1-6 Types of Pumps and Fans

43
 PART 1 Module 1/6 Types of Pumps and Fans

Transcript of 1-6 Types of Pumps and Fans

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PART 1

Module 1/6

Types of Pumps andFans

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Objectives:

•  To defne the dierent types o ansand pumps in common use.

• To defne and discuss the an / pumplaws.

•  To discuss drive systems or ans andpumps

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ITRO!"#TIO TO MO!"$%

•  The commissioning o air and water systemsrequires a basic knowledge o the dierent typeso ans and pumps that are used and anunderstanding o the mathematical laws that

govern their perormance. It is also important tounderstand the drive systems used or pumpsand ans.

• In this module we will discuss the types o ansand pumps commonly used in air and water

systems and look at the laws that can be appliedto them. e will also look at the drive systemsused and how to change an speeds by alteringpulleys and belts.

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1& P"MP' 

(ene)al

• ! pump is a device used to move "uid arounda pipework system# such as a lowtemperature hot water heating system# $achilled water system or a condenser watersystem.

• ! pump will normally consist o our mainparts% an impeller# a casing# a motor to rotate

the impeller and a drive arrangement totransmit power rom the motor to theimpeller.

• &et us look at the dierent types o pumps in

common use.

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Recip)ocatin* Pumps

• 'eciprocating (umps consists o one or morecylinders# with each cylinder having an inlet and anoutlet.

• )ach cylinder houses a piston connected to acommon crankshat# which is in turn connected to anelectric motor.

• !s the crankshat is turned by the motor# the piston ispulled down the cylinder# creating a suction whichdraws "uid into the cylinder through the inlet.

• !s the crankshat continues to turn# the piston ispushed up the cylinder# discharging# the "uid through

the outlet.• *alves located in the cylinder inlets and outletsprevent "uid being drawn in through the outlet orbeing discharged through the inlet. These valves areopened and closed automatically at the correct timeand normally operated# by the movement o the "uid#however they can also be operated by the crankshat.

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Recip)ocatin* Pumps

! sketch o a reciprocating pump is given below+

•  This type o pump is not normally used or "uid "owin heating or chilled water systems.

• ,ue to the non-compressibility o water which couldlead to damage o the pump# sealing o the cylinderagainst leakage and system pressure "uctuations.

• owever# this principle can be used or compressorsin rerigeration systems% reciprocating compressorpumps and compresses0 rerigerant in the mannerdescribed above.

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#ent)ifu*al Pumps

•  The ma1ority o pumps used or heating and chilled water "uid

movement are o the centriugal type.

• ! centriugal pump consists o a circular impeller withbackward curved vanes# connected to an electric motor via adrive arrangement. The impeller is housed in a volute shapedcasing.

•  The illustration below shows a centriugal pump% you canclearly see the shape that the casing takes.

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#ent)ifu*al Pumps

• !s the impeller rotates# "uid is drawn into the centre o the

impeller. ,ue to centriugal orce the "uid is pushed awayrom the impeller and orced through the outlet o the casing. The casing is a volute shape so that as much o thecentriugal orce kinetic energy0 is converted to pressureenergy as possible.

• 2otors can be connected to the impeller in one o two ways%

either directly or by a belt drive arrangement. 3elt drives arediscussed in (arts 4 and 5 o this module.• ,irect drive can be in one o two orms% close coupled or

direct coupled.• In a 6lose 6oupled arrangement# the impeller is directly ftted

to the motor shat as can be seen in the illustration overlea.

• In a ,irect 6oupled arrangement# the impeller is ftted to ashat# which is in turn connected to the motor shat through a"e7ible coupling.

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In+$ine #i)culato)s

• !n in-line circulator or pump0 is basically a close

coupled# direct drive centriugal pump# arranged so thatthe inlet and outlet connections are on the same centreline. This is or ease o installation.

•  Two basic types are used# "oor mounted and pipelinemounted. The let hand illustration below shows a "oor

mounted type# whilst the right hand illustration shows apipeline mounted type.

