Abstract
An oil hydraulic pilot relief valve has been empirically investigated to fully understand its static performance. Constriction components which dominate the flow in the valves have been individually examined in detail, revealing that the static relation between the pressure drop, flow rate 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 flow rate and the fluid viscosity and inversely proportional to the square of the opening area. The new characteristic equation has proved to consistently predict the experimental findings in which the rise in oil temperature results in an increase in the piston displacement, but causes little changes as regards regulated pressure. It has also turned out that, contrary to conventional preconception, the fluid force exerted on a poppet is negligible. On the other hand, that regarding a piston can be influential and works to increase the pilot flow.
