Instrument techs say a valve is hunting when it cycles continuously, often a few percent each way, chasing a process variable that never settles. Causes include aggressive loop tuning, an oversized valve working near its seat, stiction in the packing, or a positioner with poor calibration. Hunting wears packing and trim and spreads instability to other loops.
Steam valve to the heater's hunting, 30 to 45 percent every minute, I'll put the loop in manual and check it for stiction.
Also heard as
- cycling
- oscillating
Related terms
Stiction
Static friction that makes a control valve stick, then jump, instead of moving smoothly with its signal.
Positioner
A device on a control valve that compares the control signal with actual valve position and adjusts air to match.
Control valve
A power-operated valve that modulates flow on a controller signal to hold pressure, level, flow or temperature at setpoint.
Rangeability
The ratio of the largest to the smallest flow a control valve can regulate while keeping its characteristic.