User Manual
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)
25 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
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
5 240 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
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
5 240 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