On-Board Refueling Vapor Recovery (ORVR) System
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On some vehicles, ORVR system is used to recover fuel vapors into EVAP canister that are generated during refueling. ORVR system consists of fuel inlet pipe, overfill check valve and EVAP canister.
When fuel tank cap is removed, atmospheric pressure is applied to port "A" on overfill check valve. See Fig 1. Overfill check valve may also be referred to as ORVR-OCKV or fill check valve. When fuel flows into fuel inlet pipe and fuel tank, pressure in fuel tank increases. Increased pressure in fuel tank causes valve "B" on overfill valve to open, allowing fuel vapors to flow into EVAP canister. When fuel tank is full, valve "C" closes, shutting off vapor flow to EVAP canister.