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Health and Safety
Executive
Compressed air safety
This is a free-to-download, web-friendly version of HSG39
(Second edition, published 1998). This version has been adapted for online
use from HSEs current printed version.
Youcanbuythebookatwww.hsebooks.co.ukandmostgoodbookshops.
ISBN 978 0 7176 1531 5
Price 7.50
Thisbookaimstopromotethesafeuseofcompressedairanddescribesthemany
waysinwhichcompressedaircanbedangerousaswellashowtominimisethe
riskofsuchdangersoccurring.
Itisaimedatdesigners,manufacturers,installers,usersandothersconcernedwith
orresponsibleforhealthandsafetyatwork.
HSE Books
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Crown copyright 1998
Firstpublished1990
ISBN9780717615315
Allrightsreserved.Nopartofthispublicationmaybereproduced,storedin
aretrievalsystem,ortransmittedinanyformorbyanymeans(electronic,
mechanical,photocopying,recordingorotherwise)withoutthepriorwritten
permissionofthecopyrightowner.
Applicationsforreproductionshouldbemadeinwritingto:
TheOfficeofPublicSectorInformation,InformationPolicyTeam,
Kew,Richmond,SurreyTW94DUore-mail:[email protected]
ThisguidanceisissuedbytheHealthandSafetyExecutive.Followingtheguidance
isnotcompulsoryandyouarefreetotakeotheraction.Butifyoudofollowtheguidanceyouwillnormallybedoingenoughtocomplywiththelaw.Healthand
safetyinspectorsseektosecurecompliancewiththelawandmayrefertothis
guidanceasillustratinggoodpractice.
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ContentsINTRODUCTION 5
COMPRESSOR PLANT 6
Groups of compressors 6
Hazards 6
General information and advice 6
Precautions 7
Safetyvalves 7
Pressureindication 7
Thermalprotection 7
Coolantprotection 8
Lubricantprotection 8
Explosionprotection 8
Airinlet/outletmonitoring 8 Otherinstrumentation 8
Airinlet/outletcontrol 9
AIR RECEIVERS 11
Statutory requirements 11
Hazards 12
General information and advice 12
Precautions 12
COOLERS 13
Hazards 13
General information and advice 13Precautions 13
AIR DRYERS 14
Hazards 14
General information and advice 14
Refrigerant 14
Dessicant 14
Precautions 14
INSTALLATION OF COMPRESSORS 16
Precautions 16
Smallcompressors 16
Mediumandlargecompressors 16Noise 16
MAIN LINE SYSTEMS 18
Hazards 18
General information and advice 18
Precautions 18
Pipe-runs 18
Filters,traps,separatorsandlubricators 21
Pressureregulators 22
PORTABLE PNEUMATIC EQUIPMENT 23
Statutory requirements 23Hazards 23
General information and advice 23
Precautions 24
Flexiblehoses 24
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Blowguns 24
Portabletools 25
PNEUMATIC POWERED MACHINERY 26
Hazards 26
General information and advice 26
Precautions 26
ACTUATORS 28
Hazards 28
General information and advice 28
Precautions 28
INTERLOCKING METHODS AND CIRCUIT DESIGN 31
General information and advice 31
Interlocking systems 31
Singlecontrolsysteminterlocking 31Dual control system interlocking 32
Power interlocking 40
Circuit design 41
Pistonarrest 41
Pistonarrestandhold 41
Overridinglockedposition 41
Predeterminedposition 41
INSPECTION AND MAINTENANCE 42
Statutory requirements 42
Hazards 42
General information and advice 42Maintenance of compressors and ancillary plant 42
Supervisionandprocedures 42
Daily 43
Checks mainly directed to reciprocating compressors 43
Weekly 43
600hours 43
Six-monthly 43
2000hrsorannually 44
Precautions 44
Maintenance of air powered equipment 44
Supervisionandprocedures 44
Daily 44
Weekly 45Monthly 45
Threemonthly 45
Sixmonthly 45
Precautions 45
TRAINING 46
Statutory requirements 46
Hazards 46
Precautions 46
Further information 46
British standards 47
Health & Safety Executive publications 48Legal requirements 49
FURTHER INFORMATION 50
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Introduction1 Thisguidancebookletaimstopromotethesafeuseofcompressedair
bygivingadvicetodesigners,manufacturers,installers,usersandothers
concernedwithorresponsibleforhealthandsafetyatwork.Itwasoriginally
producedin1990duringarapidlychangingsituationinEuropearisingfrom
thepreparationforthesinglemarketandwasfurtherrevisedunderthe
ReviewofRegulationsandGuidanceundertakenbytheHealthandSafety
Executive(HSE)in1996.
2 Therearemanywaysinwhichcompressedaircanbedangerous,for
example:
(a) itcanenterbodyorificessuchasthemouth,earsandanus,causing
severeandoftenfatalinjuries;
(b) athighpressureitcanpenetratetheskin; (c) particlesoroilcarriedinanairjetcandamagetheeyes;
(d) oil-cokedepositsinasystemcanspontaneouslyigniteandcausean
explosion;
(e) vesselscontainingcompressedair,evenatcomparativelylowpressure,
canexplodeviolentlyoncetheirintegrityislost;and
(f) dirtyorwetaircanleadtocorrosionandblockedvalveswhichmay
makethesystemunsafe.
3 Thisbookletexplainshowtominimisethelikelihoodofsuchproblems,
butitdoesnotgivespecificadviceonairseparationplant,thepneumatic
transportationofmaterialsthroughpipelinesorthesupplyofrespirableair.
Referenceinthisguidancebooklettoaparticularstandarddoesnotprecludeusinganequallyeffectivealternativestandard.
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Compressor plant
Groups of compressors
4 Forthepurposesofthisbookletcompressorsaredividedintothreegroups:
small,mediumandlarge.
5 Asmallcompressordeliversupto40litrespersecondoffreeairand/orhas
apowerinputofnomorethan15kW.Suchcompressorsmaybemobileor
fixedandmaybesuppliedaspackagedunits.Atypicalonewouldcomprise
areciprocatingcompressordrivenbyanelectricmotorontopoforalongside
anairreceiver.
6 Amediumcompressordeliversbetween40and300litrespersecondoffree
airand/orhasapowerinputofbetween15and100kW.
7 Alargecompressordeliversmorethan300litrespersecondoffreeairand/
orhasapowerinputofmorethan100kW.
8 Manymediumandlargecompressorsaresuppliedaspackagedunits.A
typicalonewouldcompriseacompressor,airintakefilter,motorandair
cooler,allonacommonbedframewithfactory-connectedpipingand
factory-installedelectricalcontrolsandwiring.Itcouldbeenclosedinasheet
metalhousingtreatedwithsoundproofingmaterialtoreducenoiselevels.
