Safety Relief Valves - Capacities vs. Pressure
Maximum safety valve free air relief capacity.
Safety valves and maximum relief free air capacity:
For full table - rotate the screen!
Maximum Relieving Capacity of Free Air (cfm) | ||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Valve Diameter (inches) | Gauge Pressure (psi) | |||||||||||||||
50 | 100 | 150 | 200 | 250 | 300 | 350 | 400 | 500 | 600 | 800 | 1000 | 1200 | 1600 | 2000 | 2400 | |
1/4 | 12 | 20 | 27 | 33 | 38 | 43 | 48 | 53 | 61 | 70 | 84 | 97 | 109 | 128 | 147 | 160 |
3/8 | 17 | 27 | 36 | 44 | 51 | 58 | 65 | 72 | 83 | 95 | 115 | 133 | 149 | 176 | 197 | 215 |
1/2 | 20 | 32 | 42 | 51 | 59 | 67 | 74 | 111 | 129 | 147 | 177 | 205 | 230 | 270 | 304 | 330 |
3/4 | 37 | 59 | 78 | 96 | 112 | 127 | 141 | 176 | 224 | 232 | 242 | 346 | 386 | 423 | 474 | 518 |
1 | 58 | 94 | 124 | 152 | 178 | 202 | 224 | 248 | 286 | 324 | 390 | 450 | 500 | 586 | ||
1 1/4 | 84 | 135 | 180 | 221 | 259 | 293 | 325 | 352 | 400 | 443 | 509 | |||||
1 1/2 | 114 | 186 | 248 | 302 | 354 | 400 | 444 | 478 | 528 | 568 | 634 | |||||
2 | 189 | 306 | 410 | 501 | 592 | 668 | 741 | |||||||||
2 1/2 | 282 | 457 | 613 | 750 | 880 | 998 | 1114 | |||||||||
3 | 393 | 638 | 856 | 1050 | 1230 | 1398 | 1557 |
- 1 inch = 25.4 mm
The relief capacity for a safety valve depends on
- the relief discharge area
- the compressibility factor of the actual gas
- the temperature of the gas
- the geometry of the safety valve
A safety relief valve must be capable of relieving the capacity of the connected compressor(s) at operating pressure. Note that the relief pressure can not be set higher than the maximum rated working pressure of any equipment in the system. If the operating pressure is right below the relief pressure of the valve the valve may start leaking.
A "rule of thumb" is to set the relief pressure 10% above the working pressure of the system.