Mixed Flow Pumps
Mixed flow pumps borrow characteristics from both radial flow and axial flow pumps.
As liquid flows through the impeller of a mixed flow pump, the impeller blades push the
liquid out away from the pump shaft and to the pump suction at an angle greater than
90o. The impeller of a typical mixed flow pump and the flow through a mixed flow
pump are shown in Figure 8.
Figure 8 Mixed Flow Centrifugal Pump
Multi-Stage Centrifugal Pumps
A centrifugal pump with a single impeller that can develop a differential pressure of more than
150 psid between the suction and the discharge is difficult and costly to design and construct.
A more economical approach to developing high pressures with a single centrifugal pump is to
include multiple impellers on a common shaft within the same pump casing. Internal channels
in the pump casing route the discharge of one impeller to the suction of another impeller.
Figure 9 shows a diagram of the arrangement of the impellers of a four-stage pump. The water
enters the pump from the top left and passes through each of the four impellers in series, going
from left to right. The water goes from the volute surrounding the discharge of one impeller to
the suction of the next impeller.
A pump stage is defined as that portion of a centrifugal pump consisting of one impeller and its
associated components. Most centrifugal pumps are single-stage pumps, containing only one
impeller. A pump containing seven impellers within a single casing would be referred to as a
seven-stage pump or, or generally, as a multi-stage pump.