9 Usingapackagedunithasanumberofadvantages;itsimplifiesfoundation
work,reducesinstallationtimeandprovidesaproperlyengineeredand
adequatelyguardedassemblyofcomponentsinacompactspace.However,
theuserisstillresponsibleforsitingthesystemsothatincomingairisasdry
andfreefromcontaminantsassiteconditionsallow.Boththeairenteringthe
compressorplantandthedeliveredairmustbeasdry,cleanandcoolas
possible.Adviceonsitingisgiveninparagraphs60to67.
Hazards
10 Themajorhazardassociatedwithcompressorsisoverpressurisation,which
mayarisefrom:
(a) ablockedoutletorsomeotherrestrictiontoflow; (b) failureofautomaticcontrolscombinedwithlowairconsumption;
(c) compressormalfunction,egoverspeeding;
(d) anexternalfirenearthepressuresystem;and
(e) overheatingandthebuild-upofcarbonaceousdeposits,bothofwhich
canleadtofiresorexplosions.Althoughtheyarerare,firesand
explosionscanalsooccurasaresultofoiloroilvapourbeingignitedin
thepressuresystem.
11 Dirtyorwetaircancauseasystemtofailegbycausingfineparticlesof
debristoagglomerate,blockingsafetyrelatedvalves.
General information and advice
12 Standardsforthesafedesign,construction,installationandoperationof
manytypesofstationarycompressoraresetoutinBS6244Code of practice
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for stationary air compressors.Itspecifiesrequirementstohelpminimise
compressoraccidentsanddefinesgeneralsafetypractices.BSEN1012
Parts1&2coverCompressors and vacuum pump safety requirements.
NOTE: It is important that records are amended following
modifications to plant and pipework.
Precautions
13 TransmissionmachineryegVbelts,pulleysandotherdangerousparts,
shouldbeguardedtopreventaccess,seeBS5304Code of Practice for
Safety of machinery.
Safety valves
14 Onallmediumorlargemulti-stagepositivedisplacementcompressorsa
safetyvalveshouldbefittedbetweeneachstageand,whereappropriate,in
theinteroraftercoolercircuit.
15 Whereanisolatingvalveisinstalledinthedischargepipeworkbetweenthe
compressorandreceiver,thepipeworkonthecompressorsideofthevalve
shouldbeprotectedbyasuitablesafetyvalvethatcomplieswithBS6759,
Part2Specification for safety valves for compressed air or inert gasesand
isinstalledtoBS6244,clause21,unlessthesystemhasbeendesigned
towithstandthemaximumpressurethatcanbegenerated.(Thisvalveisin
additiontotheairreceiversafetyvalve.)Onsmallfixedandsmallandmedium
transportablecompressorunits,wheretheoutletofthecompressorisdirectly
connectedwithoutshut-offornon-returnvalvestoanairreceivertowhichno
othersourceofpressureisattached,onesafetyvalveontheairreceiveris
sufficient.
Pressure indication
16 Anaccuratelycalibratedairpressuregaugewithareadilyvisibleappropriate
scale-readingshouldbeprovidedaftereachstageofcompression.However,
onsmalltwo-stagecompressorsthisisnotrequiredafterthefirststage
ofcompression,butasuitabletappingtoenableatestdevicetobefitted
shouldbeprovided.GaugesshouldbeconstructedtocomplywithBSEN
837-1Part1-Bourdon tube pressure gauges- Dimensions, metrology,
requirements and testing andinstalledtocomplywithBSEN837-1Part2
Selection and installation recommendations for pressure gauges.
17 Onmediumandlargereciprocatingcompressorswithforcedfeedlubrication
systemsitisimportantthatagaugeisprovidedintheappropriatepositiontoindicateoilpressure.
Thermal protection
18 Tominimisetheriskofoverheating,largecompressorsshouldbeprovided
withasuitablethermalprotectivedeviceasnearaspracticabletothelast
stagedischargevalveor,wherethereismorethanonevalve,atacommon
pointofdischargewhichwouldautomaticallyshutdownthecompressor
whenapredeterminedtemperatureisexceeded.Note - where automatic
compressor shut-down may adversely affect the safety of pressure-
dependent systems, additional high temperature warning devices
may be required so that action can be taken prior to automatic
shut-down.
19 Onlargetwo-stagecompressorsathermalprotectivedeviceshouldalso
beprovidedasnearaspossibletothefirst-stagedischargevalve.Large
compressorswiththreeormorestageswouldrequireaseparatedevicefor
eachstage.
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20 Formediumandlargeair-cooledcompressorsprotectivedevicesshouldbe
providedtomonitorgeneralcompressoroverheatingwhichmaybecaused
bycooling-fanfailureorthefoulingofcoolingsurfaces.
21 Oil-floodedrotarycompressorsshouldhaveanautomaticshut-downdevice
topreventthetemperatureofthecompressedairfromexceedingasafelimit.
Coolant protection
22 Ifthecompressoriswatercooled,athermostatshouldbeprovidedtothe
coolingwateroutletorwaterreturntotheradiatorheadertanktoshutdown
thecompressorwhenthewatertemperatureexceedsthemanufacturers
recommendedmaximum.Wherethethermostatdevicedoesnotgiveno
waterornoflowprotection,awaterflowdetectiondeviceshouldalsobe
provided.Sufficientgoodqualitycoolingwaterisrequiredtocoolallparts
ofthesystemandinhibitblockagesandcorrosion.Thesupplymayrequire
protectionagainstfreezinginlowtemperatures.
Lubricant protection
23 Onmediumandlargecompressorsapressure-sensingdeviceshouldbe
providedtoshutdownthecompressorandactivatevisibleandaudible
alarmsifthelubricatingoilpressuredropsbelowthemanufacturers
recommendedminimum.Gravity-feedlubricationsystemsshouldbefitted
withalevelsensingdevice.Athermalsensingdeviceshouldbefittedtoset
offanalarmandshutdownthecompressoriftheoilinthecrankcase,sump
orscavengesystemsexceedsthetemperaturespecifiedbythelubricant
manufacturer.Therecanbesafetyadvantagestousingsyntheticester-based
oilsforlubricatingcompressors.
Explosion protection24 Ifcomponentsrunhot,oroilcokedepositsspontaneouslyignite,theremay
beanexplosion.BS6244describesthechemistryofsuchconditionsand
explainshowoilcokedepositscanbeprevented.Toreducetheexplosion
riskonmediumandlargecompressors,afusibleplugcanbefittedonthe
undersideofthepipebetweenthecompressorandthereceiverascloseasis
practicabletothecompressor.Whenorderingsuchaplug,userswillneedto
providethefollowinginformationforthemanufacturer:
(a) maximumdesignworkingpressure;
(b) makerandgrade,orclosedflashpointoftheoilusedforcylinder
lubrication;
(c) maximumdesignoutlettemperatureofair;and
(d) boreofoutletpipefromcompressor.
25 Fusibleplugsaregenerallyavailableforpressureupto340bar(5000psi).
Asanadditionalprecautionregularinspectionsofthecompressorshouldbe
carriedout(seeparagraphs142to170).
