The low stage of a cascade system typically operates below -80°F. At these temperatures, standard refrigeration oils may begin to gum-up and lose their ability to flow around the sytem. Systems that run short periods of time, or cycle through warmer temperatures, may be able to keep the oil returning to the compressor; however, systems that run longer stretches of time at cold temperatures need to add hydrocarbons to thin the oil and provide consistent oil return. In some cases, the hydrocarbons are used as the low stage refrigerant.
National provides a variety of hydrocarbons in small quantities to be used for addition to very low temperature systems. Larger quantities can be specially ordered.