Lift control spool valve - Open Centre


The BOSCH ELC (EHR5) lift control spool valve is installed to tractors equipped with an open centre hydraulic system. It is fitted to the left-hand hydraulic cover of the centre housing. It regulates the flow rate of oil to and from the lift rams, according to the signals that it receives from the electronic
linkage calculator (ELC). It comprises a series of spools and valves, most of which cannot be repaired as separate parts.

Layout of components and identification of ports

Layout of components
The BOSCH ELC (EHR5) hydraulic spool valve comprises two parts:

Hydraulic part (1) Non-return valve (2) Lifting spool valve (3) Lowering spool valve (4) Flow rate control spool (5) Shock valve (200 to 210 bar) (6) Flow control spool spring (9) Lifting spool spring
(10) Lowering spool spring (11) Restrictor 
(12) Lift control spool valve Identification of ports:
N Continuity channel
P : Pressure
R, R1 Return to housing
V Port to lift rams

Electric part
(7) Lowering solenoid valve (8) Lifting solenoid valve

To tell a hydraulic problem apart from an electrical problem, operate the push-buttons at the end of the solenoid valves. This allows to manually control solenoid valve movement.

Neutral position


When the engine is stopped:
- the lift control spool valve (12) is in neutral position;
- the lifting and lowering solenoid valve spools (2) and (3) are held in position by their respective springs;
- the flow rate control spool (4) is held down by its own spring


When the engine is running:
The hydraulic pump supplies the lift control spool valve (12) via the trailer braking spool valve (13) (if fitted) and the auxiliary spool valves. The pressure arriving from the port (P) moves the flow rate control spool (4) upwards, thus allowing the oil to flow into the continuity channel (N) and the hydraulic pump via the transfer pipe.

The continuity channel (N) connects the oil flowing in the Open Centre system and also controls the hydraulic flow of brake lubricant via a restrictor and a valve.


Lifting position


The solenoid valve (8) is activated to lift the drawbars. The lifting spool (2) is moved downwards, thus directing the main flow to the non-return valve (1). As soon as the pressure acting on the valve exceeds the pressure in the rams, the valve opens and the flow enters the port (V) to raise the hitch.
When the hitch is in the required position, the tractor electronic system stops the supply to the solenoid valve (8). As a result:
- the non-return valve closes;
- the lifting spool valve is positioned on the return channel R1;
- the flow rate control spool (4) is fixed in raised position, allowing the oil to flow again in the continuity channel N.

Lowering position


The solenoid valve (7) is activated to lower the drawbars. The lowering spool (3) is moved downwards. Its position allows oil to return from the rams via the port (V) to the return R1. The lowering phase has no effect on the flow rate control spool (4). The continuity flow rate N is thus directed to the pump via the transfer pipe.

Shock valve

Location
The shock valve is housed at the front bottom of the left-hand hydraulic cover.

Function
It directs oil from the rams to the return in case of overpressure in the circuit. Hitch bounces when transporting an implement.


Characteristics
The shock valve is calibrated at 200 to 210 bar.

Removing and install the spool valve

Immobilise the tractor. Chock the front wheels. Take off the rear wheel concerned. Position a safety stand. Detach the fuel tank from the gearbox or, if necessary, remove it after draining.

Removal


Identify then disconnect the wiring harnesses from the lifting (8) and lowering (7) solenoid valves. The lowering solenoid valve is turned towards the front of the tractor.


Mark, disconnect and block:
- the hose (1) from the auxiliary spool valves;
- the supply or return pipe (2) from the lift rams.
Extract the screws (1) and remove the lift control spool valve (12) without losing the O’rings (2) and (3).


Install
Clean the mating faces of the cover and lift control spool valve.
Replace the O’rings (if necessary).

Reinstall the spool valve.
Install and tighten the screws to a torque of 36 - 46 Nm.
Reconnect:
- the pipes and hoses;
- the solenoid valve harnesses.
Attach the harnesses using one or more clip retainers, if necessary.

Attach or reinstall the fuel tank.
Install the wheel. Remove the safety stand and trolley jack.
Start the engine. Check the operation of the lift control system and the oil tightness of the seals and unions.