LOAD KING 80-160, Operator'S Manual

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321
Cylinder Leakage
Hydraulic cylinders may retract due to the cooling of the oil in cylinder. Oil shrinks approximately
1% per 25°F of cooling, or as an example, if a cylinder is extended 100" and cools 100°F, it will shrink 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 thumb wheel on the joystick in the full “extend” position for
approximately 15 minutes.
4. Return the telescope thumbwheel joystick 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 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 the hold valve would be to disconnect the two hoses coming from the valve
bank and then elevate the boom . If oil continues to flow slowly from the extend line then it is a hold
problem. If oil continues to flow from retract, then it is faulty or leaking by piston in cylinder.
NOTE:
With hollow rod telescope cylinders you can drain in excess of 40 gallons of oil from the rod.
If the boom comes in while doing this test, then the cylinder is faulty or leaking by the piston in the
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 hydraulic line within the boom assembly does
not cause leak-down without also having one or more of the above conditions present.