XCMG QAY220, Operation Manual, Page: 121 / 172

QAY220 All Terrain Crane Operation Manual
7-5 Slewing circuit
Max. pump displacement is 56 ml/r, constant motor displacement is 45 ml/r.
The opening of slewing brake is controlled by a solenoid valve. If the solenoid valve is not
energized, the brake is closed; if the solenoid valve is energized, the brake is opened by the action of
pressure oil. So, during slewing operation, operator must press the button for controlling the solenoid
valve.
A free sliding solenoid valve is fitted in the slewing main oil circuit, its function is to prevent the
boom from being broken due to a lateral force applied to it in load lifting, especially when the load is
about to leave the ground. Depressing the free sliding control switch may simultaneously energize the
solenoid valve for controlling slewing brake and the free sliding solenoid valve, and then two working
oil ports of slewing motor are connected and the slewing brake is opened, thus the whole superstructure
is in the floating state and under the force of wire rope the boom will automatically swing over the
center of load gravity, consequently the boom is protected.
The refilling pump of the slewing pump may refill oil in time for the slewing oil circuit during
slewing operation, so as to prevent the motor and oil pump being sucked empty. An oil filter and a
luminous pollution indicator are fitted in its pressure circuit. When the filter screen is clogged, its
indicator is red to remind replacement of the filter element. It is recommended that to install a cold
start valve in the oil filter so as to protect oil pump from damaging. The refilling pump not only has the
function of refilling oil but also provides power for controlling the variable displacement of slewing oil
pump and opening the slewing brake.
7-5 Hydraulic system
Chapter 7
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