from The Century Dictionary and Cyclopedia
- n. In a steam-engine, a valve which shuts off the steam in its passage to the slide-valves when the piston has travelled a certain distance in the cylinder, leaving the remaining part of the stroke to be performed by the expansion of the steam. See expansion-gear.
- n. Same as expansion-cock.
Sorry, no etymologies found.
The steam-valve is a packed slide with but little lap, and the expansion-valve is an adjustable slide working on the back of the steam-valve.