Tractor hydraulic system

The hydraulic system of tractor is closed centre with controlled pressure and flow rate. It consists of two separate systems (high and low pressure), supplied by a variable displacement pump with a maximum flow rate of 45 cm3 per revolution. The variable displacement pump is supplied by a charge pump.
The two pumps are driven by:
- a gear which is driven by the engine flywheel (GPA30 rear axle);
- the PTO clutch external teeth (GPA20 and GPA40 rear axles).

Charge pump
The charge pump is fitted to the left-hand cover plate. It sucks oil through a strainer from the common tank formed by the centre housing and gearbox. The charge flow rate is then directed towards the right-hand cover plate and passes through the main filter before flowing towards the variable displacement pump and the oil manifold of the centre housing (GPA20 and GPA40 rear axles) or the intermediate housing (GPA30 rear axle) to lubricate the following components;
- trumpet housings,
- the rear PTO clutch (GPA20 and GPA40);
- the hydraulic pump drive gear/bearing (GPA30);
- mechanical parts of the rear PTO;
- the 4WD unit (GPA30 and GPA40);
- rear bearing of the pinion (GPA20);
- the pinion bearings and the hand brake mechanism (GPA40).
The safety valve set to 5 bar, located on the internal face of the right-hand cover plate, maintains the charge pressure.

Variable displacement pump
The variable displacement pump supplies either one or two priority blocks fitted on the right-hand cover plate:
- one unit for tractors without hydraulic trailer braking;
- two units for tractors with hydraulic trailer braking;
- two units for tractors fitted with high-pressure brakes with or without hydraulic trailer braking.
The first unit supplies:
- first priority, the steering system;
- second priority, the 17 bar or 21 bar slave device system.
If a second unit is fitted, it shares the priority between the steering system and the trailer braking system.
Once the priorities have been met, the remaining oil flow becomes available to the auxiliary spool valves and the linkage spool valve. All the control signals from the various high-pressure valves are directed to the priority block(s) to then be transmitted to the variable displacement pump regulator. The regulator takes into account the control signal corresponding to the function requiring the highest pressure.

Principle of the tractor hydraulic system
The purpose of the closed centre Load Sensing hydraulic system is to limit the power absorbed by the engine. If no hydraulic slave device is actuated, no flow is discharged by the variable displacement pump.
When a function is activated, the pump only supplies the output required for that function. If the housing is drained, or if the main filter is replaced or any servicing operation results in air entering the system, it is essential to prime the hydraulic system.

Hydraulic component specifications 

 Suction strainer (13)
- Type: cartridge
- Filtering threshold: 150 μ

Charge pump (12)
- Brand: Rexroth - Sigma
- Displacement: 60 cm3 per revolution
- Flow rate: 165 l/min at 2200 rpm

Main filter (37)
- Filtering threshold: 15 μ
- With differential pressure bypass: 3.5 bar
- With differential pressure switch: 2.4 bar

Safety valve (46)
- Setting: 22 bar or 24 bar
- Fitted on the low-pressure system

Safety valve (50)
- Setting: 5bar
- Unused slave devices: re-supply charge pump
- Switch: 5 bar (blockage indicator placed on main filter)
- opening: 3 bar
- closing: 2bar
- fitted in parallel to filter
- linked to indicator light on instrument panel

Variable displacement pump (49)
- Brand: Brueninghauss
- Type: Axial pistons
- Variable displacement between 0 and 45 cm3 per revolution
- Flow rate: 0 to 105 l/min at 2200 rpm
- Minimum pressure: 22 bar
- Maximum pressure: 200 bar
- Internal lubrication with return to housing

Power Shuttle suction system for GBA10 and GBA20 gearboxes

Power Shuttle suction system for gearbox type GBA10 (GPA30 rear axle)

A Gearbox
B Intermediate housing
D Strainer
G Suction pipes

Power Shuttle suction system for gearbox type GBA10 (GPA40 rear axle)

A Gearbox
B Centre housing
D Strainer
G Suction pipes

Power Shuttle suction system for gearbox type GBA20 (GPA20 rear axle)

A Gearbox
D Strainer
G Suction pipes
H 4WD unit cover plate

Suction - blue colour in all figures