 12
Properties of Saturated Steam 13
Steam Flow in Pipes 15
Condensation in Pipes 15
Chapter 2
Flash Steam Explanation and Calculation 16
Operating Pressure Limits 17
Installation and Calculating Differential Pressure 18
Drip Traps for Distribution Pipes 20
Chapter 3
Selecting Traps for Heat Exchangers 24
Lock-out Traps for Start-up Loads 27
Draining Condensate to Overhead Returns 28
Draining Submerged Coils 29
Jacketed Kettles 30
Cylinder Dryers 31
Unit Heaters 31
Steam Radiators 32
Typical Piping for Steam Heating 33
Trapping Steam Tracer Lines 39
Chapter 4
4-Step Method for Sizing Steam Lines 40
4-Step Method for Sizing Return Lines 42
Chapter 5
Testing Steam Traps 43
Chapter 6
Definition of Heating Terms 46

Steam Trap
Functional
Requirements
Selecting the
proper type of
steam trap is an
important element
in steam systems.
There are many types of steam traps each
having its unique characteristics and system
benefits. Hoffman Specialty offers thermostat-
ic, thermodisc, float and thermostatic, and
bucket traps which are the most commonly
used types. Deciding which type of trap to use
is sometimes confusing and, in many cases,
more than one type can be used. The follow-
ing is intended to point out system conditions
that may be encountered and the characteris-
tics of each type of trap.
Within steam systems, important considera-
tions must be taken into account. These con-
siderations include venting of air during
start-up; variations of system pressures and
condensing loads; operating pressure and
system load; continuous or intermittent opera-
tion of system; usage of dry or wet return
lines; and overall probability of water hammer.
Air Venting
At start-up all steam piping, coils, drums, tracer
lines, or steam spaces contain air. This air
must be vented before steam can enter.
Usually the steam trap must be capable of
venting the air during this start-up period. A
steam heating system will cycle many times
during a day. Fast venting of air is necessary
to obtain fast distribution of steam for good
heat balance. A steam line used in process
may only be shut down once a year for repair
and venting of air may not be a major con-
cern.
Modulating Loads
When a modulating steam regulator is used,
such as on a heat exchanger, to maintain a
constant temperature over a wide range of
flow rates and varying inlet temperatures, the
condensate load and differential pressure
across the trap will change. When the conden-
sate load varies, the steam trap must be
capable of handling a wide range of condi-
tions at constantly changing differential pres-
sures across the trap.
Differential Pressure Across Trap
When a trap drains into a dry gravity return
line, the pressure at the trap discharge is nor-
mally at O psig. When a trap drains into a wet
return line or if the trap must lift condensate
to an overhead return line, there will normally
be a positive pressure at the trap discharge.
To assure condensate drainage, there must
be a positive differential pressure across the
trap under all load conditions.
Water Hammer
When a trap drains high temperature conden-
sate into a wet return, flashing may occur.
When the high temperature condensate at
saturation temperature discharges into a
lower pressure area, this flashing causes
steam pockets to occur in the piping, and
when the latent heat in the steam pocket is
released, the pocket implodes causing water
hammer. Floats and bellows can be damaged
by water hammer conditions.
When traps drain into wet return lines, a
check valve should be installed after the trap
to prevent backflow. The check valve also
reduces shock forces transmitted to the trap
due to water hammer. Where possible, wet
returns should be avoided.
Application
The design of the equipment being drained is
an important element in the selection of the
trap. Some equipment will permit the conden-
sate to back up. When this occurs the steam
and condensate will mix and create water
hammer ahead of the trap. A shell and tube
heat exchanger has tube supports in the
shell. If condensate backs up in the heat
exchanger shell, steam flowing around the
tube supports mixes into the condensate and
causes steam pockets to occur in the conden-
sate. When these steam pockets give up their
latent heat, they implode and water hammer
occurs, the water hammer often damages the
heat exchanger tube bundle. The trap selec-
tion for these types of conditions must com-
pletely drain condensate at saturation
temperature under all load conditions.
Steam mains should be trapped to remove all
condensate at saturation temperature. When
condensate backs up in a steam main, steam
flow through the condensate can cause water
hammer. This is most likely to occur at expan-
sion loops and near elbows in the steam
main.
Applications such as tracer lines or vertical
unit heaters do not mix steam and conden-
sate. In a tracer line, as the steam condens-
es, it flows to the end of the tracer line. Back
up of condensate ahead of the trap does not
cause water hammer. Steam does not pass
through condensate.
Vertical unit heaters normally have a steam
manifold across the top. As the steam con-
denses in the vertical tubes, it drains into a
bottom condensate manifold. Because steam
does not pass through the condensate, water
hammer should not occur.
4
Introduction

