Hunting
Hunting turns up in 2 fields: valves, HVAC. Here is what it means to the people in each one.
Hunting in valves
A control valve or loop swinging back and forth around setpoint instead of settling.
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."
Hunting in HVAC
A TXV or control swinging back and forth, alternately overfeeding and starving the evaporator instead of settling.
A hunting expansion valve opens wide, floods the coil and drops superheat to near zero, then clamps down and lets superheat soar, over and over. Causes include an oversized valve, a bulb mounted in the wrong spot or loose, flash gas in the liquid line, and very light loads. Watching superheat on a data logger for several minutes is the way to catch it.
"Superheat's bouncing between 2 and 20 every minute, the TXV's hunting, check where that bulb is clamped."