•  8ou can see that the "oor mounted pump has a base

rame. (ipeline mounted pumps are light enough to bemounted directly in the pipeline.

Pipelinemounted

Floo) mounted

 

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'ump Pumps

• 9ump pumps are oten a type o directcentriugal pump# arranged so that theinlet and outlet connections are on thesame centre line.

• In this type o pump however# the inletconnection is normally open# that is# itdoes not have a pipe attached to it.

 The inlet is normally protected with a

screen to prevent solids entering thepump.

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Multi+'ta*e Pumps

• ! multi-stage pump is a type o centriugal pump#however# instead o one single impeller# a numbero impellers are mounted on a common shat.

•  This type o pump is normally used or very highpressure applications and operates on the principlethat two impellers in series will produce almost

double the pressure o one impeller.• !n illustration o a multi-stage pump is given below.

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,& FA' 

(ene)al

• ! an is a device used to move air inventilation and air conditioning systems#such as those studied in the previous

module.• ! an# 1ust as a pump# will normally consist

o our main parts% an impeller# a casing# amotor to rotate the impeller and a drive

arrangement to transmit power rom themotor to the impeller.

• &et us look at the dierent types o ans in

common use.

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#ent)ifu*al Fans

• 6entriugal ans have a multi-bladed impeller

housed in an volute casing.• !ir is drawn into. the a7is o the impeller#

turns a right angle and is discharged radiallyby centriugal orce.

•  The impeller blades may be straight or aceeither backwards or orwards# dependentupon the an perormance required.

•  The motor is normally outside the an casingand is connected by a belt drive arrangement#although on small ans the motor may belocated in the centre o the impeller.

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Paddle -lade

• ! paddle blade impeller is the simplest

type o centriugal impeller.

• It normally consists o a number o straightblades f7ed to a backplate.

• ,ue to its nature it is the least e:cient othe centriugal impellers# however#because the blades are straight# they willnot clog when used with air systems that

have a high dirt content# such as duste7tract systems.

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Fo).a)d #u)ved• ! orward curved impeller has a large number o short

blades# curved towards the direction o rotation.• ith this type# air leaves the impeller at a higher speed

than the impeller tip speed. 3ecause o this act# theimpeller can be o a smaller diameter and run at a lowerspeed than other types o centriugal an.

• owever# because the blades are shallow# the velocity othe air across the blades does not decrease# making theorward curved impeller very ine:cient.

•  This means that the motor can easily be overloaded i thesystem resistance has been over estimated and the an

passes too much air.

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-ac.a)d #u)ved

• ! backward curved impeller has between ten

and si7teen blades o either curved or straightorm# inclined away rom the direction orotation.

•  The blades are relatively deep.

• ith this type# air leaves the impeller at alower speed than the impeller tip speed. Thislow air speed# combined with the deep bladesgives the backward curved impeller a nonoverloading power characteristic.

• It also makes it very e:cient when comparedagainst the orward curved type and will

generate much higher pressures i necessary.

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Ae)ofoil -lade•  This type o impeller is a refnement o the

backward curved type# however# it has aerooilsection blades.

•  That is# the blades are o aerodynamic designsimilar to the wing o an aeroplane0.

•  This type o blade gives a higher volumetriccapacity air"ow0 and a higher e:ciency than thestandard backward curved blade.

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A0ial Fans• !7ial ans basically consist o an impeller with a number o blades#

usually o aerooil cross section# housed in a cylindrical casing. Theimpeller is mounted directly# on to the motor shat% the motorbeing housed inside the casing behind the impeller. There isnormally a very fne clearance between the blades and the casing%the closer the blade is to the casing# the higher the an e:ciency#pressure development and output.

•  The pitch angle o the blades can be altered within limits to

increase or decrease the an perormance# however i the pitchangle is altered too ar# the an will stall. The centre o the impelleris always blanked o with an aerodynamic hub to prevent air shortcircuiting around the impeller and to act as a airing or the motor.;uide vanes can be ftted to the impeller at either the inlet oroutlet to correct <swirling< o the air stream and increase e:ciency.

