Proportional Valve With Spool Feedback Oscillates Badly on Start-up

By Robert Sheaf, CFPAI/AJPP, CFPE, CFPS, CFPECS, CFPMT, CFPMIP, CFPMMH, CFPMIH, CFPMM, CFC Industrial Training.

A dam out west had a hydraulic system installed to replace an old system that was just giving them too many maintenance problems.

The new system was very similar to the old unit except its directional valve was ungraded to a proportional pilot operated valve with spool feedback on the main spool. The unit would open gates allowing flow to all the downstream rivers during the dry season to keep them from totally drying up and causing large fish kills.

Every time they would start it up, which could be about every 2 to 3 months, the proportional valve would stutter and oscillate making it difficult to trust and worried that it could fail at a critical time, possibly spilling too much water. The oscillation would only last 30 to 50 seconds and then smooth out and work fine.

The unit was built with the reservoir mounted over the pump motor units and the valving and filters were mounted on top above the reservoir to conserve floor space. Replacing the expensive valve did not solve the problem.

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