Anonymous
Answer may depend on type of Feedback. However, note that if you have a Tapco system with MTS feedback transducer the problem may be the servo valve amplifier. You note valve is still “changing position” so I would assume it is still controlling on auto control.
If this is the case it would mean the LDT (Linear Displacement Transducer) is still functioning and allowing auto/servo control. The servo amplifier circuit board can still control the closed-loop circuit after its output signal (signal back to control room) is lost.
This circuit board output is a typical control component and can be caused to fail by things like a lightning strike.
Does this look like the failure you have found? Do you have continued control but no position signal back to the control room?
Slide-Valve Wally
Stinson Valve-Actuation LLC
stinson.w@sbcglobal.net