Towards an Improved Understanding of Water-Hammer Column-Separation Due to Rapid Valve Closure

Column separation phenomenon occurring downstream of a closing valve, simulating the closure of non-return/check valve downstream of pumps due to pump trip is simulated. An improved understanding of how cavity is opened, grows and collapses is supported by comparing numerical results with measured values and analyzing video frames. In the present study two models, discrete vapor cavity and gas cavity models, of column separation are compared for the modeling of column separation. Both models showed considerable degree of stability with variation of number of sections into which the pipe is divided. An experimental setup was built to provide the means of obtaining reliable experimental data for transient flow in viscoelastic pipes to verify the numerical model. Two valve closure schemes were tested using solenoid globe and ball valves. Video photographs of column separation during the vapor cavity formation, growth and collapse were processed and video films are transformed into frames using computer software. The video frames representing the cavity development and pressure measurements downstream of the valve are compared with corresponding cavity and pressure traces predicted by the model at each time step of the framing process at the same location. It was also shown that the characteristic of check valve closure scheme seriously affects the cavity formation and the extent of pressure surges due to cavity collapse.