Hydraulic ram analysis: a new look at an old problem

Abstract

The discretized method of characteristics was used to develop a new numerical model for the analysis of the wave processes in the hydraulic ram. The model encompasses all parts of the device including, for the first time, the air chamber and the delivery pipe. This in turn allows a comprehensive study of the unsteady flows in the unit as the air chamber extensively interacts with the supply side of the ram. The program accounts for all possible flow states of the ram, i.e. with impulse and discharge valves closed, with both valves open and with either of the valves closed or open. The state of the partially or fully open discharge valve requires extensive and careful treatment of all physical phenomena involved, namely the transient boundary conditions, relevant to the air chamber and its connection to the drive pipe. The treatment is for the special case of constant sonic velocity in each of the ram pipes. The numerical model was validated against experimental data obtained from various test set-ups. Comparing the velocity and pressure head variations from numerical and experimental tests at selected points along the ram supply pipe performed the most stringent test. Excellent agreement was shown to exist, validating the analytical approach.