Difference Between Valve Hunting & Chattering?

Frequency!....
Chattering is realtively quick, like chattering of teeth, it's an oscillation, bounce, rattle, vibration.
Hunting is a much slower thing, it may still be an oscillation but it is more damped as a system is hunting for the correct balance or operating point, overshooting and then drifting back repeatedly.
Back to the human physiology, if you had a toothache, you might slowly work your jaw back and forth looking for a comfortable position....
OK it's a bit of a thin analogy...sue me.

I'd say chattering is more often applied to a tool or specific part whereas hunting is more often applied to a system.
Other than that, I have no idea
Del

Dear Mr. Maroof ali,

Supplementing to the Post No.1, by Del the cat, chattering is related to impact of the flow control where there is no back feed signal, where as for the hunting back feed signal is essential from the output end.

DHAYANANDHAN.S

Typically, modulating control valves 'hunt', when the control system continuously alters the control signal seeking an ideal control point. Since the control point around which the valve is oscillating is some mid-point along the valve's stroke, say 43%, the valve doesn't reach the end of its stroke. 35% to 42% to 47% to 43% to 36% to 41%, etc. etc.

Solenoid on-off valves, on the other hand, reach the 'end of their stroke' each time the valve cycles, by design; it's an on-off valve. When that happens at a fairly high frequency (a couple times per second, say) it will definitely sound like 'chatter'.

Hunting is basically an OVER-SIZED Valve. Check the pressure gauge and it will oscillate rapidly with a "thug" sound at every off and on while chattering sound you can make out if you have been married over 30 years with the same wife.