head gate vs penstock

head gate and penstock both are nouns.

Word	Noun	Adjective	Verb	Adverb
head gate	Yes	No	No	No
penstock	Yes	No	No	No

As nouns, head gate and penstock are synonyms defined as:

head gate and penstock: regulator consisting of a valve or gate that controls the rate of water flow through a sluice

Other synonyms of head gate include floodgate, sluice valve, sluicegate, water gate.

head gate (noun)	penstock (noun)
a gate upstream from a lock or canal that is used to control the flow of water at the upper end	conduit that carries a rapid flow of water controlled by a sluicegate
regulator consisting of a valve or gate that controls the rate of water flow through a sluice	regulator consisting of a valve or gate that controls the rate of water flow through a sluice