U-shaped pipe component backed up (4)
I believe the answer is:
trap
'u-shaped pipe' is the definition.
(I know this)
'component backed up' is the wordplay.
'component' becomes 'part' (a component is a part of something).
'backed up' is a reversal indicator.
'part' written backwards gives 'TRAP'.
(Other definitions for trap that I've seen before include "Gin - hidden danger" , "Part (anag.)" , "Driver's obstacle" , "one would be ill advised to enter?" , "Catch; two-wheeled carriage" .)