Answer / carl_ellis

1) Actuator loses air supply or diaphragm leaks

2) Positioner loses control signal input

3) Positioner mechanical feedback is damaged or disconnected

4) Air supply does not meet instrument air requirements,
dirt and moisture accumulate and cause positioner shuttle
valve to stick

5) Stiction - valve internals are sticky, stem does not move
smoothly through its range

6) Poor positioner tuning creates overshoot

7) Mechanical backlash creates deadband that causes poor
control action

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