The concepts behind Bernoulli`s equation and energy conversion are introduced and briefly discussed along with the definition of pump net positive suction head. Using these constructs, the three most common problems experienced by centrifugal pumps when pumping saturated liquid refrigerant in low-temperature freezing or cooling systems are discussed - cavitation, vapour entrainment, and recirculation. The effects of design decisions are discussed as they relate to the relationship between pump net positive suction head required (NPSHR) and the problem of recirculation. The symptoms of each problem are listed along with recommendations on how to avoid these problems in new installations and remedy them in existing installations. Since the symptoms of all three problems are similar, distinguishing between them can seem difficult, but a few general guidelines for diagnosis are presented.

KEYWORDS: maintenance, refrigerants, pumps, circulation pumps, centrifugal pumps, suction, refrigeration, freezers, recirculating, designing, head, operations.