Running Loss With ORVR System
The system has the following features:
- on-board refueling vapour recovery (ORVR) to reduce the fuel vapour vented directly to atmosphere from the filler nozzle when refueling.
- two charcoal canisters are connected in series to reduce the concentration of fuel in vapour vented to atmosphere.
- a tank pressure sensor and canister close valve are fitted to allow the on-board diagnostic facility to test for leaks in the fuel and evaporative system.
The canister close valve is a solenoid operated device controlled by the ECM. The valve is normally open and is closed only during the leak test sequence.
The fuel pressure sensor is fitted to the evaporative loss flange and provides a voltage to the ECM which is proportional to tank vapour pressure.
Operation of ORVR System
The ORVR system enables fuel vapour generated during re-fueling to be collected by the charcoal canisters. During normal running of the vehicle, the vapour is collected and purged in the same way as for non-ORVR systems.
The ORVR system features are:
- Narrow fuel filler pipe and tank check valve.
- Fuel level vent valve (FLVV) fitted to the evaporative flange and consisting of a two stage shut-off valve with rollover protection and a pressure relief valve.
- Grade vent valve with rollover protection, fitted to the evaporative flange and with an outlet pipe connected to the FLVV vapour outlet pipe.
- Large bore vapour vent pipes.
The fuel filler pipe has a reduced diameter between the nozzle guide and the tank, providing a liquid seal when re-fueling and preventing the fuel vapour venting directly to atmosphere. There is no breather tube fitted between the tank and the filler nozzle. To prevent spit back when re-fueling, a check valve is fitted at the lower end of the filler pipe inside the tank (see image).
During re-fueling, the tank is vented to atmosphere via the fuel level vent valve (FLVV), large bore vapour pipes and the charcoal canisters. The FLVV incorporates a float valve which is closed by the rising fuel level, creating a back pressure and causing the fuel delivery to stop. In the closed position, the FLVV also sets the fuel level.
With the FLVV closed (tank full), any increase in pressure or overfilling is relieved by a separate rollover protected grade vent valve. The outlet from this valve feeds into the main FLVV vapour outlet pipe, bypassing the closed FLVV.
When the fuel level is below full, the FLVV opens to allow unrestricted venting via the canisters.
A pressure relief valve is incorporated into the FLVV assembly and has an outlet pipe to the filler nozzle. If a blockage or other restriction (eg, canister close valve failing in the closed position) occurs in the vapour vent system, the pressure relief valve opens to allow venting to atmosphere via the filler nozzle guide and fuel filler cap.
Canister purge operation is as described in Evaporative Emissions Control System (EVAP).
Filler Tube and Check Valve:
The fuel filler cap is the same as that used on non-ORVR systems.
The check valve assembly is a push fit into the end of the fuel filler tube and is accessible with the evaporative flange removed. The valve has a light spring loading and opens under the inflow of fuel.
ORVR Evaporative Loss Flange Assembly:
The evaporative loss flange assembly is fitted to the top of the tank via a seal and locking ring arrangement identical to that used for non-ORVR systems. The assembly is removable complete with the fitted components.
The fuel level vent valve (FLVV) is mounted in the ELF assembly via a bayonet fitting: it is turned approximately 90 ° clockwise to release. The grade vent valve and pressure sensor are push in fits via sealing grommets: note that, due to the tight fit, removal of these components may require cutting the grommets. The fuel pump connector is push fitted and crimped into a location tube on the underside of the flange.
Canister, CCV and Fittings:
The canisters are fixed to the underside of the vehicle either directly or via semi-enclosed mounting brackets. Two fixing bolts are used at the front of the canister (or bracket) and a single rear bolt supports the canister and the canister close valve (CCV).
The vapour pipes to the canisters, other than the CCV, use multi-tang connectors which are push fitted and pulled out without the use of tools.
The canister close valve has a stub pipe with "O" ring seal which is a simple push fit into the canister. A mounting bracket on the canister close valve enables it to be secured to the underbody via the canister rear mounting bolt.
A hose connects the CCV to the bracket mounted adaptor into which the vent system air filter is screwed.