Chapter No 3 Air Compressors (1)

8/16/2019 Chapter No 3 Air Compressors (1)

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Chapter No: 3

AirCompressors


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#or operatin! pneumatic tools such asdrills, screw drivers, hammers, chiessels

#or pneumatic cranes #or pneumatic bra"es of automobiles,

railways and presses #or a!ricultural accessories such as

dusters and sprayers


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#or drive of CNC machine tools #or pneumatic conveyin! of materials #or pneumatic !au!in!, inspection and low

cost automation systems


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An air compressor is a mechanical devicethat increases the pressure of air byreducin! volume.

Air is compressible, the compressor

reduces the volume of air and inducespressure in the air

An air compressor converts electricalener!y into "inetic ener!y in the form of

the air


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$he compressed air is stored in the airreceiver and can be used for cleanin!under pressure, !eneratin! tor%ue anddevelop force usin! actuators

$his source is free of cost, safe, e'ibleand convenient

Air compressor has very few parts hencemaintenance is very low


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Air compressors are classied accordin! tomethod of ener!y transfer and pressure!eneration i.e. positive displacement anddynamic compressors

Positive displacement compressors wor"on the principle of increasin! the pressureof air by reducin! the volume of air in anenclosed chamber


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(ynamic compressors wor"s on theprinciple of impartin! the ener!y byrotatin! vanes of impeller on air owin!throu!h casin! that increases pressure in

air


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Accordin! to number of sta!es)in!le sta!e, double sta!e, three sta!e of

multiple sta!e Accordin! to action)in!le actin! or double actin! Accordin! to position of cylinder w.r.t.

cran"shaftCylinders inline, vertical, radial position, *+

type cylinder arran!ement


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Accordin! to prime moverlectric motor drive or IC en!ine drive, -as

turbine drives Accordin! to coolin! mediumAir cooled, water cooled air compressors


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eciprocatin! air compressors are positivedisplacement type of air compressors.

$hese are piston & diaphra!m type, vane

type, !ear type, screw type compressors.


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$he principle of operation is same butaccordin! to sta!es the delivery pressureis di/erent in each compressor.


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A reciprocatin! air compressor consist of apiston which is enclosed within a cylinderand e%uipped with suction and dischar!evalve

$he piston receives power from electricmotor or IC en!ine.


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$he compression of air is done by rstdrawin! a volume of air into the cylinderthrou!h suction valve durin! suctionstro"e of piston and then compressed anddischar!ed throu!h delivery valve durin!delivery stro"e


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In this type the entire compression iscarried out in a sin!le cylinder


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0hen piston starts movin! downwards,the pressure inside the cylinder falls belowatmospheric pressure that opens suctionvalve.

$he pressure of the air in the cylinder risesdurin! compression and at the end ofcompression, delivery valve opens and

dischar!es the compressed air into thereceiver tan".


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)in!le sta!e air compressor developpressure upto 1 bar.

#or hi!her pressures multista!e

compressors are suitable


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$he fresh air is drawn inside the .P.cylinder throu!h inlet suction lter.

$his air is compressed by piston

As the piston moves towards the end ofcylinder, the air compression too" place.


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$he delivery valve opens and thiscompressed air from .P. cylinder isdirected to enter inside the hi!h pressurecylinder.

In hi!h pressure cylinder this pressurisedair is further compressed to hi!herpressure.


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$he hi!h pressure air from 4.P. cylinder isthen delivered to receiver throu!hdischar!e valves.

In this compressor, a pressure of airdelivered is upto 53 bar.


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)imple in desi!n ower initial cost asy to install

4i!her e/eiciency


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Number of movin! parts are more 4i!her maintenance cost 4eavy foundation is re%uired as it has

vibration problem Cannot run at full capacity


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It is positive displacement typecompressor.

It provides hi!her e6ciency and ow ratesover a wide ran!e of pressure

otary vane compressor consist of rotorwith a number of vanes inserted in theradial slots cut in rotor.


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As the rotor turns, compression isachieved as the volume !oes from ama'imum at inta"e port to minimum atthe e'haust port.

An oil is in7ected into the air inta"e andalon! the stator walls to cool the air andlubricate bearin! and vanes and to

provide a seal between the vane andstator wall to reduce internal lea"a!e.


