Safety Valves in Gas and Vapor Systems

Calculate the minimum discharge area of relief safety valves in gas or vapor systems using either flow rate in lb/hr or SCFM, accounting for temperature, pressure, gas properties, and system coefficients.

Safety Valves in Gas and Vapor Systems

Calculate the minimum discharge area of a relief safety valve in a gas or vapor system.

Calculation Methods:

Method 1 - Flow in lb/hr:

  • Formula: A = m T^(1/2) / (C kd kbp P M^(1/2))

Method 2 - Flow in SCFM:

  • Formula: A = qs (SG T)^(1/2) / (1.175 C kd kbp P)

Common Coefficients (C) by Gas:

Air: 356, Nitrogen: 356, Oxygen: 356, Natural Gas: 344, Propane: 330, Ammonia: 347, Hydrogen: 357, Methane: 348, Carbon Dioxide: 346

Calculator

Inputs

Results

Absolute Temperature-- °R
Relieving Pressure-- psia
Minimum Discharge Area (lb/hr method)-- in²
Minimum Discharge Area (SCFM method)-- in²
GasMolecular WeightCoefficient (C)Specific Gravity*
Acetylene26.043420.9
Air28.973561
Ammonia17.033470.59
Argon39.943771.38
Benzene78.113292.7
N-Butane58.123352.01
Iso-Butane58.123362.01
Carbon Dioxide44.013461.52
Carbon Disulphide76.133382.63
Carbon Monoxide28.013560.97
Chlorine70.93522.45
Cyclohexane84.163252.91
Ethane30.073361.04
Ethyl Alcohol46.073301.59
Ethyl Chloride64.523362.23
Ethylene28.033410.97
Helium4.023770.14
N-Heptane100.23213.46
Hexane86.173222.98
Hydrochloric Acid36.473571.26
Hydrogen2.023570.07
Hydrogen Chloride36.473571.26
Hydrogen Sulphide34.083491.18
Methane16.043480.55
Methyl Alcohol32.043371.11
Methyl Butane72.153252.49
Methyl Chloride50.493371.74
Natural Gas193440.66
Nitric Oxide303561.04
Nitrogen28.023560.97
Nitrous Oxide44.023481.52
N-Octane114.223213.95
Oxygen323561.11
N-Pentane72.153252.49
Iso-Pentane72.153252.49
Propane44.093301.52
R-11137.373314.75
R-12120.923314.18
R-2286.483352.99
R-114170.933265.91
R-123152.933275.28
Sulfur Dioxide64.043442.21
Toluene92.133263.18