A piston's a component of reciprocating engines, pumps and gas compressors. It's located in a cylinder and's made gas-tight by piston rings. In an engine, its purpose's to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod. In a pump, the function's reversed and force's transferred from the crankshaft to the piston for the purpose of compressing or ejecting the fluid in the cylinder. In some engines, the piston also acts as a valve by cove… (More on Piston)