On-board refueling vapor recovery function - GF47.10-P-3004MMA

ENGINE 157.9 in MODEL 212, 218 with CODE 494 (US version) 

ENGINE 278.9 in MODEL 207, 212, 218 with CODE 494 (US version) 

Schematic diagram 

Fig 1: On-Board Refueling Vapor Recovery Function Diagram

Courtesy of MERCEDES-BENZ USA

On-board refueling vapor recovery, general points 

The law requires, that the refueling gases in the vehicle are collected (Onboard Refueling Vapor Recovery).

Fuel and refueling vapors must be separated in order to prevent fuel from flowing into the activated charcoal canister due to inappropriate refueling or a defective nozzle.

Function sequence for on-board refueling vapor recovery 

Thanks to its shape, the fuel filler neck functions as a suction jet pump. The fuel out from nozzle thus accelerates in the filler neck and the air around the nozzle is suctioned into the fuel tank.

As a result of this air intake, the refueling vapors are not able to rise and escape into the atmosphere at the fuel filler neck.

The fuel vapors flow through the aeration/vent valves and aeration/vent lines to the activated charcoal canister, where they are stored. The fueling/limiting/vent valve also prevents overfilling by closing off the aeration/vent line.

Rollover valves are integrated at the top of the aeration/vent valves. If fuel gets into aeration/vent valves, they close off the aeration/vent lines to the activated charcoal canister, thus preventing fuel from flowing into the activated charcoal canister.

The aeration/vent valves can also close briefly if there is sudden braking or acceleration, or when cornering.

When purging is enabled, the fuel vapors are drawn off through the purge line by the engine, and burnt together with the fuel gases from the activated charcoal canister.