Start to operate PC in store - it controls flow
I believe the answer is:
stopcock
'it controls flow' is the definition.
The definition suggests a singular noun which matches the answer.
'start to operate pc in store' is the wordplay.
'start to' indicates taking the first letters.
'in' means one lot of letters goes inside another.
'store' becomes 'stock' (synonyms).
The initial letter of 'operate' is 'o'.
'o'+'pc'='opc'
'opc' placed within 'stock' is 'STOPCOCK'.
Can you help me to learn more?
(Other definitions for stopcock that I've seen before include "It controls the flow of fluid through a pipe" , "Water/gas supply valve" , "Desist, male bird! it's a valve in a pipe" , "main controller" , "Water controlled by this" .)