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Hydrant flow test (Pitot), projected to 1.4 bar
Enter static pressure, residual pressure during flow and Pitot pressure at the outlet. Get test flow and the supply available at 1.4 bar residual.
Quick answer
The hydrant flowed 2,023 L/min (33.7 L/s) with 3.00 bar residual. Projected to 1.4 bar residual, the supply delivers about 49.9 L/s.
Preliminary results
Test flow33.7L/s
L/min2,023L/min
Available at residual 1.4 bar49.9L/s
| Step | Result | Basis |
|---|---|---|
| Test flowQ = 0,6664 × 0.9 × 63.5² × √0.70 | 2,023 L/min | NFPA 291 |
| Pressure-drop ratio(Ps − Pr)/(Ps − Pf) = (4.50 − 1.4)/(4.50 − 3.00) | 2.067 | NFPA 291 |
| Available flowQR = QF × ratio^0,54 | 2,994 L/min = 49.9 L/s | NFPA 291 ⚠ |
Sources and assumptions. NFPA 291: Q = 0.6664·C·d²·√Pp (L/min; d mm; Pp bar), QR = QF·((Ps − Pr)/(Ps − Pf))^0.54. 1.4 bar (20 psi) residual is the usual reference for fire water supply ⚠. ⚠ = code table value to be checked against the original standard. Preliminary results for material selection and budgeting; not a substitute for an approved fire protection design.
Frequently asked questions
Why project to 1.4 bar residual?
1.4 bar (20 psi) is the minimum residual commonly used to rate a water main: the flow at this point shows what the hydrant and main can supply to fire engines.
How is the Pitot reading taken?
Hold the Pitot blade in the centre of the stream about half a diameter from the outlet; read static and residual on a cap gauge at the test hydrant.