Working Principle of Check Valves

Check valves are primarily used in pipelines where media flow is unidirectional, allowing media to flow in only one direction and preventing reverse flow to avoid accidents. Check valves belong to the category of automatic valves. Under the pressure of fluid flowing in one direction, the valve disc opens; when the fluid flows in the reverse direction, the combined effect of fluid pressure and the disc's own weight forces the disc against the valve seat, thereby cutting off the flow.

Check valves can be classified into four types based on their connection methods: threaded check valves, flanged check valves, welded check valves, and wafer check valves.

Based on their structure, check valves can be categorized into three types: lift check valves, swing check valves, and butterfly check valves. Lift check valves can be further divided into vertical lift check valves and horizontal lift check valves. Swing check valves are classified into single-disc swing check valves, double-disc swing check valves, and multi-disc swing check valves. Butterfly check valves are a type of straight-through check valve.

Swing check valves feature a hinge mechanism and a disc that rests freely against the inclined surface of the valve seat, resembling a door. To ensure the disc reaches the correct position on the valve seat surface every time, it is mounted on the hinge mechanism, allowing sufficient swinging space and ensuring contact between the disc and the seat. When fully open, swing check valves offer minimal resistance to fluid pressure, resulting in a relatively low pressure drop across the valve. The disc can be made entirely of metal or may incorporate leather, rubber, or synthetic coatings embedded into the metal, depending on performance requirements.

In lift check valves, the disc rests on the valve seat sealing surface located on the valve body. Apart from the free vertical movement of the disc, the rest of the structure resembles that of a globe valve. Fluid pressure lifts the disc from the valve seat sealing surface, while reverse flow causes the disc to fall back onto the seat, cutting off the flow. Similar to globe valves, the flow path through lift check valves is narrow, resulting in a higher pressure drop compared to swing check valves. Depending on the application, the disc may be entirely metallic or may feature rubber gaskets or rings embedded in the disc holder.