Safety Valve Discharge Capacity and Control Valve Cv Charts
Reference tables for sizing safety relief valves and globe control valves, published by Supreme Valves India. Capacities follow the IBR discharge formula; flow coefficients are for globe-style trim.
Direct answer · Updated August 2026
How do I size a safety relief valve and control valve?
Safety valve capacity under IBR is E = C x A x ((P x 0.980) + 1.033) in kg/hr of saturated steam, using C = 40 for full-nozzle and C = 24 for modified-nozzle designs. Control valves are selected on flow coefficient Cv, which runs from 13.9 at 25 mm to 372 at 150 mm on an equal percentage plug. The charts below give orifice areas, capacities, and Cv values in full.
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Safety valve orifice areas
| Designation | Seat diameter | Flow area |
|---|---|---|
| E | 12.7 mm | 1.2645 cm² |
| F | 19.0 mm | 2.83385 cm² |
| G | 23.0 mm | 4.154 cm² |
| G1 | 25.0 mm | 4.90625 cm² |
| H | 28.0 mm | 6.154 cm² |
| J | 31.8 mm | 7.942 cm² |
| K | 36.0 mm | 10.178 cm² |
Discharge capacity — full nozzle (C = 40)
Saturated steam capacity in kg/hr, calculated as E = 40 x A x ((P x 0.980) + 1.033).
| Set pressure (kg/cm²g) | E — 12.7 mm | F — 19.0 mm | G — 23.0 mm | G1 — 25.0 mm | H — 28.0 mm | J — 31.8 mm | K — 36.0 mm |
|---|---|---|---|---|---|---|---|
| 1 | 102 | 228 | 334 | 395 | 496 | 639 | 820 |
| 2 | 151 | 339 | 497 | 587 | 737 | 951 | 1,219 |
| 3 | 201 | 450 | 660 | 780 | 978 | 1,262 | 1,617 |
| 5 | 300 | 673 | 986 | 1,164 | 1,460 | 1,885 | 2,415 |
| 7 | 399 | 895 | 1,312 | 1,549 | 1,943 | 2,507 | 3,213 |
| 10 | 548 | 1,228 | 1,800 | 2,126 | 2,667 | 3,441 | 4,410 |
| 14 | 746 | 1,672 | 2,451 | 2,895 | 3,632 | 4,687 | 6,006 |
| 17 | 895 | 2,006 | 2,940 | 3,472 | 4,355 | 5,621 | 7,203 |
| 21 | 1,093 | 2,450 | 3,591 | 4,242 | 5,320 | 6,866 | 8,799 |
| 25 | 1,291 | 2,894 | 4,243 | 5,011 | 6,285 | 8,111 | 10,395 |
Discharge capacity — modified nozzle (C = 24)
Applies to thermal and pressure relief valves on steam lines and small industrial boilers.
| Set pressure (kg/cm²g) | E — 12.7 mm | F — 19.0 mm |
|---|---|---|
| 1 | 61 | 137 |
| 2 | 91 | 204 |
| 3 | 121 | 270 |
| 5 | 180 | 404 |
| 7 | 240 | 537 |
| 10 | 329 | 737 |
| 14 | 448 | 1,003 |
| 17 | 537 | 1,203 |
| 21 | 656 | 1,470 |
| 25 | 775 | 1,737 |
Control valve flow coefficient (Cv)
| Nominal size | Equal percentage | Linear | Quick opening |
|---|---|---|---|
| 25 mm | 13.9 | 16.8 | 16.3 |
| 40 mm | 30.4 | 30.2 | 30.9 |
| 50 mm | 55.2 | 55.4 | 58.7 |
| 65 mm | 77.0 | 76.0 | 82.8 |
| 80 mm | 102.0 | 118.0 | 120.0 |
| 100 mm | 170.0 | 166.0 | 155.0 |
| 150 mm | 372.0 | 377.0 | 369.0 |
Sizes above 150 mm are quoted against the specific duty. Send your flow, inlet and outlet pressure, and fluid state for a calculated Cv.
Frequently asked
How is safety valve discharge capacity calculated under IBR?
IBR gives discharge capacity as E = C x A x ((P x 0.980) + 1.033), where C is the certified constant, A is the orifice flow area in cm², P is set pressure in kg/cm²g, and E is capacity in kg/hr of saturated steam. Full-nozzle designs use C = 40 and modified-nozzle designs use C = 24.
What is the flow area of a 19 mm safety valve orifice?
A 19.0 mm orifice (designation F) has a flow area of 2.83385 cm². At a set pressure of 7 kg/cm²g it passes about 537 kg/hr of saturated steam on a C = 24 modified-nozzle valve, or about 895 kg/hr on a C = 40 full-nozzle valve.
What is the Cv of a 50 mm globe control valve?
A 50 mm globe control valve has a flow coefficient of approximately 55.2 with an equal percentage plug, 55.4 with a linear plug, and 58.7 with a quick-opening plug.
Which orifice sizes are available on safety relief valves?
Designations run E (12.7 mm), F (19.0 mm), G (23.0 mm), G1 (25.0 mm), H (28.0 mm), J (31.8 mm), and K (36.0 mm). The 12.7 mm orifice is offered for small industrial boiler duty only.
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