Emission control - K Series 1.8 (EVAP Control): Description and operation

EVAP Control

The EVAP control system reduces the level of hydrocarbons released into the atmosphere by fuel vapour venting from the fuel tank. The system comprises a two way valve, a vapour separator, an EVAP canister, a purge valve and interconnecting vent pipes. The vent pipes are connected to the system components and the fuel tank by quick release connectors. On the fuel tank, the vent lines are connected to three roll over valves. The roll over valves are float valves that prevent fuel from entering the vent pipes due to fuel slosh or if the vehicle overturns.

Fuel vapour, generated in the tank as the fuel heats up, is stored in the tank until the pressure is sufficient to open the outward venting side of the two-way valve. When the two-way valve opens, excess pressure is released through the vapour separator and the EVAP canister to atmosphere. The vapour separator and the EVAP canister remove fuel from the vapour and relatively fuel free air vents to atmosphere. When the fuel tank cools and vapour pressure decreases below ambient pressure, the two-way valve opens and outside air is drawn through the EVAP canister and vapour separator into the tank.

Some of the fuel removed from the vapour vented from the fuel tank is stored in the EVAP canister. Since there is a limit to the volume of fuel that can be stored in the EVAP canister, when the engine is running fuel is purged from the EVAP canister, through the purge valve, and burned in the engine.

EVAP System Schematic

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M17 0311

1 Vapour separator 2 EVAP canister 3 ECM 4 Throttle 5 Purge valve

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6 Fuel tank 7 Roll over valve 8 Two-way valve 9 Fuel filler cap 10 Filler tube

Two-way Valve The two-way valve is installed in the vent pipe from the tank, next to the fuel tank pump unit. The two-way valve opens, to release pressure from the fuel tank, at 0.018 to 0.050 bar (0.26 to 0.73 lbf/in²). Air is allowed to flow back into the fuel tank, as the pressure in the tank decreases, through a non return valve within the body of the two-way valve.