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Massey Ferguson 7480, 7485 load sending hydraulic system - flowrate circuit

MF 7400-7700 Series Tractors Repair Operations

Massey Ferguson 7485, 7480 tractors are fitted with a closed centre hydraulic circuit with controlled pressure and flowrate.

Only tractors with a Powershift gearbox can be fitted, depending on options, with a 150 l/min flowrate circuit.

It is composed of two separate high and low pressure circuits, supplied by a variable displacement pump located on the external face of the right-hand side cover.

This pump has a maximum output of 60 cm3 per revolution and is itself fed by a 80 cm3 booster pump.

Both pumps are driven by a pinion fitted on the upper shaft of the PTO located in the intermediate housing.

A “relay” pinion mounted on a bearing located on the internal side of the cover, ensures the rotation of the driven pinion of the variable displacement pump.

The MF 7480, 7485 booster pump fitted on the left-hand cover sucks oil through a suction strainer to feed the common tank formed by the centre housing, intermediate housing and gearbox.

The booster flowrate is then directed towards the right-hand cover and passes through the main filter before flowing towards the variable displacement pump and the oil manifold of the centre housing to supply the following components:

- the trumpet housings
- the PTO clutch
- the hydraulic pump bearing
- the 4WD unit
- the handbrake mechanism
- the creeper unit (if fitted).

The variable displacement pump supplies one or two priority blocks, depending on options, that are fitted on the right-hand side cover:

- one block for MF 7485, 7480 tractors without hydraulic trailer braking
- two blocks for tractors with hydraulic trailer braking.

The first block supplies:

- its first priority, steering system
- its second priority, the 17 bar rear axle hydraulic circuit, the auxiliary spool valves and the lift control valve.
- If a second block is fitted, it shares the first priority between the steering circuit and the trailer braking.

Once the first priorities have been met, the remaining oil flow becomes available to the auxiliary spool valves and the lift control valve.

All the pilot signals from the various high pressure valves are directed to the priority block(s) to then be retransmitted to the variable displacement pump controller.

The controller takes into account the pilot signal corresponding to the function requiring the highest pressure.

Component characteristics

Suction strainer

- Type: cartridge
- Filtration threshold: 150

Booster pump

- Trademark Rexroth Sigma
- Capacity: 80 cm3 per revolution
- Output: 215 l/min at 2200 rpm

Main filter

- Filtration threshold: 15 u
- With differential pressure bypass: 3.5 bar
- With differential pressure switch: 2.4 bar

Safety valve

- Calibration: 22 bar
- fitted on the low pressure circuit

Safety valve

- Calibration: 5 bar
- No slave device used resupplies booster pump
- Switch: 5 bar (clogging indicator placed on main filter)
- Opens: 3 bar
- Closes: 2 bar

Massey Ferguson 7480, 7485 Variable displacement pump

- Trademark: Brueninghaus
- Type Axial pistons
- Variable capacity 0 to 60 cm3 per revolution
- Output: 0 to 150 l/min at 2200 rpm
- Min. pressure: 22 bar
- Max. pressure: 200 bar
- Internal lubrication with return to housing.