Check valves, or non return valves are used to prevent reverse flow in pipelines. They are critical in that they prevent media flowing in wrong direction, thus protecting equipment such as pumps, meters etc from damage. In addition, check valves can be used to prevent and minimise sudden shocks in the system, which can lead to major problems such as water hammer and overpressure.
Valves may be wafer pattern or flanged. The non return mechanism may be a disc/gate, a ball, or a rubber sleeve. Bodies may be reinforced rubber, cast iron, carbon steel, or stainless steel to suit application. With suitable coatings and linings, valves may be used on a wide variety of media, including aggressive and corrosive types.