Relief Valve Sizing: D to H
API 526/520 standard pressure relief valve orifice designations — effective orifice areas, rated discharge coefficients (Kd), back-pressure correction factors (Kb), and inlet/outlet connection sizes for orifices D through T
| orifice | Kb balanced bellows 50pct (dimensionless) | Kb conventional (dimensionless) | Kd (dimensionless) | Ksh sat (dimensionless) | area in2 (in2) | area mm2 (mm2) | inlet size in (in) | notes | outlet size in (in) |
|---|---|---|---|---|---|---|---|---|---|
| D | 0.9 | 1 | 0.975 | 1 | 0.11 | 71 | 1 | Smallest standard orifice; D orifice typical 1x2 connection | 2 |
| E | 0.88 | 1 | 0.975 | 1 | 0.196 | 126 | 1 | E orifice typical 1x2 connection | 2 |
| F | 0.87 | 1 | 0.975 | 1 | 0.307 | 198 | 1.5 | F orifice typical 1.5x2.5 connection | 2.5 |
| G | 0.86 | 1 | 0.975 | 1 | 0.503 | 325 | 1.5 | G orifice typical 1.5x2.5 connection | 2.5 |
| H | 0.86 | 1 | 0.975 | 1 | 0.785 | 506 | 2 | H orifice typical 2x3 connection | 3 |
This is a sample. Search the full relief valve sizing dataset and 300+ more by creating a free account and accessing the database.
Get started for FREE