Pressure Drop Leak Detection Calculator
Estimates the volumetric leak rate and equivalent orifice diameter from an observed pressure drop in a closed pressurized system over a known time interval.
Formulas Used
1. Volumetric Leak Rate (Isothermal Ideal Gas):
Qatm = (ΔPabs × V) / (Patm × t)
where ΔPabs = P₁abs − P₂abs (absolute pressures), V = system volume, t = test duration.
2. Equivalent Orifice Diameter — Subsonic:
Qupstream = Cd × A × √(2 × ΔPgauge,avg / ρupstream)
d = 2 × √(A / π)
3. Equivalent Orifice Diameter — Choked (Sonic) Flow:
ṁ = Cd × A × P₁abs × √(γ / (Rs × T)) × (2/(γ+1))(γ+1)/(2(γ−1))
Choked condition: P₁abs/Patm ≥ ((γ+1)/2)γ/(γ−1) ≈ 1.893 for air (γ=1.4)
4. Air Density:
ρ = P × Mair / (R × T) [Ideal Gas Law]
Assumptions & References
- Isothermal process — temperature remains constant during the test (valid for slow leaks).
- Ideal gas behavior for air (Mair = 28.97 g/mol, γ = 1.4, R = 8.314 J/mol·K).
- Leak is modeled as flow through a sharp-edged circular orifice.
- Default discharge coefficient Cd = 0.61 (sharp-edged orifice, ISO 5167).
- Atmospheric pressure default: 14.696 psi (101.325 kPa) at sea level.
- Severity thresholds are indicative; refer to system-specific standards (e.g., ASME B31.3, ISO 15848, SAE J1455).
- References: ISO 5167 (orifice flow), ASME PTC 19.3, Crane TP-410 (Flow of Fluids), ISO 15848-1 (industrial valve leakage).