The Behavior of PVC Pipe Under the Action of Water Hammer Pressure Waves

Introduction: Hydraulic transients, commonly referred to as water hammer, occur in a hydraulic system whenver the velocity of flow in any one of the pipes in the system is caused to change. The magnitude of the pressure waves generated by a given change in velocity depends on the geometry of the pipe system, the magnitude of the velocity change and the elastic wave velocity in the system componenets. In turn, the elastic wave velocity depends on the modulus of elasticity of the fluid and the pipe material, the size and thickness of the pipe, the method by which the pipe is constrained or tied down and the Poisson\u27s ratio for the material of which the pipe os constructed. The extensive engineering analysis and design of piping systems in which water hammer occurs is relatively common in recent years. Most piping systems in previous years have been constructed of metal or concrete pipe or some other equally rigid material and experimental verification of the theories predicting water hammer wave velocity, intensity and duration has been realized. Recently, however, there has been an increase in the use of plastic material to construct pipes. There has been little coordinated work done on the extent to which the classical theory of hydraulic transients will predict water hammer in these plastic pipes. It appears that use of plastic matierals in constructing water pipe will increase dramatically in the next few years and, therefore, research into the behavior of this pipe under water hammer pressures is justified and timely. Late in 1969 the Johns-Manville Corporation undertook preliminary studies of water hammer occurring in the PVC (polyvinylchloride_ pipe which they manufacture. The results of this work cast considerable doubt as to the validity of applying the classical equations predicint water hammer to PVC pipe. As a result of this conclusion, the Johns-Manville Corporation retained the Utah Water Research Laboratory to generate conclusive results on the behavior of this type of pipe under water hammer pressures