SECTION 7 – HYDRAULICS
7-6
USTC
January 15, 2001
5. If the pressure is incorrect, remove the acorn
nut or loosen the jam nut on the relief valve
cartridge to access the adjustment screw.
If the pressure is too low, turn the adjustment
screw clockwise to increase the pressure setting.
If pressure is too high, turn the adjustment
screw counterclockwise to decrease the pres-
sure setting.
6. Tighten jam nut while holding the adjusting
screw or install the acorn nut.
7. Repeat step 4 to ensure that the pressure set-
ting is correct.
CYLINDERS
Holding Valves
Each hydraulic cylinder on the crane (except the
outrigger extend cylinder) has an integral holding
valve to prevent the cylinder from retracting if a line
breaks or is accidentally punctured. The holding
valves use small orifices which can become clogged
if dirt enters the hydraulic system.
Holding valves prevent movement in one direction
only, such as retraction. Some applications require
holding valves for both directions. When multiple
holding valves are used, it is possible to trap oil in
the cylinder between the holding valves. To avoid
this, do not remove the holding valves when the
cylinder is fully extended or retracted.
To remove a holding valve:
1. Loosen the hoses into the cylinder to relieve any
pressure.
2. Fit the wrench on the cartridge and cover with a
rag to prevent hydraulic spray.
3. Remove the cartridge.
CAUTION: NEVER ADJUST HOLDING
VALVES.
Note: Cylinders vary depending upon the
application. The procedures described herein are
general. If specific questions arise contact the USTC
Customer Service Department. If not equipped with
cylinder disassembly tools, refer to a specialty
hydraulic shop.
IMPORTANT: Perform cylinder disassembly and
assembly on a clean work surface in a dirt free
environment.
Dissasembly
1. Connect a suitable auxiliary hydraulic power
source to the cylinder ports.
WARNING: DO NOT FULLY EXTEND
CYLINDER. RETRACT CYLINDER
SLIGHTLY TO PREVENT TRAPPING
PRESSURE.
2. Operate hydraulic power source and extend
cylinder.
3. If applicable, remove holding valve(s) and
fittings from cylinder port block. Discard o-
rings.
4. Remove bleeder blugs and seal washers from
cylinder port block.
5. Secure cylinder barrel in a suitable holding
device. Clamp butt end of barrel to prevent
distortion and barrel damage.
6. Remove nylon plug, if installed, and set screw
from cylinder head cap.
7. Use a spanner wrench to loosen the cylinder
head cap. Tap with a hammer, if necessary.
Remove head cap from cylinder barrel.
IMPORTANT: Take care not to damage the
chrome plating on the rod.
8. Attach a suitable pulling device to the cylinder
rod.
IMPORTANT: Extreme care should be taken when
removing cylinder rod, head and piston. Avoid
pulling rod off-center, which could damage the
piston or cylinder barrel surfaces.
9. With barrel clamped securely, apply pressure to
the rod pulling device and carefully withdraw
complete rod assembly from barrel.
10. Using suitable protection for the rod, clamp
cylinder rod in a vise or holding fixture as close
to the piston as possible.
