XCMG QAY220, Operation Manual, Page: 122 / 172

QAY220 All Terrain Crane Operation Manual
7-6
7-6 Elevating circuit
Max. pump displacement (confluence
condition) is 280 ml/r.
The max. system setting pressure is 10
MPa during boom lowering. Boom lowering
depends on deadweight. In order to lower the
boom smoothly or stop lowering reliably, an
electro-proportional control balance valve is
fitted in the circuit.
7-7 Telescoping circuit
Max. pump displacement is 140 ml/r.
The crane has six boom sections, in which
2nd, 3rd, 4th, 5th and 6th section are telescoped
sequentially and synchronously by the single
cylinder pinning telescoping system.
During extending boom, the cylinder pin is
ejected to reach boom, and boom pin is ejected
to reach boom when boom is extended in place,
and any one of boom sections may be extended
out.
During retracting boom, pull out boom
pin first, and then retract boom and take back
cylinder pin.
I n o r d e r t o p r e v e n t p i s t o n r o d f r o m
bending due to excessive pressure during boom
extension, pressure limit valve is set to 18MPa.
A b a l a n c e v a l v e f i t t e d i n s i d e o f t h e
telescoping cylinder ensures stable boom
retraction and reliable stopping.
Do not adjust the pressure valve on the
balance valve. It is no necessary to depress
accelerator during boom lowering, because
it depends on boom deadweight.
Please carry out operation according to
the telescoping procedure. Never regulate
the pressure limit valve randomly.
Hydraulic system
Chapter 7
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