II. TYPES OF PUMPS
Two types of pumps are commonly used for water-pumping applications: Positive displacement and centrifugal.
Both centrifugal and positive- displacement pumps can be
further classified into those with motors that are surface
mounted, and those that are submerged into the water
(‘‘submersible’’). Displacement pumps have water output
directly proportional to the speed of the pump, but almost
independent of head. These pumps are used for solar water
pumping from deep wells or bores. They may be piston-type
pumps or use a diaphragm driven by a cam or rotary screw, or
use a progressive cavity system. The pumping rate of these
pumps is directly related to the speed, and hence constant
torque is desired.