Analysis of Anomalies in Water-Hammer Experiments with Partially-Open Valves

In this study, the water hammer pressure due to the sudden closure of the partially-open valve was investigated experimentally and analytically. Because the partially-open valve could produce local non-uniform flow, a supplementary Joukowsky's water hammer equation was derived based on the assumption of the local non-uniform flow and the kinetic energy equation. A physical model was set up to measure the maximum water hammer pressure of the first positive wave due to the sudden closure of partially-open valve under different conditions, including different water heads, flow velocities, pipe diameters and valve types. The results showed that Joukowsky's equation obtained by the momentum theorem in the uniform flow field was applicable to the uniform flow field with the valve fully open. The experimental results of the partially-open valve-closure water hammer pressure were 3.5%~21% larger than Joukowsky's equation, which consisted with the theoretical analysis of the supplementary Joukowsky's water hammer equation. This phenomenon had repeatability and was unrelated with the water head, the inlet flow velocity, the pipe diameter and the valve type. This study could provide guidance for water hammer protection in hydropower stations and pump stations.