•  This type o a7ial an is known as a single stage an. Thesketches below show a7ial impellers without guide vanes and withguide vanes.Axial-flow (with guide vanes) Axial-flow (without guide vanes).

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Multi+sta*e

• ! multi-stage an is two or moresingle stage ans placed in series.

• I guide vanes are ftted to theassembly# the pressure developed

over a single stage an correspondsto. the number o stages.

• Thereore a two stage an will producetwice the pressure that a single stagean will or the same volume "ow rateand it ollows that a three stage anwill produce three times the pressure.

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#ont)a Rotatin*

• ! contra rotating an is two a7ial ansplaced in series# however theimpellers rotate in oppositedirections.

• This type o arrangement willproduce appro7imately two and a haltimes the pressure that a single stagean will or the same volume "owrate.

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Tan*ential Fans• ! Tangential or cross"ow0 an is constructed in a similar

way as a lengthened =orward 6urve 6entriugal =an but inthe air instead o entering through the centre or eye0 o theimpeller enters tangentially.

•  These ans are quiet in operation and give an even air"owover three length o the impeller# but have very little abilityto develop pressure.

• ,ue to these characteristics# these types o ans aretypically ound in an coil units and an convector heaters#or e7ample overdoor heaters in shops etc.

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Mi0ed Flo. Fans

• ! mi7ed "ow an consists o an impeller with a

number o blades# oten o aerooil crosssection# similar to an a7ial "ow an. The hub othe impeller is o a conical shape# such that thepassage o air- through the impeller has botha7ial and radial characteristics -- hence theterm <mi7ed "ow<.

• 9tatic guide vanes are normally ftteddownstream o the impeller to remove the swirlgenerated by this type o an. The mi7ed "ow

an has a very high e:ciency and can develophigher pressures than a7ial ans.

• 2i7ed "ow impellers can be either direct drivenor powered by a drive belt arrangement.

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P)opelle) Fans• (ropeller ans have an impeller o two or more blades#

very much like the propeller o a boat or an aeroplane. The impeller is normally connected directly to themotor shat% hence it is direct driven.

• (ropeller ans can deliver a high volume "ow rate#however they have a very low pressure development%

hence they are normally used in situations where theyare not connected to ductwork such as window andwall ans.

•  The sketch below shows a typical propeller animpeller.

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& FA / P"MP $A2' • It is a act o lie that a pipework or ductwork

system will not be installed e7actly to the originaldesign. This may be due to subtle changes in thebuilding design# the impracticality o installing thesystem in the way it was designed or errors mighthave been made in the system design. =ortunately#

this situation can oten be resolved very easily. Theperormance o a an or a pump is governed by aseries o mathematical laws known as the =an &aws.

• I the an laws are used properly by acommissioning engineer# they will enable him to re-

assess the design perormance o a an or pump tosuit the resistance o the ductwork or pipeworklayout that has been installed. e will look at theselaws frst and then e7plain how they can be usedpractically.

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Fan $a.s

• The primary an laws allow the perormance o

ans and pumps0 to be predicted# at dierentspeeds and duties by relating "uid "ow#pressure# density# impeller speed and diameterand the power required to drive the impeller.

• 3ecause the temperature o the "uid acrossthe impeller remains constant to all intentsand purposes# the density o the "uid in itspassage through the an or pump can be

neglected.• 9imilarly# the diameter o the impeller will

remain constant under normal operatingconditions# this can also be neglected.

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Fan $a.s

3y discounting density and impeller diameter# a simplifed seto an laws can be obtained. These are+>? @ >A  7 B?

BA

(? @ (A  7 B??

BA

?  @ A  7 B?4

BA 

here+

> @ =luid *olume =low m4/s0( @ (ressure developed (a0

@ (ower input k0B @ Impeller 9peed rp0• The 9u:7 A ater a letter indicates the letter applies to the

initial situation.• The 9u:7 ? ater a letter shows the letter applies to the new

situation# the one you are looking or.

