Block valves for steering and low pressure systems

Valves block Description

The single valves block (7), Installed to the right-hand hydraulic cover plate (8), is fitted to 40 kph tractors without trailer braking. Valves block has two spools and receives the flow rate from the variable displacement pump. It ensures priority for the steering system and the 17 or 21 bar low pressure system. The oil is then directed to the auxiliary spool valves and linkage spool valve. 

This section primarily describes the single block valves (7) without trailer braking. The hydraulic unit with two priority blocks and with 40 kph trailer braking or trailer braking for tractors fitted with a high-pressure braking unit is described in its own section.

 Identification of 110 l/min or 150 l/min Load Sensing (LS) ports on the single valves block (7) 

A Orbitrol supply
B High pressure (HP) supply from variable displacement pump (drilled port on the mating face of priority block and cover plate)
C LS pilot flow to the variable displacement pump hydraulic regulator
D LS pilot flow from the Orbitrol
F Spool valve (auxiliary and linkage) supply.
G LS pilot flow from spool valves (auxiliary and linkage).
H Internal channel 

I 17 or 21 bar outlet
J Plug
HP High-pressure (HP) spool
BP Low-pressure (BP) spool
GPA20 rear axle
GPA30 and GPA40 rear axles


1st position - Steering
The spool (2) moves to the left under the action of spring (3). The flow coming from the variable displacement pump via channel B is by priority directed towards the Orbitrol spool valve via channel A.

- Steering at neutral:
The steering spool valve (Orbitrol) is in closed position. The pump pressure moves spool (2) to the right and the flow is directed into channel H.
- Steering activated:
A pilot flow pressure from the Orbitrol arrives at port D and pushes the spool (2) to the left, allowing the flow to enter port A and supply the Orbitrol. A flow of approximately 0.5 l/min is directed through port A towards port D via a drilled hole and restrictor in spool (2). This flow rate creates pressure of approximately 6 bar at port D. The LS line directs this pressure to the variable displacement pump regulator which is adjusted to 22 bar in order to obtain a standby pressure of 28 bar.

2nd position - 17 or 21 bar pressure control valve
The spool (4) moves to the left under the action of the spring (5), allowing the flow from channel H to be directed into port I (17 or 21 bar low pressure). As soon as the pressure in this port reaches 17 or 21 bar, the spool reaches equilibrium thus allowing the low pressure to be maintained and the flow to be directed towards port F (linkage and auxiliary). When the linkage and auxiliary spool valves are used, an LS pilot flow pressure is sent to the block via port G to join the LS line at port C.

Checking after servicing
If the single priority block (7) had to be replaced:
- Lightly smear the thread of screws V with Loctite 542 or equivalent. Tighten these screws to a torque of 25 - 35 Nm.
- Carry out hydraulic tests.

Check the tightness of the unions and "O" rings fitted between the single priority block and the right-hand hydraulic cover plate. Carry out a road test.

Removing and install and disassembling and reassembling the hydraulic pump drive bearing

Disconnect the tractor between the gearbox and the intermediate housing.
Remove the components of the creeper unit (if fitted) that might hinder the removal of the hydraulic pump drive gear (1)Remove:
- the stop ring (2)
- the tab washer (3)
- the spring (12)
- the drive gear (1) fixed to the bearing (11)

Removing the bearing (11) 
Unscrew the plug (8).
- the pin (7) using a threaded rod, such as to free the spacer (5);
- the bearing (11) such as to remove it from its bore through the front of the intermediate housing.

Reinstall the bearing (11)
Check that:
- neither the channel nor drilled hole in the spacer (5) is blocked;
- the circlip (14) is present on the upper PTO shaft. Reinstall the bearing (11).
Position the groove of spacer (5) along the axis of the port provided for plug (8).
Slide the pin (7) into its bore, inserting its flat sections into the groove of the spacer (5). Tighten the plug (8).
Ensure that the bearing is correctly held by the pin (7) and that it rotates freely. Reinstall the gear (1).
Lightly smear the thread of the screws (4) with Loctite 242 or equivalent. Tighten these screws to 72-96 Nm.
- the spring (12)
- the tab washer (3)
- the stop ring (2)

Disassembling the hydraulic pump drive bearing

Remove the circlip (10). Extract the rollers (6) from the bearing. Remove the spacer (5).

Reassembling the bearing (11) 
Clean and check all components. Replace those that are defective.
Using a press and a suitable fixture, insert the rollers (6), separated by the spacer (5), into the bearing (11). The force of the press must be applied to the internal ring of the rollers.
Reinstall the circlip (10). The rollers of the hydraulic pump drive bearing
(11) are lubricated by an oil flow from the right-hand hydraulic cover plate via the union (9)Install and adjust the creeper unit components.
Reconnect the tractor between the gearbox and the intermediate housing.
Carry out a road test of all controls.
Check the tightness of the mating faces and hydraulic unions.