FLOAT & THERMOSTATIC TRAP
The condensate port is normally closed during
no load. As condensate enters the float cham-
ber, the seat opens to provide drainage equal
to the condensing rate.
Primary Applications
Heating main drip traps.
Shell & tube heat exchangers.
Tank heaters with modulating temperature
regulators.
Unit heaters requiring fast venting.
Steam humidifiers.
Air blast heating coils.
Air pre-heat coils.
Modulating loads.
Fast heating start-up applications.
TRAP OPERATION
A review of the trap operating principle will
show how various types of traps meet the dif-
ferent system characteristics.
Float & Thermostatic Traps
Advantages
Completely drains condensate at satura-
tion temperature.
Modulates to handle light or heavy loads,
continuous discharge equal to condensing
load.
Large ports handle high capacities.
Separate thermostatic vent allows fast
venting of air during start-up.
Modulating ports provide long life.
Cast iron bodies.
Disadvantages
Float or bellows may be damaged by water
hammer.
Primary failure mode is closed.
Does not withstand freezing temperatures.
Pressure limit of 175 psig.
FLOAT & THERMOSTATIC TRAP
During start-up the thermostatic vent is open
to allow free passage of air.
The thermostatic vent will close at near satu-
ration temperature. The balanced design will
allow venting of noncondensables that collect
in the float chamber, when operating at
design pressure.
Operation,
Advantages,
Disadvantages,
and Primary
Applications
5

Bucket Traps
Advantages
Completely drains condensate at saturation
temperature.
Open bucket will tolerate moderate
water hammer.
Available in pressures up to 250 psig.
Normal failure mode is open.
Cast iron bodies.
Disadvantages
Marginal air handling during start-up.
Cycles fully open or closed.
May lose prime during light loads and blow
live steam.
Requires manual priming to provide
water seal.
Does not withstand freezing temperatures.
Primary Applications
Process main drip traps.
Where condensate is lifted or drains into wet
return line.
Drum type roller dryers.
Steam separators.
Siphon type or tilting kettles.
6
INLET OUTLET
COVER
BODY
V
BUCKET
A
STEAM BUBBLES
THROUGH WATER
INLET OUTLET
COVER
BODY
V
BUCKET
A
STEAM BUBBLES
THROUGH WATER
INLET OUTLET
COVER
BODY
V
BUCKET
A
BUCKET TRAP
The trap body must be manually primed at ini-
tial start-up. Under operation the body will
remain full of condensate.
During start-up, air is vented through the
bleed hole in the top of the bucket into the
return line.
Condensate entering the trap will flow around
the bucket and drain through the open seat.
BUCKET TRAP
As steam flows into the trap it collects in the
top of the bucket. The buoyancy of the steam
raises the bucket and closes the seat.
BUCKET TRAP WITH OPTIONAL
THERMAL VENT.
An optional thermal vent installed in the buck-
et allows faster air venting during start-up.

Applications
Radiators, convectors, unit heaters.
Cooking kettles.
Sterilizers.
Heating coils.
Tracer lines.
Evaporators.
NOTE: A solid fill expansion element (see
Hoffman Specialty 17K) thermostatic trap
should be used where water hammer (cavita-
tion) may occur.
Thermostatic Bellows Type Trap
Advantages
Sub-cools condensate usually 10° to 30°F.
Normally open at start-up to provide fast
air venting.
Follows steam saturation curve to operate
over wide range of conditions.
Brass bodies.
Self draining.
Energy efficient.
Compact size and inexpensive.
Fast response to changing conditions.
Fail open models.
Disadvantages
Water hammer can damage bellows.
Superheat can damage bellows if it
exceeds trap temperature rating.
Pressure limit of 125 psig.
Cooling leg required in some applications.
THERMOSTATIC TRAP
Thermostatic traps are normally open. This
allows fast venting of air during start-up.
THERMOSTATIC TRAP
Cold condensate during start-up drains
through the trap. As temperatures reach 10°
to 30° F of saturation, the trap closes.
During operation, thermostatic traps find an
equilibrium point to drain condensate approxi-
mately 10° to 30°F below saturation at a con-
tinuous flow.
7
INLET
OUTLET
INTERNAL
FLEXIBLE DIAPHRAGM
INLET
OUTLET
INTERNAL
FLEXIBLE DIAPHRAGM

Disc Traps
Advantages
Completely drains condensate at satura-
tion temperature.
May be installed vertically, to drain trap
body when steam is off, to prevent freezing.
Compact size.
Easily serviced in line, replaceable seat
and disc (some models).
All stainless steel.
Will tolerate water hammer and superheat.
Disadvantages
Noise.
Sensitive to dirt, prevents tight closing
of disc.
Available in sizes up to 1” only.
Applications
Steam tracer lines where maximum tem-
perature is required.
Outdoor applications including drips on
steam mains.
Drying tables.
Tire mold press and vulcanizing equipment
Dry kilns.
Pressing machines.
Rugged applications (superheat & water
hammer).
Description
Thermodisc steam traps provide dependable
performance for applications with light to
moderate condensate loads. Thermodisc
traps are excellent for high pressure drip
and steam tracing applications.
Because the disc is the only moving part,
the traps are rugged and resistant to dam-
age. However, if the seat and disc require
servicing they may be easily replaced with-
out removing the trap body from the piping.
8

