Manual

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
385 724 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
385 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
385 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
385 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