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| Illustration 1 | g00834730 |
Boom hydraulic system (boom extend and boom raise) (5) Bank valve (17) Joystick (21) Implement section of bank valve (boom extend/retract) (22) Pilot control valve (23) Solenoid valve (24) Solenoid valve (25) Solenoid valve (26) Solenoid valve (differential lock valve) (30) Hydraulic tank (31) Piston pump (37) Implement section of bank valve (boom raise/lower) (38) Load control valve for the telescoping cylinder (boom extend/retract) (39) Boom cylinder (boom raise/lower) (41) Load control valve (boom raise/lower) (44) Telescoping cylinder (boom extend/retract) (CP1) Pressure oil for boom extend (CP2) Pressure oil for boom raise (PP) Pump pressure oil (S) Suction oil (LS) Load sensing oil (P) Pilot oil (R) Return oil | |
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.
Joystick (17) is moved to the right and pilot pressure to implement section (21) for extending the boom is transmitted through pilot control valve (22). The joystick is pulled backward and pilot pressure for raising the boom is transmitted directly to implement section (37) .
Pump oil flows from implement section (21) to the piston side of telescoping cylinder (44). Pump oil flows from implement section (37) to the piston side of boom raise cylinder (39). Return oil from the rod sides of the cylinders flows to hydraulic tank (30) through bank valve (5) .
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 (31) through the resolver network of bank valve (5). The pressure and flow compensator valve matches the pump output pressure to the highest pressure requirement in the system.
If the oil supply fails, the load control valves would be closed by spring force. This would lock oil into the piston side of boom cylinder (39) and the piston and rod sides of telescoping cylinder (44) in order to hold the boom at the selected angle and length.
Load control valve (38) for telescoping cylinder (44) 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 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.