Orifice Traps
Advantages
No moving parts to wear.
Disadvantages
Does not close against steam.
Small hole easily plugs due to dirt.
Backs up condensate on heavy loads and
during start-up.
Does not respond to modulating loads.
Does not vent air when handling conden-
sate—causes slow system start-up and
may cause water hammer.
Not easily recognized as trap during
energy survey.
Built-in small screen plugs easily.
Discharges condensate at saturation
temperature with some live steam, often
causes excessive condensate tempera-
tures and cavitation at condensate pumps.
Waste energy.
Sizing critical.
Applications
Should be limited to constant load
continuous operation.
Start-Up
The disc is pushed off the seat by the inlet
pressure and is held open by the impact force
of the condensate hitting the disc.
Operating
As the condensate nears saturation tempera-
ture, greater amounts of flash steam will
appear. Some of the flash steam escapes to
the area above the disc, causing the pressure
above the disc to increase, pushing the disc
closer to the seat.
Closing
When all the condensate is discharged, flash
steam enters the seat-disc chamber at high
velocity. This high velocity causes a sudden
pressure drop at the lower side of the disc
and it snaps closed against the seat.
Closed
At the instant the disc snaps closed on the
seat, the pressure above the disc is approxi-
mately equal to the upstream line pressure.
The disc is held closed because the pressur-
ized area above the disc is much larger than
the inlet area. The pressure above the disc
decreases either by steam condensation or by
non-condensables being removed via the
micro-bleed on the disc. When the pressure is
low enough, the disc is pushed off the seat
and the process is repeated.
9
Disc Trap Operation

Selection
Guide Chart The proper type of steam trap selected is an
important consideration in steam systems.
There are many types of steam traps. Each
has unique characteristics and system bene-
fits. Hoffman Specialty offers thermostatic,
float and thermostatic, bucket
and disc traps. This line chart points out sys-
tem conditions that may be encountered and
suggests a trap that may best handle the
requirement. Several types of traps may be
used for a specific application. The line chart
should be used only as a guide.
10
Chapter 1
Condensate must be completely
removed at saturation condition
to prevent water hammer
Type of Steam Trap Required
Based on System Conditions
Modulating load,
wide range of
condensate load
Water hammer
due to
wet returns or lifts
Float and
thermostatic Bucket trap
with thermal
vent Bucket
trap Disc trap
Constant
load Outdoor
location
Super heat or
water hammer
Fast air
venting
required
Air vent
rate not
important
Fast air
venting
required
Condensate may be sub-cooled
ahead of trap to improve
operating efficiency of system
Varying pressure and load where fast
response is required
Pressure
up to 125 psig
Thermostatic bellows type trap
Pressure
over 175 psig

Step 1:
Collect All Required Information.
A. Determine maximum condensate load in
Lbs./Hr. (Pounds per Hour). See “Helpful
Hints—Approximating Condensate Loads”
on page 12.
B. Inlet pressure at steam trap. It could be
different than supply pressure at boiler.
Heat exchanger applications with modulat-
ing control valves are good examples.
C. Back-pressure at steam trap. Pressure
against outlet can be due to static pres-
sure in return line or due to lifting to
overhead return.
D. Determine Pressure Differential.
Inlet pressure (B) - Back-pressure (C)
= Differential Pressure.
Step 2:
Select Proper Type ot Trap.
A. Other Things to Consider.
1. Condensate Flow—Fluctuate?
1. Continuous?
2. Large Amount of Air?
3. Pressure—Constant? Fluctuate?
B. Application.
1. Main.
2. Drip Leg.
3. Process Heat Exchanger.
4. Other.
C. Critical Process.
1. Fail Cold.
2. Fail Hot.
Step 3:
Apply Safety Factor.
A. SFA Recommended.
1. Float & Thermostatic Trap 1.5 to 2.5.
2. Bucket Trap 2 to 4.
3. Thermostatic 2 to 4.
4. Disc Traps 1 to 1.2.
See specific applications.
B. The SFA Will Depend On Degree of
Accuracy at Step 1.
1. Estimated Flow.
2. Estimated Pressure—Inlet.
3. Estimated Pressure—Back.
Step 4:
Select Correct Trap Size.
A. Use manufacturer’s capacity table to size
trap. Capacity tables should be based on
hot condensate (some specified tempera-
ture below saturation) rather than cold
water rating. Hoffman Specialty published
actual test data, unless stated, is 10°F.
below saturation.
B. The trap seat rating must always be
higher than the maximum inlet pressure
specified.
C. When inlet to equipment is controlled by a
modulating control valve, the trap size
should be selected with a pressure rating
greater than the maximum inlet pressure
at the trap. The capacity should be
checked at the minimum differential pres-
sure to assure complete condensate
removal under all possible conditions.
4 Step Method
for Sizing
11

