Which of the following is a key feature of stationary air compressor systems?

A key feature of stationary air compressor systems is that they typically include a storage tank for compressed air. This storage tank serves several important functions, such as providing a reserve of compressed air, helping to stabilize the pressure during operation, and allowing for the efficient use of the compressor by minimizing the need for continuous running. The presence of a storage tank is essential in many applications, as it supplies air on demand and ensures a steady flow of air, thus enhancing the reliability and efficiency of the entire system.

While energy efficiency and noise levels can be considerations, they are not defining characteristics of stationary systems compared to their portable counterparts. The incorporation of a storage tank is what sets stationary systems apart and is crucial in applications requiring consistent and readily available compressed air.