Zoomlion ZRT850, Operator'S Manual

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Operator’s Manual for Rough Terrain Crane

An extended boom can retract a short distance if the boom is extended for
a long period of time. The items that follow are the possible causes for the
movement:

A change in the hydraulic oil temperature

A change in the angle of the boom

Lubrication status.
Solutions:

Make sure that the hydraulic oil temperature does not increase too
high.

Extend the boom to the correct length.

Do not extend / retract the boom with a suspended load.
7.14 DERRICKING OPERATION (OPERATE – BOOM DERRICK)
A. To move the boom up or down (derricking), the hydraulic oil is pumped in or vented
out of the derricking cylinder.
B. The boom angle (boom derricking) is adjusted from -2° – 80°, by the derricking
cylinder. When the boom is in the front at a -2° angle, jib assembly, line parts change
and boom head parts maintenance can be carried out easily.
C. The derricking cylinder has a balance valve. The balance valve, in the hydraulic
system, helps the derricking components move smoothly. When the boom is set at
the correct length, the valve stops the hydraulic oil flow out of the derricking cylinder.
This helps to lock the boom in position.
D. The right joystick controls the derricking movements. Refer to Figure 7-15.
E. The speed of the derricking up / down movements change by:

Joystick – how far you move the joystick left or right

Throttle pedal – increase or decrease the engine RPMs.
Move the
joystick
rightwards:
Move the
joystick
leftwards:
derrick the
boom up
Neutral position:
stop
Right
joystick
7-24 ZRT850 Rough Terrain Crane