I have successfully used PWM on 24V DC bang-bang valves with position feedback. However there is huge spool-overlap to contend with which isn't a problem in my case because I use a microcontroller and my PID-loop is easy to modify. It will never be a servo-valve but it works fine if all you need to do is hit a target-count.
There are many applications that can benefit from programmable positioning but the cost of full-blown servo-hydraulics is not justifiable.
Regards,
Craig
