SkyTrak 6036 Service Manual - Manual (Page 32)

Section 3. Boom
3-14 Model 6036 S/N 9B0499 and Before
Fig. 3.19 Counterbalance Valves on Boom Hoist
Cylinders
After the boom has been retracted fully, proceed as
follows:
1. At the base of each hoist cylinder, locate the
counterbalance valve cartridges, Fig. 3.19.
Loosen the retainer nut on each cartridge and
turn the adjusting screws in (clockwise) until
they bottom out. Doing this will render each
counterbalance valve inoperative.
2. Remove the blocking that is supporting the
boom.
3. Clear the area around the machine of all
personnel and return to the operators cab.
4. Move the boom control lever forward to lower
the boom.
IMPORTANT: This procedure is to be used in
emergency situations only. By turning the counter-
balance cartridge adjusting screws to make the
valve inoperative, 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 JLG Distributor 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.
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. 3.18. 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. 3.19. 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 re-
moved.
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 procedure
will make boom lowering much easier. At
the base end of each hoist cylinder, locate
the counterbalance valve cartridges, Fig. 3-
19. Loosen the retainer nut and control the
rate of boom lowering by turning the
Warning !
RETAINER
NUT
ADJUSTING
SCREW
COUNTERBALANCE
VALVE
BOOM HOIST
CYLINDERS
OA0552