4-17
Published 9-04-2014, Control # 422-08
RT765E-2 SERVICE MANUAL BOOM
11. Extend the boom approximately 6 in (15 cm). Retract the
boom again until one of the stop blocks just contacts its
boom section.
12. Again check the gap as in step 10 and if necessary,
make further adjustments.
13. Repeat steps 11 and 12 until there is a 0.125 in (3 mm)
gap at the outer mid section’s stop block when the fly
section’s stop block has just made contact.
14. Lock the retract cable adjustments with the jam nut.
TELESCOPE CIRCUIT
Description
The boom telescope circuit consists of the telescope
hydraulic remote controller, telescope directional control
valve, holding valve, boom lock valve and the upper and
lower telescope cylinders.
NOTE: If the crane is equipped with an auxiliary hoist, the
telescope function is controlled by a foot pedal
instead of a controller.
The telescope control valve is the closed spool type and is
described in Valves, page 2-30.
Refer to Valves, page 2-30 for a complete description of the
hydraulic remote controller.
Cranes equipped with a telescope cylinder charge system
will have an additional valve manifold in the telescope circuit
to prevent boom retraction due to thermal contraction under
the following operating conditions: If the crane is operated
with a long boom length and low boom angle, and the
hydraulic oil in the telescope cylinders cools and contracts,
the friction forces in the extended boom will prevent the
boom from retracting. Then, if the operator begins to elevate
the boom without telescoping out slightly, the crane may
reach a boom elevation angle where the weight of the boom
sections and load overcomes the friction forces in the boom
sections, causing the boom to retract until the column of oil
inside the cylinders once again supports the boom sections.
The telescope cylinder charge system will prevent the boom
from retracting under these conditions by automatically
replenishing the volume of hydraulic oil lost in the telescope
cylinders due to thermal contraction.
Additionally, the system utilizes a pressure switch plumbed
into the telescope extend circuit, which will turn on the
telescope cylinder charge indicator and sound the warning
buzzer in the operator’s cab if the charge system is not
functioning properly (see Telescope Cylinder Charge
Indicator in Section 3 of the applicable Operator’s Manual).
Refer to Valves, page 2-30 for a complete description of the
telescope cylinder charge valve manifold. Refer to the sub-
section titledTelescope Cylinder Charge System - Electrical
Schematic (If Equipped), page 3-20 for an electrical
schematic of this system.
A boom lock valve is located on the retract circuit of the
upper telescope cylinder. The boom lock valve prevents
cylinder drift during pinning of boom extensions.
Theory Of Operation
Flow from the pump travels to the telescope directional
control valve. Movement of the telescope hydraulic remote
controller (foot pedal, when equipped with optional auxiliary
hoist) for telescope functions from neutral sends a pilot
pressure signal to the directional control valve to shift the
spool in the directional control valve. This aligns the
appropriate passages in the control valve to route oil to the
telescope cylinders.
For more information, refer to Theory of Operation, page 4-1.
The telescope cylinder charge valve manifold, on cranes
equipped with the telescope cylinder charge system,
receives oil from port 6 of the hydraulic swivel, which is
supplied oil from pump 3 through the power beyond valve in
the integrated outrigger/rear steer valve; all excess oil
through the telescope cylinder charge valve manifold goes to
the pressure reducing sequence valve.
Only when the boom is elevated above 35 degrees will the
rated capacity limiter (RCL) energize the solenoid valve in
the telescope cylinder charge valve manifold, allowing oil to
flow through the pressure reducing valve and on to the
extend circuits of the upper and lower telescope cylinders.
Should the system pressure in the telescope extend circuits
drop below 13.8 bar (200 psi) due to thermal contraction, the
telescope cylinder charge system will charge the telescope
extend circuits with 13.8 bar (200 psi) of pressure to prevent
the boom from retracting. Oil pressure is maintained in the
telescope extend circuits by check valves in the telescope
cylinder charge valve manifold.
CAUTION
Over tightening of the retract cable will damage the cable.
take care when retracting the boom fully, while adjusting
the cable, to avoid full boom retraction if the fly section
contacts its stop block more than 0.125 in (3 mm) before
the outer mid section contacts its stop block on the inner
mid.
Reference Only
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