3. Steam heats a solid or slurry indirectly
through a metallic wall.
—Clothing press, cylinder driers, platen
—press.
Lbs./hr. condensate =
970 x (W1-W2) + W1x (T2-T1)
L x T
When:
W1= Initial weight of product
W2= Final weight of product
T1= Initial temp.
T2= Final temp.
L = Latent heat in Btu/lb.
T = Time required for drying (hours).
Note: 970 is the latent heat of vaporization
at atmospheric pressure. It is included
because the drying process requires that
all moisture in the product be evaporated.
4. Steam heats a solid through direct
contact.
—Sterilizer, autoclave
Lbs./hr. condensate =
W = Weight of material being
heated in Ibs.
Sh= Specific heat of material
being heated.
T1= Initial temp.
T2= Final temp.
L = Latent heat Btu/lb.
T = Time to reach final temp. (hours)
Conversion Factors
One Boiler Horsepower = 140 sq. ft. EDR or
33,475 Btu/hr. or 34.5 Ibs./hr. steam at 212° F.
1,000 sq. ft. EDR yields .5 gpm condensate.
To convert sq. ft. EDR to Ibs. of condensate—
divide sq. ft. by 4.
.25 Ibs./hr. condensate = 1 sq. ft. EDR.
One sq. ft. EDR (Steam) = 240 Btu/hr. with
215°F. steam filling radiator and 70°F. air
surrounding radiator.
To convert Btu/hr. to Ibs./hr.—
divide Btu/hr. by 960.
One psi = 2.307 feet water column (cold).
One psi = 2.41 feet water column (hot).
One psi = 2.036 inches mercury.
One inch mercury = 13.6 inches water column.
Size condensate receivers for 1 min. net
storage capacity based on return rate.
Size condensate pumps at 2 to 3 times
condensate return rate.
W x Shx (T2-T1)
L x T
Helpful Hints,
Formulas and
Conversion
Factors
Helpful Hints
Approximating Condensate Loads
Heating Water with Steam
lbs./hr. Condensate = GPM
x Temperature Rise °F.
Heating Fuel Oil with Steam
lbs./hr. Condensate = GPM
x Temperature Rise °F.
Heating Air with Steam Coils
lbs./hr. Condensate = CFM
x Temperature Rise °F.
SHEMA Ratings
Thermostatic traps and F & T traps for low
pressures may be rated in accordance with
the Steam Heating Equipment Manufacturers
Association (SHEMA). SHEMA ratings have a
built-in safety factor.
Formulas
1. Steam heats a liquid indirectly through
a metallic wall.
—Cooking coils, storage tanks, jacketed
—kettles, stills.
Lbs./hr. condensate =
Qlx 500 x Sgx Shx (T2-T1)
L
When:
Ql= Quantity of liquid being
heated in gal/min
Sg= Specific gravity
Sh= Specific heat
L = Latent heat in Btu/lb
500 = Constant for converting
gallons per minute to
pounds per hour.
T2= Final temperature
T1= Initial temperature
2. Steam heats air or a gas indirectly
through a metallic wall.
—Plain or finned heating coils,
—unit space heaters.
Lbs./hr. condensate =
Qgx D x Shx (T2-T1) x 60
L
When:
Qg= Quantity of air or gas in ft3/min.
D = Density in Ib/ft3
Sh= Specific heat of gas being heated.
T1= Initial temp.
T2= Final temp.
L = Latent heat in Btu/lb
60 = Minutes in hour
12
2
4
900

The Properties of Saturated Steam table
provides the relationship of temperature and
pressure. The table also provides Btu heat
values of steam and condensate at various
pressures and shows the specific volume of
steam at various pressures.
Saturated Steam:
Pure steam at the temperature corresponding
to the boiling point of water.
Pressure psig:
Gauge pressure expressed as Ibs./sq. in. The
pressure above that of atmosphere. It is pres-
sure indicated on an ordinary pressure gauge.
Sensible Heat:
Heat which only increases the temperature of
objects as opposed to latent heat. In the sat-
uration tables it is the Btu remaining in the
condensate at saturation temperature.
Latent Heat:
The amount of heat expressed in Btu required
to change 1 Ib. of water at saturation temper-
ature into 1 Ib. of steam. This same amount
of heat must be given off to condense 1 Ib. of
steam back into 1 Ib. of water. The heat value
is different for every pressure temperature
combination shown.
Total Heat:
The sum of the sensible heat in the conden-
sate and the latent heat. It is the total heat
above water at 32° F.
Specific Volume Cu. Ft. Per Lb.:
The volume of 1 Ib. of steam at the corre-
sponding pressure.
See Properties of Saturated Steam table on
the following page.
Properties of
Saturated
Steam
13

