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| Illustration 1 | g00757007 |
Boom Hydraulic System (1) Bank valve (2) End section of bank valve (3) Joystick (4) Implement section of bank valve (quick coupler) (5) Implement section of bank valve (frame leveling or towing hitch) (6) Implement section of bank valve (auxiliary services) (7) Frame leveling cylinder ( TH63, TH82, TH83) or towing hitch cylinder ( TH62) (8) Load control valve for frame leveling cylinder or towing hitch cylinder (9) Brake reservoir (10) Implement section of bank valve (coupler tilt) (11) Dual relief valve (12) Relief valve (coupler tilt) (13) Pilot control valve (14) Solenoid valve (15) Solenoid valve (16) Solenoid valve (17) Solenoid valve (differential lock valve) (18) Line (service brake system) (19) Line (differential lock cylinder) (20) Lines to steering system (21) Metering pump (22) Filter (23) Hydraulic tank (24) Line (load sensing) (25) Piston pump (26) Compensating cylinders (27) Inlet section of bank valve (28) Implement section of bank valve (boom raise/lower) (29) Implement section of bank valve (boom extend/retract) (30) Load control valve (boom extend/retract) (31) Telescoping cylinder (boom extend/retract) (32) Load control valve (boom raise/lower) (33) Boom cylinder (boom raise/lower) (34) Relief valve (coupler tilt) (35) Relief valve (36) Implement relief valve (37) Control valve (compensating cylinders) (38) Load control valve (coupler tilt) (39) Tilt cylinder (coupler tilt) (40) Diverter valve (41) Coupler cylinder (42) Load control valve (coupler cylinder) (PP) Pump delivery (CP1) Boom extend pressure (CP2) Boom raise pressure (R) Return oil (S) Suction oil (P) Pilot oil (LS) Load sensing oil | |
The pilot pressure to bank valve (1) which operates implement section (29) for the cylinder of the boom extend/retract is transmitted through pilot control valve (13). The arrangement of the machine controls determines whether solenoid valves (14), (15) and (16) will be energized or de-energized.
Note: Refer to Operation and Maintenance Manual, SEBU7370 for information regarding control arrangements.
When more than one movement is selected at the same time, the bank valve acts as a flow divider. At all pump speeds, available flow is divided between the services that are selected. The flow is in proportion to the amount of offset of the spool and to system pressures.
The following description refers to a machine that is equipped with a type B control arrangement.
To extend the boom, the joystick (3) is moved to the right. This transmits the pilot pressure to implement section (29) through solenoid valve (14) which is de-energized. To raise the boom, the joystick is pulled backward. This transmits pilot pressure directly to implement section (28) .
Pump oil flows to the piston side of telescoping cylinder (31) via load control valve (30). Also, pump oil flows to the piston side of boom cylinder (33) via load control valve (32). Return oil from the rod side of both cylinders flows to hydraulic tank (23) via bank valve (1) .
The system pressures would usually 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 of piston pump (25) through the resolver network of bank valve (1). The pressure and flow compensator valve of the pump matches the pump output pressure to the highest pressure requirement in the system. Illustration 1 indicates boom raise pressure as being higher than boom extend pressure.
If the oil supply failed, the load control valves would be closed by spring force. This would lock oil into the piston side of boom cylinder (33) and the piston and rod sides of telescoping cylinder (31) in order to hold the boom at the selected angle and length.
The load control valve (30) for telescoping cylinder (31) locks oil into both sides of the cylinder in order to prevent the cylinder from extending or retracting when the boom is operating above the horizontal position or below the horizontal position.
When telescoping cylinder (31) or boom cylinder (33) are being retracted the respective load control valves (30) and (32) meter oil from the piston sides of the cylinder in order to ensure positive speed control and response to changes in the position of the joystick (3).