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| Illustration 1 | g00790993 |
The Illustration above shows the Boom Hydraulic System when the Boom is being Extended and the Boom is being Raised. (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) 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) (PP) Pump delivery (CP1) Boom extend pressure (CP2) Boom raise pressure (R) Return oil (S) Suction oil (P) Pilot pressure (LS) Load sensing pressure | |
When more than one movement of the boom is selected at the same time, bank valve (4) acts as a flow divider. At all pump speeds, available flow is divided between the movements that are selected. The flow is in proportion to the amount of offset of the spool and to system pressures.
Piston pump (29) supplies oil to bank valve (4). Pressure reducing valve (26) in inlet section (32) provides pilot pressure to joystick (16) .
In Illustration 1, joystick (16) is moved to the right and pilot pressure to implement section (20) is transmitted through pilot control valve (21). Also, the joystick is pulled backward and pilot pressure for raising the boom is transmitted directly to implement section (36) .
Oil (CP1) flows from implement section (20) to the piston side of telescoping cylinder (43), and oil (CP2) flows from implement section (36) to the piston side of boom cylinder (38). Return oil (R) from the rod sides of the cylinders flows to hydraulic tank (28) through bank valve (4) and filter (30) .
Usually, the system pressure for the boom extend/retract and for the boom raise/lower would be different. The respective system pressure will depend on the weight of the load, the angle of the boom, and the length of the boom. The highest pressure is connected to the pressure and flow compensator valve on piston pump (29) through the resolver network of the bank valve. The pressure and flow compensator valve matches the pump output pressure to the highest pressure requirement in the system.
If there is no hydraulic power, the load control valves would be closed by spring force. This would lock oil into the piston side of the boom cylinder and the piston side of the telescoping cylinder in order to hold the boom at the selected angle and length.
When the boom is below the horizontal position and there is no hydraulic power, the spool in implement section (20) locks oil in the rod side of the telescoping cylinder in order to prevent the cylinder from extending.
When the telescoping cylinder is being retracted or the boom cylinder is being retracted, the respective load control valve meters oil from the piston side of the cylinder in order to ensure positive speed control and response to changes in the position of the joystick.