SAFARI

POWER STEERING

Vane Pump :

XII Maintenance instruction and functional

description

I. Maintenance and oils :

1. Checks:

The pump is lubricated by the hydraulic oil, meaning

that no additional servicing of the bearings is

necessary. On the other hand, it is important that the

oil level in the tank be checked at regular intervals.

We recommended that this check be carried out at

least every 5000 kilometers travelled. The possibility

of air being trapped at various points within the oil

circuit and the fact that very small air bubbles still

remain in the oil even after air bleeding make it

necessary for the oil level to be checked while the

pump is running.

The trapped air is then under operation pressure,

subsequently expanding under normal atmospheric

pressure when the pump has been shut down.

Experience has shown that this causes the oil level

to rise approximately 1 to 2 cm in the oil tank when

the pump has been shut down.

It is recommended to check the oil level in the oil

tank prior to starting the pump and, if necessary, to

top up the oil level until it is approximately 2 cm above

the upper mark when the pump is at a standstill. Only

then should the pump be started. If the oil level then

drops excessively (in other words more than 1 to 2

cm), the entire hydraulic system must be bled. Refer

to the section “Oil filling and air bleeding “

In order to prevent the intake of air, all screw

connections and pump lines should be checked for

tightness and, if necessary, retightened when the

vehicle involved is in for general servicing.

2. Filter change:

Normally after every 72,000 Kms/43000 miles running

of the vehicle the filter is to be changed.

The filter in the oil tank should also be changed when

repairs are performed on the pump or the steering unit

and during the main steering unit inspection (refer to

the inspection instructions II - 6.1).

3. Steering oil:

Normally oil is to be changed at every 80,000 Kms/

48000 miles running.

A suitable hydraulic oil must be used in order to ensure

perfect functioning of the pump.The hydraulic oil also

lubricates the pump, meaning that only one type of oil

is required for the entire system.

The unit should be filled with suitable ATF oils, having

a viscosity of approximately 26mm

/s (cSt) at 50

degree, a setting point below –35 degree and having

a low foaming tendency. Oils of higher viscosity may

result in an excessive under pressure in the inlet line,

thus possibly causing pump noise and destruction.

Some of the types of oil recommended by us for the

first filling of pumps are listed on the Oil –Tank.

II. Functional description :

ZF vane pumps have been specifically designed to

supply oil to hydraulic- assisted steering systems.The

low number of moving parts (drive shaft, rotor and

vanes) and the minimum possible face – end play of

these elements with respect to the drive – side and

cover – side faceplate ensure high efficiency and,

consequently, the best possible utilization of power.

This efficiency is also partially the result of the pairs

of two opposite suction and pressure lines, a design

whereby the ten pump cells each convey twice their

own cell volume per revolution.The double arrangement

of the suction and pressure lines results in mutual

cancellation of the hydraulic radial forces acting upon

the rotor.

When turning the drive shaft and the rotor connected

to it, the vanes guided the ring are also driven.

Centrifugal force and pressure oil which can pass via

bores and grooves from the pressure chamber on the

inside faces of the rotor, force the vanes against the

track of the camring. The pump cells are thus

separated from each other, causing intake as the

volume rises and discharge as the volume decreases.

The oil passes from the two pressure chambers into

the space between the cover and the cover – side

faceplate, which is thus forced against the camring at

operation pressure, also to the flow – limiting valve,

and via throttle to the discharge line.

An increase speed and or increase flow results in an

increasing pressure drop downstream of the choke

and, consequently, on the spring side of the valve