TROUBLESHOOTING
CYLINDER LEAKAGE
Hydraulic cylinders may retract due to the cooling of the oil
in cylinder. Oil shrinks approximately 4% per 100°F of cool-
ing, or as an example, if a cylinder is extended 100” and it
cools 100°F, it would shorten approximately 4”.
TELESCOPE CYLINDER
If excessive leak-down is encountered, check items in the fol-
lowing sequence:
1 With boom offside and horizontal, extend the boom
approximately 6 ft. per section. Mark the first telescop-
ing section at the end of the base section.
2 Elevate the boom to maximum angle and suspend a load
on the hook. (7 tons on a 2-part line would approximate
manufacturer’s inspection procedures.)
3 With engine shut off, hold or tie the telescope function
lever in the full “extend” position for approximately 15
minutes.
4 Return the telescope lever to neutral, start engine,
ground the load, and return the boom to horizontal. Re-
mark the boom section as in (1). Measure the distance
between marks to determine leak-down of the cylinder.
The manufacturer’s allowable drift specification for produc-
tion machines is as follows:
With 14,300 lb. hook load, 2-part hoist line, boom extended
about 6 ft. per section at maximum boom angle, and 160
degree F. hydraulic oil temperature, the leak-down per cylin-
der is not to exceed 3/4 inch in a 15-minute period.
IDENTIFY A DEFECTIVE HOLD VALVE in the cylinder
which drifts excessively by interchanging the hold valve car-
tridge with one removed from a cylinder that is not drifting,
or by replacement with a new cartridge. Before installing
the cartridge, visually inspect the external “O” rings and
backup washers. Retest per the procedure above to deter-
mine if hold was defective.
An alternate method to test hold valve would be to elevate
boom and then disconnect the two hoses coming from valve
bank. If oil continues to flow slowly from line to extend then
it is a hold problem. If oil continues to flow from retract,
then it is faulty or leaking by piston in cylinder.
IF THE HOLD VALVE IS NOT FOUND DEFECTIVE, the
cylinder must be removed from the boom assembly for
repacking and checking. Prior to reassembly of the cylinder,
conduct an air test on the piston rod by blocking the retract
ports on the rod near the piston end. Slip a plastic bag over
piston end of rod and retain and seal with rubber band.
Apply and hold a slight amount of air pressure at the retract
port of the rod. (Port stamped with “R”.) Expansion of the
plastic bag indicates a defective rod weldment or seals on the
port tube in the rod.
WHEN REASSEMBLING THE CYLINDER, care should be
taken to keep the piston rod assembly parallel in all planes
with the cylinder barrel as the piston enters and is pushed
down the barrel prior to gland engagement.
NOTE: An external leak from telescope cylinders or hydrau-
lic line within the boom assembly does not cause leak-down
without also having one or more of the above conditions
present.
BOOM LIFT CYLINDER
The suggested procedure for identifying the specific cause of
leak-down should be performed in the following sequence:
ELEVATE THE BOOM TO NEAR MAXIMUM ANGLE, not
completely extended, with a boom length sufficient to winch
up a convenient payload approximately one (1) foot from
ground level. Shut of engine.
RT700 Series Page 5 - 29 Issued: August 2003
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