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Fan $a.s%0ample

&et us assume that a an running at CDD rpm will discharge ? m4

/s o airagainst a ductwork system e7ternal static0 resistance o ?DD B/m? and will absorb 4 k o power in the process. I the an speed. isincreased by ADE+

>? @ >A 7 B? @ ? 7 CCD @ ?.?m4/s

BA CDD

(? @ (A 7 B? ? @ ?DD 7 CCD ? @ ?5?B/m? or (a

BA CDD

? @ A 7 B? 4 @ 4 7 CCD 4  @ 5k

BA CDD

 8ou can see rom the e7ample that i the an speed is increased by ADE

a0 The volume handled by the an will increase by ADE rom ?m4/s to?.? m4/s0

b0 The pressure developed by the an will increase by ?AE rom ?DDB/m? to ?5? B/m?0

c0 The power input to the an will increase by 44E rom 4k to 5k0.

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3& APP$4I( T5% FA $A2' PRA#TI#A$$4 

• 8ou can see rom the e7ample in (art 4

that the perormance o a an or pump canbe altered by changing its rotationalspeed.

• This is very useul# or e7ample# when aan is ound to be developing only FDE oits design requirement. 3y increasing thean speed slightly# the an can be made to

develop its design duty. 9imilarly# this canbe applied to a pump.

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Metods of 'peed #ont)ol 

Direct Driven Fans and Pumps

• It is di:cult to change the impeller speed o anydirect driven an or pump# because the impeller isconnected directly to the shat o the motor. Inthis instance# the impeller siGe is changed instead.

! smaller impeller will give a lower duty# whilst alarger impeller will give a higher duty.

• In the case o a7ial ans# the angle o the impellerblades pitch angle0 can be altered within limits.

 This again can be complicated and is best let tothe an manuacturer or a very e7periencedcommissioning engineer. I the pitch angle ismade too steep or too shallow# the motor maystall or eather respectively.

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Metods of 'peed #ont)ol 

Belt Drive Arrangements

• The speed o any an or pump that isdriven through a belt drive arrangementcan be varied by altering the siGe o the

pulleys.• (art C o this module looks at this type o

arrangement and (art H considers alteringthe arrangement to change the impeller

speed.

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Metods of 'peed #ont)ol 

Electronic Speed Control 

•  The motor o any an or pump can# i required#be speed controlled by a number o electronicmethods% requency inverters and eddycurrent controllers are avoured.

•  This type o control gives the motor aninfnitely variable speed# so that thecorresponding impeller speed can be fnelytuned to suite site conditions.

•  This type o speed control can be e7pensiveand is normally used or specialistapplications only# such as variable volume

systems.

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Metods of 'peed #ont)ol 

Note:

• Impellers are normally driven by electric motors. !emotor is si"ed in accordance #it! t!e design po#erabsorbed by t!e impeller $typically %an. po#erabsorbed is &'( o% t!e motor po#er rating)*t!ere%ore t!e available increase in %an speed or a+ial

blade pitc! angle is limited by t!e available capacityo% t!e motor.

• !ere is al#ays a ma+imum sa%e speed %or animpeller , t!is must never be e+ceeded- i% in doubt-re%er to t!e manu%acturer.

• Prior to altering t!e speed o% a %an- t!e %an bearingsmust be c!eced to ensure t!at t!ey are capable o%taing any additional load t!at may be imposed ont!em.

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%7%R#I'% 1 

! backward curved centriugal an has been

designed to supply A.AC m4/s at ?CD pascals#when running at AA?D rpm and absorbing ?.Ck. hen the volume "ow rate o the anwas checked on site it was ound to be

delivering only A.DC m4

/s. The an is drivenby a 4.D k motor running at A55D rpm.

sing the an laws# calculate+

a0 The an speed increase required to obtain

the design volume "ow rate.b0 The increase in absorbed power that thespeed increase will cause.

