Auxiliary spool valves - Open Centre


The Rexroth SM12 auxiliary spool valves are fitted on the high flow rate circuit. They are fed by oil coming from the trailer braking valve or the closing plate fitted in its place (depending on version). When the spool valves are not activated, the oil is available for the lift control valve fitted downstream. The auxiliary spool valves are mounted on a support which is itself fitted to the rear of the lift cover. Quick-disconnect couplings are fitted directly on the spool valve body. To obtain sufficient distance between couplings, the spool valves are fitted with blocks serving as spacers. These blocks are also used to let the oil flow to the next spool.

Available sets of spool valves 

Set A - 2 spool valves
• Spool valve 1 and 2: 3-position, SA / DA with spring loaded return to neutral
Set B - 2 spool valves and flow divider
• Spool valve 1: 3-position, SA / DA with automatic return to neutral
• Spool valve 2: 4-position, DA with automatic return to neutral
Set C - 2 spool valves and flow divider
• Spool valve 1: 3-position, SA / DA with automatic return to neutral
• Spool valve 2: 3-position, SA / DA and zero leakage
Set D - 3 spool valves and flow divider
• Spool valve 1: 3-position, SA / DA with spring loaded return to neutral
• Spool valve 2: 3-position, SA / DA with automatic return to neutral and zero leakage
• Spool valve 3: 4-position, DA with automatic return to neutral
Set E - 3 spool valves and flow divider
• Spool valve 1: 3-position, SA / DA with automatic return to neutral
• Spool valve 2 and 3: 4-position, DA with automatic return to neutral
Set F - 4 spool valves and flow divider
• Spool valve 1: 3-position, SA / DA with spring loaded return to neutral
• Spool valve 2 and 3: 3-position, SA / DA with automatic return to neutral and zero leakage
• Spool valve 4: 4-position, DA with automatic return to neutral

Parts list 
(1) Inlet unit with flow control valve (2) Plates with seals (3) Excess flow rate pipe (4) Adjustment knob (flow divider) (5) Single / double acting (SA / DA) change-over screw (6) Spool valves (all versions) (7) Intermediate block (excess flow rate) (8) Set (2, 3 or 4 spool valves)
(9) Intermediate block (10) Support (11) End plate (connection with lift control valve) (12) Screw (13) Plug and seal (provisional return) (14) Screw (15) Cap and seal (filling) (16) Plug and seal (provisional return) (17) Studs and nuts (18) Pin (19) Stirrup (20) Pin (21) Support (control cable) (22) Screw



Characteristics



Functions: Double acting; Single and double acting (convertible).
These functions are also recognised via the abbreviations SA and DA.

Positions : Three; Four with one in floating position.

Return to neutral: By spring or by an automatic system.

Zero leak: With or without.

Each spool valve is activated by a lever in the cab and it has three phases of travel:
- 35% reduced flow rate;
- 45% progressive increase of flow rate and pressure;
- 20% full flow rate.
The spool valve placed against the flow divider is spool valve No. 1.
The progressive increase of flow rate and pressure ensures uniform operation of the implements. This characteristic also allows two spool valves to be activated simultaneously, the total flow rate being shared. The flow rate to each quick-disconnect coupling is proportional to the position of the control lever.


Layout of channels and ports












Legend 

A - B Outlets or returns going to or coming from hydraulic slave device

N Oil connection to lift control valve

P Pressure (HP)

QX Outlet port for excess flow rate

R Return

X Flow rate regulated to 1st spool valve

Vr Outlet port to lift control valve










Operating and adjusting the flow divider

Function of the flow divider
For operations requiring low oil flow rate, the flow divider allows to vary supply to the hydraulic slave device via a knob (4) used to adjust flow rate between “maximum stop” and “minimum stop”. It is fitted at the inlet of the auxiliary spool valve assembly. It is supplied by oil from the high flow rate circuit passing through the trailer braking valve or the closing plate (depending on version).


Operation 
The oil coming from port (P) is directed to port (X) and supplies the first spool valve. The flow is regulated according to the position of the knob (4). Simultaneously, the pressure in channel (P) allows oil to pass through drilled hole (a) and restrictor (b). The piston (1) is then moved to the right, allowing oil to be directed towards port (Qx). The intermediate block (7) receives the excess flow rate via the pipe (3).


Adjustmen
Remove the stop screw (6), the locknut (1) and the washer (2).


Unscrew and remove the knob (4).
Without forcing the screw (3), tighten it until the valve (7) abuts against its seat. Place the knob (4) in contact with the sleeve (5).
Unscrew the knob two full turns. Install and tighten the stop screw (6) to a torque of 20 Nm. Turn the knob to its closed position.
Install washer (2) and tighten the locknut (1) to a torque of 30 - 40 Nm.