Control valves
Safety valves
Page 4 of 5
Set pressure psi g
15
20
40
60
80
100
120
140
160
180
200
220
240
250
Saturated steam temperature °F
250
259
287
308
324
338
350
361
371
380
388
395
403
406
Total steam
temperature
°F
280
300
320
340
360
380
400
420
4.7.33
1.00
1.00
-
-
-
-
-
-
-
-
-
-
-
-
1.00
1.00
1.00
-
-
-
-
-
-
-
-
-
-
-
1.00
1.00
1.00
1.00
-
-
-
-
-
-
-
-
-
-
0.99
0.99
1.00
1.00
1.00
-
-
-
-
-
-
-
-
-
0.99
0.99
0.99
0.99
1.00
1.00
1.00
-
-
-
-
-
-
-
0.98
0.98
0.99
0.99
0.99
1.00
1.00
1.00
1.00
-
-
-
-
-
0.98
0.98
0.98
0.98
0.99
0.99
0.99
1.00
1.00
1.00
1.00
1.00
-
-
0.97
0.97
0.97
0.97
0.98
0.98
0.98
0.99
0.99
0.99
0.99
1.00
1.00
1.00
Safety valve sizing information
For steam service:
For organic fluid vaporizers - lb / h:
Where:
A =
P =
Formulas:
Required orifice area in square inches
Relieving pressure in pounds per square inch absolute = set pressure (psi g) + overpressure + 14.7 where the overpressure is
3% or 2 psi, whichever is the greater. P = 1.03 x set pressure + 14.7 or P = set pressure + 2 psi + 14.7.
Coefficient of discharge, 0.955 for steam, air and vapour service.
Steam superheat correction factor. See Table 1 below.
Average molecular weight of vapour. See Table 2, page 5.
Gas or vapour flow constant. See Table 3, page 5.
Compressibility factor corresponding to T and P. If this factor is not available, compressibility correction can be safely ignored using
a value of Z = 1.0.
Inlet temperature, °F. Absolute (°F plus 460).
T =
= Required steam capacity in pounds per hour.
= Required vapor capacity in pounds per hour.
K
d
=
K
sh
=
M =
C =
Z =
Table 1 Ksh superheat correction factor
SV73 Cast Iron Safety Valve
TI-S13-25 CH Issue 11
Page 4 of 5
