The many inherent benefits that double-helical rotary screw compressors bring to vapor compression have caused them to be well accepted on an increasing number of applications in the conservative refrigeration industry. Screw compressors incorporate relatively new technology compared to reciprocating compressors and are seeing a high level of developmental activity today for the continued advancement of their design. Recent developments in control systems and bearing materials, combined with innovative compressor design, have brought about significant improvements in compressor efficiency, durability, and cost. Some of the more recent changes include providing automatic variable volume ratio, incorporating complete antifriction bearings, and providing new methods of capacity control. These developments mark the latest steps in the continuing evolution of refrigeration compressors for today's refrigeration and cooling needs.Units: Dual