Hydraulic research on new and in-service PVC pipe has confirmed that industry-recommended flow coefficients are conservative for design of pressure and non-pressure pipes.

The PVC pipe industry has long recommended hydraulic design values of 150 for Hazen-Williams “C” coefficient and 0.009 for Manning’s “n” number. Recent hydraulics tests have confirmed that designs using these values are conservative. The first testing was conducted at the Water Research Laboratory at Utah State University. New 6- and 12-inch pipe was tested to determine values of “C” and “n” under a variety of flow conditions. The second testing program was run on 8-inch pipe that has been in service since 1976 in West Valley City, Utah. Values of “C” were determined for two flow velocities.

Results are described in a report titled “Hydraulic Testing of PVC Pipe: Laboratory and Field Tests Confirm Coefficients.”


for the report.

Designers of PVC piping systems can be confident that there is no need to design with a higher-friction PVC coefficient. The testing shows that even with varying flow rates and long use, the HW “C” factor remains above 150 and the Manning’s “n” stays below 0.009. The use of higher-friction coefficients results in engineering designs that are not consistent with previous and current findings of PVC pipe’s hydraulic attributes and may result in adding unnecessary project and operational costs.