penstock

Perhaps from pen (“an enclosure”) + stock.

penstock (plural penstocks)

1. A sluice or pipe which allows the controlled flow of water from behind a dam, typically routing it to a turbine of a power plant.
   • 2017, Fiona Farrell, Decline and Fall on Savage Street, →ISBN, page 30:

     It amazes him still, this effortless journey powered by the fall of water. Water surging through tunnel and penstock.

2. The barrel of a wooden pump.

• pentstock

• topnecks