Specifications, Service and Repair of Farm and Lawn Tractors

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Massey Ferguson 7715, 7718 Load sending and twin flow load sending - Lift control spool valve

The function of the MF 7715, 7718 lift control valve is to regulate the oil flow to and from the lift rams according to the signals transmitted by the ELC calculator.

The lift control valve contains an LS port for the Load Sensing system. This pilot port allows the valve to send pressure data to the regulator via the priority block(s).

This lift control valve is made up of elements themselves comprising spools and valves. Some of the elements cannot be repaired as spare parts.

Layout of components and identification of ports

The Bosch/Rexroth lift control valve consists of two parts: Hydraulic part (spool valve) and Electrical part (solenoid valves).



Hydraulic part (spool valve) - (1) Non-return valve, maintaining the oil in the rams (2) Spool valve assembly used in the lowering phase (4) Control spool valve (5) Flow regulating spool valve (6) Shock valve (9) Flow regulating spool spring (10) Control spool spring (11) Spool valve assembly spring, Electrical part (solenoid valves) - (7) Lowering solenoid valve (8) Lifting solenoid valve

In order to determine whether the fault is of hydraulic or electric type, press the push-buttons at the ends of the solenoid valves; this eliminates the electronic effect of the lift function.

Identification of ports (GPA20 and GPA40 rear axles)

On the inlet block

HP supply from the two-cylinder pump via the priority block(s) (depending on model)
LS signal to the balance block via the priority block(s)

On the lift control valve

Rams return pipe or hose to housing
HP ram supply



Identification of ports (GPA30 rear axle)

On the right-hand end plate - (9) LS hose from the priority block(s)

On the oil manifold (21) - (30) High pressure hose from the priority block(s)

On the lift control valve (17) - (16) Lift ram supply pipes

Removing - install the spool valve block and the lift control valve (GPA30 rear axle)

Removing the Massey Ferguson 7715, 7718 auxiliary spool valves

Remove the complete auxiliary spool valve block/lift control valve in order to reach the lift control valve under optimum conditions of cleanliness.

Install the spool valve block.
Reinstall the complete auxiliary spool valve block/lift control valve.
If necessary, carry out the hydraulic tests related to the operations performed.

Disassembling and Reassembling the MF 7715, 7718 lift control valve

Carefully clean the complete auxiliary spool valve block/lift control valve before carrying out servicing.
Split the components of the auxiliary spool valve block down to the lift control valve.
Reassemble the complete auxiliary spool valve block/lift control valve.

Neutral position



When the Massey Ferguson 7715, 7718 tractor engine is not running and the spool valve is in the neutral position, the control spool (4) and the spool valve assembly (2) are maintained respectively by the springs (10) and (11).

The flow rate adjustment spool (5) is pushed downwards by spring (9). When the engine is running and the spool valve is at rest, no pressure information is transmitted to the variable displacement pump. The LS line communicates with the return.

Up position



When the Move Up solenoid valve (8) is activated, the control spool (4) is moved upwards. The LS pressure information acting on the upper face of the flow rate regulating spool (5) (spring (9) side) moves the spool downwards thus directing the flow to the control spool and the non-return valve (1).

The movement of the flow regulating spool valve is dampened by the volume of oil present in chamber D. As soon as the pressure on the valve (1) is greater than that in the rams, the lifting arms rise.

The LS line communicates with the outlet line (16) to the lift rams thus informing the variable displacement pump regulator.

If the pressure in the rams is too high (shocks received by the lifting arm), the valve (6) opens and the excess pressure is directed to the return.

Down position

When the solenoid valve (7) is activated to lower the lifting arm, the spool valve assembly (2) allows the oil coming from the rams to flow into the return.

The LS pressure information is transmitted to the side of the flow rate regulating spool (5) (spring (9) side) and to the variable displacement pump.

 

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