On-Board Refueling Vapor Recovery System (ORVR)

On-Board Refueling Vapor Recovery System (ORVR)
The ORVR system controls the volume of vaporized fuel released into the atmosphere from the fuel tank during fuel replenishment. Additionally, the system provides optimum fuel line diameter to prevent vaporized fuel from reaching The atmosphere through the fuel neck during replenishment. Vaporized fuel is instead purged to the canister through the shut-off-valve (SOV). Purge volume varies with conditions inside the fuel tank.

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.

Component Description

Filler line
Pipe and hose through which the new fuel from the fuel nozzle passes to reach the fuel tank.

Vapor line
Delivers vaporized fuel from the fuel tank through the rollover valve to the vent line.

Vent line
Delivers vaporized fuel from the fuel tank to the canister.

Recirculation line
Returns vaporized fuel from the filler neck to the fuel tank. It allows a controlled volume of vaporized fuel to pass to the filler neck. The volume of returned fuel is determined by the size of the orifice built-in to the recirculation line.

Control line
Equalizes the pressure in the fuel tank and the filler neck.

Check valve
Prevents spit-back when fuel flow is stopped.

Shutoff valve (SOV)
Closes when the fuel level in the fuel tank is nearly full (float). When open, it allows vaporized fuel to pass to the canister.

Diaphragm (Liquid and vapor separator)
Operates during fuel replenishment to open the vent line. During vehicle operation, it does not operate and the vent line remains closed.

Relief valve
Built-in to the filler cap. If pressure in the fuel tank rises or falls abnormally, it opens to bleed excess fuel tank pressure into the atmosphere or closes to prevent air from being drawn into the fuel tank.

Rollover valve
Allows vaporized fuel to be passed to the canister.