Check valves are valves designed to prevent the backflow in piping systems. They are activated by the pressure of the substance flowing in them. That is, when the fluid is flowing in a certain direction, its pressure forces the valve to open and allow flow through. But when the flow is reversed, the valve closes automatically. Closure is achieved either by back pressure, a spring, a check mechanism, or a combination of all these.
Quality swing type check valves are offered from Bonney Forge, Apollo, Titan, and Sharpe among others.