14
Properties of Saturated Steam
Specfic Heat Content Latent
Vacuum Saturated Volume Btu per Ib. Heat of
Inches of Temp Cu. ft. Saturated Saturated Vaporization
Mercury °F. per Ib. Liquid Vapor Btu per Ib.
29 79 657.0 47 1094 1047
27 115 231.9 83 1110 1027
25 134 143.0 102 1118 1017
20 161 74.8 129 1130 1001
15 179 51.2 147 1137 990
10 192 39.1 160 1142 982
5 203 31.8 171 1147 976
1 210 27.7 178 1150 971
BELOW ATMOSPHERIC PRESSURE ABOVE ATMOSPHERIC PRESSURE (Cont.)
ABOVE ATMOSPHERIC PRESSURE
Specfic Heat Content Latent
Pressure Saturated Volume Btu per Ib. Heat of
PSI Temp Cu. ft. Saturated Saturated Vaporization
(Gauge) ° F. per Ib. Liquid Vapor Btu per Ib.
0 212 26.8 180 1150 970
1 215 24.3 183 1151 967
2 218 23.0 186 1153 965
3 222 21.8 190 1154 963
4 224 20.7 193 1155 961
5 227 19.8 195 1156 959
6 230 18.9 198 1157 958
7 232 18.1 200 1158 956
8 235 17.4 203 1158 955
9 237 16.7 205 1159 953
10 239 16.1 208 1160 952
11 242 15.6 210 1161 950
12 244 15.0 212 1161 949
13 246 14.5 214 1162 947
14 248 14.0 216 1163 946
15 250 13.6 218 1164 945
16 252 13.2 220 1164 943
17 254 12.8 222 1165 942
18 255 12.5 224 1165 941
19 257 12.1 226 1166 940
20 259 11.1 227 1166 939
25 267 10.4 236 1169 933
30 274 9.4 243 1171 926
35 281 8.5 250 1173 923
40 287 7.74 256 1175 919
45 292 7.14 262 1177 914
50 298 6.62 267 1178 911
55 302 6.17 272 1179 907
60 307 5.79 277 1181 903
65 312 5.45 282 1182 900
70 316 5.14 286 1183 897
75 320 4.87 290 1184 893
80 324 4.64 294 1185 890
85 327 4.42 298 1186 888
90 331 4.24 301 1189 887
95 334 4.03 305 1190 884
100 338 3.88 308 1190 882
105 341 3.72 312 1189 877
110 343 3.62 314 1191 877
115 347 3.44 318 1191 872
120 350 3.34 321 1193 872
125 353 3.21 324 1193 867
130 355 3.12 327 1194 867
135 358 3.02 329 1194 864
140 361 2.92 332 1195 862
145 363 2.84 335 1196 860
Specfic Heat Content Latent
Pressure Saturated Volume Btu per Ib. Heat of
PSI Temp Cu. ft. Saturated Saturated Vaporization
(Gauge) ° F. per Ib. Liquid Vapor Btu per Ib.
150 366 2.75 337 1196 858
155 368 2.67 340 1196 854
160 370 2.60 342 1196 854
165 373 2.53 345 1197 852
170 375 2.47 347 1197 850
175 378 2.40 350 1198 848
180 380 2.34 352 1198 846
185 382 2.29 355 1199 844
190 384 2.23 357 1199 842
195 386 2.18 359 1199 840
200 388 2.14 361 1199 838
210 392 2.05 365 1200 835
220 396 1.96 369 1200 831
230 399 1.88 373 1201 828
240 403 1.81 377 1201 824
250 406 1.75 380 1201 821
260 410 1.68 384 1201 817
270 413 1.63 387 1202 814
280 416 1.57 391 1202 811
290 419 1.52 394 1202 807
300 421 1.47 397 1202 805
325 429 1.37 405 1202 797
350 436 1.27 412 1202 790
375 442 1.19 419 1202 782
400 448 1.09 426 1202 774
425 454 1.06 432 1202 770
450 459 .972 438 1202 761
475 465 .948 444 1202 757
500 469 .873 449 1201 748
525 475 .850 455 1201 746
550 480 .820 461 1200 740
575 485 .784 466 1200 734
600 490 .733 472 1199 727
625 493 .721 476 1198 723
650 498 .692 481 1197 718
675 502 .645 485 1197 712
700 505 .642 490 1195 703
750 513 .598 498 1195 697
800 520 .555 514 1194 680
850 527 .521 523 1193 670
900 534 .489 532 1192 661
950 540 .462 540 1191 651
1000 548 .435 547 1189 642
1050 553 .413 550 1187 637
1100 558 .390 564 1185 621
1150 563 .372 572 1183 612
1200 567 .353 579 1182 603
1300 579 .322 593 1176 583
1400 588 .295 606 1172 565
1500 597 .271 619 1167 548
1570 604 .2548 624 1162 538
1670 613 .2354 636 1155 519
1770 621 .2179 648 1149 501
1870 628 .2021 660 1142 482
1970 636 .1878 672 1135 463
2170 649 .1625 695 1119 424
2370 662 .1407 718 1101 383
2570 674 .1213 743 1080 337
2770 685 .1035 770 1055 285
2970 695 .0858 801 1020 219
3170 705 .0580 872 934 62

