Check valve refers to the valve that automatically opens and closes the valve flap depending on the flow of the medium itself to prevent the medium from flowing back. It is also called check valve, one-way valve, reverse flow valve, and back pressure valve. The function of check valve is
The check valve is a kind of automatic valve, its main function is to prevent the back flow of the medium, prevent the pump and the drive motor from reversing, and the discharge of the container medium. The check can also be used to supply pipelines for auxiliary systems where the pressure may rise above the system pressure.
Classification of check valves
According to its structure and installation method, the check valve can be divided into:

1. Swing check valve
The disc of the swing check valve is disc-shaped and rotates around the shaft of the valve seat passage. Because the passage in the valve is streamlined, the flow resistance is smaller than that of the lift check valve. It is suitable for low flow rates and non-return valves. Large diameter occasions with frequent changes, but not suitable for pulsating flow, and its sealing performance is not as good as the lifting type. Swing check valves are divided into three types: single valve, double valve and half valve. These three types are mainly classified according to the valve diameter. The purpose is to prevent the medium from stopping or flowing backwards and weaken the hydraulic shock.

2. Lift check valve
A check valve whose disc slides along the vertical centerline of the valve body. The lift check valve can only be installed on a horizontal pipeline, and a round ball can be used for the wide disc on the high-pressure small-diameter check valve. The valve body shape of the lift check valve is the same as the stop valve (which can be used in common with the stop valve), so its fluid resistance coefficient is relatively large. Its structure is similar to the stop valve, and the valve body and disc are the same as the stop valve. The upper part of the valve disc and the lower part of the valve cover are processed with guide sleeves. The disc guide sleeves can rise and fall freely in the valve cover guide sleeves. When the medium flows downstream, the valve discs are opened by the thrust of the medium. When the medium stops, the valve discs rely on their own It falls on the valve seat to prevent the medium from flowing backward. The direction of the medium inlet and outlet channel of the straight-through lift check valve is perpendicular to the direction of the valve seat channel; the vertical lift check valve has the same direction of the medium inlet and outlet channels as the valve seat channel, and its flow resistance is smaller than that of the straight-through type.

3. Disc check valve
The valve is a check valve that rotates around the pin shaft in the valve seat. The disc check valve has a simple structure and can only be installed on a horizontal pipeline, with poor sealing performance.

4. In-line check valve
The valve is a valve that slides along the centerline of the valve body. In-line check valve is a new type of valve. It is small in size, light in weight, and good in processing technology. It is one of the development directions of check valves. However, the coefficient of fluid resistance is slightly larger than that of the swing check valve.
5. Compression check valve
This kind of valve is used as a boiler feed water and steam shut-off valve, it has a comprehensive function of lift check valve and stop valve or angle valve.