It goes round or back to the far end (5)
I believe the answer is:
rotor
'it goes round' is the definition.
(I've seen this before)
'or back to the far end' is the wordplay.
'back' is a reversal indicator.
'end' suggests the final letters.
The final letter of 'far' is 'r'.
'or' backwards is 'ro'.
'ro'+'to'+'r'='ROTOR'
(Other definitions for rotor that I've seen before include "Turning part of machine, palindromic" , "Dynamo part" , "part of chopper" , "Palindromic moving part" , "Reversible piece of moving machinery?" .)