Check valves are also known as a one way valve, non- return valve or as a clack valve. These are devices that are mechanical and usually allow liquid, gas to flow only in one direction. There are mainly two ports or passages in such valves. One is for the fluid or the gas to enter and the other is for the fluid or the gas to exit. These are mainly comprised in household items of usage. The composition of these check valves is principally of metal or plastic.

The check valves are mainly operated for cracking pressure at specific values. There are various types of these valves such as:

Ball check valve: These are very small and less expensive than the conventional ones. They are mainly found in spray gel devices or rubber bulbs which are used in pumping air. These are mainly made of metal. The unique part of such a valve is the spherical ball that is used as the movable part to block the flow of the fluid or the gas.

Diaphragm Check Valve: This is a rubber diaphragm which is made of rubber and creates a normal closed valve.

Swing Check Valves: these are valves which are shaped like a butterfly, the movable part to block the flow, swings on a hinge. These are often large in size.

Clapper Valve: This is mainly used in fire fighting and safety systems .This has a gate that will remain open only in the opposite direction.

Stop-Check valve: This has an override control to ensure the stoppage of the flow. The valve can be closed to shut the flow.

Lift Check valve: This is where the disc can be lifted up by higher pressure to allow flow to the downstream side.

Apart from these valves there are the double check valves and the double ball check valves which can be seen being used in various applications.

These valves are often used in pumps such as diaphragm pumps, metered pumps, chromatography pumps, power plants, chemical plants, industrial processes, used as irrigation sprinklers, irrigation emitters, used as home made snow makers, etc.