About 100 request instrument (8)
I believe the answer is:
recorder
'instrument' is the definition.
(I know that recorder is a type of pipe)
'about 100 request' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'r00' becomes 'C' (Roman numeral).
'request' becomes 'order' (an order is a request from someone in authority).
're'+'c'+'order'='RECORDER'
(Other definitions for recorder that I've seen before include "Wind instrument - instrument for transferring sound to tape" , "One taking down notes" , "Wind instrument - historian, perhaps" , "Maybe video" , "Woodwind instrument; official" .)