What is the purpose of the lube supply check valve?

The purpose of the lube supply check valve is primarily to prevent oil from draining into the sumps when the engine is off. This is important because, during engine shutdown, the oil should remain in the lubrication system rather than flowing back down into the sump. By doing so, the check valve maintains an adequate oil supply for starting the engine again, ensuring that all moving parts receive proper lubrication immediately upon restart. This function helps protect engine components from wear and damage that could occur if they were to start without adequate lubrication present.

The other options, while related to the lubrication system, do not accurately describe the main function of the lube supply check valve. For instance, regulating oil flow to the pump involves different mechanisms, and filtering impurities is handled by oil filters in the system, while allowing excess oil to escape is managed by relief valves or other components designed for that purpose.