Electric hydraulic auxiliary spool valves - GPA20 and GPA40 rear axles

The Bosch/Rexroth SB23 LS spool valves controlling supply to the hydraulic couplers are comprised of:
• an hydraulic part;
• an electrohydraulic part comprising:
- an ON/OFF solenoid valve and a 3-way pressure relief valve located on the end plate of the spool valve block,
- a pilot valve fitted in the electrohydraulic unit.
This section shall concern the hydraulic part only. The Bosch/Rexroth SB23 LS electric hydraulic control spool valves are supplied by high flow rate, high pressure oil from the priority blocks. When no functions are being activated, the entire flow rate is directed towards the spool valves. When certain functions are being supplied, the excess flow then remains available to the auxiliary spool valves. The adjustment of the flow rate, expressed as a percentage, may be displayed on the onboard computer (Datatronic) by the operator (see chapter 11). The electric hydraulic spool valves controlled by a Joystick are fitted with a floating Kick-out position (automatic return to neutral). The main spool of the spool valve directs oil towards the outlet ports A or B. Each outlet port is linked to the LS pilot line of the variable displacement pump regulating valve via the priority block(s). The spool valves consist of both electronic and hydraulic components, the latter containing spools and valves. Some elements cannot be repaired as spare parts.

Different types of spool valve block components

A spool valve block can consist of three, four or five of the following components. It can combine components of similar type of or different types.

Component a
Electrohydraulic component (Joystick)
Component b
Electrohydraulic component (Dual Control)
Component c
Mechanically controlled component.

Parts list 
(1) Auxiliary spool valves (6) End plate (14) Inlet block (17) Lift control spool valve (18) ON/OFF solenoid valve (19) Electronic units

Hydraulic connections between spool valves and couplers 
M Black and yellow, mechanical spool valve
X Red, Joystick
Y Green, Joystick
DC Black, Dual Control
VR Lift control valve
(5) Support (6) Joystick lever

 Operation of the pressure relief valve and electrohydraulic unit

When the ON/OFF solenoid valve (18) located on end plate (6) is open, the flow from the pump is directed to the 3-way pressure relief valve (3)

The 3-way pressure relief valve supplies the pilot valve (5) with a pressure of 21 - 24 bar via a pressure balancing valve. 

The pilot valve receives a signal from the digital device (6) and moves the main spool (1) of the auxiliary electric hydraulic spool valve according to the information received from the Joystick. 

The digital device is informed of the position of the main spool by a displacement sensor (7)

The pilot valve and the digital device are housed in the unit (2) fixed below the spool valve. 

The pilot valve (5) is protected from possible oil contamination by a set of FP filters (25 microns)

Electronic unit (2) channels P and R are connected to channels P1 and R1 of the auxiliary electrohydraulic spool valve.

Parts list 
(1) Main electric hydraulic valve spool (2) Electrohydraulic unit (3) Return spring (4) Piston (5) Pilot valve
(6) Digital electronic system (7) Displacement sensor

FP Set of filters (25 microns)
P Pressure
R Return

Operation of the auxiliary electric hydraulic spool valve

When the spool (1) is moved electric hydraulically upwards by the pilot valve (5), oil penetrates via channel P and travels to the flow regulation control spool restrictor (5) and the grooves of the main spool (1). The oil is then carried towards a main channel and lifts the ball of valve (2) to enter a
chamber. Displacement of the spool (1) simultaneously opens the one-way valve (3). The oil flows from the chamber towards port B and returns to the housing through port A via the hydraulic slave device. The operating principle is identical when the spool (1) is electro hydraulically moved down by the pilot valve (5)

The oil then flows from the chamber towards port A and returns to the housing through port B via the hydraulic slave device. The electrohydraulic spool valves can be manually controlled using a lever screwed onto the reversing lever (2).

Layout of components and identification of ports

Layout of components 

(1) Main spool (2) Valve (3) Non-return valve (4) Pressure balancing valve (5) Cover

Identification of ports

on the inlet block (14) 

P High pressure inlet from the variable displacement pump via the priority block(s) (depending on version).
R Return from auxiliary spool valves (beneath the oil level)
LS Signal to the pump regulating valve via the lift control spool valve and the priority block(s) (depending on version)

on the auxiliary spool valves 

A Outlet to coupler
B Outlet to coupler
C Restrictor
D Grooves
E Channel
F Chamber
P, R and LS
Marks identical to those of the inlet block (14)


Parts list 
(17) Lift control spool valve

BP Priority block(s)
P Balance block