Experimental Validation of Modelled Fluid Forces in Fast Switching Hydraulic On/Off Valves

A prototype of a fast switching valve for a digital hydraulic machine has been designed and manufactured. The valve is composed of an annular seat plunger connected with a moving coil actuator as the force producing element. The valve prototype is designed for flow rates of 600 l/min with less than 0.5 bar pressure drop, and the models predicts a switching time in the region of a millisecond with a travel length of 3.5 mm using an average power of 250 W. The total machine efficiency when neglecting losses not related to the valves is above 98 %. The objective of this paper is to experimentally validate a transient computational fluid dynamics (CFD) model of the fluid forces that oppose the valve plunger when moving rapidly through the surrounding oil during switching. Due to the fast switching of the valve, the fluid forces which oppose plunger movement increases drastically as the plunger approaches the closed position. Fast switching is essential for digital hydraulic machines to achieve a high efficiency. As the fluid forces influences the response obtaining an accurate model is important. To validate the model tests are carried out on the prototype where the valve is closed, both with and without oil surrounding the valve plunger. The transient CFD model is then verified by comparing measurements with simulation results.