Lift control spool valve – Load sending and twin flow load sending


The function of the 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

Layout of components 
The Bosch/Rexroth lift control valve consists of two parts:

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 (14) 
(12) HP supply from the two-cylinder pump via the priority block(s) (depending on model)
(13) LS signal to the balance block via the priority block(s)


On the lift control valve (17) 
(15) Rams return pipe or hose to housing
(16) 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 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 the 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.

Reassembling the lift control valve
Reassemble the complete auxiliary spool valve block/lift control valve.

Diagram

GPA20 and GPA40 assembly fits
Legend 
BP Priority block(s)
D To auxiliary spool valves
P High pressure from variable displacement pump via the priority block(s) (depending on version)
P2 Secondary high pressure port
R Return from auxiliary spool valves (beneath the oil level)
R1 Return from lift rams
V Lift rams
LS Signal to pump regulator via the priority block(s) (depending on version)

GPA30 assembly fit
Parts list 
(1) Auxiliary spool valves
(7) or [(7) and (7A)]
Priority block(s)
(21) Oil manifold
Legend
A,B Outlets to couplers
P Pressure
P2 Pressure connector (provision for)
R Return
V Lift rams
LS Signal

Neutral position


When the 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.