In an automobile, a canister purge solenoid circuit is part of an evaporative emission control system, which prevents hydrocarbons in gasoline vapor from escaping into the atmosphere. Gasoline vapors from the fuel tank are trapped in a charcoal canister and periodically purged into the intake manifold of the engine.
A canister purge solenoid -- a coil of wire wound around an iron core -- is connected into a hose between the charcoal canister and the intake manifold. A programmable control module (PCM) energizes the coil, causing the iron core to move inside the coil.
Typically, gasoline vapors from the fuel tank are stored in the charcoal canister until the engine speed reaches 1,100 rpm and the vehicle speed reaches 20 mph. At this point, the operation of the canister purge solenoid allows negative pressure, or vacuum, to purge vapors from the canister.
The charcoal canister also contains a trap that collects condensed fuel vapor or liquid fuel. The trap prevents liquid fuel from contaminating the charcoal.
