Inspection Course

Water Supply

Coefficient of discharge (Cd)

This takes friction into consideration. A Cd of 1.0 is an ideal frictionless discharge. An actual hydrant orifice will have a lower Cd, reflecting friction factors that will slow the velocity of the water.

The Cd will vary according to the interior of the hydrant outlet or nozzle used;


Actual diameter of hydrant discharge in inches. 2-1/2 is only nominal. Inaccuracies could account for up to 5% error in calculation.


Pressure as recorded by the Pitot tube.

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FPT 102 - Fire Prevention and Inspection // Instructor: Kevin M. Kolb        Slide #3