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