Non return valves are also known as check valves. They are specially designed for allowing the medium to flow only in one direction. A non return valve is fitted in the system to ensure that the medium flows in the right direction where the pressure condition may cause a reverse flow which needs to be avoided. The bodies of most check valves are made up of plastic or metal.
A necessary requirement for the valve to operate is the cracking pressure that opens the valve to enable the medium to flow through. These valves are available in different size and specification as per the requirement of the system. There are different types of non return valves available like spring load, swing type, clapper type, lift-check valve, stop-check valve, in-line check valve and duckbill valve. These valves are used in pumps, chemical plants, power plants, irrigation sprinklers, drip irrigation emitters etc.
There are 3 main type of pressure in regards with the check valve:
- Cracking pressure: Minimum pressure to start the flow
- Reseal pressure: Indicates no flow
- Back pressure: differential pressure between inlet and outlet pressure
Knife Gate Valve 