Definition function and classification of check valve

A check valve, also known as a non-return valve, one-way valve, reverse flow valve, or back pressure valve, is a valve that relies on the flow of the medium itself to automatically open and close the valve disc, thereby preventing the backflow of the medium.

Check valves are a type of automatic valve, whose primary function is to prevent the backflow of media, prevent the reverse rotation of pumps and driving motors, and facilitate the release of container media. Check valves can also be used on pipelines that supply auxiliary systems where the pressure may rise above the system pressure.

Check valves can be classified according to their structure and installation method as follows:

1. Swing check valve

The disc of a swing check valve is disc-shaped and rotates around the axis of the valve seat passage. Due to the streamlined passage inside the valve, the flow resistance is lower than that of a lift check valve, making it suitable for low flow rates and large-diameter applications where flow variations are infrequent. However, it is not suitable for pulsating flows and its sealing performance is inferior to that of a lift check valve. Swing check valves are divided into three types: single-disc, double-disc, and multi-disc. These three types are mainly classified according to the valve port diameter, with the aim of reducing hydraulic shock when the medium stops flowing or flows backward.

2. Lift check valve

The check valve, where the valve disc slides along the vertical centerline of the valve body, and the lift check valve can only be installed on horizontal pipelines, can adopt a round ball for the valve disc in high-pressure small-diameter check valves. The shape of the valve body of the lift check valve is similar to that of the globe valve (can be interchanged with the globe valve), so its fluid resistance coefficient is relatively high. Its structure is similar to that of the globe valve, with the valve body and disc being identical to those of the globe valve. The upper part of the valve disc and the lower part of the valve cover are machined with guide sleeves, and the valve disc guide sleeve can freely ascend and descend within the valve petal guide sleeve. When the medium flows downstream, the valve disc opens by the thrust of the medium; when the medium stops flowing, the valve disc falls onto the valve seat by gravity, preventing the reverse flow of the medium. The direction of the medium inlet and outlet channels of the straight-through lift check valve is perpendicular to the direction of the valve seat channel; for the vertical lift check valve, the direction of the medium inlet and outlet channels is the same as that of the valve seat channel, and its flow resistance is smaller than that of the straight-through type.

3. Disc check valve

A check valve where the valve disc rotates around a pin shaft inside the valve seat. The disc check valve has a simple structure, can only be installed on horizontal pipelines, and has poor sealing performance.

4. Pipeline check valve

A valve in which the valve disc slides along the centerline of the valve body. The pipeline check valve is a newly emerging type of valve, featuring small size, light weight, and good processability, representing one of the development directions for check valves. However, its fluid resistance coefficient is slightly higher than that of the swing check valve.

5. Compression check valve

This valve is used as a boiler feedwater and steam shut-off valve, combining the functions of a lift check valve, a globe valve, or an angle valve.