injector vs petcock

injector

noun
  • An apparatus by which a stream of water is forced into a steam boiler. 

  • An object that realizes a dependency injection. 

  • One who injects (himself or herself with) psychoactive drugs. 

  • Any of various devices that are used to inject something. 

petcock

noun
  • A small valve, spout, or faucet operated by hand, usually used to release pressure or drain fluid. 

How often have the words injector and petcock occurred in a corpus of books? (source: Google Ngram Viewer )