Swing Check Valve Flange End

When the pressure at the inlet end (upstream) is sufficient to overcome the weight of the valve disc and the fluid resistance, the fluid pushes the valve disc to rotate around the pin shaft to open.

When the inlet pressure drops or disappears, or even reverse flow occurs (backflow), the reverse fluid and gravity (or sometimes spring force) work together to push the valve disc to swing back around the pin shaft, quickly closing and sealing with the valve seat, thereby cutting off the flow. In the fully open position, the valve disc is almost parallel to the flow channel, causing very little obstruction to the fluid.