flume vs petcock

flume

noun
  • An open channel or trough used to direct or divert liquids. 

  • A ravine or gorge, usually one with water running through. 

verb
  • To transport (logs of wood) by floating them along a water-filled channel or trough. 

petcock

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

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