47-0030 Fuel Tank Air Admission and Ventilation
47-0030 Fuel Tank Air Admission And VentilationA. All models
40 Filler cap
41 Seal
42 Closing clamp
43 Compression spring
44 Filler neck
Filler cap
The fuel evaporation gases can escape through the filler cap at an overpressure of 100-300 mbar (emergency ventilation, e. g. if vent line crimped or vent valve faulty).
If the system is operating properly, a pressure of 30 - 50 mbar is produced in the fuel tank.
NOTE: As a phased implementation measure, the filler cap is provided with a plastic slide ring to facilitate operation. The filler cap (40) slides on this ring with minimal friction and locks in both end positions.
Function of vent valve (51)
If a pressure of 30-50 mbar is exceeded in the fuel tank, the vent valve (4) opens and the fuel vapours flow to the active charcoal filter.
NOTE: The pressure in the fuel tank improves fuel supply and counteracts the formation of vapour bubbles.
Vent valve (51) open to active charcoal filter
Vent valve open if overpressure exists.
Ventilation to atmosphere (without fuel evaporation system).
1 Compression spring
2 Valve housing
3 Spring retainer
4 Vent valve
5 Valve plate
6 Air admission valve
7 Connection fitting
A Active charcoal filter connection
B Fuel tank connection
If a vacuum of 1-16 mbar is produced in the fuel tank, the air admission valve (6) opens. On vehicles fitted with fuel evaporation system, air is admitted to the fuel tank through a cup seal on the left wheelhouse panel and through the active charcoal filter (see 47-0200).
Vent valve (51) open to fuel tank
B. Model 107
Function diagram fuel tank air admission and ventilation
50 Fuel tank
51 Vent valve
52 Active charcoal filter
52/1 Air admission cap
53 Regeneration valve
55 Fuel expansion tank
64 Pipes
64/1 Vent line
A separate fuel expansion tank (55) is positioned above the fuel tank. The fuel expansion tank (55) is connected to the fuel tank (50) by 5 pipes (64). Depending on fuel level and fuel temperature in the tank, these pipes may act as overflow, discharge or vent lines.
The vent line (64/1) runs from the fuel expansion tank (55) through the tail floor panel to the vent valve (51).
Air is admitted to and released from the fuel tank through the air admission cap (52/1) of the active charcoal filter (52).
On vehicles without fuel evaporation system, air is admitted to the fuel tank and released from the tank by the vent valve (51) directly to atmosphere.
For function of fuel evaporation system see 47-0200.
C. Models 124, 126 and 201
Function diagram fuel tank air admission and ventilation
50 Fuel tank
51 Vent valve
52 Active charcoal filter
52/2 Cup seal
54 Central pipe
54/1 Interruption vessels
64/1 Vent line
In the case of the sheet steel fuel tank, the ventilation system consists of a central pipe (54) with interruption vessels (54/1).
The interruption vessels prevent the fuel escaping along the vent line (64/1). The vent line (64/1) runs from the central pipe to the vent valve (51).
Air is admitted to and released from the fuel tank (50) via the cup seal (52/2) and the active charcoal filter (52).
On vehicles without fuel evaporation system, air is admitted to the fuel tank and released from the fuel tank by the vent valve (51) directly to atmosphere.
Note regarding plastic fuel tank
The integrated air admission chamber above the plastic fuel tank replaces the central pipe and performs the air admission and release function.
D. Model 126 with ASR first version and special protection vehicles
Function diagram fuel tank air admission and release
50 Fuel tank
51 Vent valve
52 Active charcoal filter
52/2 Cup seal
54 Central pipe
54/1 Interruption vessels
64 Vent line
On vehicles with ASR the active charcoal filter (52) is positioned below the rear floor. Air is admitted to the fuel tank (50) through the air-permeable floor (arrows) of the active charcoal filter (52). The cup seal in the left front wheelhouse is discontinued. The line (A) runs to the regeneration valve.
E. Model 129
Function diagram fuel tank air admission and release, model 129
36 70°C thermo valve (black with white surround)
45 Throttle valve body
50 Fuel tank
51 Vent valve
52 Active charcoal filter
52/3 Front, left side member
53 Regeneration valve
The vent line (64/1) runs from the fuel tank (50) through the vent valve (51) to the active charcoal filter (52).
Air is admitted from the front, left side member (52/3), air is released through the fuel evaporation system.
Location of components
Vent valve (51)
The vent valve (51) and the fuel return line (70) are only accessible if the exhaust has first of all been detached at the rubber rings (49-100) and the left input shaft has been disconnected at the inner connection flange (35-620).
Active charcoal filter (52)
Positioned in front, left wheelhouse behind front wheel.
To perform repair work, remove inner fender, install (88-130).
52 Active charcoal filter
64/1 Vent line
A Regeneration line
B To fuel tank