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Part 1
Part 2

Centrifugal Pumps: Basic Concepts of Operation, Maintenance, and Troubleshooting 
(Part- II, Understanding Cavitation)

Introduction

In Part I of the article, two basic requirements for trouble free operation and longer service life of centrifugal pumps are mentioned in brief. 

1.      PREVENT CAVITATION
                        Cavitation of the pump should not occur throughout its operating capacity range.

2.       MINIMIZE LOW FLOW OPERATION

Continuous operation of centrifugal pumps at low flows i.e. reduced capacities, leads to a number of unfavorable conditions. These include reduced motor efficiency, excessive radial thrusts, excessive temperature rise in the pumping fluid, internal re-circulation, etc. A certain minimum continuous flow (MCF) should be maintained during the pump operation.

Operating a pump under the condition of cavitation for even a short period of time can have damaging consequences for both the equipment and the process. Operating a pump at low flow conditions for an extended duration may also have damaging consequences for the equipment.

The condition of cavitation is essentially an indication of an abnormality in the pump suction system, whereas the condition of low flow indicates an abnormality in the entire pumping system or process. The two conditions are also interlinked such that a low flow situation can also induce cavitation.

The concept of cavitation is explored in detail under following topics:

1. Meaning of the term ‘cavitation’ in the context of centrifugal pumps.
2. Important definitions: Static pressure, Dynamic pressure, Total pressure, Static pressure head, Velocity Head, Vapor pressure.
3. Mechanism of cavitation.
4. General symptoms of cavitation and its effects on pump performance and pump parts.
5. Types of cavitation:
1. Vaporous cavitation

i.      Classic cavitation

ii.      Internal re-circulation cavitation

2. Gaseous cavitation

i.      Air ingestion induced cavitation

6. Methods to prevent cavitation

The topics 1 to 4 are covered in detail in this part of the article. The topics 5 to 6 shall be explored in next part of the article.

Readers of Part I showed keen interest and appreciation about the approach in which the topic of Centrifugal Pumps has been discussed. The same enthusiasm, response and feedback are solicited from the readers.

Concept of Cavitation

By: Mukesh Sahdev, Associate Content Writer (read the author's Profile)
SAHDEVM@iocl.co.in