Centrifugal Pump

by Bustanul Arifin

Basically, the centrifugal machine is built around an impeller, which is in series of radial vanes of various shapes and curvatures, spinning in a circular casing. Fluid enters at the "eye" or axis of rotation and discharges more or less radially into a peripheral chamber at a higher pressure corresponding to the sum of the centrifugal force of rotation and the kinetic energy given to the fluid by the vanes.

The centrifugal pump is the type most widely used in the chemical industry for transferring liquids of all types raw materials, materials in manufacture, and finished products as well as for general services of water supply, boiler feed, condenser circulation, condensate return, etc. These pumps are available through a vast range of sizes, in capacities from 0.5 m3/h to 104 m3/h (2 gal/min to 105 gal/min), and for discharge heads (pressures) from a few meters to approximately 48 MPa (7000 lbf/in2). The size and type best suited to a particular application can be determined only by an engineering study of the problem.

The primary advantages of a centrifugal pump are simplicity, low first cost, uniform (nonpulsating) flow, small floor space, low maintenance expense, quiet operation, and adaptability for use with a motor or a turbine drive. A centrifugal pump, in its simplest form, consists of an impeller rotating within a casing. The impeller consists of a number of blades, either open or shrouded, mounted on a shaft that projects outside the casing. Its axis of rotation may be either horizontal or vertical, to suit the work to be done. Closed-type, or shrouded, impellers are generally the most efficient. Open- or semiopen-type impellers are used for viscous liquids or for liquids containing solid materials and on many small pumps for general service. Impellers may be of the single-suction or the double-suction type--single if the liquid enters from one side, double if it enters from both sides. Casings.

There are three general types of casings, but each consists of a chamber in which the impeller rotates, provided with inlet and exit for the liquid being pumped. The simplest form is the circular casing, consisting of an annular chamber around the impeller; no attempt is made to overcome the losses that will arise from eddies and shock when the liquid leaving the impeller at relatively high velocities enters this chamber. Such casings are seldom used. Volute casings take the form of a spiral increasing uniformly in cross-sectional area as the outlet is approached. The volute efficiently converts the velocity energy imparted to the liquid by the impeller into pressure energy. A third type of casing is used in diffuser-type or turbine pumps. In this type, guide vanes or diffusers are interposed between the impeller discharge and the casing chamber.

Losses are kept to a minimum in a well-designed pump of this type, and improved efficiency is obtained over a wider range of capacities. This construction is often used in multistage high-head pumps.

I prepare other articles about pump at : deep well pump | sump pump About the author: I'm a process engineer consultant and have experience in building a refinery plant as piping engineer. This article was wrote base on my experience and text book. To study other kind of pump, you can visit : sump pump | deep well pump