Page 126 - Vauxhall 20-60 H.P. (R Type) Chassis Shop Manual

VAUXHALL 20-60 SHOP MANUAL

GROUP XIV

PETROL SUPPLY SYSTEM

AUTOVAC ( Before R 4237 )

SECTION Description — The Autovac Petrol Feed System employs a small tank
560 installed under the bonnet, and is connected by metal tubing to the petrol
tank mounted at the rear of the chassis, also to the induction manifold and
carburettor.

The engine draws its supply of petrol through the carburettor by reason
of the pumping action of the pistons, and it is this same pumping action
transmitted to the Autovac tank through its connection with the induction
manifold that draws petrol along the pipe connecting the Autovac with the
petrol tank.

The Autovac consists of two chambers — one inside the other; the inner
one is the filling chamber from the main tank and the outer one is the
emptying chamber to the carburettor.

At the bottom of the inner chamber is a drop valve. The suction of the
pistons on the intake stroke creates a vacuum in the inner chamber and this
vacuum closes the valve between the two chambers and also sucks up the
petrol from the main supply tank into this inner chamber.

As the petrol flows into the chamber it raises a valve float. In the event of the
float becoming punctured, the Autovac continues to function unimpeded.

When the valve float has risen to a certain point, it operates a valve which
shuts off the suction and at the same time opens an air valve. This admission
of outside air releases the vacuum suction, causing the valve leading to the
emptying chamber to open.

Petrol then flows to the emptying chamber which is always open to the
outside air. Consequently there is always an uninterrupted supply of petrol
to the carburettor, providing the Autovac tap is open.

TO DISMANTLE

SECTION – Disconnect main petrol supply pipe, and suction pipe from top of
561 Autovac. -Remove all screws round flange of top cover.

– Run the blade of a knife carefully around between flange of top cover
and body, to separate washers without damaging them. The top cover
can then be lifted off complete with float and top valves.

The inner chamber can afterwards be lifted out, but care must be taken not
to damage the flange.

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