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Cavitation

This document discusses cavitation in centrifugal pumps. It defines cavitation as the formation of vapor bubbles in water when pressure drops too low, which then collapse violently and cause noise, vibration and damage to pumps. Cavitation occurs when the pressure head available at the pump inlet is less than the net positive suction head required by the pump. The document provides guidelines to avoid cavitation, such as minimizing suction line components, keeping the suction line short, and ensuring adequate submergence of the suction intake. It notes that lowering pump speed or redesigning the pumping system may be necessary if cavitation cannot be avoided through these measures.

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231 views1 page

Cavitation

This document discusses cavitation in centrifugal pumps. It defines cavitation as the formation of vapor bubbles in water when pressure drops too low, which then collapse violently and cause noise, vibration and damage to pumps. Cavitation occurs when the pressure head available at the pump inlet is less than the net positive suction head required by the pump. The document provides guidelines to avoid cavitation, such as minimizing suction line components, keeping the suction line short, and ensuring adequate submergence of the suction intake. It notes that lowering pump speed or redesigning the pumping system may be necessary if cavitation cannot be avoided through these measures.

Uploaded by

mcsfuv
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Natural Resources and Water

Managing Queensland's natural resources...for today and tomorrow

water series

Cavitation in centrifugal pumps


Cavitation is a common occurrence but is the least
understood of all pumping problems.
Your pump is cavitating if knocking noises and
vibrations can be heard when it is operating. Other
signs may be erratic power consumption and
fluctuations or reductions in pump output.
If you continue to operate your pump when it is
cavitating, it will be damaged. Impeller surfaces and
pump bowls will pit and wear, eventually leading to
mechanical destruction.

What is the cause?


When water enters a pump, its velocity increases
causing a reduction in pressure within the pumping
unit. If this pressure falls too low, some of the water
will vaporise, forming bubbles entrained in the liquid.
These bubbles collapse violently as they move to
areas of higher pressure creating the noise and
vibration from the pump.
The pressure required to operate a pump without
causing cavitation is called net positive suction head
(NPSH). Therefore the pressure head available at the
pump inlet should exceed the NPSH required. This is
specified by the pump manufacturer, and is a function
of the pump design.

How to avoid cavitation


As cavitation relates only to the suction side of the
pump all prevention measures should be directed at
this area.
Suction lifts that are too high will only encourage
cavitation. As a general rule, centrifugal pumps
located less than 4 metres above the water level
should not experience cavitation.

W8

March 2006

Queensland the Smart State

The following guidelines should be applied to avoid


the problem:
minimise the number of valves and bends in the
suction line
use eccentric reducers, not concentric
ensure the straight side of the eccentric reducer is
installed along the top of the suction line
suction length should be as short as possible
suction pipe should be at least the same diameter
as the pump inlet connection
use long radius bends
increase the size of valves and pipework
do not allow air into the suction line
ensure adequate submergence over the foot
valve. The submergence should be at least
5.3 times the suction diameter.

Alternative solutions
One solution may be to reduce the required net
positive suction head. This can done by lowering the
pump speed. However, this will also result in reduced
output from the pump which may not suit your system.
If pump suction conditions cannot be improved, you
should seek expert assistance. It may be that your
pumping system needs to be redesigned.

Assistance
Your local office of the Department of Natural
Resources and Water may be able to assist you
further with this topic or water supply, irrigation or
drainage generally. Call them for details of other fact
sheets, available services and associated charges. g

Produced by: South East Region

Author: G. Swann

QNRM03169

Natural Resources and Water

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