Rotary Screw Air Compressors from premium manufacturers, such as; FS Curtis, Chicago Pneumatic, Hertz Kompressoren, Industrial Gold are designed to provide high volumes of air flow for extended periods. These screw-type air compressors have the capability to have a 100% duty-cycle. Most Rotary Screw Air Compressors have enclosures that help to reduce sound levels. There are two main types of Rotary Screw Air Compressors. The most common is a "Fixed Speed". A "Fixed Speed" machine runs at one speed and does not fluctuate. The second type is a "Variable Speed". This type of compressor uses electronics to vary the frequency of the electric motor. This will speed up or slow down the motor in order to match how much air needs to be made. Generally, a Fixed Speed Air Compressor should be used when there is a constant demand for air and a Variable Speed Air Compressor should be used when the demand varies from day to day or hour to hour.