pen·stock /ˈpɛnˌstɑk/
 水門,水道,水渠
 Pen·stock n.
 1. A close conduit or pipe for conducting water, as, to a water wheel, or for emptying a pond, or for domestic uses.
 2. The barrel of a wooden pump.
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 penstock
      n 1: regulator consisting of a valve or gate that controls the
           rate of water flow through a sluice [syn: sluicegate,
           sluice valve, floodgate, head gate, water gate]
      2: conduit that carries a rapid flow of water controlled by a
         sluicegate [syn: sluice, sluiceway]