Servo Valve Diagnosis

Servo valves used in bend arms are very sensitive to contamination and require a lot of cleanliness to work properly. A 40 micron particle can cause a servo valve to "stick." (1 micron = 0.001 mm. 40 microns = 0.0016 inches) Even valves that are not completely stuck can act strangely if they are not completely clean.

Servo valves require filters in the system. The first time a system is turned on is the most critical. Particles that are in the system from installation can migrate and they must be stopped by the filter before the valve.

Signs of a sticking valve

1. The servo controller cannot be tuned.
2. The axis drifts in one direction at power up when it did not drift before.
3. The axis oscillates
4. The axis overshoots then recovers by pulling back when it did not do so before.
5. The valve was pulled off the system then put back on - at which point it stopped working

Fixes

1. Throughly clean the valve
2. Check the valve for need of repair
3. Change out the filter periodically
4. Leave the valve on the system if it is working well

Source: Hydraulics/Pneumatics Magazine

Other

• CNC Bender Technical Notes
• CNC Bender