Evaporative Emissions: ORVR: Operation

The emission control principle used in the ORVR system is that the fuel flowing into the fuel filler tube (3) creates an aspiration effect which draws air into the fuel filler tube (3). During refueling, the fuel tank (2) is vented to the EVAP canister (7) to capture escaping vapors. With air flowing into the fuel filler tube (3), there are no fuel vapors escaping to the atmosphere. Once the refueling vapors are captured by the EVAP Canister (7), the vehicle's computer controlled purge system draws vapor out of the canister for the engine to burn. The vapor flow is metered by the EVAP purge solenoid (6) so that there is minimal or no impact on driveability or tailpipe emissions.

As fuel starts to flow through the Fuel Filler Tube (3), it opens the normally closed Fuel Filler Tube Check Valve (4) and enters the fuel tank (2). Vapor or air is expelled from the tank through the tank vent/rollover valves (1) to the EVAP canister (7). Vapor is absorbed in the canister (7) until vapor flow in the lines stops, either following refueling shut-off or by having the fuel level in the tank rise high enough to close the check valves in the tank vent/rollover valves (1). The fuel filler tube (3) also incorporates a fuel tank overfill check valve (5). As fuel level rises, the fuel tank overfill check valve (5) seals the in-tank end of the fuel filler tube (3). This largely prevents overfilling of the fuel tank (2). At this point in the fueling of the vehicle, the tank pressure increases, the fuel filler tube check valve (4) closes (preventing tank fuel from spitting back at the operator), and fuel then rises up the filler tube (3) to shut-off the dispensing nozzle.