Steam Flow in Pipes
15
REASONABLE VELOCITIES for fluid flow through pipes
Pipe Size, Inches 1⁄23⁄411
1⁄411⁄222 1⁄233 1⁄244 1⁄25678910
Capacity Factor 2.0 3.5 5.5 10.0 13.5 22.5 31.5 48.5 65.0 84.0 105. 131.5 190. 255. 329. 430. 539.
COMPARATIVE CAPACITIES of different sizes of pipe
STEAM PRESSURE PSI (Gauge)
Pounds Condensed Per Hour, Per Lineal Foot of Pipe
12468102030405075100125150200
.11 .13 .14 .14 .15 .15 .16 .18 .20 .22 .26 .29 .32 .35 .40
.15 .15 .16 .16 .17 .18 .20 .23 .25 .27 .31 .35 .39 .42 .49
.21 .21 .22 .23 .23 .24 .28 .33 .36 .39 .45 .50 .55 .60 .69
.24 .25 .26 .27 .27 .29 .33 .38 .42 .46 .54 .61 .68 .74 .81
.30 .31 .32 .33 .34 .36 .41 .46 .51 .55 .65 .73 .81 .88 .97
.38 .39 .40 .41 .43 .44 .50 .56 .61 .66 .77 .86 .94 1.03 1.19
.46 .47 .48 .49 .51 .53 .61 .68 .76 .83 1.04 1.11 1.23 1.33 1.50
.55 .56 .59 .60 .62 .64 .74 .83 .91 1.00 1.24 1.32 1.46 1.59 1.81
.34 .35 .36 .37 .39 .41 .47 .53 .59 .65 .73 .81 .90 1.00 1.15
CONDENSATION RATES at 70°F. (for bare steel pipe with natural movement of air)
Pipe
Size
(Inches)
3⁄4
1
11⁄2
2
21⁄2
3
4
5
Per Sq. Ft.
Heat. Surface
Sq. Ft. of
Surface =
to 1 Lineal
Ft. of Pipe
.275
.345
.497
.622
.752
.917
1.179
1.459
EXAMPLE: To get size of pipe to serve a 1⁄2" and 3⁄4" pipe, add factors: 1⁄2" factor (2) + 3⁄4" factor (3.5) = 5.5 (1" factor).
Condensation in Pipes
Fluid Pressure PSI (Gauge) Service Velocities—FPM
SATURATED STEAM 0-15 Heating Mains 4000-6000
SATURATED STEAM 50-up Miscellaneous 6000-8000
SUPERHEATED STEAM 200-up Turbine and Boiler Leads 10000-15000
WATER 25-40 City Service 120-300
WATER 50-150 General Service 300-600
WATER 150 Boiler Feed 600
Pipe Size PRESSURE PSI (GAUGE)
(Inches) 5 10 15 30 50 75 100 125 200 250
1⁄230 40 45 60 90 120 150 180 270 330
3⁄455 70 80 110 160 220 280 340 510 620
1 90 110 125 180 270 390 460 560 840 1020
11⁄4160 200 225 325 480 650 820 990 1490 1830
11⁄2220 270 300 450 650 900 1100 1300 2060 2550
2 370 455 520 750 1100 1500 1900 2300 3450 4200
21⁄2525 650 750 1050 1600 2175 2750 3300 4950 6050
3 800 950 1350 1600 2500 3350 4250 5150 7700 9450
31⁄21100 1350 1550 2200 3300 4550 5700 6900 10200 12700
4 1450 1800 2000 2900 4300 5850 7400 8900 13450 16400
5 2300 2800 3200 4600 6900 9300 11700 14100 21200 26000
6 3200 3900 4500 6400 9800 13200 16800 20300 30800 36900
8 5700 7000 8000 11400 17200 23300 29300 35400 53100 65200
10 9300 11400 13000 18900 28200 38000 48100 58100 87100 106500
12 13500 16600 18900 27000 40800 55300 69700 84200 126500 154700
SATURATED STEAM (lbs/hr) at 6000 ft/min (velocity) in iron or steel pipe
DIAMETER OF PIPE IN INCHES
3⁄411 1⁄222 1⁄2345681012
233445678111315
233445679111415
3344556710121417
3344557911131518
33455581012151821
34556791113162024
CONDENSATION (lbs/hr) per 100 ft. pipe with 2-in. thick 85% magnesia insulation
Pressure
PSI
(Gauge)
1
3
5
10
20
30
DIAMETER OF PIPE IN INCHES
3⁄411 1⁄222 1⁄2345681012
445679111316192428
4567810131518222732
5578912151820253137
5678913161922283541
66891014172124313845
67891115192428354451
Pressure
PSI
(Gauge)
50
70
100
125
150
200
Condensation in 3" and larger pipe are corrected for heat loss due to friction. Velocity taken at 8000 ft./min. Based on standard formulas.

Flash Steam
Explanation
and
Calculation
Flash Steam
When hot condensate above the saturation
temperature under pressure, is released to
atmospheric pressure, the excess heat is
given off by reevaporation or what is common-
ly referred to as flash steam.
Flash steam is important because it contains
heat which can often be utilized for economy.
It is necessary to know how it is formed and
how much will be formed under given condi-
tions.
The Btu values given in the Properties of
Saturated Steam tables provide the neces-
sary data for calculating energy loss due to
flash steam.
Float and thermostatic traps, bucket traps,
and disc traps discharge condensate at
approximately saturation temperature.
Thermostatic traps discharge condensate 10°
to 30°F. below the saturation temperature.
Flash Steam Heat Loss Calculation
The form provided to the right will allow you to
easily calculate the flash steam loss and
associated energy cost.
Lines A, B, C, D, and E are based on the actu-
al operating conditions. It may be necessary
to estimate the average conditions when
loads fluctuate.
Lines F, G, H and I can be filled in using the
values from the Properties of Saturated
Steam table.
The calculation for flash loss may now be
made with the annual loss determined.
The calculation of energy cost may now be
made to determine the flash loss and
required heating of make-up water to replace
the flash loss.
The amount of make-up water and water cost
can also be determined using this form.
How to Calculate Your Own Flash Steam
and Energy Loss
List Operating Conditions:
A. ____Initial Saturation Pressure.
B. ____Reduced Pressure.
C. ____System Load in Lbs. Per Hr..
D. ____Cost of Steam Per 1,000 Lbs.
E. ____Make-up Water Temperature ° F.
From Properties of Saturated Steam Table:
F. ____Btu/Lb. in Condensate at Initial
F. ____Pressure.
G. ____Btu/Lb. in Condensate at Reduced
G. ____Pressure.
H. ____Btu/Lb. Latent Heat in Steam at
H. ____Reduced Pressure.
I._____Btu/Lb. in Make-up Water.
Calculation of Flash Steam Loss
F – G x 100 = % flash loss
______ x 100 = ______% of flash loss
C x % flash loss = lbs. per hr. loss
To obtain annual loss multiply Ibs. per hr.
Ioss x hr. per day x days per year process
operates = Ib. of flash steam annually.
Calculation of Energy Loss:
This calculation must take into consideration
that, not only are we reducing the tempera-
ture of the returns, but that the condensate
removed in the form of flash steam must be
replaced with cooler make-up water.
% of returns x system load Ibs./hr. x (F - G)
= Btu/hr. condensate cooling.
% of flash loss x system load Ibs./hr. x (F - I)
= Btu/hr. make-up water loss.
Btu condensate cooling + make-up loss
= Btu/hr. Ioss.
Btu/hr. Ioss x hr. per day x days per year
= annual Btu loss.
Btu annual loss ÷ H = equivalent Ib./yr. Ioss.
Lb./hr. Ioss ÷ 1,000 x D
= annual cost of flash steam loss.
Lb./Year Flash Loss ÷ 8.33
= Gallons per year make-up water.
16
H

