Head Loss Characteristics

Head Loss Characteristics of Water Flow Through Rigid Plastic Pipe

This nomograph provides approximate values for a wide range of plastic pipe sizes. More precise values should be calculated from the Williams & Hazen formula. Experimental test value of C (a constant for inside pipe roughness) ranges from 155 to 165 for various types of plastic pipe. Use of a value of 150 will ensure conservative friction loss values. Values for head loss on PVC and CPVC fittings and valves are not available at the present time. Since directional changes and restrictions contribute the most head loss, use of head loss data for comparable metal valves and fittings will provide conservative values.

The values of this graph are based on the Williams & Hazen formula

f = .2083 Head Loss Formula

Where:

f = Friction head in feet of water per 100 feet
d =Inside diameter of pipe in inches
g = Flowing gallons per minute
C = Constant for inside roughness of the pipe (C = 150 for thermoplastic pipe)

The nomograph is used by lining up values on the scales by means of a ruler or straight edge. Two independent variables must be set to obtain the other values. For example line (I) indicates that 500 gallons per minute may be obtained with a 6 inch inside diameter pipe at a head loss of about 0.65 pounds per square inch at a velocity of 6.0 feet per second. Line (2) indicates that a pipe with a 2.1 inch inside diameter will give a flow of about 60 gallons per minute at a loss in head of 2 pounds per square inch per 100 feet of pipe. Line (3) and dotted line (3) show that in going from a pipe 2.1 inch inside diameter to one of 2 inches inside diameter the head loss goes from 3 to 4 pounds per square inch in obtaining a flow of 70 gallons per minute. Our raw material supplier does not recommend velocities in excess of 5.0 feet per second.

 

Head Loss Chart

 

Nomograph courtesy of Plastics Pipe Institute, a division of The Society of The Plastics Industry.