SkyTrak 6036 Service Manual - Manual (Page 33)

Section 3 Boom
Model 6036/6036T S/N 9B0500 thru 14833 3-15
Warning
1. Block the boom so it cannot be lowered.
2. If the line failure is isolated to the hoist circuitry
only, boom retraction can be performed by
operating the boom control lever in the normal
fashion.
3. If the line failure is in the boom extend line the
boom must be retracted by following the next
step:
(a) At the base of the extend/retract cylinder,
locate the counterbalance valve cartridge,
Fig. 3.19. Loosen the retainer nut and
control the rate of retraction by turning the
adjusting screw into the cartridge very
slowly clockwise. Hydraulic oil from
inside the extend/retract cylinder will
escape through the fault in the line.
4. If the line failure is in the boom retract line the
boom must be retracted by following the next
3 steps:
(a) At the base of the extend/retract cylinder,
locate the counterbalance valve cartridge
Fig. 3.20. Loosen the retainer nut and
turn the adjusting screw in (clockwise)
until it bottoms out. Doing this will render
the counterbalance valve inoperative.
(b) Clear the area around the machine of all
personnel and return to the operators cab.
(c) Move the boom control lever to the left to
retract the boom.
5. If the line failure was isolated to the extend/
retract circuit only, the boom can now be
lowered by operating the boom control lever in
the normal fashion after the blocking is
removed.
After the boom has been retracted fully, proceed
as follows:
1. Remove the blocking that is supporting the
boom.
2. If the line failure is in the boom hoist line the
boom must be lowered by following the next
step.
(a) Using two people to perform this proce-
dure will make boom lowering much
easier. At the base end of each hoist
cylinder, locate the counterbalance valve
cartridges, Fig. 3-20. Loosen the retainer
nut and control the rate of boom lowering
by turning the adjusting screw on each
cartridge simultaneously into the cartridge
very slowly clockwise. Hydraulic oil from
inside the hoist cylinders will escape
through the fault in the line.
3. If the line failure is in the boom lowering line
the boom must be lowered by following the
next 3 steps:
(a) At the base of each hoist cylinder, locate
the counterbalance valve cartridges,
Fig. 3-20. Loosen the retainer nut on
each cartridge and turn the adjusting
screws in (clockwise) until they bottom
out. Doing this will render each counter-
balance valve inoperative.
(b) Clear the area around the machine of all
personnel and return to the operators cab.
(c) Move the boom control lever forward to
lower the boom.
IMPORTANT: This procedure is to be used in
emergency situations only. By turning the
counterbalance cartridge adjusting screws to
lower the boom, the pressure settings of the
cartridge have been altered. DO NOT attempt to
reset these cartridges. Remove and replace all
three cartridges with new parts. Failure to replace
these cartridges with new parts will result in erratic
(extreme bouncing) lowering action, which may
cause damage to other components.
3.2.2 Hydraulic Line Failure
In the event of a hydraulic line failure in any of
the boom control circuits, extreme CAUTION
must be taken when attempting to lower an
elevated load. Hydraulic oil under high pressure
will escape through the fault in the line which
may result in the boom retracting or lowering at
a rapid rate. DO NOT perform this procedure
unless you are absolutely sure of what you are
doing. Consult your local JLGDistributor or the
JLG Service Department before proceeding.
IMPORTANT: If the boom has been extended, you
must first retract the boom before you attempt to
lower the boom.