bibcock vs vacuum tube

bibcock

noun
  • An appliance (typically a valve with a threaded outlet) allowing the provision of hose connections outside of buildings. 

vacuum tube

noun
  • A type of electron tube that controls electron current through vacuum between electrodes within a sealed container, usually of glass or metal and often designed to be easily installed in and removed from the equipment in which it is used. 

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