Troubleshooting Hydraulic Cylinders
Tech Talk 06/01/99
Table of Contents
Symptom: Hydraulic Cylinder Drifts
- Piston seal leak. Pressurize one side of cylinder piston and disconnect fluid line
at opposite port. Observe leakage. One to three cubic inches per minute is considered
normal for piston rings. Virtually no leak with soft seals on piston. Replace seals as
required.
- Other circuit leaks. Check for and correct leaks through operating valve. Correct leaks
in connecting lines.
- Open-center valve with conventional single-rod cylinder will creep if restriction
on tank port is sufficiently high. Use tandem-type valve spool configuration or spool with
pump dumped through one cylinder port with the other blocked.
- Closed centre valve can cause similar results, except creep will be according to the amount
of clearance flow in the valve. Proper notching of valve spool can prevent pressure buildup
in cylinder between lines.
- Spools with pressure blocked and cylinder ports completely relaxed will also prevent drift
if the moving element is not affected by gravity or vibration.
- Pilot-operated check valves can positively lock fluid in cylinder lines. Care must be
exercised to insure adequate pilot pressure when rod differential may cause intensification.
Symptom: Cylinder Fails to Move the Load When Valve is Actuated
- Pressure too low. Check pressure at cylinder to make sure it is set to circuit
requirements.
- Piston seal leak. Operate valve to cycle cylinder and observe fluid flow at valve exhaust
ports at cylinder stroke end. Replace seals if flow is excessive.
- Cylinder is undersized for load. Replace cylinder with one of a larger bore size.
- Piston rod broken at piston end. Disassemble and replace piston rod.
- Contamination in hydraulic system resulting in scored cylinder bore. Disassemble and
replace necessary parts.
Symptom: Erratic or Chatter Operation
- Excessive friction due to load misalignment. Correct cylinder to load alignment.
- Cylinder sized too close to load requirements. Reduce load or install larger cylinder.
- Larger difference between static and kinetic friction. Install speed control valves to
provide back pressure to control stroke.
Symptom: Excessive or Rapid Piston Seal Wear
- Excessive back pressure due to over-adjustment of speed control valves. Correct
valve adjustment.
Symptom: Cylinder Body Seal Leak
- Loose tie rods. Torque tie rods to manufacturer's recommendations for that
bore size.
- Excessive pressure. Check maximum pressure rating on cylinder nameplate
or vendor product catalog. Reduce pressure to rated limits. Replace seal
and retorque tie rods, as in 1. above.
- Pinched or extruded seal. Replace cylinder body seal and retorque tie rods as in 1. above.
- Seal deterioration (soft or gummy). Check compatiblity of seal material with lubricant
used of air cylinder or operating fluid of hydraulic cylinder. Replace with a seal
compatible with lubricant or operatiing fluid.
- Seal deterioration (hard or loss of elasticity). Usually due to exposure to elevated
temperature. Shiedl cylinder from head source. Replace seal as in 1. above.
- Seal deterioration (Loss of radial squeeze due to flat spots or wear on OD or ID). Can
occur as normal wear due to high cycle rate or length of service. Replace seal as in 1.
above.
Symptom: Rod Gland Seal Leak
- Torn or worn seal. Examine piston rod for dents, gouges or score marks.
Replace piston rod if surface is rough. Check gland bearing for wear. If clearance is
excessive, replace gland and seals.
- Seal deterioration (soft and gummy). Repeat setp 4 of Cylinder Body Seal Leak section.
- Seal deterioration (hard or loss of elasticity). Repeat step 5 of Cylinder Body Seal
Leak section.
- Seal deterioration (flat spots on ID). Repeat step 5 of Cylinder Body Seal Leak
section.
|
