valve-sector

from The Century Dictionary.

• noun A link with a slot struck with an arc of a circle as center-line, used in the operation of certain valve-gears. Called also a quadrant.
• noun A special name for a link in the valve-gear of certain types of oscillating engines.
• noun The notched sector into which the latch catches on the levers which operate throttle-valves, so that the lever can be locked in position.
• noun The notched sector or quadrant in which the lock or latch of the reverse lever in Stephenson link-motions can be engaged to hold the lever in desired positions.