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what is npsh and how to calculate it for a centrifugal pump
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Answer Posted / saravanan
NPSH is Net Positive Suction Head.. As the name indicates
it is the Positive suction head that should be necessarily
available at suction to prevent the liquid from boil up due
the vapor pressure of the liquid at pumping temperature. It
is also said as the Head necessary at the suction to over
come the vapor pressure of the liquid at pumping
temperature.
Liquid if pumped at low pressure & high temperature (close
to boiling point) nullifies vapor pressure and cavitates.
NPSH available should always be greater than NPSH required
defined by the pump vendor (NPSH R is function of the pump
impeller geometry) to get improved performance.
NPSH available = Suction Pressure - Vapor Pressure + Static
Head - Frictional loss across the suction line.
Since the velocity at the suction is minimum, dynamic head
can be ignored. Hence the only deciding factor is Static
Head, Suction pressure & Operating Temperature..
Higher the static head, higher is the suction pressure &
lower is the pumping temperature better would be the NPSH
avaialble at the impeller eye.
| Is This Answer Correct ? | 37 Yes | 11 No |
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