When we run hydrant flow tests, we usually use both 2-1/2" side-outlets of a typical dry fire hydrant. We hook up one, threaded, swivel 45-elbow on each side to divert water in a direction that won't destroy anything.

What is the appropriate Coefficient of Discharge when measuring the pitot on the centerline of the elbow?

Traditionally flowing straight out of the side outlet of a hydrant, NFPA 291 gives three Coefficients (0.90, 0.80, and 0.70) based on how the outlet projects into the barrel. NFPA 291 also states that a coefficient of 0.85 is suggested for stream straighteners, unless the coefficient of the tube is known.

Is there a known Coefficient for a single 45-degree elbow?

Any help is greatly appreciated.

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Fire hydrant flow test question - is the pitot the same as the residual pressure on a water flow test from a fire hydrant?

Is it possible to know the residual pressure and 'chart out' the flow of the fire hydrant, or is there a way to determine the flow with only the static and residual pressures?

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