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

ENGINE 276.8 in MODEL 207, 212 as of model year 2014 with CODE 494 (US version) 

ENGINE 276.8 in MODEL 218 as of model year 2015 with CODE 494 (US version) 

ENGINE 276.9 in MODEL 204, 207, 212 (except 212.095), 218 with CODE 494 (US version) 

Fig 1: On-Board Refueling Vapor Recovery Flow Diagram

Courtesy of MERCEDES-BENZ USA

Schematic diagram 

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 any inappropriate refueling or a defective nozzle.

Function sequence for on-board refueling vapor recovery 

Owing to its form, the 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 vapor are not able to gather at the filler neck and are able to escape.

The fuel vapors flow through the aeration/vent valves and aeration/vent lines to the activated charcoal canister, where they are stored. The fueling, pressure limitation valve and the vent valve also prevents any 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.