Twin flow hydraulic circuit right-hand cover


Some model of tractors may be equipped with an open centre, closed centre or Twin flow load sensing hydraulic circuit.  The right-hand cover is Installed to the rear axle housing and has two main functions:
- it supports numerous hydraulic system components
- it incorporates various suction and cooling channels of the high and low flow circuits (high and low pressure).
On its inside face, the cover receives:
- two-stage hydraulic pump and its drive pinion
- suction pipe
- inlet manifold
- left-hand cover transfer pipe.
On its outside faces, it receives:
- four or five control solenoid valves for low pressure functions (depending on option) including one "proportional" solenoid valve for the PTO clutch function
- safety valve in the high pressure circuit
- trailer brake valve (if fitted) or a closing plate (depending on option)
- three “diagnostic” connectors
- strainer
- main 15 micron cylinder and its base
- low pressure switch (17 bar)
- filtration switch
- engine speed sensor.


Parts list
(1) Cover (2) Screw (3) High pressure (high flow rate) valve (4) Screw
(5) Low pressure 17 bar diagnostics connector (6) 17 bar low pressure switch
(7) Proportional solenoid valve (PTO clutch) (8) PTO brake solenoid valves
(9) Front and rear differential lock solenoid valves (10) 4WD solenoid valves
(11) Hare / Tortoise solenoid valve (12) Engine speed sensor (13) Low flow rate diagnostics connector (14) Strainer (15) Filtration switch (16) High flow rate, high pressure diagnostics connector (17) Balance block (18) Brake valve (19) Screw (21) Locating pins (22) O’ring (23) O’ring (24) Seal
(25) Transfer pipe (26) O’rings (27) Nut (28) Washer (29) Pinion (30) Key (31) Screw (32) Hydraulic pump (33) Pin (34) Flange (35) Screw (36) Screw (37) Deflector (38) Suction pipe (39) Seal (40) Inlet manifold (41) O’rings (42) Pipe (43) Threaded end-piece (44) Seal

Identification of channels and ports

Under the cover (1) 



A : Channel to auxiliary spool valves
B : Port to front and rear differential locks (if fitted)
C : 17 bar pressure inlet from distribution block
D : Low flow rate channel to main filter (15 microns) and Orbitrol steering unit
E : Port to 4WD clutch port (if fitted)
F : Suction
G : Oil outlet to pump via strainer
H : Port for filtration switch
I : Continuity port towards auxiliary spool valves
J : High pressure port, pump outlet
K : Port to PTO brake
L : Port to PTO clutch

On the solenoid valves


Proportional solenoid valve fitted only to PTO clutch circuit.
A : Supply ports to PTO clutch
P : 17 bar low pressure inlet
R : Port to return line

Solenoid valve 


Standard (8) to (11): PTO brake – differential lock – 4WD – Hare / Tortoise circuit

On the high pressure, low flow rate valve (3) 
P : 200 bar high pressure inlet
R : Port to return line



Disassembling and reassembling the high pressure valve

Operation 
If pressure "P" rises above 200 bar ± 5 bar, the spring (4) is compressed, opening the valve (7) to allow oil to pass into the housing via port R.


 If necessary, take off the right-hand side rear wheel. Place an axle stand.

Disassembly 
Unscrew the plug (1). Recover the shims (2) and take out the spring (4).
Remove the O’ring (5), extract the body (6) with the valve (7) and the washer (8) from the right-hand cover. The ball (9) is crimped in the body of the valve.


Reassembly 
Check that the valve (7) slides freely in the valve body (6).
Place the washer (8), Install the valve body (6) with the valve (7) into the cover. Position the O’ring (5).
Install the spring (4), the shims (2) and tighten the plug (1) to a torque of 50 - 60 Nm.
Reinstall the wheel (if removed). Tighten the wheel nuts to a torque of 400 - 450 Nm.

Disassembling and reassembling the cover

Disassembly
Take off the cover. Place the cover (1) in a vice fitted with plastic jaws.

On the outside face 


Mark the locations and types of solenoid valves (7) to (11) and remove them.
Mark the location of the switches (6) (19) and remove them.
Remove the engine speed sensor.
Remove the hydraulic unions and plugs, fitted according to the version.
Remove the diagnostics connectors. On tractors not fitted with trailer braking, if necessary, remove the cover plate (3). Take off the high pressure valve (3).

On the inside face 
Take out the screws (31) and remove the inlet manifold (40), seal (24) and pipe (42). Remove seals (41).

Removing the drive pinion
Unscrew nut (27). Take off washer (28), pinion (29) and key (30).
Take off the pump.


Reassembly
Clean the cover mating faces.
Check that no channels (low and high flow rate) are blocked. Check for the presence of the rivets ensuring oil tightness at the end of each channel.

On the inside face 
Reinstall the pump.

Reinstall the drive pinion
Position the key (30). Install the pinion (29) on the shaft while ensuring that the key is correctly engaged. Install washer (28).
Smear the nut (27) with Loctite 241 and tighten to a torque of 50 - 60 Nm.
Replace the O'rings (41) on the pipe (42).
Reinstall the seal (24), the pipe and the inlet manifold (40). Install and moderately tighten the screws (31).

On the outside face 
Install the high pressure valve (3). On tractors not equipped with trailer braking, if removed, refit the cover plate (3).
Install the diagnostics connectors.
Install the plugs and hydraulic unions.
Install and adjust the engine speed sensor.
Install the switches (6) (19) in their respective locations, having lightly smeared the threads with Loctite 542.
Install the solenoid valves according to the type and locations marked during disassembly.

Maximum tightening torque
- Solenoid valve body: 15 - 20 Nm
- Solenoid: 1.7 - 2.8 Nm.
Reinstall the cover.