Choked Sonic Gas Flow Calculator

Size a restriction orifice for choked (sonic) gas flow at the critical pressure ratio.

Choked sonic gas flow

Choked sonic gas flow is computed deterministically from the parameters encoded in this page's address, so the same inputs always produce the same result and the same OAS-XXXX verification hash.

Critical pressure ratio

Critical pressure ratio is computed deterministically from the parameters encoded in this page's address, so the same inputs always produce the same result and the same OAS-XXXX verification hash.

Required orifice diameter

Required orifice diameter is computed deterministically from the parameters encoded in this page's address, so the same inputs always produce the same result and the same OAS-XXXX verification hash.

Engineering summary

Governing parameters and computed results for Choked Sonic Gas Flow Calculator.

Governing parameters and computed results for this calculation
Parameter Value
Fluid air

Frequently asked questions

When does gas flow through an orifice become choked?
Gas flow chokes when the downstream-to-upstream absolute pressure ratio falls to or below the critical ratio (2/(k+1))^(k/(k−1)) — about 0.528 for air. Below that ratio the flow is sonic and further downstream pressure reduction adds no flow.
How do I convert between Cv and Kv?
Kv = 0.865 · Cv. Cv is the US gallons-per-minute of water at 60 °F that flows through the restriction at a 1 psi drop; Kv is the metric equivalent in cubic metres per hour at a 1 bar drop.
What discharge coefficient should a sharp-edged orifice use?
A sharp-edged, square-shouldered orifice uses a discharge coefficient near 0.62 for a fully turbulent liquid. The coefficient falls in the laminar regime, which is why a Reynolds-number viscosity correction matters at low flow.