Air inlet/outlet monitoring
26 Awatermanometerorotherpressure-indicatingdeviceshouldbefittedto
eachinletairfilteronlargecompressors.Thedevicemeasuresthepressure
dropacrossthefilter,indicatinghowcleanitis.Itisrecommended,whereit
isreasonablypracticabletodoso,thatsuchdevicesbefittedtosmalland
mediumcompressors.
Other instrumentation
27 Onmediumandlargecompressorsconsiderationshouldbegiventofitting
temperaturereadingorrecordinginstrumentstoindicate:
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(a) airtemperatureat:
(i) theinlettothecompressor;
(ii) theoutletfromthefirststageofcompression,neartothedischarge
valve;
(iii) theinlettothelaststageofcompression;
(iv) theoutletfromthelaststageofcompression,neartothedischarge
valve;and
(v) theoutletfromtheaftercooler
(b) oiltemperatureat:
(i) thecrankcase;or
(ii) withforcedfeedandscavengelubricationsystem,thepointwhere
theoilleavesthecrankcase;
(c) watertemperatureat:
(i) theinlettoeachcoolingcircuit(exceptonradiator-cooledsets);and
(ii) theoutletfromeachcoolingcircuit.
Itisimportantthattheuserandmanufacturerdiscusswhethersuchinstrumentsareneeded.
Air inlet/outlet control
28 Theinletvalvecaneitherbedesignedsothatitcannotbeusedinapartially
openposition,orbefittedwithvisibleandaudiblewarningsthatindicate
whetherthevalveisfullyopenorclosedduringplantoperation.Thevalve
operationisnormallyautomaticexceptwhenrequiredforstartingupthe
compressor.Oil-floodedrotarycompressorshavebuilt-inself-regulatinginlet
throttles.Constantspeedcompressorsshouldbeprovidedwithsuitable
controlgearsothattheamountofairdeliveredcanbecontrolledtosuit
demand.
29 Figure1showsanillustrationofalargecompressorinstallationandthe
positionsatwhichsafeguardsarerequiredorrecommended.Itisunlikelythat
anyinstallationwillrequireallthesafeguardsindicated.Thefinalrequirement
willdependonrelevantstatutoryrequirements,thedegreeofsupervisionthe
installationwillreceiveandthelocalenvironment.
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Figure 1 Illustrationofalargecompressorinstallationshowingthepositionatwhichsafeguardsare
requiredorrecommended
Thermal protective device to
monitor air-cooled
compressor general
overheating
Stopvalve
Receiver
identification
Cooling water feed
Compressor Aftercooler
Intercooler
Lowpressurecylinder
Highpressurecylinder
Air inletfilter
Totalclosure
unloader
Cooling water discharge
Receiver
Manhole
AR1SWP
Oil pressure protective device
Manometer
Thermometer
Safety valves or relief valves
Non return valves Drain
G
H
I
L
J
K
A
B
C
D
EF
Fusible plug
Thermal protective device
Water flow protective device
Oil level protective device
Oil pressure gauge Air pressure gauge
It is unlikely that any installation will require all the safeguards
indicated. However, a combination of these should be fitted,taking into account the statutory requirements and the degree of
supervision the installation will receive.
Instruments will normally be mounted on a common panel
NOTEKEY
Water or air flow
I
I J F
II L
B F I
I
J K J F I
A
I L
F
J
A
I
L
I
B C I
I
B
D
E
G
I
I
B
I
H
B
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Air receivers
Statutory requirements
30 Bothmanufacturersandusersshouldbefamiliarwiththestatutory
requirementsapplyingtocompressedairsystemsandairreceivers.These
areprincipallycontainedinthePressureSystemsandTransportableGas
ContainersRegulations1989.Additionalrecommendationsaregiveninthe
ApprovedCodeofPracticeSafety of pressure systems.
31 Inpremiseswheretheairreceiversmustbecleanedandexaminedat
regularintervalsandforairreceiverswithavalueofpressuretimesvolume
greaterthan250barlitres,thenatureandfrequencyoftheexaminationmust
becontainedinawrittenschemeofexamination.Thewrittenschemeof
examinationdrawnuporcertifiedbyacompetentpersonwillnormallyspecifyaperiodbetweenexaminationsof24to48months.
32 Whenconnectedtoanaircompressingplantareceivershouldeitherbe
constructedtowithstandthecompressorsmaximumpressuresafely,or
befittedwithasafetyvalveandapressure-reducingvalvetopreventthe
receiverssafeworkingpressurefrombeingexceeded.Whenproviding
asafetyvalveandpressuregaugeforasetofairreceiversthatare
interconnectedandcollectivelysuppliedthroughasinglepipe,theymaybe
treatedasonereceiver,providedthat:
(a)anyreducingvalveorothersuitableapplianceisprovidedinthesingle
supplypipe;and
(b)thereisnomeansofisolatinganyinterconnectingpipework.
33 ThereceivershouldbefittedwithasuitablesafetyvalvecomplyingwithBS
6759,Part2orsimilarequivalentstandardandadjustedsothatairisallowed
toescapeassoonasthesafeworkingpressurehasbeenexceeded.Itis
essentialthatthevalveiscapableofdischargingmoreairthanthesystem
cansupplytothereceiver.
34 Thereceivershouldbefittedwithacorrectpressuregaugecomplyingwith
BS1780orsimilarequivalentstandardandwhichindicatespressureinbar,
lbf/sqin,orothersuitableunits.
35 Thereshouldbeasuitableappliance,eithermanualorautomatic,fordrainingthereceiver.Itisrecommendedthatmanualdrainvalvesshouldbefullbore
andstraightthrough,tominimiseanybuild-upofdebriswhichcouldprevent
tightshutoff.Automaticdrainvalvesshouldhaveadequatecapacityfor
liquiddischarge,bedesignedtominimisedebrisbuild-upandhaveamanual
overridetocheckperformance.Astrainerpositionedimmediatelyupstream
ofthevalvewillhelppreventdebrisbuild-up.Protectionagainstfreezingof
valveswillberequiredininlowtemperatureconditions.
36 Areceivershouldhaveasuitablemanhole,handholeorothermeans(as
determinedbytherelevantstandards,forexampleBSEN286-1Specification
for simple unfired pressure vessels designed to contain air or nitrogenandBS
5169Specification for fusion welded steel air receivers)toenabletheinteriortobethoroughlycleanedandinspected.
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37 Areceivershouldbeclearlymarked,inaconspicuousposition,withitssafe
workingpressureandotherrelevantinformationrequiredbythePressure
SystemsandTransportableGasContainersRegulations1989.Thedetails
shouldbeclearlyvisibleonthevesseloraplateattachedtoit.
38 Areceivershouldbereadilydistinguishable.Thiscanbeachievedbypainting
onidentificationmarkingsorbyaffixingamanufacturersplate,givingthe
nameofthemanufacturer,serialnumberetc.
