TL;DR
Jerky or erratic movement is usually air in the cylinder, a sticking directional control valve, or a pressure-compensator setting that is chasing load fluctuations. Purge air, inspect the valve spool, and verify the compensator setting.
What you might see
- actuator jerking or lurching during movement
- inconsistent speed during a single stroke
- actuator fails to respond or responds with delay
- position control hunting or oscillating
Likely causes
Air trapped in the cylinder or actuator lines causing compressible spongy response
Sticking or contaminated directional control valve spool preventing smooth flow metering
Pressure-compensator set too close to load pressure, causing hunting under varying load
Worn flow-control valve providing inconsistent metering
Required tools
- LOTO kit
- Multimeter for solenoid coil check
- O-ring kit for directional valve
- Lint-free cloths and hydraulic solvent
- Torque wrench for valve mounting bolts
- Pressure gauge
Safety first
- Depressurize the manifold completely before removing a directional valve. Residual pressure launches the spool with dangerous force.
- Do not use cleaning solvents incompatible with the system seals. Check the Parker seal material specification.
Procedure
- 1
Check the hydraulic fluid for air (see the noisy-pump-cavitation procedure on this machine). Purge air from the system first before diagnosing the valve.
- 2
Stroke the directional control valve electrically from the PLC or manual override button. Confirm the solenoid clicks and the valve shifts smoothly both directions.[1]
- 3
Lock out the pump and remove the directional valve from its manifold. Inspect the spool and bore for varnish, scoring, or contamination deposits.
Warning: Depressurize the manifold fully before removing the valve. Residual pressure will eject the spool. - 4
Clean the spool and bore with lint-free cloths and an appropriate hydraulic solvent. Do not use shop rags that leave fibers.
- 5
Reinstall the valve using a new O-ring kit. Torque the mounting bolts evenly to the Parker specification.[1]
- 6
Check the pressure-compensator setting on the PV pump. The compensator should be set 3-5 bar above the maximum load pressure, not at the minimum.
- 7
Check any flow-control or meter-out valves for contamination or wear and clean or replace as needed.
- 8
Cycle the actuator at low speed after repairs and confirm smooth, consistent movement before returning to full duty.
Sources
Parker PV Series Variable Volume Piston Pump Service Manual, Parker Hannifin Corporation
Parker PV Series and Directional Control Valve Service Manual, valve spool inspection and pressure compensator settings (general)
View source
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