Vehicle System Testing and Adjusting 37
Hydraulic Control Valve
Problem: The control spools do not move freely.
Probable Cause:
1. The temperature of the oil is too high.
2. There is foreign material in the fluid.
3. The fitting connections in the valve body are too
tight.
4. The mounting bolts of the valve assembly do not
have the correct torque and have twisted the body.
5. Linkage of the lift and tilt levers does not operate
smoothly.
6. Bent lift or tilt spools.
7. Damage to the return springs of the spools.
8. The valve is not at normal temperature for
operation.
Problem: Control valve spools have leakage
around the seals.
Probable Cause:
1. There is foreign material under the seal.
2. The valve spools are worn.
3. The seal plates are loose.
4. The seals have damage or are badly worn.
Problem: The load lowers when the lift spool is
moved from the neutral position to the raise
position.
Probable Cause:
1. There is foreign material in the load check valve
area.
2. The load check valve and seat show wear.
3. Sudden loss of pump oil pressure.
4. Damage to the relief valve which causes low oil
pressure.
Problem: Spools do not return to neutral.
Probable Cause:
1. The springs are broken.
2. The spool is bent.
3. The system or valve has foreign particles in it.
4. The control linkage is not in alignment.
5. The fastening bolts of the valve have too much
torque.
Problem: No motion or slow, then a too sudden
action of the hydraulic system.
Probable Cause:
1. The relief valve is not correctly set, or will not
move in base and/or is worn.
2. There is air in the system.
3. Dirt or foreign particles between relief valve
control poppet and its seat.
4. Valve body has a crack inside.
5. Spool not moved to a full stroke.
Lift and Tilt Cylinders
Problem: Leakage around the cylinder rod.
Probable Cause:
1. Cylinder head (bearing) seals are worn.
2. Cylinder rod is worn, scratched or bent.
Problem: There is leakage of oil inside the
cylinder or loss of lift or tilt power.
Probable Cause:
1. The piston seals are worn and let oil go through.
2. Cylinder has damage.
Problem: The piston rods show wear.
Probable Cause:
1. The cylinders are not in correct alignment.
2. Oil is dirty.
To Next Page
Loading...
