Calculators›Drain Orifice
💧

Drain Orifice Sizing

API 14E AGA 3 ISO 5167

Calculation Mode:
Verify if a given orifice size meets requirements

System Configuration

psig
in
in
ft
in
ft

Tank & Gas Properties

gal
ft
ft
oz/in²
air=1
°F

Pipe Material

Typical Gas SG Values

Methane0.55
Natural Gas0.60–0.70
Propane1.52
Air1.00

📚 Learn the Theory

API 14E methods, discharge coefficients, critical flow, and blowdown calculations

Read Engineering Guide →

Engineering Basis

Orifice Flow (AGA 3 / ISO 5167)
ṁ = Cd × Ev × Y × A × √(2ρ₁ΔP)

Cd = discharge coefficient, Ev = velocity approach = 1/√(1-β⁴), Y = expansion factor

Critical (Choked) Flow
(P₂/P₁)crit = (2/(k+1))^(k/(k-1)) ≈ 0.55 for natural gas

Flow becomes sonic when pressure ratio drops below critical—further ΔP increase won't increase flow.

API 14E AGA Report No. 3 ISO 5167 Crane TP-410

Design Limits

Beta ratio (β) 0.20 – 0.75
Vent velocity ≤ 120 ft/s
Tank pressure per API 650
Typical Cd 0.60 – 0.65

💡 Mode Guide

  • Size Orifice: Find max orifice for your constraints
  • Check Design: Verify existing orifice meets limits
  • Find Flow: Calculate flow rate with sensitivity

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