throttle valve

a valve for throttling the working fluid of an engine, refrigerator, etc.

Origin of throttle valve

First recorded in 1805–15

The throttle-valve T in that pipe, near the cylinder, is regulated by a system of levers connected with the governor.

The Steam Engine Explained and Illustrated (Seventh Edition) |Dionysius Lardner
It represents, in the phrase of the inventor, the finger laid upon the throttle-valve of a steam-engine.

A Popular History of Astronomy During the Nineteenth Century |Agnes M. (Agnes Mary) Clerke
In that position the passage within the tube would be necessarily unobstructed by the throttle-valve.

The Steam Engine Explained and Illustrated (Seventh Edition) |Dionysius Lardner
The fly-ball governor replaced the throttle-valve which was at first used by Watt to regulate the speed of his engines.

The Story of Great Inventions |Elmer Ellsworth Burns

The engineer may draw his throttle-valve and give the piston full head.

The Seat of Empire |Charles Carleton Coffin