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Purge Valves are part of the vehicle's Evaporative Emission Control (EVAP) system.

  • The system stops fuel vapors in the fuel tank from escaping into the atmosphere. The EVAP system holds fuel vapors from the fuel tank and temporarily stores them in the charcoal canister.
  • The canister may have a vacuum-operated vapor vent valve or purge valve when the engine is running, intake-manifold pulls up the purge valve diaphragm. This shuts off the vapor flow from the canister so little fuel vapor can enter. When the engine stops, a spring opens the valve and fuel vapor flows freely into the canister. 
  • Some evaporative control systems have the purge valve in the purge line. It connects to the throttle body and discharges vapor just above the throttle valve into the intake air. Regardless of how canister purging is controlled the purpose is to burn the trapped fuel vapor.