Main Features of a Centrifugal Pump

What are the main features of a centrifugal pump?

There are two main families of pumps: centrifugal and positive displacement pumps.  In comparison to the latter, centrifugal pumps are usually specified for higher flows and for pumping lower viscosity liquids, down to 0.1 cP.  In some chemical plants, 90% of the pumps in use will be centrifugal pumps.  However, there are a number of applications for which positive displacement pumps are preferred.

What are the limitations of a centrifugal pump?

The efficient operation of a centrifugal pump relies on the constant, high speed rotation of its impeller.  With high viscosity feeds, centrifugal pumps become increasingly inefficient: there is greater resistance and a higher pressure is needed to maintain a specific flow rate.  In general, centrifugal pumps are therefore suited to low pressure, high capacity, pumping applications of liquids with viscosities between 0.1 and 200 cP.

Slurries such as mud, or high viscosity oils can cause excessive wear and overheating leading to damage and premature failures. Positive displacement pumps often operate at considerably lower speeds and are less prone to these problems.

Any pumped medium that is sensitive to shearing (the separation of emulsions, slurries or biological liquids) can also be damaged by the high speed of a centrifugal pump’s impeller.  In such cases, the lower speed of a positive displacement pump is preferred.

A further limitation is that, unlike a positive displacement pump, a centrifugal pump cannot provide suction when dry: it must initially be primed with the pumped fluid.  Centrifugal pumps are therefore not suited to any application where the supply is intermittent.  Additionally, if the feed pressure is variable, a centrifugal pump produces a variable flow; a positive displacement pump is insensitive to changing pressures and will provide a constant output.  So, in applications where accurate dosing is required, a positive displacement pump is preferred.

The following table summarises the differences between centrifugal and positive displacement pumps.

Pump Comparison: Centrifugal vs Positive Displacement

Property  Centrifugal Positive Displacement 
Effective Viscosity Range Efficiency decreases with increasing viscosity (max. 200 Cp) Efficiency increases with increasing viscosity
Pressure tolerance  Flow varies with changing pressure Flow insensitive to changing pressure
Efficiency decreases at both higher and lower pressures Efficiency increases with increasing pressure
Priming Required Not required
Flow (at constant pressure)  Constant Pulsing
Shearing (separation of emulsions, slurries, biological fluids, food stuffs)  High speed damages shear-sensitive mediums Low internal velocity. Ideal for pumping shear sensitive fluids 

What are the main applications for centrifugal pumps?

Centrifugal pumps are commonly used for pumping water, solvents, organics, oils, acids, bases and any ‘thin’ liquids in both industrial, agricultural and domestic applications.  In fact, there is a design of centrifugal pump suitable for virtually any application involving low viscosity fluids.

Type of centrifugal pump Application  Features 
Canned motor pump Hydrocarbons, chemicals where any leakage is not permitted   Sealless; impeller directly attached to the motor rotor; wetted parts contained in can
Magnetic drive pump  Sealless; impeller driven by close coupled magnets
Chopper/grinder pump Waste water in industrial, chemical and food processing/ sewage Impeller fitted with grinding teeth to chop solids
Circulator pump Heating, ventilation and air conditioning  Inline compact design
Multistage pump  High pressure applications Multiple impellers for increased discharge pressures
Cryogenic pump  Liquid natural gas, coolants  Special construction materials to tolerate low temperatures
Trash pump  Draining mines, pits, construction sites  Designed to pump water containing solid debris
Slurry pump Mining, mineral processing, industrial slurries  Designed to handle and withstand highly abrasive slurries 

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