Hazards
39 Themainhazardisthatthevesselmayexplodebecauseitssafeworking
pressurehasbeenexceededorbecauseitsabilitytowithstandpressurehas
beenreducedthroughcorrosionfatigueorinternalcokefiresforexample.
General information and advice
40 AllnewairreceiversshouldconformtoBSEN286-1orBS5169,where
applicable,ortoastandardprovidingequalintegrity.
Precautions
41 Todeterminetherequiredcapacity,thecompressoroutputanddemand
patternneedtobetakenintoaccount.Asaguide,thiswillbebetweensix
andtentimesthefreeairoutputofthecompressoratnormalpressure(litres/
second).Manyuserstrytosaveoninitialcostandmakethemistakeofbuyingareceiverthatistoosmall.
42 Thedrainvalve,safetyvalve,examinationholesandmanholesneedtobe
accessible.
43 Thescaleofanygaugesneedstobeclearlyvisible.
44 Onlargecompressorsystemstheairreceivershouldbefittedwithafusible
plugconformingtoBS1123,Part1.Ifafirebreaksoutnearby,theplugwill
helptopreventanexplosionbyguardingagainst:
(a) theairtemperaturerisingtothecompressorlubricatingoilflashpoint;or
(b)anexplosionoccurringbelowthedesignedworkingpressurebecauseof lostintegrityowingtoheat.
45 Welded-onbracketsareoftenusedtomountcompressor-motor
combinationsontoairreceivers.Wherethisisthecase,weldingshouldbeto
thespecificationandapprovaloftheairreceivermanufacturer.Itshouldnot
becarriedoutindiscriminatelybecausetheweldermayunwittinglyweaken
thereceiver.Mountingbracketsshouldbedesignedandfittedinaccordance
withtheapplicableairreceiverstandard.Itisgoodpracticetoweldmounting
bracketsontointermediatereinforcingplatesratherthandirectlytotheair
receiver.
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Coolers
Hazards
46 Manyaftercoolersarepressurevesselsandtheassociatedhazardsare
similartothoseofairreceivers(seeparagraph39).
General information and advice
47 Coolingplaysanimportantpartinthesupplyofgoodqualitycompressedair.
Intercoolersandaftercoolerslowerthetemperatureofthecompressedair.
Thesecoolersareusuallywateroratmosphericaircooled.Withverysmallair
compressorsthefunctionoftheaftercooler(ietheloweringofthedewpoint
ofthecompressedair)isperformedbytheairreceiver.Forothercasesaseparateaftercoolerwillnormallybenecessary.
Precautions
48 Air-cooledcoolersusuallyrelyonagoodcirculationofexternalairoverthe
heatexchangersurfacetoensureeffectivetransferofheat.Thereshouldbe
adequatespaceavailablearoundtheseheatexchangerstoalloweffective
cleaningofallsurfaces.Thecoolingairinletsandoutletsshouldnotbe
obstructedbylooseequipment,materialsetcorbyanysubsequentlyerected
building.Wherepossibletheairinletshouldbesitedonthenorthsideofthe
building.
49 Itisrecommended,particularlyatmediumandlargecompressors,that
aftercoolersarefittedtothedischargesideimmediatelyafterthecompressor.
Thesearefrequentlyprovidedwithseparatorstoremoveoilandmoisture
fromtheair.
50 Acondensateseparatorwithanautomaticdrainvalveshouldbeprovided
atasuitabledrainagepointatthecoolerscompressedairoutlet.Protection
againstfreezingofthevalvewillberequiredinlowtemperatureconditions.
51 Whereafluidisusedasthecoolingmedium,acoolantdrainvalveshouldbe
fittedandthecoolingcircuitprotectedagainstcorrosion.Thereshouldbe
somewayofmeasuringtheinletandoutlettemperaturesofthecompressedairandofthecoolant.
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Air dryers
Hazards
52 Thehazardsassociatedwiththeshellsoflargedryersdesignedonthe
tube-in-shellprinciplearesimilartothoseofanairreceiver(forinformation
onhazardsseeparagraph39).Asecondaryhazard,shouldanairdryernot
functionproperly,isthatmoisture-ladenaircancauseasafetysystemtofail.
General information and advice
53 Airdryersaresometimesdesirablewherepiperunshavetoberoutedoutside
buildingsorwherethecompressedairisusedoutsidebuildingsegfor
operatingvalves.Whereexceptionallydryairisneeded,egforpurgingdoubleglazingunits,airdryersareessential.Therearetwomaintypes:refrigerant
anddesiccant.FurtherclassificationcanbefoundinBS6754Specifications
and testing of compressed air dryers.
Refrigerant
54 Refrigerantairdryerscanusuallyreducethedewpointofthecompressed
airto2C.Thispreventscondensationfromforminginthedistributionpipes
wheretheambienttemperatureexceeds2C.Thismaybesuitableeven
whereshortrunsofpipeareroutedintheopenair,providedtheyareproperly
insulated.
Dessicant55 Desiccantdryerscanreducethepressuredewpointofthecompressedairto
verylowlevels,exceptionally,aslowas-100Cbutnormally,between-20C
and-40C.Thereductioninthepressuredewpointofcompressedairshould
becloselyrelatedtotherequirementsoftheplantorequipmentinstalled.
Adesiccantdryernormallyconsistsoftwochambersthatbothcontain
desiccant-oneonstream,theotherbeingregenerated.Anautomaticinlet
valvedirectsairfromthecompressortoeachchamberinturn,thusensuring
aconstantsupplyofdryair.
56 Positioningoftheairdryerwilldependonthecustomersparticular
requirements,butwillbeeitherimmediatelybetweentheaftercoolerand
receiver(wherefitted)orimmediatelyafterthereceiver.Wheretheneed
forexceptionallydryairrepresentsonlyasmallpercentageofthetotalcompressedairused,adryermaybelocatedimmediatelyupstreamofthe
particularplantwherethedryairisneeded.
Precautions
57 Thechambersofairdryersarepressurevesselsandshouldconformwith
BS5500Specifications for unfired fusion- welded pressure vesselsortoa
standardprovidingequalintegrity.Ifmeansareprovidedforisolatingthe
dryer(anditisgoodpracticetoprovidemeansofisolationforallequipment),
eitherthechambersshouldbeconstructedtowithstandthemaximum
pressurethatcanbegeneratedbythecompressororasuitablepressurereducingvalveandasafetyvalveshouldbefittedtopreventthesafeworking
pressureofthechambersfrombeingexceeded.
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58 Wherethereisnomeansofisolatingthedryerfromasuitablesafetyvalve,eg
onthereceiver,andwherenon-returnvalvesarefittedtothedryeroutlet(to
protectitfromstoredenergyinthesystem),nosafetyvalvesareneeded.
59 Somedryersregeneratethedesiccantsimplybypassingaproportionof
thedrierairthroughit.Othersuseheatercoilsembeddedinthedesiccant.
