Pressure Decay Leak Test Calculator
Turn the pressure drop seen during a pressure decay (pressure hold) test into a leak rate, correcting for any change in gas temperature during the test.
- P₂ corrected = P₂ × T₁ ÷ T₂ = 6.95 bar a
- ΔP = P₁ − P₂ corrected = 50 mbar
- Leak rate = V × ΔP ÷ t = 200 L × 50 mbar ÷ 1,800 s = 5.556 mbar·L/s
Pressure Decay Formula
P₂ corrected = P₂ × T₁ ÷ T₂ (absolute)
1 mbar·L/s ≈ 59.2 sccm
Q is the leak rate, V the gas filled internal volume under test, ΔP the temperature corrected pressure fall and t the test time. Pressures are absolute and temperatures in kelvin. The result is the leak at the test pressure expressed as gas at standard conditions.
Worked example
A 200 L system at 7 bar a falls by 50 mbar in 30 minutes with constant temperature: Q = 200 × 50 ÷ 1800 = 5.56 mbar·L/s, about 329 sccm.
Frequently Asked Questions
What is a pressure decay test?
The system is pressurised, isolated and the pressure fall is recorded over time. The fall, the volume and the time give the leak rate.
Why does temperature matter?
Gas pressure is proportional to absolute temperature. Sun, cooling or compression heat can change pressure more than a small leak.
What is sccm?
Standard cubic centimetres per minute: the volume of leaking gas at standard pressure and temperature.
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