An oil pressure regulating valve limits oil pressure to a predetermined value, depending on the installation. [Figure 6-6] This valve is sometimes referred to as a relief valve but its real function is to regulate the oil pressure at a present pressure level. The oil pressure must be sufficiently high to ensure adequate lubrication of the engine and its accessories at high speeds and powers. This pressure helps ensure that the oil film between the crankshaft journal and bearing is maintained. However, the pressure must not be too high, as leakage and damage to the oil system may result. The oil pressure is generally adjusted by loosening the locknut and turning the adjusting screw. [Figure 6-10]On most aircraft engines, turning the screw clockwise increases the tension of the spring that holds the relief valve on its seat and increases the oil pressure; turning the adjusting screw counterclockwise decreases the spring tension and lowers the pressure. Some engines use washers under the spring that are either removed or added to adjust the regulating valve and pressure. The oil pressure should be adjusted only after the engine’s oil is at operating temperature and the correct viscosity is verified. The exact procedure for adjusting the oil pressure and the factors that vary an oil pressure setting are included in applicable manufacturer’s instructions.
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