Electro-hydraulic turbine controller hunting


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Electrohydraulic turbine controller (Bosch Rexroth STW high response prop valve) was found to be hunting over a range of almost 10% which resulted in a load throw off of almost 40-60 MW suddenly. Trend shows that the actual position of the piston driven by the prop valve started hunting first followed by load throw off. Checked for airlock and vented out some oil. But again in sometime started responding the same way. Need some help in this regard.

Peter Nachtwey

Bosch has some very good servo-solenoid valves. I haven't heard of a STW valve. Do you have the complete part number or better yet a link to the pdf file?

You should be able to compare the spool position to the command position and see how well they are matched. If the spool position is following the command signal the perhaps the command signal or outer PID is not right or the valve spool is non-linear or has a dead band.

This should be easy.