from The Century Dictionary and Cyclopedia
- n. A reciprocating valve resembling a working piston, moved in a tubular passage to open or close a port or ports for alternately admitting steam to or exhausting it from the cylinder of an engine.
- n. A valve located in a piston.
Sorry, no etymologies found.
When the exhaust valve closes, the cylinder has a charge of fresh air, drawn in through the exhaust valve, and the further motion of the piston causes a partial vacuum; by the time the piston reaches bottom dead centre the piston-valve has moved up to give communication between the cylinder and the crank case, therefore the mixture is drawn into the cylinder.
It had been made from a bicycle foot-pump, by reversing the piston-valve, and was fitted with a glass nozzle and a small detachable glass receiver for collecting the dust, at the end of a flexible metal tube.