
QAY220 All Terrain Crane Operation Manual
7-2 Hydraulic system description
7-2
The superstructure hydraulic system of QAY220 All Terrain Crane consists of two parts: the first
part is open circuit, in which variable displacement double-pump is used for main and auxiliary winch,
elevating and telescoping system. Advanced electric proportion pump-controlled system is used. Two-
way cartridge valve suitable for large flow is employed as main control valve, less inner pressure loss.
When output signal changes, the control oil pressure output is changed by the proportional signal
delivered from remote module, and then the inclination of pump swash plate is changed, thus pump
displacement is changed. Variable displacement pump has summation power control function, which
controls the output signal of remote module by PLC program, as a result, optimizes the pressure
and flow of the pump, thus control performance and energy-saving effect are improved greatly. Pilot
joystick is electric proportional control lever, its moving angle is in direct proportion to the input
current of remote control module, thus the output current of variable displacement pump is in direct
proportion to the moving angle of the lever, consequently fine inching control is gained.
The second part is closed circuit, it consists of swash plate axial variable displacement piston
pump and bend axial constant displacement motor made by Rexroth Germany. The working port of
slewing pump is connected directly to the working port of motor, thus a closed circuit is formed, change
valve is not necessary, the flow and pressurized oil direction of the pump are changed by adjusting
the inclination of pump swash plate, consequently the rotation speed and direction of the motor are
changed, and fine inching control and smooth slewing movement are gained. There are auxiliary pump
and refilling device inside the variable displacement piston pump, they may effectively improve the
rotation speed of the pump and prevent the pump being sucked empty.
Hydraulic system
Chapter 7
Summary of Contents for QAY220
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