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.
Purpose
This paper aims to propose a new scuffing model caused by the depletion of additives in boundary lubrication condition.
Design/methodology/approach
The differential equation governing the distribution of additive content in the fluid film was used. This formula was derived from the principle of mass conservation of additives considering the consumption due to surface adsorption of wear particles. The occurrence of scuffing was determined by comparing the wear rate of the oxide layer with the oxidation rate.
Findings
If the additive becomes depleted while sliding, the scuffing failure occurs even at a low-temperature condition below the critical temperature. The critical sliding distance at which scuffing failure occurred was suggested. The experimental data of the existing literature and the theoretical prediction using the proposed model are shown to be in good agreement.
Originality/value
It is expected to be used in the design of oil supply grooves for sliding bearings operating under extreme conditions or in selecting the minimum initial additive concentration required to avoid scuffing failure under given contact conditions.
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