Piston n. (Mach.) A sliding piece which either is moved by, or moves against, fluid pressure. It usually consists of a short cylinder fitting within a cylindrical vessel along which it moves, back and forth. It is used in steam engines to receive motion from the steam, and in pumps to transmit motion to a fluid; also for other purposes. Piston head (Steam Eng.), that part of a piston which is made fast to the piston rod.
Piston rod, a rod by which a piston is moved, or by which it communicates motion.
Piston valve (Steam Eng.), a slide valve, consisting of a piston, or connected pistons, working in a cylindrical case which is provided with ports that are traversed by the valve.
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