Stop endlessly walking round equipment (4,2,2)
I believe the answer is:
pack it in
'stop' is the definition.
(I've seen this before)
'endlessly walking round equipment' is the wordplay.
'endlessly' means to remove the last letter.
'walking' becomes 'pacing' (pacing is a kind of walking).
'round' indicates putting letters inside.
'equipment' becomes 'kit' (kit is a kind of equipment**).
'pacing' with its last letter taken away is 'pacin'.
'pacin' enclosing 'kit' is 'PACK IT IN'.
(Other definitions for pack it in that I've seen before include "Give over" , "How will you get all that stuff into your suitcase" , "Stop working - or stuff suitcase?" , "Slangily, stop doing it - stuff suitcase" , "Quit" .)