DAF CF65, CF75, CF85 Series . Manual - part 970

©

 200423

1-5

General

STEERING PUMP

ΧΦ65/75/85 series

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4

Regulated output control
In principle, the pump output depends on the 

speed.

The steering gear however should be provided 

with an oil volume which is as constant as 

possible. To achieve this constant oil volume, the 

pump is equipped with a regulated output control.

The output at the steering box is controlled by a 

calibrated opening (1) in the internal delivery pipe 

and the flow control valve (6) with spring (4).

If the pump output has not yet reached the preset 

output, the flow control valve (6) is pushed at the 

front against a stop, thus closing the internal 

circulation channel (5).

The flow control valve (6) is held against the stop 

by the spring (4) and the oil pressure in the 

delivery pipe (2) which is exerted through the 

channel (3) at the back of the flow control valve.

The entire pump output flows through the 

calibrated opening (1) to the delivery pipe 

connection (2).

If the pump output exceeds the preset output 

because the engine speed has increased, 

pressure builds up at the front of the flow control 

valve (6) which exceeds the delivery pressure at 

the back of the valve. The valve moves to the 

right and the connection to the internal circulation 

channel (5) is opened. Part of the pump output is 

returned to the pump inlet channel through the 

circulation channel.

If the pump output drops because the engine 

speed has been reduced, the flow control valve 

will move to the left and the connection to the 

internal circulation channel (5) will partly close 

again. A smaller part of the pump output is 

returned to the pump inlet channel.

This control system supplies a fairly constant oil 

output to the steering gear, despite the engine 

speed variations.

Note:

The pressure-limiting valve is fitted into the 

steering box.

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S7 00 039

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S7 00 040

STEERING PUMP

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©

 200423

General

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ΧΦ65/75/85 series

7

1.4 OPERATION OF EMERGENCY STEERING PUMP

The emergency steering pump is a radial plunger 

pump. This pump is driven by the gearbox output 

shaft.

The pump is driven when the vehicle is moving. 

The direction of rotation is not important for this 

pump.

The pump is equipped with eight hollow 

plungers (7), arranged around an eccentric (10). 

The eccentric takes care of the upward plunger 

stroke.

The downward stroke is activated by a spring (9) 

which is fitted in the plunger (7).

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S7 00 049

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 200423

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General

STEERING PUMP

ΧΦ65/75/85 series

7

4

At the bottom the plunger is equipped with 

bores (12). These bores are connected to the 

supply line (15).

At the end of the downward stroke the plunger is 

filled with oil. The oil is pressed away during the 

upward stroke.

The pump output is limited because an increase 

in engine speed reduces the amount of time 

during which the steering oil can flow into the 

hollow plunger, thus decreasing the filling volume 

of the hollow plungers.

A flow control valve is therefore not necessary.

Every cylinder is equipped with a delivery 

valve (16). Behind the delivery valves there is a 

cushioning chamber (18) in which the pulsating 

action of the plunger on the oil is dampened.

The pump is equipped with a suction valve (17).

A suction valve is required in a plunger pump 

because this pump type cannot draw in oil via the 

plungers when the pump is at a standstill.

The suction valve (17) is opened when an 

underpressure exists in the emergency steering 

pump delivery line (19). Such an underpressure 

can be caused if steering takes place when the 

main steering pump is switched off and the 

vehicle road speed is low. In such a situation, 

partial mechanical steering takes place. Such 

steering requires more oil than the emergency 

steering pump can supply at that moment.

The underpressure will open the suction 

valve (17), connecting the supply line (15) with 

the delivery line (19).

If the emergency steering pump output is 

sufficient, the suction valve is closed due to the 

pressure difference between the supply line and 

the delivery line.

STEERING PUMP

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©

 200423

General

4

ΧΦ65/75/85 series

7