There are several types of pumps used in HVAC heating & cooling systems, but the most common in use today is the centrifugal pump. Types of centrifugal pumps include volute or axial flow pumps. The volute takes water from the impeller and discharges the water perpendicular to the shaft. A centrifugal pump with a diffuser casing (axial flow pump) discharges the water parallel to the pump shaft. Centrifugal pumps are available in many types including circulator, single- and multi-stage end-suction, single- and multi-stage split-case, and vertical in-line pumps.