 | |
| Illustration 1 | g00791345 |
The Illustration above shows the Closed Hydraulic Circuit of the Compensating System. (1) Diverter valve (2) Coupler cylinder (quick coupler) (3) Load control valve for coupler cylinder (4) Bank valve (5) Signal relief valve (6) Line (load sensing) (7) Work tool cylinder (8) Rear section of stabilizer control valve (9) Front section of stabilizer control valve (10) Stabilizer control valve (11) Stabilizer cylinder (right side) (12) Stabilizer cylinder (left side) (13) Load control valve for left side stabilizer cylinder (14) Load control valve for right side stabilizer cylinder (15) End section of bank valve (16) Joystick (17) Implement section of bank valve (frame leveling) (18) Dual stage relief valve (19) Relief valve (coupler tilt) (20) Implement section of bank valve (boom extend/retract) (21) Pilot control valve (22) Solenoid valve (23) Solenoid valve (24) Solenoid valve (25) Solenoid valve (26) Pressure reducing valve (27) Brake reservoir (28) Hydraulic tank (29) Piston pump (30) Filter (31) Line (load sensing) (32) Inlet section of bank valve (33) Metering pump (34) Compensating cylinders (35) Valve (quick coupler pins) (36) Implement section of bank valve (boom raise/lower) (37) Load control valve for telescoping cylinder (38) Boom cylinder (boom raise/lower) (39) Implement section of bank valve (coupler tilt) (40) Load control valve for boom cylinder (41) Relief valve (coupler tilt) (42) Relief valve (43) Telescoping cylinder (boom extend/retract) (44) Implement section of bank valve (auxiliary section) (45) Control valve (46) Load control valve for frame leveling cylinder (47) Frame leveling cylinder (48) Load control valve for tilt cylinder (49) Tilt cylinder (coupler tilt) (B) Blocked oil | |
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 compensating system consists of tilt cylinder (49), control valve (45), compensating cylinders (34), relief valve (41), and relief valve (19) .
Control valve (45) consists of a cartridge valve that is installed into a valve manifold which has internal oil passages. The cartridge valve prevents excessive pressure from developing in the piston sides of the compensating cylinders when the boom is being raised.
The piston rod ends of the compensating cylinders are attached to the boom and the cylinders are attached to the machine frame. The piston rods of the compensating cylinders extend when the boom is raised. The piston rods of the compensating cylinders retract when the boom is being lowered.
Oil (B) is locked into the lines between the tilt cylinder and the compensating cylinders in order to create a closed hydraulic circuit.
The volume in the piston side of the tilt cylinder is matched to the total volume in the piston sides of the compensating cylinders. The rod side of the tilt cylinder and the rod sides of the compensating cylinders are similarly matched. Therefore, movement of the tilt cylinder will be in proportion to the movement of the compensating cylinders.
When the boom is being lowered, the compensating cylinders are retracting. Oil is displaced from the piston sides of the compensating cylinders. The oil then flows through control valve (45) and through load control valve (48) into the piston side of the tilt cylinder. The oil flow extends the tilt cylinder which tilts the quick coupler backward. Oil is displaced from the rod side of the tilt cylinder and flows to the rod sides of the compensating cylinders.
When the boom is being raised, the compensating cylinders are extending and oil which is displaced from the rod sides of the compensating cylinders flows into the rod side of the tilt cylinder. The pressure that is developed in the rod side of the tilt cylinder pilots load control valve (48) open. The piston rod of the tilt cylinder retracts and the quick coupler is tilted forward. The load control valve opens in proportion to the pressure that is applied. This controls the flow of oil from the piston side of the tilt cylinder to the piston sides of the compensating cylinders.
 | |
| Illustration 2 | g00791392 |
Location of Relief Valves (Coupler Tilt) in the Bank Valve (4) Bank valve (19) Relief valve for coupler tilt (39) Implement section of bank valve (coupler tilt) (41) Relief valve (coupler tilt) | |
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 cylinders would continue to move with the boom. In this event, the pressure in the lines between the compensating cylinders and the tilt cylinder would rise sharply. In order to control the rise of pressure in the system, relief valves (19) and (41) are installed in implement section (39) of the bank valve. Relief valve (41) will operate when the boom is being raised. Relief valve (19) will operate when the boom is being lowered.
Relief valve (19) and relief valve (41) have anticavitation features which allow makeup oil to flow into the compensating system from the return gallery of the bank valve, if the pressure in the compensating system falls below the return oil pressure.
 | |
| Illustration 3 | g00791405 |
Relief Valve (coupler tilt) (50) Service port (51) Anticavitation piston (52) Tank return port (53) Orifice (pilot stage) (54) Piston (pressure relief) (55) Pilot valve (56) Spring (57) Spring (58) Valve seat (59) Spring (60) Anticavitation chamber (61) Hole | |
Pressure Relief
Pressure in service port (50) for tilting the quick coupler acts on the face of anticavitation piston (51). Pressure also acts on pilot valve (55) and at the rear of piston (54) through orifice (53) .
At the set pressure, pilot valve (55) is unseated and the pilot valve moves away from valve seat (58) against the force of spring (56). Pressure in anticavitation chamber (60) is now relieved around the outside of anticavitation piston (51) into the tank return port (52) .
The pressure in service port (50) moves piston (54) away from the seat in anticavitation piston (51). This allows pressure in service port (50) to be relieved through holes (61) in the anticavitation piston.
Makeup Flow
If pressure in service port (50) falls below the pressure in tank return port (52), anticavitation piston (51) is offset by pressure in the tank return port and spring (57) is compressed. Oil enters the service port from the tank return port. When the pressure in the service port is equal to the pressure in the tank return port, the anticavitation piston is reseated by spring (57).