Check Valves, also known as One Way Valves or Non-Return Valves (NRV), are automated valves that generally lets fluid (liquid or gas) to flow through it in only a single direction. Check the valve open with the onward flow and close counter to reverse flow. Check valves vary considerably from other members of the valve family and the main function of a check valve is to guard mechanical equipment in a piping system by preventing the reverse of flow by the liquid or gas. Check valves are completely automatic in their operation, having no obligation for any operator or external control, so most do not have any stem or valve handle. Check valves are driven by the fluid flow and the pressure difference that exists between their inlet and outlet ports.
Why is it Required?
Flow reverse in fluid-handling systems is probable and can be caused by accidental gear stoppage or automated fail-safe devices. For this purpose, check valves are fixed in pipelines to prevent such a reverse flow and to allow the flow of product in only one direction. When the flow is moving in the right direction, the valve remains open. The valve closes automatically when the flow reverses. The use of a check valve is certainly essential in the case of compressors and pumps, where backflow could damage the internals of the equipment and cause a pointless shutdown of the system and, in extreme cases, the complete plant.
Types of Check Valves
Some of the basic types ofFlow Check Valveare the following.
Swing Check Valve: The swing check valve swings about a hinge, which is mounted outside the seat.
Piston and Lift Check Valves: The closure member travels in the way standard to the plane of the seat.
Ball Check Valve: The closure member comprises a ball, which travels in the direction standard to the seat’s plane and revolves constantly.
Tilting-Disc Check Valve: The closure member tilts about an axis, which is mounted near, but above, the middle of the seat.
Diaphragm Check Valve: The closure member comprises a diaphragm, which rebounds from or against the seat.
Stop Check Valve: Stop Check Valve is a combo of a globe valve and a lift check valve and a globe valve. It can either be employed as a check valve or as a segregation (stop) valve like a globe valve.
Spring Loaded Check Valve: The closure member comprises a focus guided stem-disc assembly along with a compression spring.
Duckbill Check Valve: The closure member comprises of a soft tube of which the end has a standard flattened shape.