When dealing with refrigerant pumps, it is important to understand that unlike pumps in other types of systems that are pumping steady state liquids like water or oil, refrigerant pumps are pumping boiling liquid. When a pump that is designed to handle liquids is supplied with a mixture of liquid and gas, it is said to cavitate. Most any pump can tolerate a certain amount of cavitation but it is detrimental if at all extreme.

To understand the complexities involved in pumping refrigerant, one must have a firm grasp of the relationship between pressure and temperature with refrigerants, and by extension, sub cooling.