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A'2%R' TO %7%R#I'% 1 

>? @ >A  7 B?

BA

3y transposition+

B? @ BA 7 >? @ AA?D 7 A.AC @ A??H rpm

>A A.DC

 This is a speed or air"ow increased in the ratio o A.AC @ A.DFC or F.CE increase

?  @ A  7 B?4  @ A??H 4 @ 4.?J Kw

BA AA?D

Lnce you understand that air"ow varies directly with speed the ratio o increaseabove o A.DFC can be put into the pressure and power equations.

i.e. ? @ A A.DFC04 @ ?.C 7 A.4A5 @ 4.?J k

In this particular instance# it would be impossible to upgrade the an speedbecause the motor is not large enough to cope with the additional an power.'emember# the motor siGe is only 4.D k.

 This e7ample has been used to highlight that# even a ADE increase in speed willcause a large increase in an power. In this case# a larger motor would have to be

installed 5 k motor0 to cope with the increase.

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8& -%$T !RI9% '4'T%M' (ene)al

3elt drive systems consist o our main elements+• 9hats

• (ulley wheels

• ,rive belts

• ,rive guards(ulley wheels are ftted to both the motor shat and the an/pumpshat. (ower is transmitted rom the motor shat to the an or pumpshat by drive belts connecting the pulleys on both shats. ;uards areftted over the complete drive assembly or saety purposes.

Lne o the largest manuacturers o belt drive systems is =enner(ower Transmission.

In order to progress urther within this module you will need to obtaina copy o their ,rive ,esign M 2aintenance 2anual

=enners ead L:ce can be contacted on DA?C5 HN5ANA. They have

many regional o:ces throughout the .K.

# t I t ll ti d

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#o))ect Installation andOpe)ation

• (ages 5F and CD rom the =enner 2anual give

instructions on the correct installation andoperation o belt drives and also belt tensioninginstructions.

• ! large amount o inormation can be obtainedrom the condition o drive belts. 6racking o

belts shows that the belts are too loose% theyshould be renewed and correctly tensioned.3lack dust indicates wear% pulley alignment andcondition should be checked and i necessaryboth the pulleys and belts replaced.

• Bever attempt to change belts# pulleys# etc.#without having frst electrically isolated the itemo plant. Keep all lubricants o the drives andbelts and never allow water or any othersubstance to drip onto them.

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6& '%$%#TI( P"$$%4 #5A(%' TO 9AR4

'P%%!

• It has already been stated in this module that the

usual method o altering the speed o belt drivenans and pumps is by changing the pulley speed. This part o the module aims to show you how toselect pulleys and the corresponding belts.

• e shall use pages AC# AH# ?D# 4A# 4N and 4J o the

=enner 2anual to siGe some pulleys to meet theoriginal design requirements. The site conditionswill be as in the e7ercise at the end o (art 5# (ageA5.

•  The an was designed to supply A.AC m4/s at ?CD

pascals# when running at A?D rpm and absorbing?.4 k. &et us assume that the an and motor bothhave a 4?mm diameter shat and that they areCDDmm apart. =or the reasons given in the originale7ample let us assume that the an is served by a

5k motor running at A55D rpm.

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6& '%$%#TI( P"$$%4 #5A(%' TO 9AR4

'P%%!• (rimarily we need to calculate the speed ratio between

the an and motor. This is achieved by dividing the lowerspeed by the higher+

9peed ratio @ A55D @ A.?JH

AA?D

• Be7t we need to obtain the service %actor  rom table 4

on page AH. e know that we are looking at a an motorthat is below N.C k. &et us assume that the motor willhave a direct on-line starter and the an will be run or ?5hours a day.

• =rom table 4 we can see that our an alls into 6lass A

and has a service actor o A.4. I the motor had a star-delta starter# the actor would be A.?. In the special casescolumn o the table# we can see that the actor should bemultiplied by A.DC or the speed ratio that we calculatedabove. This gives us an ad1usted service actor o+

A.4 7 A.DC @ A.4HC

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6& '%$%#TI( P"$$%4 #5A(%' TO 9AR4

'P%%!

