On-Board Refueling Vapor Recovery (ORVR) Evaporative Emission (EVAP) System

The basic elements forming the ORVR system are as follows:

• 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.
• The fill limiting vent valve (FLVV) controls the flow of vapors out of the fuel tank. The valve closes when the liquid level reaches a height associated with fuel tank usable capacity. The 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, as well as when tipped well beyond a horizontal plane as part of the vehicle rollover protection in road accidents.
  • - Minimizes vapor flow resistance during anticipated refueling conditions.
• Fuel vapor tubing connects the FLVV to the EVAP canister. This routes the fuel tank vapors, displaced by the incoming liquid, to the EVAP canister.
• A check valve in the filling system prevents liquid from rushing back up to 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 to again store vapors accumulated during engine soaks or subsequent refueling events. The vapors drawn off of the carbon in the EVAP canister are consumed by the engine.