On-Board Refueling Vapor Recovery EVAP System
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The basic elements forming the ORVR system operation are as follows when fuel is dispensed: See Fig 1 and Fig 2 .
- The fuel filler pipe forms a seal to prevent vapors from escaping the fuel tank, while liquid is entering the fuel tank (liquid in the one inch diameter tube blocks vapors from rushing back up the fuel filler pipe).
- A fuel vapor control valve controls the flow of vapors out of the fuel tank (valve closes when liquid level reaches a height associated with the fuel tank usable capacity). This valve accomplishes the following:
- Limits the total amount of fuel that can be dispensed into the fuel tank.
- Prevents liquid gasoline from exiting the fuel tank when submerged (and also when tipped well beyond a horizontal plane as part of the vehicle roll-over protection in road accidents).
- Minimizes vapor flow resistance during anticipated refueling conditions.
- Fuel vapor tubing connects the fuel vapor control valve to the EVAP canister. This routes the fuel tank vapors (displaced by the incoming liquid) to the EVAP canister.
- A check valve in the bottom of the fuel filler pipe prevents liquid from rushing back up the fuel filler pipe during the liquid flow variations associated with the filler nozzle shut-off.
Between refueling events, the EVAP canister is purged with fresh air so that it may be used again to store vapors accumulated during engine soaks or subsequent refueling events. The vapors drawn off of the carbon in the EVAP canister are consumed in the engine.