valve knocking

例句：

1. 1. The valve is responsible for controlling the flow of gases in the pipeline.
   阀门负责控制管道中气体的流动。
2. 2. The valve was designed to prevent leaks and ensure safe operation.
   阀门被设计用来防止泄漏并确保安全运行。
3. 3. The valve operator must be trained to handle emergency situations.
   阀门操作员必须接受培训以处理紧急情况。