Thislattertypeshouldbeequippedwithathermalprotectivedevicethat
candetectanytemperatureriseabovethethermostatsetting.Excessive
temperaturerisesduetothermostatfailureshavebeenknowntoleadtooil
mistexplosions.
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Installation of compressors
60 Smallcompressorinstallationsmayeasilybeoverlooked,especiallyifsited
inaseparateenclosureoutsidetheworkingarea,andconsequentlymay
notreceivepropermaintenance(seeparagraph146-158).Thedesignof
largeinstallationswillneedtoincorporateadequateaccessandsuitable
liftingequipmenttofacilitatemaintenance.Ifnormallightingislikelyto
beinadequate,locallightingshouldbeprovidedsothattheworking
areaisadequatelylit.Considerationshouldalsobegiventocompressor
specificationsiftheyaretobeinstalledinpossiblehazardousareas,e.g.in
garagepitswhereaflammableatmospheremaybepresent.
Precautions
Small compressors
61 Wherepossiblethecompressorunitshouldbemountedatgroundleveland/
orinanareabigenoughtoallowforinspectionandmaintenance.
62 Anyplatformusedforaccessorasaplaceofworkshouldbebigenoughfor
apersontostandsafelyonit,andhaveguardrailsandtoeboards.
63 Theunitshouldnotbemountedonaplantstructurewherethereisexcessive
vibration.
64 Smallunitsusedtosupplyworkshopsandsimilarinstallationsshouldbesited
wheretheyareaccessibleandphysicallyprotectedagainstdamagefrommaterial,toolsandequipment.Wheretheriskofdamageishightheyshould,
wherepossible,beinstalledinseparateroomsadjacenttothemainbuilding
(seeparagraphs60and67).
Medium and large compressors
65 Whereusersareresponsibleforon-sitesystemdesignandinstallationthey
shouldfollowthemanufacturersinstructionscarefully.Mediumandlarge
compressorsshouldbelocatedinaposition(usuallypermanent)bestsuited
forthepurposeandwithaccessforeaseofmaintenance.Thismeansthat
thecompressor,includingitsprimemover,airreceiver,cooleretc.shouldbe:
(a) nearthecentreoftheloadtominimisepiperuns;
(b) housedinabuildingthatisinsulatedorheatedtokeeptheambient temperatureabovefreezing;
(c) providedwithadequateventilatingairtopreventoverheating,andsited
sothattheintakeofmoistureisminimised;and
(d) sitedawayfromdustyatmospheresandprovidedwithadequatefacilities
fordrainingofcondensate.
66 Thereshouldbesomemeansofcontrollingairbornedustandcontaminants
inthevicinityofthecompressor.Theairintakeshouldbeprovidedwithan
efficientfilter.
Noise
67 Compressornoiseisoneofthemostcommonnoiseproblemsassociated
withtheworkplaceandispotentiallydamaging.Referenceshouldbemade
tothePreventionofDamagetoHearingfromNoiseatWorkRegulations,
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enactedon1January1990,andtheassociatedguides1and2and3to
8.Wherenoisefromcompressorsislikelytocauseexposuretohazardous
levelsofnoise,thisshouldbeincludedinthenoiseassessment(required
undertheNoiseatWorkRegulations1989)andtheassessmentshould
indicatethedegreeofnoisereductionrequiredtoreducetheexposureto
safelevels.Compressorsshouldbesuppliedwithnoiseemissioninformation.
Ifthisisnotthecase,purchasersshouldrequestthisinformationwhichcan
beusedintheassessment.Noisecontrolmeasures,ifrequired,includethe
following:
(a) sitingthecompressorawayfromworkareas;
(b) providingthecompressorwithanacousticenclosure(theneedfor
accessandremovalformaintenancewillneedtobeaddressed);
(c) providinganti-vibrationmountings;
(d) thefittingoforimprovingtheperformanceofsilencers;
(e) accesstoenclosuresprovidedforcompressorsshouldonlybe
permittedtopersonswearingsuitableandeffectiveearprotection.
68 HSE Guidance note PM 56givesinformationandadviceaboutnozzledesign
toreducenoise.
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Main line systems
69 Thissectiondealswiththesystemofpipes,valvesandfittingsfromthe
sourceofthesupplytothepointofapplicationorcontrol.
Hazards
70 Inadequatelysizedanddesignedsystemscanleadtotheoperatingunits
beingstarvedofair,causingmachinemalfunction.Repeatedmalfunctions
maytemptoperatorstoadoptunsafepracticestoovercomeanyproblems.
Badlydesignedpiperunsandlackofisolationvalvesmayexpose
maintenancestafftounnecessaryrisks.Somegradesofplasticpipeworkare
notrecommendedforuseincompressedairinstallationsanddesignersare
advisedtoconsultmanufacturerswhenselectingmaterials.
71 Incorrectmaintenanceofnon-metallicbowlsusedonfilters,traps,
separatorsandlubricatorscanleadtoexplosions.Itisimportanttoensure
thatalllubricantsusedtoreplenishlubricatorsarecompatiblewiththe
lubricatorbowlandtheequipmenttobelubricated.Attentionisdrawnto
BS6005Specification for moulded transparent polycarbonate bowls used
in compressed air filters and lubricators,regardinginstallation,useand
maintenanceofunitsfittedwithpolycarbonatebowls.
General information and advice
72 Compressedairsystemsinvariablygrow.Itisimportanttotakeintoaccount
anyforeseeableexpansionofthesystem,andgenerousallowanceshouldbe
madeonthesizeofpipingprovided.Thecostofinstallinga50mmdiameter
pipeislittlemorethana25mmone,anydifferencebeinginthecostof
material.However,flowcapacityofa50mmpipeisfourtimesthatofa25
mmoneandusingthelargersizeensuresbetterperformanceandfacilitates
futureadditionstothesystematlittleextracost.Asageneralguidethepipe
sizewouldbesuchthatthepressuredropbetweenthereceiverandthemost
remotetakeoffpointswouldnotexceed5%oftherequiredsupplypressure
withamaximumof0.3bar(4psi).Thepipesizeforinitialmainrunsinany
systemwouldnotnormallybelessthantheoutputportofthecompressor.
73 Therearetwomaintypesofcompressedairsystem;singlelineandringmain.Figures2and3showtypicallayouts,withpositionsindicatedfor
variousvalves,drains,filters,airlinelubricatorsandpressuregauges.
74 Usersshouldkeepaschematicdrawingoftheairsystemshowingpipe
runs,intendeddirectionofairflow,andthepositionsoffittingssuchas
valves,drains,etc.Thedrawingsshouldbeamendedwhenmodificationsor
additionsaremadetothesystem.Anygraphicsymbolsusedshouldcomply
withBSISO1219Fluid power systems and components. Graphic symbols
and circuit diagrams.
Precautions
Pipe-runs
75 Therouteofthepiperunandthepositionofvalvesandoperatingpoints
shouldbesafeandconvenientforthosewhowilluseandmaintainthe
system.