Steam Trap Operating Pressure Selection
A given size float and thermostatic trap or
bucket trap is offered with various orifice
sizes which determine the maximum pressure
rating. A Hoffman Specialty F & T trap for
example is offered with seats rated 15 psi,
30 psi, 75 psi, 125 psi and 175 psi. A low
pressure seat and pin has a larger orifice size
which provides a higher condensate rating
than a high pressure seat.
When actual operating pressure is higher than
the seat rating, the differential pressure
across the seat will prevent the trap from
opening. Thus, the trap must be selected for
the maximum differential pressure that will be
encountered. The trap capacity tables show
capacities at lower pressures to allow selec-
tion at various operating points.
A high pressure seat may be used at lower
differential pressures, however, the capacity
rating will be less than the same size trap
with a low pressure rated seat.
Operating
Pressure
Limits
17
,
,
ATMOSPHERIC
PRESSURE
STEAM
PRESSURE
WEIGHT OF
BUCKET
Excessive Steam Pressure
Forces Trap Closed

Installation
and
Calculating
Differential
Pressure
Trap Installation
Steam traps should be installed in an acces-
sible location at least 15 inches below the
condensate outlet of equipment or steam
mains being drained. A 15 inch static head at
the trap will provide approximately 1⁄2psi differ-
ential across the trap when it drains into a
vented gravity return system. During start-up,
before a positive steam pressure is achieved,
the static head is the only differential pres-
sure across the trap. When the steam equip-
ment is controlled by a temperature regulator,
the steam pressure will be reduced as the
valve modulates toward the closed position.
When the pressure drops to O psi, the static
head is the only differential pressure across
the trap. The differential pressure across the
trap can be increased by lowering the trap be-
low the steam equipment.
A 2.4 ft. static head
will provide 1 psig. A greater differential pres-
sure will reduce the size of the trap required.
Piping Details
A dirt pocket should be provided ahead of the
steam trap to collect scale and dirt. A shut-off
valve should be provided ahead of the trap to
permit service.
Strainers should be provided ahead of the
steam trap to prevent dirt from entering the
trap. Dirt entering the trap can deposit on the
seat and prevent tight closing. A blow-off valve
on the strainer will permit strainer screen
cleaning. Unions or flanges should be provid-
ed to allow removal of the trap for testing,
repair or replacement.
A test and relief valve installed after the trap
permits visual indication of the trap operation,
and assures that internal pressures are
relieved prior to servicing.
A shut-off valve in the trap outlet to the return
line isolates the trap from the return line for
service.
18
“Y”
STRAINER
EQUIPMENT DRAIN POINT
SHUT-OFF VALVE
DIRT
POCKET
STATIC
HEAD TRAP
TO DRAIN
TEST &
PRESSURE
RELIEF
TO RETURN LINE
GRAVITY RETURN TO
VENTED RECEIVER
“Y”
STRAINER
EQUIPMENT DRAIN POINT
SHUT-OFF VALVE
DIRT
POCKET
STATIC
HEAD TRAP
TO DRAIN
Trap Installation
Trap draining to open drain
Trap Installation
Trap draining to gravity return line

