1. Overview
Valves are important pipeline pressure components in petrochemical plants, with a wide range of quantities and types, among which check valves are one of the most commonly used valves. In general, a petrochemical plant has thousands of valves, among which the number of check valves accounts for about 5% of the total number of process valves.

The main function of a check valve is to prevent the backflow of fluid in the pipeline. When the medium flows in the clockwise direction, the valve disc automatically opens, and when the medium flows in the reverse direction, the valve disc automatically closes. Therefore, check valves are also known as one-way valves.

The check valve of petrochemical equipment is mainly used in the following parts to prevent fluid backflow:
1. Outlet pipelines of centrifugal pumps and vortex pumps
2. Compressor outlet pipeline
3. Backpressure turbine exhaust steam pipelines
4. Process medium pipelines entering and exiting the device (excluding pipelines that are also used for starting oil introduction and stopping oil return)
5. Utility pipelines connected to pipelines and equipment for flammable gases, liquefied hydrocarbons, and flammable liquids
6. The pipeline for injecting other media into the overhead distillation line such as ammonia, corrosion inhibitor and water.
7. A pipeline for injecting water or steam into the heating furnace tube

2. Types of commonly used check valves
The commonly used check valves in petrochemical plants are mainly made from carbon steel, alloy steel, stainless steel, nickel based alloy, copper alloy, and composite materials according to their material types. Common valve pressure ratings include Class l50, Class 300, Class 600, Class 800, Class 900, Class 1500, and Class 2500. The main types of commonly used check valves according to their structure include lift check valves, swing check valves, tilting disc check valves, double plate check valves, and axial flow check valves. Petrochemical plants also use some other types of check valves, but the quantity is relatively small.