It goes up and down as it whirls! (5)

I believe the answer is:

rotor

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'it whirls' is the definition.
(I've seen this in another clue)

I cannot understand how the rest of the clue works.

(Other definitions for rotor that I've seen before include "one lifting chopper?" , "Chopper blade" , "Palindromic revolving part of machine" , "Revolving part of machinery" , "Reversible piece of moving machinery?" .)

I've seen this clue in the Evening Standard.

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