This type of valve is designed to allow fluid flow in only one direction while preventing reverse flow. These valves typically operate automatically: the disc opens under the pressure of fluid flowing in the forward direction, whereas reverse flow-combined with the fluid pressure and the disc's own weight-forces the disc against the seat, thereby shutting off the flow.
This category includes swing check valves and lift check valves. A swing check valve features a hinge mechanism and a door-like disc that rests freely against an inclined seat surface. The disc is designed with a hinge mechanism that provides sufficient room for it to swing and ensures it makes true, full contact with the seat surface every time it closes. Depending on performance requirements, the disc may be made entirely of metal or feature inserts such as leather, rubber, or synthetic facing materials.
When a swing check valve is fully open, fluid flow meets minimal obstruction, resulting in a relatively low pressure drop across the valve. In a lift check valve, the disc rests on the seat surface within the valve body. Apart from the freely lifting disc, the valve's construction resembles that of a globe valve; fluid pressure lifts the disc off the seat, while backflow causes it to drop back onto the seat, shutting off the flow.
Depending on operating conditions, the disc may be of all-metal construction or feature a rubber pad or ring inserted into the disc holder. Like globe valves, lift check valves have restricted flow passages, resulting in a higher pressure drop compared to swing check valves, which offer less restriction to flow.
