The valve that used to prevent backflow in a piping system is known as a check valve. It is also known as a non-return valve or NRV. The pressure of the fluid passing through a pipeline opens the valve, while any reversal of flow will close the valve. It allows full unobstructed flow and automatically shuts as pressure decreases. The exact operation will vary depending on the mechanism of valve.
The Dual Plate Check Valve design is the result of attempts
to solve the problems associated with swing check valve
and lift check valve. The Dual Plate Check Valve employs
two spring-loaded plates hinged on a central hinge pin.
When the flow decreases, the plates close by torsion spring
action without requiring reverse flow.
This design offers the twin advantages of No Water Hammer and Non Slam simultaneously. All features put together make the Dual Plate Check Valve one of the most efficient design. It is
also referred as SILENT CHECK VALVE
The tilting disc check valve is designed to overcome some of the weaknesses of conventional swing check valves. The design of tilting disk enables the valve to open fully and remain steady at lower flow rates and close quickly when the forwarding flow stop. The dome-shaped disc floats in the flow and fluid flow on both bottom and top of disk surfaces. As the disk is spring loaded, when forward flow pressure reduces, the spring force helps valve to close fast. In the image above, you can see the flow from the valve.
Lift Check valves are particularly suitable for high-pressure service where the velocity of flow is high. The disk is perfectly set on the seat with full contact. They are suitable for installation in horizontal or vertical pipelines with upward flow.
Here you can see the plug or piston type and ball type check valve. These valves provide superior leak tight characteristics to those of swing check valves. Some design in plug type uses spring to retain the disk in closed position. This will ensure that valve allows flow only when there is enough pressure in the flow direction.