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76 Thepiperouteitselfshouldnotpresentahazardorobstructaccessand
shouldberoutedawayfromanyareaswhereitmaybevulnerableto
mechanicaldamage.
77 Thereshouldbeadequateandsufficientaccessways,workingplatforms
andclearancespaceprovidedtoenablethecompressedairsystemtobe
operatedandmaintainedwithoutexposinganyonetounnecessaryrisk.
78 Piperunsshouldhaveaslightfallinthedirectionofairflow,anddrainage
valvesshouldbefittedatthelowestpoint,insuchawaythatmoistureand
aircanbedischargedsafely.Adrainvalveshouldbefittedatthebottomof
verticalpiperuns.Sectionsofpipeandvalvesthatmayhavewaterinthem
andmaybeexposedtofrostshouldbesuitablyinsulated.Note: receiver
drains generally have a heavier duty than normal pipe run drains-see
paragraph 35.
79 Piperunsshouldbesecuredbybracketsorothersupportsinstalledatappropriateintervalstosupportthepipesystemsuchthateachremovable
sectionisself-supportingandtheremainingpipeisstableafterremoval.To
allowforexpansion,particularlyatthecompressor/receiverdischargeor
onstraightrunsexposedtosunlightorheatfromtheprocess,suitableand
adequateexpansiondevicesshouldbefitted;egbellows,loopbends,flexible
pipes.BS3974:Parts1-3Specification for pipe supportsgivesdetailsof
suitablemethods.
Figure 2 Singlelinesystem-typicallayout
Symbols Description
Shut-off valve
Manual drain (water trap)
Automatic draining valve
Lubricator
Pipe fall in direction of air flow
Filter, pressure regulatorpressure gauge, lubricator
Filter with manual control
Control valve
Pressure gauge
Air cylinder(spring return)
KEY
Chuteoperation
Maintenance area
Airgrinder
Compressorinstallation
Airpoint
Todrain
Todrain
To drain
Air
vent
Bin gate
operation
DO NOT CROSS-CONNECT AIRLINES
IN A SINGLE LINE SYSTEM
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Figure 3 Ringmainsystem-typicallayout
80 Pipingandassociatedfittingsconnectedbetweenthecompressorand
airreceivershouldbeeasytoclean.Ifcarbondepositsbuildupinsuch
pipeworktheremaybeanexplosion(seeparagraph24).
81 Alloutletpointsshould,wherepracticable,betakenfromthetopofthe
piperun,andastopvalveorself-ventingballvalve(wherenecessary
completewithhandle)shouldbeprovidedadjacenttotheconnectionpoint.
Theconnectionpointatanyoutletshouldbearrangedhorizontallyorfacedownwards;upwardfacingconnectionpointsinvariablyfillwithdirtand
promptthebadpracticeofblowingoutbeforeuse.Outletpointsshould
beprovidedatconvenientplacesforallroutineactivitieswhichrequire
compressedair.Theyshouldbepositionedsothathosesattachedtothem
willnotcrossorobstructthenormalaccesstotheworkplace,andcanbe
connectedwithouttheneedforclimbing.
82 Piperunsshouldbeidentifiedbypaintingthepipelightblue(BScolour
reference20.E.51)inaccordancewithBS1710.Whereapplicabletheriskof
couplinguptothewrongcompressedgassupplycanbefurtherreducedby
theuseofnon-interchangeableconnections(seealsoparagraph100).
83 Stopvalvesshouldbeprovidedandpositionedsothatthecomplete
pipeworksystemcanbeisolatedfromthecompressedairsupply.Allbranch
linesofsubsectionsofthesystemshouldalsohavestopvalvesfittedtoallow
separateisolation.Whereappropriateeachvalveshouldhaveafacilitytobe
lockedintheclosedposition.
Symbols Description
Shut-off valve
Manual drain (water trap)
Automatic draining valve
Lubricator
Pipe fall in direction of air flow
Filter, pressure regulatorpressure gauge, lubricator
Filter with manual control
Control valve
Pressure gauge
Air cylinder (spring return)
KEY
B
A
Control
point
To
drain
Air
pump
Air
point
Chute
operation
Maintenance area
Air
grinder
Compressor
installation
Compressor
installation
Bin gate
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84 Forringmainsorsystemswithdualsupply,stopvalvesmustbeprovided
whichenableeachindividualairsupplytobeisolatedfromthepipework
system.Thisarrangementofstopvalveswillallowsafeoperatingprocedures
tobeadoptedduringmaintenanceofthesystemandancillaryequipment.
85 Whereaircannotbeventedfromthesystemoranypartofthesystem
throughthenormaloutlets,valvesshouldbefittedforthispurpose.The
valvesspecifiedshouldbesuitablefortheapplication.Inmostcasesthree-
portvalvesorself-ventingballvalvesarethemostsuitabletypeforisolating
andventing;thesevalvesshouldbearrangedsothatwhenthesupplyisshut
off,thedownstreampartoftheairsystemisventedthroughtheexhaustport
ofthevalveandprovisionmadetolockthevalveinthisposition.
86 Wherevalvesaregrouped,orwherethepurposeorlocationofthevalve
isnotobvious,anoticeshouldbeprovidedindicatingthepositionand/or
purposeofthevalve.
87 Leveroperatedstopvalvescanbeinadvertentlymovedtotheopenposition.
Duringmaintenancetheyshouldbeeitherlockedintheclosedpositionorthe
leverhandleshouldberemoved.
Filters, traps, separators and lubricators
88 Filtrationandlubricationtoastandardofcleanlinessappropriatetoend
usagearenecessary.Airlinelubricatorsshouldbeprovidedforoperations
whichinvolveairtools,aircylindersoraircontrolvalves;theyshouldbe
positionedafterthestopvalveandafteranyfilterorseparator.Inbothcases
itisessentialthatfiltersandlubricatorsarepositionedafterandadjacenttoa
stopvalvetoallowsafeserviceandmaintenance.Theyshouldnotbefitted
intoringmainswherethedirectionofairflowisnotcontrolledbutintothebranchlinesleadingfromthem.Highstandardsoffiltrationwillberequiredfor
instrumentcontrolorintheelectronicsindustry.Ultra-highefficiencyfiltration
willberequiredinhospitalsandthepharmaceutical,foodstuffspreparation
andbrewingindustries,andappropriatefilters,trapsorseparatorsshould
befitted.Whereextremelycleanorsterileairisrequiredspecialistequipment
suppliersshouldbeconsulted.Precautionsshouldbetakenagainstthe
ingressofdirtandothercontaminantsfromthesurroundingareathrough
carefulsitingofthecompressor.Theuseofexhaustportfiltersshouldbe
considered.
