The main difference is in how they compress air. A rotary vane compressor turns a rotor, and centrifugal force pushes out the vanes to create compression. A rotary screw compressor uses two interlocking screws to force air into a smaller volume. Rotary vane compressors tend to be more reliable, but rotary screw compressors have a lower initial cost and are usually very quiet, making them popular in locations where people have to work alongside them.