Open centre hydraulic system (100 l/min)


The 100 l/min open centre hydraulic system comprises two separate systems:
- low flow rate system supplied by a gear pump located on the internal face of the left-hand transmission cover plate.
- high flow rate system supplied by two gear pumps located on the internal face of the right-hand transmission cover plate.


The pumps suck transmission oil from the common tank formed by the centre housing and the gearbox. A 150 micron suction strainer (44) ensures filtration during suction. A 15 micron main filter (39), and a blockage indicator (40) are fitted to the low flow rate system upstream of the Orbitrol steering spool valve. The pumps are driven by the ring gear of the PTO clutch unit.


 System schematic diagrams Low-pressure system, low flow rate

The low-pressure system is supplied by a gear pump that provides the pressure to the following equipment:
- the steering,
- the cooling system,
- the lubrication system,
- the transmission components operating under 17 bar.

Hydraulic flow
After supplying the Orbitrol steering spool valve as required, the oil is directed to the left-hand cover plate attached to the centre housing. This cover plate performs several low-pressure functions.
It ensures:
- operating pressure for the various transmission components via a 17 bar valve (21) fitted downstream from the Orbitrol unit,


- cooling and lubrication of the gearbox and connected components,
- pressure for the brake master cylinders (excluding MERITOR master cylinders).

Tractor transmission components
The 17-bar system supplies, in parallel, the various transmission functions via solenoid valves flanged on the reverse shuttle clutch unit, on the Speedshift control and in the main channel of the right-hand cover plate. None of these functions has priority and they may be activated simultaneously. The reverse shuttle solenoid valves are proportional. The other solenoid valves are non-proportional. The functions supplied by the low flow rate system are as follows:
- the hydrostatic steering,
- the Hare / Tortoise range shifting (Hi / Lo),
- the differential lock (front and rear),
- the 4WD clutch,
- the Speedshift,
- The clutch control valve,
- the clutch unit of the reverse shuttle,
- the power take-off system,
- clutch,
- brake,
- front PTO (depending on option).

Cooling and lubrication
When the various components of the transmission are supplied, the left-hand cover plate directs oil towards the cooler when it is hot, or directly towards to the gearbox and PTO when it is cold. The lubrication pressure is maintained by a valve (10) set to 1.5 bar and fitted on the front left-hand side of the gearbox.


Pressure for brake master cylinders
Only unassisted master cylinders receive pressure from the hose connected upstream to the 1.5 bar valve (10).

High-pressure system, high flow rate

The high-pressure system has two pumps (19 cc and 14 cc), used respectively for the linkage and for auxiliary hydraulics. The flow rates of these two pumps can be coupled to use the auxiliary spool valves only. Coupling is performed by a solenoid valve (41) controlled from the cab by a button (2)


The solenoid valve is located on the rear axle right-hand cover plate. When the pump flow rates are coupled, linkage is locked in position. It can only be used once the flows have been uncoupled and linkage reactivated.

19cc pump
The 19cc pump supplies:
- the trailer brake valve, as a priority,
- the auxiliary spool valves

14cc pump
The 14cc pump supplies:
- the linkage spool valve (22).


Coupled 19cc + 14cc pumps
When the pumps are coupled, they supply the auxiliary spool valves through the coupling solenoid valve (41). The 19cc pump always supplies the trailer brake valve as a priority (if fitted). The oil not used by the trailer brake spool valve supplies the auxiliary spool valves fitted to the rear of the linkage cover plate. Surplus spool and linkage valve flows return to the pump inlet manifold via a restrictor, without passing through the 150 micron filter. A safety valve, set to 200 bar, is fitted in the pump discharge channel on the right-hand cover plate to protect the high pressure system. Two non-return valves (A and B) are fitted to the pump system to isolate the pumps from each other towards the safety valve.


 Pump suction system

The pumps, located inside the left- and right-hand cover plates, suck the oil through the 150 micron strainer (17). A tube connects the suction manifolds of the two pumps (15)(42). The left-hand cover plate supports the oil return, which opens into the low pressure pump manifold (15) through a restrictor (16).



Layout of the main Speedshift and Power Shuttle system components


Parts list 
(1) Front differential lock (2) Steering ram (3) Cooling system pressure connector (4) Hydrostatic spool valve (Orbitrol) (5) Forward clutch (reverse shuttle) (6) Reverse clutch (reverse shuttle) (7) Accumulator (assisted master cylinders) (8) Speedshift mechanism (9) Left-hand cover plate
(10) 1.5 bar valve (11) Temperature switch (12) Hare/Tortoise mechanism (13) PTO clutch (14) Pump suction pipe (15) Low-pressure system hydraulic pump (16) Restrictor (17) Suction strainer (Reverse shuttle clutch lubrication pump) (18) 4WD clutch (19) Brake lubrication pipes (20) Rear differential lock (21) 17 bar valve (22) Linkage spool valve (23) Oil cooler (24) Brake master cylinders (25) FTE valve (26) Bleed connector (27) Diagnostics connector (reverse shuttle lubrication) (28) Reverse shuttle proportional solenoid valves
(30) Speedshift solenoid valve (31) Gearbox control unit (32) Accumulator (33) 60 micron filter (34) Solenoid valves (Hare / Tortoise, Differential lock, PTO, PTO brake, 4WD) (39) 15 micron filter (40) Blockage indicator (41) Pump coupling solenoid valve (43) High-pressure system hydraulic pumps (19cc + 14cc) (44) 150 micron suction strainer
(45) Left and right-hand brakes (46) PTO brake



Layout of the main Speedshift and mechanical reverse shuttle system components


Parts list 
(1) Front differential lock (2) Steering ram (3) Cooling system pressure connector (4) Hydrostatic spool valve (Orbitrol) (7) Accumulator (assisted master cylinders) (8) Speedshift mechanism (9) Left-hand cover plate (10) 1.5 bar valve (11) Temperature switch (12) Hare/Tortoise mechanism (13) PTO clutch (14) Pump suction pipe (15) Low-pressure system hydraulic pump (16) Restrictor (17) Suction strainer (Reverse shuttle clutch lubrication pump)
(18) 4WD clutch (19) Brake lubrication pipes (20) Rear differential lock (21) 17 bar valve (22) Linkage spool valve (23) Oil cooler (24) Brake master cylinders (25) FTE valve (26) Bleed connector (30) Speedshift solenoid valve (33) 60 micron filter (34) Solenoid valves (Hare / Tortoise, Differential lock, PTO, PTO brake, 4WD) (39) 15 micron filter (40) Blockage indicator (41) Pump coupling solenoid valve (43) High-pressure system hydraulic pumps (19cc + 14cc) (44) 150 micron suction strainer (45) Left and right-hand brakes (46) PTO brake