There are many ways to classify pumps: according to their function, their conditions of service, materials of construction, etc. The U.S. pump industry trade association, the Hydraulic Institute, has classified pumps as shown in Figure . This classification divides pumps as follows:
A. Principle of Energy Addition
The first classification is according to the principle by which energy is added to the liquid. There are two broad classes of pumps, defined below.
Kinetic
In a kinetic (also called rotodynamic) pump, energy is continuously added to the liquid to increase its velocity. When the liquid velocity is subsequently reduced, this produces a pressure increase. Although thereare several special types of pumps that fall into this classification, for the most part this classification consists of centrifugal pumps.
Positive Displacement
In a PD pump, energy is periodically added to the liquid by the direct application of a force to one or more movable volumes of liquid. This causes an increase in pressure up to the value required to move the liquid through ports in the discharge line. The important points here are that the energy addition is periodic (i.e., not continuous) and that there is a direct application
of force to the liquid. This is most easily visualized through the example of a reciprocating piston or plunger pump . As the piston or plunger moves back and forth in the cylinder, it exerts a force directly on the liquid, which causes an increase in the liquid pressure.
B. How Energy Addition Is Accomplished
The second level of pump classification has to do with the means by which the energy addition is implemented. In the kinetic category, the most common arrangement is the centrifugal pump. Other arrangements include regenerative turbines (also called peripheral pumps) and special pumps such as jet pumps that employ an eductor to bring water out of a well.
In the PD category, the two most common subcategories are reciprocating and rotary pumps.
C. Geometry Used
The remaining levels of pump classification shown in Figure deal with the specific geometry used. With centrifugal pumps, the geometry variations have to do with the support of the impeller (overhung impeller vs. impeller between bearings), rotor orientation, the number of impellers or stages, how the pump is coupled to the motor, the pump bearing system, how the pump casing is configured, and pump mounting arrangements.
With PD pumps, as is discussed in more detail in Section VI, there are many different types of rotary and reciprocating pumps, each with a unique geometry.