89 Inmostcasesthesecomponentswillhaveeithermetallicortransparent
plasticbowls(usuallypolycarbonateorpolyamide),whichhavegood
impactstrength.Thepropertiesofthematerialsmayhoweverbeadverselyaffectedbysolvents,alcohols,cleaningsolutionsorsyntheticlubricants
andmaintenanceinaccordancewithmanufacturersrecommendationsis
essential.(NBUsefulguidanceforpolycarbonatebowlsisprovidedinBS
6005Specification for moulded transparent polycarbonate bowls used in
compressed air filters and lubricators.)Itisthereforeessentialthatcleaningof
polycarbonatebowlsiscarriedoutwithcleanrags,andthatmateriallikelyto
becontaminatedwithdilutedsolubleoilsshouldbeavoided.Wherepossible,
filters,separatorsandlubricatorsshouldbepositionedsothattheriskof
accidentaldamagetoanynon-metallicbowlsisminimised.Evensubsequent
minorknocksmayleadtodamagedbowlsexploding.Itisgoodpracticeto
shieldallnon-metallicbowlsandmanufacturersshouldensurethatsuch
bowlscanbeshielded.Specificrequirementsforfilters,traps,separatorsandlubricatorsarediscussedinparagraphs104,105and109.
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Pressure regulators
90 Whereitisnecessarytoprotectequipmentfromoverpressurisation,
pressureregulatorsshouldbeprovidedandsettomaintainaconstantsafe
downstreampressure.Anairpressuregaugeshouldbeprovidedonthe
outletside.Dependingonthelevelofriskcreatedbyoverpressurisationall
adjustablecontrolsshouldhavesomeformoftamper-resistantprotection.
Wheretheriskislow,asimplesnapactionlockshouldsuffice.Astherisk
increases,greatersecurityagainstunauthorisedadjustmentisneeded.
Considerationshouldbegiventousingmodelsincorporatingpositiveinternal
stopsorpositivemeansoflocking.Forveryhighrisks,non-adjustablemodels
maybethebestanswer;alternativelytheadjustableitemsmaybesitedin
lockableenclosureswiththekeykeptbyaresponsibleperson.
91 Apressurereliefvalve(safetyvalve)orothersuitableoverpressureprotective
deviceshouldbefittedandsettorelieveifthesafeworkingpressureofthe
equipmentorvesselisexceeded.Thereliefvalveshouldbepositionedso
thatifthevalvedischarges,therisktopersonnelisminimised.
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Portable pneumatic equipment
Statutory requirements
92 ThePressureSystemsandTransportableGasContainersRegulations1989
andtheProvisionandUseofWorkEquipmentRegulations1992setoutthe
dutiesofusersandownersofportablepneumaticequipment.
93 ThePersonalProtectiveEquipmentatWorkRegulations1992setoutwhat
eyeprotectionisneededforcertainprocessesusingcompressedair.
94 UndertheManagementofHealthandSafetyRegulations1992andthe
HealthandSafetyatWorkAct1974employershavearesponsibilitytotrain
theirstaff.Furtheradviceontrainingisgiveninparagraphs171to173.
Hazards
95 Bothblowgunsandhandheldtoolsareusuallyconnectedtoalengthof
flexiblehosewhichduringthecourseofitslifewillbesubjecttomechanical
damageandconsiderableflexing.Thisdamageand/orflexingparticularlyat
connectionpointscancausethehosetorupture.Thiscanleadtosudden
dischargesofcompressedairandmaycauseunsupportedlengthsofhoseto
whipandsnakedangerously.
96 Thepracticeofusingblowgunsforremovingswarf,powderedmaterialsetc
fromcomponentsandfrommachineryiswidespreadthroughoutindustry.
Thereareanumberofhazardsconnectedwiththeuseofblowguns
including:
(a) eye injuries-atairlinepressurestheaircausesswarforotherparticles
tomoveathighvelocitycreatingaserioushazardtotheeyesofthe
operatororanyonenearby;
(b) other injuries-injurieshavebeencausedbydischarginggunswiththe
nozzleheldclosetotheskin.Veryseriousinjuries,sometimesfatal,have
occurredwhenthenozzleofthegunhasbeenpointedtowardsthe
anus,evenatsomedistancefromit.Manyoftheinjuriesoccurwhen
clothingisdusteddownandbecauseofthiscompressedairshould
neverbeusedforcleaningclothing;insteadvacuumcleanerswithbrush
typeheadsarerecommended.Othersaretheresultofhorseplay(see alsoparagraphs172and173);
(c) dust explosions-therehasbeenatleastoneseriousexplosionofadust
cloudwhenablowgunwasusedtoremoveflammabledust;
(d) toxic hazards-theuseofcompressedairforcleaningtoxicmaterialcan
resultinthedispersalofthematerialintotheair;
(e) noise-blowgunsfrequentlyproducehighnoiselevels.
General information and advice
97 Byfollowingtheadviceintheprevioussectionsaclean,dryairsupplyshould
besafelygeneratedanddistributedtoalloutletpoints.Thetypeofequipmenttobeconnectedtotheoutletpointwilldeterminewhatextraprecautions,if
any,willberequired.Themostcommonrangeofdeviceswillbeairorblow
guns,portabletoolsorpneumaticpoweredmachinery.Eachhasitsown
particularrequirements.
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Precautions
Flexible hoses
98 Whenselectingaflexiblehose,usersshouldtakeintoaccountthesite
conditions,includingtemperatures,oilsandpressurestowhichitwillbe
subjected.Wherelubricatingoilispresentinpipelines,agradeofhose
resistanttothatparticularoilmustbeused.Asyntheticbasedgradeofhose
shouldbeusedformineraloilsandanaturalbasedgradeforvegetableoil.
Wherefireandexplosionrisksmaybepresent,theuseoffire-resistantanti-
static(FRAS)hosesshouldbeconsidered.Themanufacturersadviceshould
alwaysbefollowed.
99 Heavy,mediumandlightgradesofhoseareavailable.Wherehosesareused
forsemi-permanentdistributionofcompressedair,forexampleinquarries,
constructionsites,shipyards,farmyards,garageforecourtsetc,heavygrades
shouldbeused.Mediumandlightgradesareusedforgeneralpurposessuch
asfixedpneumaticmachineryandpneumaticcylinders,smallpowertoolsandportableequipment.Hosesusedwithhand-heldpowertoolsshouldbe
lightandflexible(butsuitablefortheduty).
100 Tubesandhosesusedtoconnectcylinderstotheircontrolvalvesare
availableinavarietyofcolourstomakefaultfindingandmaintenanceeasier
(seeparagraph143).Theyshouldbeneatlyrunandadequatelysecured.
Ifthefailureofaflexiblehosewouldbehazardousitshouldbefurther
restrainedorshielded.
