ABSTRACT
In the refrigeration industry, and also in the gas industry, where the compressors are usually hermetically sealed, valves are a noise source whose oscillatory energy is transmitted to the outside through pipes and the housing shell. Therefore, this interaction will usually have to be considered. In the air compressor industry, the discharge valves usually feed into a hermetic system and the problem is similar. Suction valves, on the other hand, are exposed to the atmosphere (except for a filter), and because gas pulsation waves or acoustic waves travel as easily against the flow as with the flow for typical, average flow velocities, they are important sources that transmit directly to the observer.
