Piston

A piston is a key part of many machines, like engines, pumps, compressors, and cylinders. It moves back and forth inside a tube called a cylinder. Pistons help change the push from hot gases into motion that makes cars and other machines work.

In engines, the piston's job is to take the force from expanding gases and send it to the crankshaft through a piston rod or connecting rod. This motion helps the engine run smoothly. In pumps, the piston works the other way, using force from the crankshaft to push or squeeze fluid out of the cylinder.

Sometimes, pistons also act like valves by covering and uncovering small openings in the cylinder, which helps control how the machine operates. Pistons are made tight inside the cylinder by special rings called piston rings, which keep everything sealed and working well.

Piston engines

Main article: Reciprocating engine

An internal combustion engine uses the force from expanding gases in the combustion chamber to move a piston up and down. This movement goes through the connecting rod to the crankshaft. The connecting rod links to the piston with a gudgeon pin, which sits inside the piston. Most engines do not have a separate piston rod or crosshead.

Pistons are usually made from strong, light aluminium alloys. They are shaped slightly oval to fit better in the cylinder. Early pistons were made from cast iron, but lighter alloys were made to handle high temperatures.

Pistons use piston rings to create a tight seal between the piston and the cylinder wall. These rings are made of iron and fit into grooves in the piston. They help keep gases contained and prevent oil from leaking.

Piston designs can vary depending on the engine's needs. Some pistons, called trunk pistons, are longer and help support forces from the connecting rod. Others, called slipper pistons, are very light and thin, made for high-speed racing engines.

Hydraulic cylinders use pistons to move in controlled directions, guided by rings that stop metal parts from rubbing against each other.

Steam engines also use pistons, but they are usually thin and round. These engines often use special valves to control the flow of steam.

Pumps

Piston pumps help move liquids or squeeze gases into smaller spaces.

Main article: Reciprocating pump

Main article: Reciprocating compressor

Air cannons

There are two special types of pistons used in air cannons: close tolerance pistons and double pistons. In close tolerance pistons, O-rings act like a valve, but O-rings are not used in double piston types.