Evaporative Check Valve: Description and Operation

Evaporative Emission Control System:

An evaporative emission control system is used to prevent emission of fuel vapor.

The vapor generated in the fuel tank while driving or the engine at a stop passes through a 2-way check valve and enters the charcoal canister where the charcoal absorbs and stores the fuel vapor.

Only when the following conditions are all satisfied, throttle body vacuum is applied to canister purge control valve and the valve opens.


^ Engine is running.

^ Engine cooling water temperature is high. (Engine is warmed up)

^ Throttle valve opens larger than idle position.


As a result, fuel vapor in the canister is sucked into intake manifold through purge control valve and purge line.

In this state, the canister is purged or cleaned by air drawn through the filter at the bottom of the canister.

When engine cooling water temperature is low, the vacuum signal line communicates with atmosphere through BVSV.

Therefore, throttle body vacuum is not applied to purge control valve, and the valve is closed. In this state, the canister is not purged.

The 2-way check valve is provided to keep the pressure in the fuel tank constant. When the pressure in the fuel tank becomes positive and reaches its specified value, it opens the valve to let the vapor flow into the charcoal canister. On the other hand, when the pressure in the fuel tank becomes negative and reaches its specified value, it opens the valve to let the air flow into the fuel tank.