The working principle of a check valve

Check valves can also be used in pipelines that supply auxiliary systems where the pressure may rise above the system pressure. Check valves are mainly divided into swing check valves (rotating according to the center of gravity) and lift check valves (moving along the axis).
This type of valve only allows the medium to flow in one direction and prevents reverse flow. Usually, this type of valve works automatically. Under the action of the fluid pressure flowing in one direction, the valve disc opens; when the fluid flows in the reverse direction, the fluid pressure and the weight of the valve disc act on the valve seat, thus cutting off the flow.
Among them, the check valve belongs to this type of valve, which includes swing check valves and lift check valves. The swing check valve has a hinge mechanism and a valve disc like a door that rests freely on the inclined valve seat surface. To ensure that the valve disc reaches the correct position on the valve seat surface each time, the valve disc is designed with a hinge mechanism to provide sufficient swing space for the valve disc and ensure that the valve disc makes true and complete contact with the valve seat. The valve disc can be made entirely of metal, or leather, rubber, or synthetic coverings can be inlaid on the metal, depending on the performance requirements. When the swing check valve is fully open, the fluid pressure is hardly obstructed, so the pressure drop through the valve is relatively small. The valve disc of the lift check valve is located on the valve seat sealing surface of the valve body. Except that the valve disc can rise and fall freely, the rest is the same as the globe valve. The fluid pressure lifts the valve disc from the valve seat sealing surface, and the backflow of the medium causes the valve disc to fall back to the valve seat and cut off the flow. Depending on the operating conditions, the valve disc can be an all-metal structure or a rubber pad or rubber ring inlaid on the valve disc frame. Like a globe valve, the passage through the lift check valve is also narrow, so the pressure drop through the lift check valve is greater than that of the swing check valve, and the flow of the swing check valve is less restricted.