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)imple desi!n Compact in si8e i!ht in wei!ht asy to install ow cost ow maintenance cost on!er life #ew movin! parts ow rotational speed 'pensive foundation not re%uired


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ower e6ciency (i6culty with hi!her pressure above 9

psi

;il in7ected desi!ns have oil carryover


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It is dynamic compressor. It consist of a rotatin! impeller which

rotates at hi!her speed An impeller tted inside casin! force the

air to the rim of impeller, increasin!velocity of air.


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A di/user section converts the velocity of air tocause an increase in pressure. $hisprocess is called dynamic compression.

$hese compressors are used forcontinuous, stationary services inindustries li"e oil reneries, chemical and

petrochemical plants, natural !asprocessin! plants.


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$hese are also used in IC en!inesuperchar!ers and turbochar!ers.

In !as turbine plants It can provide e'tremely hi!h output

pressures !reater than 5psi.


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It consist of two screws + one with conve'and the other with concave contour mostlycalled male and female rotor respectively.

$hese two screws !ets rotatin! by meansof !ear trips there by suc"in! the airthrou!h an inlet port in chamber and thencompressin! the same


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$he heli' of the male and female rotorscrew is desi!ned to permit completechar!in! of the inter lobe space before there+mesh.

;n completion of the llin! operation theinlet end of male and female lobes be!insto re+en!a!e thus reduces the volume of

air continuously.


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$hus compression be!ins and air isdischar!ed at the end of other side.

$here is no contact between male andfemale rotors and casin!. 4ence nolubrication re%uire but oil may in7ected forthe purpose of coolin!.


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It is used in applications where hi!her owat comparatively low pressure is re%uired.


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4ere two lobes are placed in a casin! $he air is transferred from suction side to

the delivery side with continuous rotationof two lobes

$he lobes are precisely maintained andthe casin! also maintained to closetolerances

It has limited compression ratio ? 5.1


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@ulti sta!e compressor is use to developpressures more than 3 "!Bcm9.

#or preparation of mineral water bottle, airpressure more than "!Bcm9 is re%uired

to produce desired shape of bottle atbottom side.

4ere two sta!e compressor is not used asit produces pressure up to 3 "!Bcm9 .

$hree sta!e compressor is use as itproduces pressure up to D "!Bcm9 .

Above four sta!e compressor is used.


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$he wor"in! is same as that of doublesta!e compressor.

In three sta!e compressor fresh air fromatmosphere enters rst sta!e cylinderthrou!h air cleaner.

4ere it is compressed by piston to "!Bcm9 and then delivered to second sta!e

cylinder throu!h intercooler for furthercompression.


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In second sta!e cylinder low pressure air iscompressed upto 5 "!Bcm9 and dischar!eto third sta!e cylinder throu!h secondintercooler to increase air pressure up to

desired delivery pressure i.e. 3 to D"!Bcm9


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)election of air compressor for !ivenapplication is !overned by several factorsas below

Pressure #low rates or capacity -eometry of cylinder )peed of piston $he layout of pipe line, system

re%uirement and the distance of usermachine from compressor plant


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Pressure : $he dischar!e pressure from the

compressor should be decided rstconsiderin! the needs of the cylinder, airmotor & pressure drop in the circuit.

@ost of pneumatic systems and tools aredesi!ned for pressure of = 2 1 bar.

A compressor used should meet there%uirement.


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Pressure : Pneumatic circuit re%uirin! air at hi!h

pressure can be supplied with air by aseparate hi!h pressure compressor

0hile any low pressure can be met byavailin! a reducin! valve.

#or hu!e air ow rates at pressures below

9 bar, a turbo+blower or low pressurerotary compressor may be used.


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-eometry of cylinder:+ #or sin!le cylinder !eometric fashion :+

vertical+sin!le actin! or double actin!

hori8ontal+ sin!le or double actin! #or two cylinders !eometric fashion:+

+ vertical inline, sin!le or double actin!

+ *+type, sin!le or double actin!

+ hori8ontal duple', double actin!


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)peed of piston:+ $he speed of piston inside the cylinder

must also be considered. #or small capacity compressor, the piston

speed 3 mBmin, whereas for lar!ecapacity compressor piston speed 9mBmin.

$he layout of pipe line, systemre%uirement and the distance of usermachine from compressor plant

Chapter No 3 Air Compressors (1)

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