Answer: Under no circumstances should flammable liquids be used to clean valves, filters, air paths, air cavities, air pipes, and other parts that come into contact with compressed air under normal working conditions. When using non-flammable liquids such as chlorinated hydrocarbons for cleaning, precautions should be taken against toxic vapors discharged after start-up, and carbon tetrachloride should not be used as a cleaning agent. When using hydrochloric acid solution to clean the cooler, the solution concentration must be controlled, and an alkaline solution must be used for neutralization after pickling.