DAF CF65, CF75, CF85 Series . Manual - part 951

©

 200423

2-9

General

STEERING GEAR, GENERAL

ΧΦ65/75/85 series

7

2

If the oil output of the main steering pump (4) 

becomes too low, the dual-circuit valve (6) adds 

the output of the emergency steering pump (13) 

to the remaining output of the main steering 

pump (4). The return pipe (8) of the main steering 

pump is also cut off.

The output of both pumps is returned to the 

emergency steering pump reservoir (10).

If more oil is supplied to the emergency steering 

pump reservoir than is drawn in by the 

emergency steering pump, the excess oil is 

discharged to the main steering pump 

reservoir (1) through the overflow pipe (9).

Dual-circuit valve
In the dual-circuit valve (6) an output 

indicator (16) is fitted to signal that the oil output 

from the main steering pump (4) is too low. The 

output indicator (16) activates the circuit 1 

warning indicator when the emergency steering 

pump (13) is activated.

The output indicator for circuit 2 is fitted in pipe 

connection (P2) (emergency steering pump (13) 

delivery pipe connection on the dual-circuit 

valve).

When the output from the emergency steering 

pump (13) is too low, the output indicator 

activates the circuit 2 warning indicator.

The emergency steering pump (13) is fitted with a 

pressure limiting valve with a higher opening 

pressure than the pressure limiting valve in the 

steering box. The function of this valve is to serve 

peak demands, which can occur when switching 

circuit 2 on and off. When the valve opens, the 

delivery pipe (14) is connected to the supply 

pipe (12).

Operation of dual-circuit valve
When the engine is running, the pressure from 

the main steering pump (P1) will cause control 

slide A to move to the left against the spring 

pressure. The supply from the main steering 

pump goes to the steering box via exit (P). The 

return from the steering box (R) is connected to 

the main steering pump reservoir via exit (R1). At 

the same time the connection of the emergency 

steering pump (P2) and the steering box is 

broken. The oil supplied by the emergency 

steering pump while the vehicle is being driven 

goes to the emergency steering pump reservoir 

via entrance (P2) and exit (R2). Control slide B is 

only used with vehicles equipped with a slave 

cylinder.

S700935

1

C1

R1 R R2 P2

P

P1

C2

C

2

B

A

STEERING GEAR, GENERAL

2-10

©

 200423

General

2

ΧΦ65/75/85 series

7

If a main steering pump failure causes the 

pressure (P1) drop to zero while the vehicle is 

being driven, the spring will move control slide A 

to the right. As a result, the emergency steering 

pump (P2) is connected to the steering box (P). 

The steering power is now produced by the 

emergency steering pump. To ensure that the oil 

of the main steering pump does not leak away in 

case of leakage, the return (R) of the steering box 

is led to the emergency steering pump reservoir 

(R2). 

1

C1

R1 R R2 P2

P

P1

C2

2

S700936

B

A

C

©

 200423

2-11

General

STEERING GEAR, GENERAL

ΧΦ65/75/85 series

7

2

2.8 SYSTEM DESCRIPTION, DUAL-CIRCUIT SYSTEM WITH SLAVE CYLINDER

The steering gear can contain a slave 

cylinder (10) for additional steering power. This 

slave cylinder is located parallel to the steering 

box cylinder and is supplied with oil through the 

dual-circuit valve.

System operation is identical to that of the dual-

circuit system.

Dual-circuit valve
The steering box is provided with an extra valve, 

which cuts off the oil supply to the slave cylinder 

(10) and connects both pipes (9) and (11) of the 

slave cylinder when the output of the main 

steering pump is too low. Just like the dual-circuit 

valve this valve is operated by the emergency 

steering pump pressure.

In the dual-circuit valve (6) an output 

indicator (19) is fitted to signal that the oil output 

from the main steering pump (4) is too low. The 

output indicator (19) activates the circuit 1 

warning indicator when the emergency steering 

pump (16) is activated.

4

R1

R2

P2

P1

C1

C2

+

1

3

5

7

13

15

16

14

9

19

17

18

10

11

12

6

20

2

S700913

8

21

STEERING GEAR, GENERAL

2-12

©

 200423

General

2

ΧΦ65/75/85 series

7

The output indicator (20) for circuit 2 is fitted in 

pipe connection (P2) (emergency steering 

pump (16) delivery pipe connection on the dual-

circuit valve).

When the output from the emergency steering 

pump (16) is too low, the output indicator (20) 

activates the circuit 2 warning indicator.

The emergency steering pump (16) is fitted with a 

pressure limiting valve with a higher opening 

pressure than the pressure limiting valve in the 

steering box. The function of this valve is to serve 

peak demands, which can occur when switching 

circuit 2 on and off. When the valve opens, the 

delivery pipe (17) is connected to the supply pipe 

(15).

Operation of dual-circuit valve
When the engine is running, the pressure from 

the main steering pump (P1) will cause control 

slide A to move to the left against the spring 

pressure. The supply from the main steering 

pump goes to the steering box via exit (P). The 

return from the steering box (R) is connected to 

the main steering pump reservoir via exit (R1). At 

the same time the connection of the emergency 

steering pump (P2) and the steering box is 

broken. The oil supplied by the emergency 

steering pump while the vehicle is being driven 

goes to the emergency steering pump reservoir 

via entrance (P2) and exit (R2).

When the main steering pump is active, control 

slide B moves to the left against the spring 

pressure. Connections (C1) and (C2) of the slave 

cylinder are connected to the connections on the 

left (1) and right (2) of the steering box.

If a main steering pump failure causes the 

pressure (P1) drop to zero while the vehicle is 

being driven, the spring will move control slide A 

to the right. As a result, the emergency steering 

pump (P2) is connected to the steering box (P). 

The steering power is now produced by the 

emergency steering pump. To ensure that the oil 

of the main steering pump does not leak away in 

case of leakage, the return (R) of the steering box 

is led to the emergency steering pump reservoir 

(R2).

If the pressure of the main steering pump drops 

to zero, the spring pressure will cause control 

slide B to move to the right. The connections (C1) 

and (C2) between the slave cylinder (1) and the 

steering box (2) are closed off. At the same time 

the slave cylinder connections (C1) and (C2) are 

interconnected. While pressure is being built up 

in the slave cylinder due to the different 

capacities of the two chambers in the cylinder, 

valve C will open.

S700935

1

C1

R1 R R2 P2

P

P1

C2

C

2

B

A

1

C1

R1 R R2 P2

P

P1

C2

2

S700936

B

A

C