There are plenty of
definitions regarding what actually is a pump. One of the simplest
way to define the pump is that the pump is generally a machine or
device which is used to transfer different quantities of fluids or
gases from one location to another. There are many different types
and models of pumps for different purposes, like centrifugal pumps,
hydraulic pumps, rotary lobe pumps and many others. But
generally the pumps are classified into two main categories:
- Rotodynamic Pumps
- Positive Displacement Pumps
The
first category, the rotodynamic pumps have the ability to transform
the rotating mechanical energy into kinetic energy in form of fluid
pressure and velocity. The liquid ring pump and the centrifugal pump
are the two main types of the rotodynamic pumps. These pumps utilize
centrifugal force in order to transfer the liquid which is being
pumped out. The second category, the positive displacement pumps, is
generally represented by the rotary lobe pumps. The rotary
lobe pump is the mostly utilized positive displacement pump type,
and the main function of this pump is to move the liquid that is
being pumped directly from the pump inlet into the outlet in discrete
volumes.
For a
proper selection of a particular type of pump, generally two type of
data is required:
- Product or Fluid Data. Such data includes density, specific gravity, viscosity, temperature, flow characteristics, solids content and vapour pressure.
- Performance Data. This data shows the capacity or the flow rate and the discharge pressure.
Because
different fluids, gases or materials have their own unique
characteristics and are pumped under varying conditions, it is very
important all product and performance data to be known before
selecting a pump.
Product or Fluid Data
Viscosity. The
viscosity of a particular fluid or gas can be described as a measure
how resistant the fluid or gas is to flow, and it is comparable to
friction of the solid bodies. This force transforms the kinetic
energy of the particular fluid that is being pumped into thermal
energy. How easily a fluid pours is an indication of its viscosity.
Two general viscosity indicators are mainly used: kinematic and
absolute viscosity.
Density. The
density of the fluid is described as the mass of the fluid per unit
of volume, generally expressed as kilograms per cubic meters kg/m3.
The density of the fluid is presented by the symbol p.
Specific
Weight. The specific weight of
the fluid is described as the weight per unit volume and it is
presented with the symbol γ.
Specific
Gravity. The
ratio of the fluid density and the density of the water gives the
specific gravity of the fluid. Because it is a ratio no unit of
measure is used.
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