Techshore Inspection Services-Kochi-official blog of Techshore Kerala: TECHSHORE INSPECTION SERVICES :CENTRIFUGAL PUMP

Introduction

A centrifugal pump is one of the simplest pieces of equipment in any process plant. Its purpose is to convert energy of a prime mover into velocity or kinetic energy and then convert into pressure energy of a fluid that is being pumped. The energy changes occur by virtue of two main parts of the pump, the impeller and the volute or diffuser. The impeller is the rotary part which converts driver energy into the kinetic energy. The diffuser is the stationary part that converts the kinetic energy into pressure energy.

Working principle

While generating the centrifugal force the process liquid enters the suction nozzle and then into eye of a revolving device known as an impeller. When the impeller rotates, it circulates the liquid in the cavities between the vanes and produce centrifugal acceleration. As liquid leaves the impeller a low-pressure area will be created causing more liquid to enter in to the inlet. Because the impeller blades are curved, the fluid is pushed in a radial and tangential direction by the centrifugal force. This force acting inside the pump is the same force that keeps water inside a bucket that is rotating at the end of a string. Figure below shows a side cross-section of a centrifugal pump indicating the movement of the liquid.

The amount of energy given to the liquid is directly proportional to the velocity at vane tip of the impeller. The faster the impeller revolves then higher will be the velocity of the liquid at the vane tip and the larger the energy imparted to the liquid. This kinetic energy of a liquid coming out from the impeller is harnessed by creating a resistance to the flow. The first resistance is created by the pump casing that holds the liquid and slows it down. In the discharge nozzle, the liquid further reduces; its velocity is converted to pressure according to Bernoulli’s principle. Therefore, the head pressure developed is approximately equal to the velocity energy at impeller expressed by the following formula handy formula for peripheral velocity .This head can also be calculated from the readings on the pressure gauges attached to the discharge and suction lines. Pump curves relate flow rate and pressure developed by the pump at different impeller sizes and rotational speeds

Basic Requirements for Trouble-Free Operation of Centrifugal Pumps;

Centrifugal pumps are simple in operation. In general there are two basic requirements that have to be obtained at all the times for a trouble free operation and longer service life of centrifugal pumps. The first requirement is that no cavitation of the pump occurs throughout the operating range and the second requirement is that a certain minimum amount continuous flow is always maintained during operation. A clear understanding of the concept of cavitation, its causes, its symptoms, and its consequences is very much essential in effective analyses and troubleshooting of the cavitation problem. Just like there are many types of cavitation, each demanding a unique solution, there are a number of undesirable conditions which may occur separately or simultaneously when the pump is operated at reduced flows. Some include

1. Cases of heavy leakages from the casing, seal and stuffing box, Deflection and shearing of shafts

2. Seizure of pump internals

3. Close tolerances erosion

4. Separation cavitation

5. Product quality degradation

6. Excessive hydraulic thrust

7. Premature bearing failures

Advantages of centrifugal pump

Friday, April 7, 2017

TECHSHORE INSPECTION SERVICES :CENTRIFUGAL PUMP

Introduction

Basic Requirements for Trouble-Free Operation of Centrifugal Pumps;

Advantages of centrifugal pump

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