HYDRAULIC FRICTION LOSS IN SMALL DIAMETER PLASTIC PIPELINES1

ABSTRACT: Although estimation of hydraulic friction loss in pipelines is one of the most frequent routine computations made by water supply engineers, almost no post-construction analysis of the accuracy of these calculations exists in the literature. This paper reports the field measured friction losses in three one-mile sections of small diameter pvc pipe which had been in service for 10 years. Hazen-Williams and Darcy-Weisbach equations are examined to provide a framework for comparing Hazen-Williams coefficients recommended by pipe manufacturers to those obtained by the field measurements. The conclusion is that the C_HW factor of 150 recommended by most pvc pipe manufacturers is too high for the diameter-velocity combinations encountered in rural dead-end small diameter lines. The measured coefficients averaged 133 which is close to that predicted by superimposing Hazen Williams coefficients on the Moody diagram from which the friction factor for the Darcy-Weisbach equation is obtained.