Valve sizing and selection (steam) – Powers 596 SI Flowrite II Heavy Duty Control Valves User Manual
Page 4

Page 4
Form TI 596SI v2
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 15 psig, use an 80% of the gauge inlet pressure as a
differential. For pressures above 15psig, use 50% 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 0 psig 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
65
554
777
1082
846
1181
1426
1624
1790
1329
1839
2203
2484
2709
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
235
2002
2809
3911
3058
4268
5157
5872
6472
4805
6650
7964
8981
9796
6
350
2981
4184
5825
4555
6357
7681
8746
9639
7156
9905
11861
13376
14589
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
65
1776
2443
2907
3255
3523
2633
3596
4242
4705
4717
6385
7454
7660
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
235
6419
8834
10511
11770
12736
9518
13001
15338
17010
17053
23084
26949
27694
6
350
9561
13156
15654
17529
18968
14176
19363
22844
25334
25397
34380
40137
41247
Steam Inlet Pressure (psig)
75
100
125
Pressure Drop
(max)
(max)
(max)
Across Valve (psi)
10
25
35
45
10
25
36
58
20
50
70
Valve
Cv
Size
Rating
2.5
65
5618
8481
9704
10615
6394
9758
11390
13610
9832
14619
16526
3
85
7347
11090
12690
13882
8361
12760
14894
17797
12857
19117
21611
4
145
12533
18918
21647
23681
14263
21767
25408
30360
21932
32611
36866
5
235
20312
30661
35084
38379
23116
35277
41178
49205
35546
52853
59748
6
350
30251
45665
52252
57160
34428
52541
61329
73284
52940
78717
88987
Steam Inlet Pressure (psig)
150
175
200
Pressure Drop
(max)
(max)
(max)
Across Valve (psi)
25
50
83
50
70
95
50
75
108
Valve
Cv
Size
Rating
2.5
65
11908
16134
19521
17518
20088
22437
18800
22254
25431
3
85
15572
21098
25527
22908
26269
29340
24585
29102
33256
4
145
26563
35990
43546
39078
44812
50051
41939
49644
56731
5
235
43051
58329
70574
63334
72627
81117
67971
80457
91944
6
350
64118
86873 105111
94327
108167
120813
101233
119830
136937