Cylinder Leakage
Hydraulic cylinders may retract due to the cooling of the oil in cylinder. Oil shrinks
approximately 4% per 100°F of cooling, 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 following sequence:
1. With boom offside and horizontal, extend the boom approximately 6 ft. per
section. Mark the first telescoping 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. Remark 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 production 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
cylinder 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 cartridge 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 determine 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.
RT500
Troubleshooting
230 REVISED:
To Next Page
Loading...
Need help?
General
