Relief valve

A relief valve is a component that controls the maximum oil pressure inside lubrication circuits.
The higher the engine speed, the higher the pressure of the oil discharged by the oil pump. Because engine oil viscosity increases as the temperature decreases, resistance will be high if the oil temperature is low, which will in turn cause engine pressure to rise. If the engine is revved high while the oil temperature is low, oil pressure will rise significantly. Relief valves are embedded in components such as the gear case and open when the oil pressure in the lubrication circuit reaches the preset relief valve pressure after pumping. Excess oil is discharged in this manner, enabling the maximum oil pressure inside lubrication circuits to be controlled.