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Brief description, ORVR

Brief description, ORVR

Cars concerned

All Saab 900 M98- for USA and Canada.

Legal requirements

ORVR, Onboard Refuelling Vapour Recovery, is a legal requirement which comes into force on September 1, 1997 in the United States. It governs hydrocarbon emissions in connection with refuelling.

All hydrocarbons formed when refuelling must be recovered by the car and not released into the atmosphere. A maximum of 0.2 grammes of hydrocarbons per gallon of fuel may be permitted to escape when filling up with 4-10 gallons of fuel per minute. It must be possible to fill up 95%% of the total tank capacity at a rate of 4-10 gallons of fuel per minute without the fuel pump nozzle shutting off prematurely and necessitating subsequent topping up.

Leakage larger than that caused by a hole corresponding to a diameter of 1 mm must be detected by the system.

System description

Fuel is poured into the tank through the filler pipe, passing a non-return valve before actually entering the tank. The fuel presses out the gaseous hydrocarbons and air in the tank, causing them to pass through the float valve and into the evaporative emission canister. The hydrocarbons are absorbed in the evaporative emission canister and the air escapes through the shut-off valve.

The float valve closes at a certain level (about 95%%). The pressure in the tank then increases and the non-return valve also closes. The fuel now rises in the filler pipe and the fuel pump nozzle shuts off when the fuel reaches it.

The volume of vapour remaining in the tank passes slowly through the rollover valve and into the evaporative emission canister. As the vapour disappears, fuel runs down from the filler pipe which empties.

When the engine is subsequently started, the evaporative emission canister is gradually purged as air is sucked into it through the shut-off valve. The hydrocarbon/air mixture passes through the evap canister purge valve and into the engine where it is burnt.