Valve sizing and selection (steam) – Powers 597 Series Flowrite II Heavy Duty Balanced Control Valves User Manual
Page 4
Page 4
TI597SI
VALVE SIZING AND SELECTION (STEAM)
Steam:
One can use the same reasoning for selecting a valve in steam applications
as would be used for water applications. Once again, pressure drop
selection is a major determining factor for good control and system
performance. In general, for steam applications, the largest possible
pressure drop should be taken without exceeding the critical pressure ratio.
On/Off Control:
These types of applications are normally line sized to reduce pressure drop.
In these applications it is important to verify valve seat leakage will not
result in system overheat or damage. If this is a concern, it is necessary to
take precautions to alleviate this potential problem.
Proportional Control:
For pressures less than 15psig, use an 80% of the gauge inlet pressure as a
differential. For pressures above 15psig, use 42% of the absolute inlet
pressure. In those cases where the required Cv falls between two valves,
select the larger size.
One may be concerned about steam entering a heating coil at 0psig when
these large pressure drops are taken at the valve. However, flow will
continue as the pressure in the coil will drop to vacuum pressures due to
the steam condensation. It is essential to use proper condensate piping
and steam trapping in these applications.
Table - 3
Steam Capacity in Pounds Per Hour
Steam Inlet Pressure (psig)
2
5
10
Pressure Drop
Across Valve (psi)
0.5
1
2
1
2
3
4
5
2
4
6
8
10
Valve
Cv
Size
Rating
2.5
56
477
669
932
729
1017
1229
1399
1542
1145
1585
1898
2140
2334
3
85
724
1016
1415
1106
1544
1865
2124
2341
1738
2405
2880
3249
3543
4
145
1235
1733
2413
1887
2634
3182
3623
3993
2965
4103
4914
5542
6044
5
240
2044
2869
3994
3123
4359
5267
5997
6610
4907
6792
8133
9172
10004
6
370
3151
4423
6157
4815
6720
8120
9246
10190
7565
10471
12538
14141
15423
Steam Inlet Pressure (psig)
15
25
50
Pressure Drop
(max)
(max)
(max)
Across Valve (psi)
3
6
9
12
15
5
10
15
20 10
20
30
32.5
Valve
Cv
Size
Rating
2.5
56
1530
2105
2505
2805
3035
2268
3098
3655
4053
4064
5501
6422
6599
3
85
2322
3195
3802
4257
4607
3443
4702
5548
6152
6168
8350
9747
10017
4
145
3961
5450
6485
7262
7858
5873
8022
9464
10495
10522
14243
16628
17088
5
240
6556
9021
10734
12020
13007
9721
13277
15665
17372
17415
23575
27522
28284
6
370
10107
13908
16548
18531
20052
14986
20469
24150
26781
26489
36345
42430
43604