- Tilt cylinder
- Compensating cylinders
- Load control valve
- Relief valves
The compensating system automatically maintains the selected angle of the quick coupler in relation to the ground, when the boom is being raised or when the boom is being lowered.
The piston rod ends of the compensating cylinders are attached to the boom and the cylinder ends are attached to the machine frame. The piston rod of the compensating cylinders extend when the boom is raised. The piston rod of the compensating cylinders retract when the boom is being lowered.
When the quick coupler is not operating, the spool in the implement control valve for the coupler tilt is in the HOLD position. Oil is locked into the lines between the tilt cylinder and the compensating cylinders in order to create a closed hydraulic circuit.
The volume of oil in the head end of the tilt cylinder is matched to the total volume in the head ends of the compensating cylinders. The rod end of the tilt cylinder and the rod ends of the compensating cylinders are similarly matched. Therefore, movement of the tilt cylinder will be in proportion to the movement of the compensating cylinders.
Boom Lower
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| Illustration 1 | g01022461 |
Boom Lower (1) Load control valve (2) Tilt cylinder (3) Compensating cylinders (6) Lock valve (7) Check valve (10) Spring (12) Check Valve (13) Block at tilt control valve (14) Block at tilt control valve (15) Check valve (16) Lock Valve | |
When the boom is being lowered, compensating cylinders (3) are retracting due to the movement of the boom. Oil is displaced from the head end of the compensating cylinders and opens check valve (15). The displaced oil then flows into load control valve (1). Check valve (7) is unseated. Oil then flows into the head end of tilt cylinder (2). The oil flow extends the tilt cylinder, which tilts the quick coupler backward in order to maintain the selected angle of the coupler relative to the ground. Oil is displaced from the rod end of the tilt cylinder and flows to the rod ends of the compensating cylinders.
Boom Raise
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| Illustration 2 | g01022501 |
Boom Raise (1) Load Control valve (2) Tilt cylinder (3) Compensating cylinders (6) Lock valve (7) Check valve (10) Spring (12) Check Valve (13) Block at tilt control valve (14) Block at tilt control valve (15) Check Valve (16) Lock valve (17) Load control valve | |
When the boom is being raised, compensating cylinders (3) are extending due to the movement of the boom and the oil which is displaced from the rod end of the compensating cylinders flows into the rod end of tilt cylinder (2). The oil opens lock valve (17) in load control valve (16). Also, the pressure that is developed in the rod end of the tilt cylinder opens lock valve (6) in load control valve (1). The piston rod of the tilt cylinder retracts and the quick coupler is tilted forward in order to maintain the selected angle of the coupler relative to the ground. Lock valve (6) in load control valve (1) opens in proportion to the pressure that is applied. This controls the flow of oil from the head end of the tilt cylinder to the head end of the compensating cylinder.
Check and Relief Valves
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| Illustration 3 | g01022526 |
Check and Relief Valves (1) Load control valve (2) Tilt cylinder (3) Compensating cylinders (4) Relief valve (5) Relief valve (6) Lock valve (7) Check valve (8) Line (9) Line (10) Spring (11) Tank gallery (12) Check valve | |
Pressure Relief
If the quick coupler is tilted fully forward or if the quick coupler is tilted fully backward and the boom is still moving the compensating cylinder would continue to move with the boom. In this event, the pressure in the lines between the compensating cylinder and the tilt cylinder would rise sharply. In order to limit the pressure in the system, relief valves (4) and (5) are installed in the implement section of the control valve for the coupler tilt. Relief valve (5) will operate when the boom is being raised. Relief valve (4) will operate when the boom is being lowered.
A sharp pressure rise in line (8) or line (9) acts on relief valve (4) or (5). As the pressure rises above the setting of the relief valve, the valve unseats against the force of spring (10). The pressure oil is then relieved to the tank through gallery (11) .
When the oil pressure returns to a level below the pressure setting, spring (10) closes the valve.
Makeup
Relief valve (4) and relief valve (5) also have anticavitation features which allow makeup oil to flow into the compensating system from the return gallery of the implement control valve, if the pressure in the compensating system falls below the return oil pressure.
If the pressure in line (8) or (9) falls below the pressure in tank gallery (11), then oil at tank pressure will unseat check valve (12) against the force of a spring. Oil then enters line (8) or (9) from tank gallery (11). The increase in the pressure in line (8) or (9) will prevent cavitation in the supply lines to the implements.
When the oil pressure between line (8) or (9) and tank gallery (11) has been equalized, the check valve (12) is reseated by the spring.