How Does an EVAP Purge Valve Work?

Written by andrea stein | 13/05/2017
How Does an EVAP Purge Valve Work?
An EVAP purge valve sends fuel vapours into the vehicle engine. (sand car engine image by Clarence Alford from

Fuel injection refers to a system designed to mix fuel with air in a vehicle's internal combustion engine. Part of this system involves the evaporative purge system, which uses an EVAP purge valve to direct fumes into the engine.

Evaporative Purge System

The evaporative purge system consists of a container and valve. The charcoal container has a opening on its bottom side which enables air to enter the purge system. The charcoal traps fuel vapours, which are sucked into the intake manifold when the engine activates. These vapours are able to enter the intake manifold via the EVAP purge valve.

EVAP Purge Valve Operation

A flap in the EVAP purge valve body restricts the motion of fluid and is magnetically attracted by the voltage applied via the valve's electrical contacts. The flap is attracted to a coil in the evaporative purge system, which closes the valve and blocks the passage of fluids.

Charcoal Buildup

Charcoal build-up between the outlet and valve flap can stop the flap from producing the necessary motion to close the valve. This results in unmeasured air entering the engine, which negatively impacts the spark plugs and can lead to rough engine idling.

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