centrifugal pump impeller

8/3/2019 Centrifugal Pump impeller

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CENTRIFUGAL PUMP:IMPELLER INTRODUCTION:

A centrifugal pump is a rotodynamic pump that uses a rotating impeller to

create flow by the addition of energy to a fluid. Centrifugal pumps are commonly used to move

liquids through piping. The fluid enters the pump impeller along or near to the rotating axis and

is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber

(casing), from where it exits into the downstream piping. Centrifugal pumps are used for large

discharge through smaller heads.

IMPELLER : The blade of a rotor (as in the compressor of a jetengine)vane, blade - flat surface that rotates and pushes against air or

water rotor - rotating mechanism consisting of an assembly of rotating

airfoils; "there are horizontal rotors on a helicopter or compressor rotors

in a jet engine"

WORKINGA centrifugal pump uses a spinning "impeller," which normally has backward swept

blades that directly push water outward. The transfer of energy from the mechanical rotation

of the impeller to the motion and pressure of the fluid is usually described in terms of

centrifugal force,. The concept of centrifugal force is not actually required to describe the

action of the centrifugal pump.
http://en.wikipedia.org/wiki/Rotodynamic_pumphttp://en.wikipedia.org/wiki/Impellerhttp://en.wikipedia.org/wiki/Impellerhttp://en.wikipedia.org/wiki/Volute_(pump)http://en.wikipedia.org/wiki/Casinghttp://www.thefreedictionary.com/vanehttp://www.thefreedictionary.com/bladehttp://en.wikipedia.org/wiki/Centrifugal_forcehttp://en.wikipedia.org/wiki/File:Centrifugal_2.pnghttp://en.wikipedia.org/wiki/File:Centrifugal_2.pnghttp://en.wikipedia.org/wiki/Centrifugal_forcehttp://www.thefreedictionary.com/bladehttp://www.thefreedictionary.com/vanehttp://en.wikipedia.org/wiki/Casinghttp://en.wikipedia.org/wiki/Volute_(pump)http://en.wikipedia.org/wiki/Impellerhttp://en.wikipedia.org/wiki/Rotodynamic_pump


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In the modern centrifugal pump, most of the energy conversion is due to the outward

force that curved impeller blades impart on the fluid. Invariably, some of the energy also

pushes the fluid into a circular motion, and this circular motion can also convey some energy

and increase the pressure at the outlet.

TYPES OF IMPELLERThere are main three types of impeller.

1. Shrouded or closed impeller2. Semi open impeller3. Open impeller

1. SHROUDED OR CLOSED IMPELLER:

In this type of impeller blades or vanes are covered with side plates on both sides as

shown in fig. Such type of impeller provides smooth passage

for the liquid. So that pump operates at high efficiency. This

type of impellers only used for liquid. Which is free from

dust and sandy element and has low viscocity? The liquid

should be clean and low viscous like water, hot water and

acids.

A disadvantage of enclosed impellers is that the front

and back shrouds, rotating in close proximity to the casing

walls, generate disc friction that lowers the efficiency of the

pump relative to that found in open impeller designs.

Another disadvantage is that the enclosed impeller is more easily plugged. Large solids that

might otherwise be broken up by the grinding action generated by a rotating open impeller

and the stationary casing wall can easily become lodged in the eye of an enclosed impeller.

This may create a mechanical or hydraulic imbalance that has the potential to damage the

pump, or at the least causes a pre-mature outage to remove the blockage


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Semi-open impeller

2. SEMI-OPEN IMPELLER:

It has a plate on the back side and other side is opened. The semi open impeller isdesigned to handle liquid containing fibrous material like paper pulp, sugar molasses and

sewage water. High axial thrust is the primary drawback of a semi-open impeller design. Axial

thrust balance is manageable through design for both open and enclosed impellers. On a semi-

open impeller, the entire backside surface of the shroud is subject to the full impeller discharge

pressure. The front side of the shroud is at suction pressure at the eye of the impeller and

increases along the impeller radius due to centrifugal action. The differential between the

pressure profiles along the two sides of the shroud creates the axial thrust imbalance. This can

be managed somewhat through the use of pump-out vanes on the back side of the shroud, but

the vanes will start to lose effectiveness if the impeller is moved forward in the casing tocompensate for wear. Some manufacturers have integrated an adjustable wear-plate into the

casing design so that clearance adjustments can be made. Combined with hard materials or

surface hardening treatments, this option provides a good design in lightly to moderately

abrasive applications

3.OPEN IMPELLER:

The open impeller vanes are open on both side, no

side plates are provided as shown in fig. such pumps are

used to handle liquid like, abrasive liquid mixture of water

and sand particles and mixture of clay. The pump with

open impeller used for rough duty.

One drawback of the open impeller is that it is

more susceptible to abrasive wear than a shrouded

impeller. High velocity fluid on the impeller blades in close


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proximity to the casing walls establishes rotating vortices that accelerate wear when abrasives

are present. A tight clearance between the impeller and the front and back casing walls is

necessary to maximize efficiency. As the impeller wears, these clearances open and efficiency

drops rapidly. The tight operating clearances required on both sides of an open impeller for

efficient operation precludes adjustment of the impeller axial position to compensate for wear.

OTHER TYPES OF IMPELLER :Impeller types can be radial, mixed flow, axial and peripheral and are selected on the

basis of the pump design and the application.

The number of vanes will affect the efficiency; in general more vanes are more efficient. Also

the number of vanes affect the steepness of the characteristic curve, see centrifugal pump tips

for a graph on this effect.

An impeller with a high number of vanes reduces the amplitude of the pressure pulses that are

caused as the impeller tip passes by thecutwater. In certain applications these pressure pulses

are undesirable such as a paper machine headbox pump which typically will be a double suction

type with 8 or more vanes. The headbox is a large specialized nozzle that feeds a continuous

stream of low consistency pulp on a traveling wire mesh which after drying produces a wide

paper web. If the pressure pulses are too high compared to the average there will be a variation

in the paper density which may affect printing quality and other operational factors.
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centrifugal pump impeller

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