• Bow we need to calculate the design power. This

is obtained by multiplying the motor siGe by thead1usted service actor+

5.D k 7 A.4HC @ C.5H

• e now reer to table ? on-page AC. I we draw a

line across rom the calculated design power C.5Hk0 and also one up rom the speed o the astershat A55D rpm0 we can see that the linesintersect in the <'PA< area o the table. This is thetype o% pulley and belt  that we will use or-our

drive.• I we now reer to table A on page AC and again

compare the calculated design power against theastest shat speed# we can see that theminimum pulley diameter  must be JDmm.

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6& '%$%#TI( P"$$%4 #5A(%' TO 9AR4

'P%%!

• 3y reerring to the centre distance table on page ?D#

looking down the speed ratio column# we can seethat we need a A5Dmm diameter 9(! pulley on thedriver motor0 and a AJD 9(! pullet on the drivenan0. 'eading across the table# we can see that thenearest centre distance to our required CDDmm is

C5Jmm. The belt length at the top o the column is9(!AHDD. The correction %actor # again at the top othe column# is D.FC.

• =rom the top section o the power rating table onpage 4A we can see that the rated po#er per belt  

or a A5Dmm diameter pulley at A55D rpm isH.DCk. e can also see rom the bottom section othe power rating table that with a speed ratio oA.?F and a motor speed o A55D rpm the additional

 po#er per belt %or speed ratio is D.4F k.

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6& '%$%#TI( P"$$%4 #5A(%' TO 9AR4

'P%%!• e now. need to calculate the corrected power per belt. This

is done by adding the rated power per belt to the additionalpower per belt then multiplying them by the correction actor+@ H.DC O D.4F0 7 D.FC@ H.A? k per belt

• I we now divide the calculated design power by the correctedpower per belt# we will arrive at the number o belts required+

C.5HDH.AAJ @ D.JF•  Thereore we only need one belt. I this fgure were 1&;# we

would need two belts.• =inally# we need to check the pulley dimension tables given

on pages 4N and 4J to ensure that our selected pulleys will

ft. e can see that both a one groove 9(! A5D pulley and aone groove 9(! AJD pulley can have a ma7imum shat siGe o5?mm.

Note: t!at s!ould t!e pulleys be eit!er increased insi"e or increased in grooves- a c!ange in Bus! Si"emay also be re/uired .

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A'2%R TO %7%R#I'% ,

9peed ratio @ A55D

A??N @ A.AN5!d1usted service actor @ A.4 7 A.DC @ A.4HC

,esign power @ 5.D k 7 A.4HC @ C.5H

=rom table ? we can see that we will need 9(! type pulleysand belts.

 Table A shows that the minimum pulley diameter must beJDmm.

3y reerring to the centre distance table# we can see thatthe nearest speed ratio to ours is A.AJ. There are a numbero options or pulley siGes at this ratio. It is best rom an

economy reason to select the smallest pulleys% in this case.a FD 9(! or the motor and a ADH 9(! or the an. Bone othe other selections are wrong# but the JD/FD given initalics would not be used or our application. This isbecause that particular one would need a cogged belt asindicated by the note at the bottom o the table0.

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A'2%R TO %7%R#I'% ,

 The nearest centre distance is C5Hmm. The belt length at thetop o the column is 9(!A5DD. The correction actor again atthe top o the column is D.FD.

 The rated power per belt or a FDmm diameter pulley at A55Drpm is ?.?F k. ith a speed ratio o A.AJ and a motor speedo A55D rpm the additional power per belt or speed ratio isD.?5 k.

 The corrected power per belt @ ?.?F O D.?50 7 D.FD @ ?.?J kper belt.

 The number o belts required @ C.5H @ ?.4F

?.?J

 Thereore we would need three belts.3y checking the pulley dimension tables we can see that botha three groove 9(! FD pulley and a three groove 9(! ADHpulley can have a ma7imum shat siGe o 5?mm.