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;

• Cd rounded = 0.9
• Cd squared = 0.8
• Cd Protrudes into barrel = 0.7

       d

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

       P

Pressure as recorded by the Pitot tube.

           
INDEX Water Supply

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