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Understanding Cavitation in Pumps

The document defines and describes cavitation, which refers to the formation of bubbles inside a liquid as it flows through a centrifugal pump. There are two types of bubbles that can form: vapor bubbles due to vaporization of the pumped liquid, and gas bubbles due to dissolved gases in the liquid. Vaporous cavitation involves vapor bubbles and occurs when the available pressure head is insufficient. Gaseous cavitation involves gas bubbles and occurs when gas enters the pump along with the liquid.

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Salim Chohan
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963 views11 pages

Understanding Cavitation in Pumps

The document defines and describes cavitation, which refers to the formation of bubbles inside a liquid as it flows through a centrifugal pump. There are two types of bubbles that can form: vapor bubbles due to vaporization of the pumped liquid, and gas bubbles due to dissolved gases in the liquid. Vaporous cavitation involves vapor bubbles and occurs when the available pressure head is insufficient. Gaseous cavitation involves gas bubbles and occurs when gas enters the pump along with the liquid.

Uploaded by

Salim Chohan
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 PPT, PDF, TXT or read online on Scribd
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Concept of CavitationThe term cavitation

comes from the Latin word cavus, which


means a hollow space or a cavity.
In the context of centrifugal pumps, the term
cavitation implies a dynamic process of
formation of bubbles inside the liquid, their
growth and subsequent collapse as the liquid
flows through the pump

Generally, the bubbles that form inside the liquid are of two
types: Vapor bubbles or Gas bubbles.
1. Vapor bubbles are formed due to the vaporisation of a
process liquid that is being pumped. The cavitation
condition induced by formation and collapse of vapor
bubbles is commonly referred to as Vaporous Cavitation.
2. Gas bubbles are formed due to the presence of dissolved
gases in the liquid that is being pumped (generally air but
may be any gas in the system). The cavitation condition
induced by the formation and collapse of gas bubbles is
commonly referred to as Gaseous Cavitation.

Generally, the bubbles that form inside the liquid are


of two types: Vapor bubbles or Gas bubbles
Vapor bubbles are formed due to the vaporisation of a
process liquid that is being pumped. The cavitation
condition induced by formation and collapse of vapor
bubbles is commonly referred to as Vaporous
Cavitation
-Gas bubbles are formed due to the presence of
dissolved gases in the liquid that is being pumped
(generally air but may be any gas in the system). The
cavitation condition induced by the formation and
collapse of gas bubbles is commonly referred to as
Gaseous Cavitation

Vaporous cavitation is the most common form of


cavitation found in process plants. Generally it
occurs due to insufficiency of the available
NPSH or internal recirculation phenomenon.
Gaseous cavitation occurs when any gas (most
commonly air) enters a centrifugal pump along
with liquid.

The bubbles form inside the liquid when it vaporises i.e. phase
change from liquid to vapor.
Vaporization of any liquid inside a closed container can occur
if either pressure on the liquid surface decreases such that it
becomes equal to or less than the liquid vapor pressure at the
operating temperature, or the temperature of the liquid rises,
raising the vapor pressure such that it becomes equal to or
greater than the operating pressure at the liquid surface

How does pressure reduction occur in a pump system?


1. -- The actual pressure drop in the external suction system
is greater than that considered during design. As a result, the
pressure available at pump suction is not sufficiently high
enough to overcome the design pressure drop inside the pump.
2. -- The actual pressure drop inside the pump is greater
than that considered during the pump design.

Therefore the pumps external suction system


should be designed such that the static pressure
available at the suction flange is always positive
and higher than the vapor pressure of the liquid
at the pumping temperature.

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