A pump is a machine that provides energy to a fluid in a hydraulic system.
It assists to increase the pressure energy or kinetic energy, or both, in the fluid by
converting the mechanical energy. The basic difference between a turbine and the
pump, from a hydrodynamic point of view, is that in the former flow takes place from
the high-pressure side to the low-pressure side, whereas in pump flow takes place
from the low pressure forwards the higher pressure. Thus in a turbine, there is
accelerated flow while in a pump the flow is decelerated. Accelerated flow throughout
the hydraulic turbines is less subjected to turbulence therefore the runner passages are
relatively short and high efficiency is available for this machine due to reduced values
for the friction losses. Decelerated flow throughout the centrifugal pumps is sensitive
to separation and vortices therefore impeller passages are relatively long and
gradually increased in cross-section area for lowering the friction losses – "centrifugal
pumps" efficiency is normally lower comparing to the turbines.
At the beginning of this chapter, one presents a classification of centrifugal pumps,
reciprocating pumps – (Fig. 5.1) and pump turbines. In addition, basic centrifugal
pump theory and a brief analysis of the net positive suction head (NPSH) that are very
useful for the design and selection of the pumps are detailed. In the next sections
similarity laws, specific speed, cavitation and selection of the pumps are available.
All these items are illustrated by solved problems.
Chapters on "similarity law, specific speed and cavitation and pumps section"
acquiring great efficiency in using the tool of mathematics and at the solved problems
are available.
Keywords: Cavitation in pump, Centrifugal pumps, Efficiencies, Force and Power,
Head of the pump, Negative suction lift, NPSH required, NPSH, Positive
Displacement Pumps, Positive suction lift, Pump Turbine, Reciprocating pump.
