System Operation

Hydraulic Schematic

Basic Hydraulic Actuator System Schematic

1. Lift cylinder-secondary; 2. Flow protector-primary; 3. Lift cylinder-primary; 4. Flow protector-secondary; 5. Cylinder;

6. Tilt cylinder; 7. Control valve; 8. Unload solenoid valve; 9. Lift lock solenoid valve; 10. CF line to steering unit;

11. LS line to steering unit; 12. Brake reservoir; 13. Brake power master cylinder; 14. Relief valve - Tilt/Aux;

15. Relief valve - Main; 16. Needle valve; 17. Drive axle; 18. Gear pump; 19. Suction filter; 20. Return oil filter;

21. Main oil supply line; 22. Return oil line; 23. Hydraulic tank; 24. Brake boost pressure line

Vehicle System 20 System Operation

The hydraulic gear pump (18) is driven off the transmission PTO which draws oil from the hydraulic oil tank (23). Oil is supplied to the first control valve (7) section through hydraulic line (21).

This section also contains the priority valve that distributes oil to the following areas based on, 1st brakes, 2nd steering, and 3rd implement flow demand (mast/tilt/auxiliary functions). A constant flow of 0.8 GPM is provided by the priority valve to the brake power master cylinder (13). From the

CF port, oil flows through hydraulic line (10) to the steering unit. From the LS port, oil flows through hydraulic line (11) to the steering unit. The remaining oil from the control valve and the power master cylinder is returned to the hydraulic tank through hydraulic lines (22).

The safety unloader solenoid of the priority valve section prevents oil flow through the control valve when the operator has left the seat thereby preventing any function regardless of lever position.

Unloader solenoid valve (8) is electrically connected to the seat switch. The solenoid valve (8) is turned off within 3 seconds of the operator leaving the seat.

System pressure drops to less than 7 bar (100 PSI) and oil is diverted to tank instead of flowing through the control valve. Once the operator returns to the seat, the solenoid valve is turned on opening oil flow to the control valve and immediately returning normal work function to the control valve.

An additional safety lift lock function is also included which works much the same as the unloader solenoid mentioned above. This solenoid valve (9) prevents lowering of the carriage and/or mast when the operator leaves the seat more then 3 seconds, or the key switch is off. When the solenoid is off, oil flow is prevented from exiting the lift cylinders if the lever is pushed accidentally. Normal operation returns once the key switch is turned on or the operator returns to the seat.

A needle valve (16) on the side of the lift section can be used in an emergency should the lowering function not work normally. Approximately one half turn counter-clockwise makes it possible to lower the mast and/or carriage when the lift spool is shifted for lowering. After lowering the mast or carriage to the ground and with the start key off, inspect for possible causes of the malfunction.

Refer to the detailed trouble shooting guide will be shown in TESTING and ADJUSTING.

The lift cylinder lowering speed is controlled by a flow regulator valve integrated into lift spool.

Levers of control valve move spools within the control valve. The movement of spool allows fluid for lift, tilt, and side shift (5) functions. The return hydraulic fluid from each cylinder flows through control valve, hydraulic line (22), through the filterreturn (20), and back to a hydraulic tank.

If the pressure in the lift circuit goes higher than the pressure setting shown in the CONTROL VALVE

SECTION of SPECIFICATION, the main relief valve

(15) opens to control system pressure and dump excess pressure to the hydraulic tank. If the pressures in the tilt and/or auxiliary circuits go higher than the pressure setting shown in the

CONTROL VALVE SECTION of SPECIFICATION, the secondary relief valve (14) opens to control system pressure and dump excess pressure to the hydraulic tank.

Flow protectors (2) & (4) integrated in the lift cylinders provide a controlled decent of the mast and/or carriage if a critical hydraulic line is broken.

Sudden dropping of the mast and/or carriage is controlled.

The speed of forward/backward tilt and side shift cylinder extension are controlled by individually adjustable flow controls internal to each section of the control valve. Additionally, the counterbalance valve (or tilt lock valve) in the tilt spool prevents cavitations (development of air pocket) in tilt cylinder. For a complete hydraulic circuit, see the foldout, in the back of this module.

Vehicle System 21 System Operation