Check & Relief Valve

ENGINE NOT RUNNING
The fuel vapor taken up into the vapor separator is fed into the check and relief valve. When the pressure of the fuel vapor becomes as high as 0.2-0.6 in. Hg, the check valve opens, allowing the vapor into the engine crankcase. While the check valve is held open, the valve at the air cleaner side remains closed preventing flow of vapor into the air cleaner.

ENGINE RUNNING
When a vacuum is developed in the fuel tank or in the engine crankcase and the difference of pressure between the relief side and fuel tank or crankcase becomes 0.2-0.6 in. Hg, the relief valve opens, allowing ambient air from the air cleaner into the fuel tank or engine crankcase.
This ambient air replaces the vapor within the fuel tank or crankcase, bringing fuel tank or crankcase back into atmospheric pressure condition.