How does an exhaust check valve function?

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　　The exhaust check valve is primarily used in the steam extraction systems of thermal power plants to prevent the backflow of fluid or water, thereby protecting important equipment such as turbine pumps. Its performance requirements are that it must close instantly in emergency situations such as backflow of fluid in the pipes, power outages, or accidents, with a closing time of less than 0.5 seconds. 　　An exhaust check valve is also known as a backflow valve, non-return valve, backpressure valve, or one-way valve. These types of valves open and close automatically due to the force generated by the flow of the medium itself within the pipeline; they are a type of automatic valve. An exhaust check valve is used in piping systems; its main functions are to prevent backflow of the medium, to stop the pump and its drive motor from rotating in reverse, and to allow the release of the medium from containers. Pneumatic check valves can also be used in pipelines that supply auxiliary systems whose pressure may rise above that of the main system. 　　Depending on the material, exhaust check valves can be used in pipelines carrying various types of media. When an exhaust check valve is installed in a pipeline, it becomes one of the fluid components of that complete pipeline, and its opening and closing process is influenced by the transient flow conditions of the system in which it is located ； Conversely, the closing characteristics of the valve disc also affect the flow state of the fluid. The operating characteristics of the exhaust check valve are large load variations and a low opening/closing frequency; once it is set in a closed or open state, it can remain in that condition for a long time, and no movement of moving parts is required. But once the requirement to “switch” again arises, flexibility is necessary, and this requirement is more stringent than typical mechanical movements. 　　In most practical applications, the exhaust check valve is designed to close quickly. At the moment the valve closes, the flow direction of the medium changes; as the valve disc closes, the reverse flow velocity of the medium drops rapidly to zero, while the pressure rises sharply. This results in the phenomenon of \"water hammer,\" which can cause damage to the piping system.