This valve type is used to perform the following functions:
prevent liquid fuel flowing out if the car has a rollover accident.
allow fuel vapours to be vented to the separator.
allow the tank to be vented if a vacuum develops inside.
This valve consists of a case and float/needle valve.
Operation
Briefly, the valve works as follows, depending on fuel level in the tank.
Full tank.
If the tank is full, float (2) blocks hole (3) to prevent liquid fuel from reaching the separator.
Intermediate fuel level.
When the level of fuel in the tank drops, float (2) falls and its side tabs (4) rest on the slots in valve case (1) to open hole (3).Gases can reach the hole through the ring section betwen float (2) and the valve case inner seat (1).This allows fuel vapours to leave the tank and reach the separator.The tank may be ventilated through the same circuit when the pressure inside is lower than the external pressure.
Seal in the case of roll over.
If the vehicle rolls over, regardless of tank fuel level, float (2) is held against hole (3) by its own weight and that of the fuel. This prevents a dangerous outflow of fuel to the activated carbon filter and the attendant risk of the vehicle catching fire.
FUEL VAPOUR FILTER (CANISTER).
Specifications.
Type.
This is fitted to the right rear wing and consists of an activated carbon filter element that absorbs the fuel vapour from the separator.One-way valve (3) allows outside air inside (flushing). This flows over the carbon granules to remove fuel vapours and convey them through the outlet (1) to the engine intake when fuel vapour solenoid (4) is open.
FUEL VAPOUR SOLENOID VALVE.
Specifications.
Type.
This is fitted directly to the canister and controlled by the injection control unit on the basis of a predetermined strategy (See assembly 1056B MULTI-POINT INJECTION (MPI) SYSTEM).The function of the valve is to allow fuel vapour stored in the canister to flow through to the engine intake.When inactive, the solenoid is closed and prevents fuel vapours from enriching the mixture excessively.
OPERATION.
General remarks.
When electromagnet (3) is excited, it attracts valve core (1) that overcomes the load of spring (2) to bring the canister into communication with the intake manifold.
MULTIFUNCTION VALVE
Operation.
Multifunction valve functions are as follows:
to prevent excessive pressure in the tank.
to prevent vacuums in the tank.
to prevent fuel flowing out in the case of rollover.
Excess pressure in tank.
Tank pressurisation is maintained between 30 - 45 mbars using a fluorosilicone rubber valve resting on a sealing edge.The valve is supported by a stainless steel plate and held in place by a counterspring.When pressure in the tank exceeds a specified value, it overcomes spring resistance and allows the valve to rise so that the fuel vapours can flow out toward the canister.When pressure drops to within specified limits, the valve recloses.
Vacuum in reservoir.
Under certain vehicle service conditions, a vacuum may develop in the tank due to:
heat fluctuations.
fuel consumption.
In this case, the function of the valve is to admit air to restore pressure in the tank.A fault in this function may lead to juddering or stalling due to the difficulty of supplying the pump with fuel.This function is performed by the goosebill valve formed by the fluorosilicone seal.
Escape of fuel in the case of roll over.
The rollover function prevents fuel emerging from the tank in the case of rollover or if the vehicle is sharply tilted.Normal vehicle operation (cornering, acceleration, braking etc.) sometimes causes the fuel to slop over into the canister.The highly sensitive rollover valve prevents this spillage.The roll-over closure angle is less than 33°.
SAFETY AND VENTILATION VALVE
Operation
This valve is built into the fuel filler cap and performs the following functions according to the pressure level in the tank.
Excess pressure in tank
When tank pressure exceeds a specified level, it acts on plate (2) and overcomes the load of spring (1) to allow the excess vapours to be vented to the outside.
Vacuum in reservoir
When an excessive vacuum builts up in the tank due to fuel consumption, this overcomes the load of spring (4) and moves valve (3) to allow air to be admitted.
