System Description

At the start of fuel replenishment, the check valve opens to allow fuel to flow into the fuel tank. As the fuel enters the tank, the pressure in the tank increases. To equalize the pressure in the tank and the filler neck, the diaphragm (liquid and vapor separator) opens. When the pressure is equalized, the fuel line is completely filled with fuel. This effectively creates a seal that prevents the escape of vaporized fuel from the fuel tank through the fuel line into the atmosphere.

Vaporized fuel trapped in the fuel tank passes through the shut-off valve and the vent line to be absorbed by the canister. At this time, an additional recirculation line allows the return of a controlled volume of vaporized fuel to the filler neck area. The vaporized fuel moving through the recirculation line prevents the entry of outside air into the fuel tank. This reduces the vaporized fuel volume and reduces fuel tank pressure to allow smooth fuel replenishment.

A float inside the fuel tank closes the shut-off valve when the fuel level rises beyond a specified point. When the shut-off valve closes, fuel tank pressure immediately increases. This increase in pressure is detected by a sensor on the fuel gun. Fuel flow is stopped. The check valve operates in response to the changing tank pressure to prevent fuel spit-back when flow from the gun stops. The rollover valve (ROV) also acts to prevent overfilling by controlling orifice diameter. It allows measured amounts of vaporized fuel to flow to the canister resulting in a gradual decrease in fuel tank pressure.

The diaphragm closes after the filler cap has been replaced and pressure in the fuel tank and filler neck has equalized.

Vaporized gas that forms in the fuel tank during vehicle operation is drawn into the canister through the rollover valve, the evaporator line, and the vent line.

Rollover valve and/or shutoff valve failure may result in a significant change in fuel tank pressure. The relief valve in the filler cap opens to allow excess pressure to escape to the atmosphere or outside air to be drawn into the tank.