The use of bypass piping around steam traps
is not recommended. Bypass valves, if
opened, may cause pressurization of conden-
sate receivers and cause a safety hazard.
Where stand-by protection is desired the use
of a stand-by trap in parallel to the normal
trap is recommended.
Where the trap drains into a pressurized
return line or to an overhead return, a check
valve should be installed after the trap to pre-
vent backflow through the trap when the
steam is off. The check valve also helps pro-
tect the trap from cavitation (water hammer)
that may occur when traps discharge high
temperature condensate into wet return lines.
Water hammer occurs when high temperature
condensate under pressure ahead of the trap
discharges into a lower pressure return line.
The high temperature condensate flashes,
causing steam pockets to form. When these
steam pockets give up their heat they implode
and cause water hammer.
Differential Pressure
The differential pressure across the trap will
be the sum of the minimum operating pres-
sure, plus the positive static head at the trap
inlet minus any back-pressure in the return
line minus static head in the discharge piping.
Trap capacities should be calculated at the
minimum differential pressure to assure com-
plete condensate drainage.
Lifts in the return piping should be avoided
wherever possible. High temperature conden-
sate discharging from the trap may flash at
the lower return line pressure. The flashing
into a wet return line will cause steam pock-
ets. As these steam pockets lose their latent
heat they implode, causing water hammer.
Water hammer can damage traps, pipe and
fittings.
Lifts in the discharge piping after a trap will
cause back-pressure. A 2.4 ft. Iift is equal to
a 1 psig pressure. This is especially important
on low pressure operation or where a modu-
lating control valve is used to control the flow
of steam. Reduced flow will cause pressure
drops. A positive differential must be assured
under all possible conditions to assure com-
plete condensate drainage.
19
“Y”
STRAINER
EQUIPMENT DRAIN POINT
SHUT-OFF
VALVE
DIRT
POCKET
STATIC
HEAD TRAP
TO DRAIN
TEST &
PRESSURE
RELIEF
CHECK
VALVE
RETURN
LINE STATIC
HEAD
AGAINST
DISCHARGE
1/2PSI/FT.
PRESSURIZED
RETURN LINE
SHUT-OFF
VALVE
TRAP
Trap Installation
Trap draining to overhead return line or pressurized return line
Differential Pressure = P1minus P2
P1(Inlet) P2(Outlet)

Drip Traps for
Distribution
Pipes
Drip Traps for Steam Distribution Piping
The steam distribution piping, often referred
to as steam mains, provides the link between
the boiler and the steam utilizing equipment.
The steam piping must be kept free of air and
condensate. This requirement is met with the
use of steam traps installed in the piping. The
traps used for draining the steam mains are
commonly referred to as drip traps. If the
steam mains are not adequately trapped the
results are often water hammer in the piping.
Water hammer is caused by slugs of conden-
sate traveling at high speed in the steam
pipes, which can damage valves and piping.
Drip traps are installed in the steam mains at
all risers, ahead of all reducing valves, ahead
of all regulators, at the end of mains, through-
out the piping at intervals at least every 500
feet, at expansion joints and at all steam
separators.
The size and type of drip traps used will
depend on the method used in heating the
steam mains to final pressure and tempera-
ture. The two methods commonly used are
automatic start-up and supervised start-up.
In systems using automatic start-up the
steam boiler is used to bring the mains up
to final pressure and temperature without
supervision. The drip traps must handle the
full condensing load during start-up of the
system.
In systems using supervised start-up the oper-
ator opens manual valves in the steam piping
before steam is admitted to the system.
When the system reaches normal pressure
and temperature, the manual valves are
closed. The drip traps for supervised start-up
are sized only for the running load.
The sizing of drip traps will depend on the
type of start-up used. During the initial start-
up of automatic startup systems, a large
amount of condensing occurs, bringing the
steam piping from ambient temperature up to
the final steam temperature.
When supervised start-up is used the drip trap
is sized only to handle the heat loss through
the steam piping.
20

Calculation of the running load is figured
using the following formula:
Ibs./hr. running load heat loss =
L x U x ∆T x E
S x H
L = Length of steam line.
U = Heat transfer from curve in Figure 1.
T = Temperature difference between steam
temperature and minimum ambient in
degrees F.
E = 1- Efficiency of insulation (for 80% effi-
cient insulation use 1.80 = .2).
S = Linear feet of pipe to provide 1 sq. ft.
surface area.
H = Latent heat of steam in Btu/lb. (see
Properties of Saturated Steam Table).
Calculation for warm-up load at start-up:
Warm-up load Ib./hr. =
W x(T1- T2)x.114 L
W = Weight of pipe (see table below for
weight per ft.).
T1= Steam temperature at saturation.
T2= Initial pipe temperature at ambient.
L = Latent heat of steam at final
operating pressure.
.114= Specific heat of steel or wrought
iron pipe.
21
S VALUE FT. OF PIPE PER
SQ. FT. OF SURFACE AREA
Pipe Size S Value
1" 2.904
11⁄4" 2.301
11⁄2" 2.010
2" 1.608
3" 1.091
4" 0.848
5" 0.686
6" 0.576
8" 0.442
10" 0.355
12" 0.299
14" 0.272
16" 0.238
18" 0.212
20" 0.191
24" 0.159
W VALUES
WEIGHT OF WELDED SEAMLESS STEEL PIPE
Schedule 40 Schedule 80
Nominal Wt. Lbs. Wt. Lbs.
Pipe Size Per Linear Ft. Per Linear Ft.
1⁄2" .85 1.09
3⁄4" 1.13 1.47
1" 1.68 2.17
11⁄4" 2.27 3.0
11⁄2" 2.72 3.63
2" 3.65 5.02
21⁄2" 5.79 7.66
3" 7.58 10.25
4" 10.79 14.98
6" 18.97 28.57
8" 28.55 43.39