Pressure surge suppression using a metallic-plastic-metallic pipe configuration

Plastic pipes [e.g., polyvinyl chloride (PVC) or high density polyethylene (HDPE)] are commonly used to replace aging metallic pipe sections (e.g., cast iron) in water-distribution networks. However, our understanding of how a combined metallic-plastic-metallic system responds to hydraulic transients is limited. This research studies such a system and focuses on answering whether the use of a plastic section to replace a metallic section can contribute to pressure surge suppression. The response of a metallic-plastic-metallic system to step and pulse pressure waves generated in the plastic section is investigated through theoretical and numerical analyses. It is found that the low impedance of plastic pipes (relative to metal pipes) plays a key role in determining the shape and amplitude of the pressure response. The metallic-plasticmetallic configuration can be used for surge suppression, especially for pulse waves that are commonly experienced in real networks attributable to customer activities. A generalized analysis finds that larger diameters and longer lengths of the plastic section contribute to better surge suppression, and the normalized results provide the selection criteria for system design. The findings are verified and demonstrated by numerical simulations using the method of characteristics, and some are also supported by the results of field trials. Some practical issues related to field applications are discussed.