A pump is a device used to move fluids, such as liquids, gases or slurries. A pump transfer fluid from lower pressure to higher pressure, and overcomes this difference in pressure by adding energy to the system. A pump displaces a volume by physical or mechanical action. Pumps fall into two major groups: a)     Positive displacement pumps b)     Dynamic pumps, A positive displacement pump causes a fluid to move by trapping a fixed amount of it then forcing (displacing) that trapped volume into the discharge pipe. The positive displacement pumps can be divided into two main classes according to the mechanism used to move the fluid:

1. reciprocating
2. rotary

  Dynamic pump is one in which energy is continuously added to increase the fluid velocities within the machine to values in excess of those occurring at the discharge such that subsequent velocity reduction within or beyond the pump produces a pressure increase. It can be classified into two categories:

1. Centrifugal pump
2. Special effect pump

 

Centrifugal pump:

A centrifugal pump is a rotodynamic pump that uses a rotating impeller to increase the pressure and flow rate of a fluid. Centrifugal pumps are the most common type of pump used to move liquids through a piping system. It pumps liquids with very wide ranging properties and suspensions with a high solid contents including cement slurries, and may be constructed from a wide range of corrosion resistant materials.   Everywhere we see mostly the centrifugal pump. you can see this type of pump in this link: http://www.google.com/search?client=opera&rls=en&q=centrifugal+pump&oe=utf-8&channel=suggest&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&hl=en&tab=wi&biw=1110&bih=490