Canister Control Valve

There are 2 types of canister control valves. See Figure . The first type of valve performs function as fuel bowl vent and canister purge. When engine is not running, spring tension holds valve open allowing venting of float bowl. When engine is running, manifold vacuum pulls plunger up to close valve.

The second type of valve performs function of both vapor vent valve and purge valve. When engine is running, manifold vacuum from PCV system pulls lower diaphragm upward. This turns off venting of carburetor float bowl.

When engine is running above idle speed, control vacuum pulls upper diaphragm upward. This allows purging of canister through PCV system.