Carbon Canister

Evaporative fumes from fuel tank are vented through hose(s) into a canister containing activated carbon. Activated carbon absorbs and holds fuel vapors when engine is not operating. When engine is started and engine speed is greater than idle (purge at idle would cause too rich a mixture), engine vacuum draws fuel vapors from canister into engine. A vacuum canister purge valve or thermostatic vacuum switch regulates vapors through this purge line.

Carbon canisters are open in design. When the engine is started, engine vacuum draws outside air into canister either through the top or bottom, and then through a filter in bottom of canister. This helps to purge vapors from the activated carbon.