What is a Pump ? How are Pumps Classified?

A Pump is a mechanical device which moves liquid from a lower level to a higher level.  The pump draws the liquid inside pressurizes it and discharges it through the outlet.  A pump is driven by a prime mover which is, generally, an electric motor.  IC engines and turbines can also be used as prime movers to drive the pump.


Pumps are usually classified into two broad categories

Rotodynamic pump and
Positive Displacement Pumps

Rotodynamic Pumps

In these pumps, a rotary device with blades, called the impeller drives the liquid.  The liquid gets kinetic energy in the process.  The kinetic energy is converted into pressure by means of the design of the pump.

The rotodynamic pumps can be divided into

Centrifugal pumps : Here, the impeller with blades drives the liquid radially outwards towards the casing.  The liquid gets pressurized as it exits the pump.

Axial Pumps:  In these pumps, the liquid is driven axially by the impeller.  The flow of the liquid is parallel to the axis of the impeller.

Positive Displacement Pumps

Positive Displacement pumps are another major category of pumps.  In positive displacement pumps, the liquid is drawn into a chamber, pressurized and expelled at the discharge side.

These pumps are in turn classified into two types

Reciprocating Pumps: In these pumps, a piston moves inside a cylinder.  The piston creates low pressure when it moves up.  This sucks the liquid inside.  Once inside, the piston moves down and pressurizes the liquid which is discharged through a port.  The handpump used to pump water is a reciprocating pump. Eg. Plunger Pump

Rotary Pump: In these types of pumps, two rotating gears or screws move inside a casing.  As the screws or the gears move, the liquid is progressively taken into the pump.  The cross section of the casing is reduced as the liquid moves.  This causes pressure at the discharge side.  Examples: Screw Pumps, Gear Pumps