Page 137 - Vauxhall 20-60 H.P. (R Type) Chassis Shop Manual

VAUXHALL 20-60 SHOP MANUAL

The head shown in ( b ) is mounted on the instrument board. It is simply a
U-tube containing a special heavy red liquid. The front half of the U-tube
is a glass tube open at the top, while the back half is a brass tube. A U-tube
containing liquid is the most accurate instrument known for measuring
pressure. The air line, from the tank unit, is connected at the top of the
brass tube on the head. Any pressure which comes through the air line
presses the liquid downward in the brass tube and upward in the glass tube.
In fact, the difference in the levels of the liquid in the two tubes is an exact
measurement of the pressure coming through the air line and hence records
the depth of petrol in the tank.

CORRECTION OF FAULTY GAUGE
READING

SECTION To have the gauge read correctly three things are necessary
584 1. The head must hold liquid and read zero when disconnected.

2. The air system must be free from leaks or obstructions.

3. The tank unit must supply air by the surging of the petrol described in
( Section 583 ) .

Necessity for the correction of a faulty telegage is only likely to arise if
unions have become slack or liquid has been lost from the head, and should
be undertaken in the following way:—

1. Disconnect air line from the head (this connection is behind the
instrument board and the positive lead from the battery should be
disconnected whenever any work is necessary behind the instrument
board or the ammeter may be damaged considerably through shorting).
The gauge should then read exactly zero, if it does not, liquid can be
added or removed at the top of the brass tube where the air line connects.
To fill use a medicine dropper, being careful not to over-fill. To remove
liquid a wooden match may be used to absorb liquid in small quantities
from the brass tube ( see Fig. 40 ).
2. Dry air line with aid of hand tyre pump. It will first be necessary to cut metal
connection from pump hose prior to pushing it over front end of air line.

By pumping air into the line any petrol which may have found its way
there will be ejected.
3. Re-connect air line, making sure that the connection at the tank unit,
the connection at the bottom of the dashboard, and the one behind the
instrument board are tight.

The gauge will still read ‘zero’ until the top bell and air tube are cleared of
petrol and again filled with air.

This is accomplished by the surging of the petrol in the tank. Stopping,
starting and turning corners will cause the liquid to come up the tube to
the correct level quickly. .

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