Static characteristics of a piston-type pilot relief valve

Abstract

Abstract

An oil hydraulic pilot relief valve was empirically investigated to fully understand its static performance. Constriction components which dominate the flow in the valve were individually examined in detail, revealing that the static relation between the pressure drop, flowrate and opening area for a constriction can be represented, not by the traditional hydraulic orifice equation which has always been used for the purpose, but by a new one including an additional pressure loss proportional to the flowrate and the fluid viscosity as well as inversely proportional to the square of the opening area. The new characteristic equation has consistently proved to predict the experimental findings in which a rise in oil temperature results in an increase in the piston displacement but causes little change as regards regulated pressure. It also turns out that, contrary to common preconceptions, the fluid force exerted on a poppet is negligible in the present case. It was discovered, on the other hand, that fluid force on a piston can be influential and works to increase the pilot flow.