101 Couplingaportabletooltotheoutletpointisusuallyachievedbyuseofa
quick-actingconnector.Theconnectorshouldbedesignedsothatwhen
disconnecteditautomaticallysealstheairpressureontheupstreamsideandslowlyventstheairpressureonthedownstreamside.Forallhosesabove10
mmbore,morethan10mlongorsubjecttoapressureexceeding7bar,the
connectorshouldhaveaself-ventingsocketwhichreleasesthedownstream
pressurebeforedisconnectionispossible.Alternatively,aplugwitha
controlledventingactionshouldbeused.Thesesafetyfeaturesprevent
inadvertenttooloperationanduncontrolledwhippingofthehosewhenits
inletendisuncoupledfromthesocket.Anotherwayofreducingwhippingor
snakingistofitemergencyshut-offvalves,hoserupturevalvesorairfuses
ascloseaspracticabletotheconnector.Thevalveswillcloseorreduceflow
toaverylowlevelintheeventofexcessiveair-flowconditionscausedbya
failureofthehose(seealsoparagraph83aboutfittingofisolationvalves).The
samerequirementcouldbenecessarywhenusingplastictubing.
102 Similarrequirementsforquick-actingconnectorsapplytomostpercussive
andvibratingairtools,whichmaybefixedorhandheld.Ifaquick-acting
couplingsocketisfittedatthehoseendadjacenttothetool,theplugshould
notbescreweddirectlyintotheinletportbutshouldbefittedontoashort
isolationhose(0.5to1.5mlong),thusisolatingtheplugandsocketfromthe
toolvibrations.
103 Wherehosesareusedtosuspendtools,theloadstrengthofhoseand
couplingsshouldbeatleastfivetimesthesuspendedload.
Blow guns
104 Blowgunsconsistingsimplyofareducedorificeindirectlinewiththesupplyhosecanbeextremelydangerous,unlesspreceededbyapre-settamper-
proofpressureregulatorsetatareducedpressurefromthenormal80psi
airlinesupply.Modelsareavailablecommerciallywhichincorporateanair
curtaindesignedtoprovideaprotectiveshroudaroundthenozzle.Although
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notcompletelysafe,thesedesignssignificantlyreducetheriskofeyeinjury
andthedangersfromcloseskincontact.Ifdesignedcorrectlysuchnozzles
canoftenhelptopreventtheoperatorfrombeingsubjectedtoexcessive
noise.Becauseairisventeddirectlyintotheatmosphere,cleandryair
isessentialandlubricatorsshouldnotbeused.Blowgunscanexhaust
significantquantitiesofairandplaceextraloadingonthecompressor
system.Inviewofthisandtheattendantriskarisingfromuseofblowguns,
theiruseshouldbeconsideredcarefullywithaviewtousingalternative
meansforcleaningdownmachineryorcomponents.
Portable tools
105 Pressureregulatorsshouldbeusedtoreducethepressuretotheoptimum
valueforthesafeandefficientuseoftheequipment.Thisvalueshouldbe
clearlymarkedonthetool.Filtersandlubricatorsshouldbefittedinthe
supplypipeasshownatAinFigure3.Topreventover-speeding,tools
withairmotorsshouldincorporateagovernororthrottle.Thereshouldbe
availableaneasilyaccessiblemeansofisolatingtheairsupplyfromthetool.EuropeanStandardprEN792Hand-held non electric power tools-Safety
coversdesignofdrills,grinders,nibblers,polishersetc.Itispoorpracticeto
pullportabletoolsusingthehoseoruseitasameansofaccessbyclimbing
ontosuspendedhose.Olddamagedhoseshouldnotbeusedtomakeup
freshhoseassemblies.
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Pneumatic powered machinery
Hazards
106 Thehazardsnormallyassociatedwithpoweredmachineryareequally
applicabletopneumaticpoweredmachineryandsuitablesafeguardsare
necessaryasdescribedinBSEN982Safety requirements for fluid power
systems and their components-PneumaticsandBS5304CodeofPractice
Safety of machinery.
107 Unlikeliquidfluidpowermedia,compressedairiselastic(compressible),
andbecauseofthis,additionalhazardscanarisefromstoredenergyand
actuatorsunderload(seeparagraphs138to141).Thishazardrequires
particularconsiderationwhenthemachineryisfittedwithinterlockingguards.Interlockingsystemsarecoveredinparagraphs129to137ofthisbooklet.
General information and advice
108 Wherepneumaticallypoweredmachineryisconnectedtotheoutletpoint
thisshouldbebymeansofconventionalconnectors,egcompressionor
push-in,push-onconnectorswithashut-offvalve.Plastictubingmade
fromPVCornyloniswidelyused,inparticularforpipinguppneumatically
operatedmachinesemployingpneumaticcylindersandvalves.Compression
orpush-in,push-on,connectorsofvarioustypescanbeusedwiththetubing
whichissuitableforconnectingtovibratingandmovingpartsbyforming
loopswhichabsorbthevibrationormovement,but,asforflexiblehoses
(Para98)itisalwaysnecessarytoconsidersiteconditionswhenapplying
plastictubing.ThespecificationfornylontubingisgiveninBS5409,Part
1.Note: To prevent errors during installation and maintenance, all
component parts should be clearly identified. The identification
should correspond to the data on the circuit diagram.
109 Themachineshouldhaveitsownfilter,pressureregulator,pressuregauge
andlubricatorset,asshownatPartBofFigure3.Withthisarrangement,
optimumconditionsfortheoperationoftheparticularmachinecanbeset
withoutaffectinganyotherequipmentconnectedtothesupply.Ifthefilter,
pressureregulator,pressuregaugeandlubricatorsetareproperlymaintained
(seeparagraphs160to170),wearonsealsinactuatorsandvalveswillbelimitedandthemachineryshouldperformcorrectlyandefficiently.The
likelihoodofmalfunctions,whichcouldleadtounintendedoperation,willalso
bereduced.
Precautions
110 Toalargeextentthedesignfeaturesneededwilldependonhowthe
machinewillbeused.However,paragraphs111to141outlinesomebasic
requirementsformachineandcircuitdesign.
111 Allcomponentsusedinthemachinedesign,includingconnectinghoses,shouldbeabletowithstandsafelythemaximumpossibleairmainpressure.
Themaximumsafeworkingpressureofthemachineshouldbeclearly,
prominentlyandpermanentlymarkedonthemachine.
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112 Allcomponentsshouldbeprotectedagainstover-pressurisationbythe
provisionofpressurereliefvalvesunlessthecomponentscanwithstandthe
compressorsmaximumpressureandwillnotbesubjectedtounacceptable
pressurebuildupduetohighexternalloads.
113 Themachineshouldbedesignedandconstructedsothatanycomponents
whichrequireadjustmentorregularmaintenanceareeasilyandsafely
accessible.
114 Supplyorcontrolsystemfailureshouldnotcauseahazard.Toensurethat
suchapossibilityisminimised,theeffectsofgravity,impactorvibration
shouldbeconsidered.Forthisreason,valvescontrollingactuatorsshouldbe
mountedwiththemainspoolhorizontal.Inaddition,anyactuatorsthathave
toadoptaspecificpositionforsafetyifthesupplyorcontrolsystemfails
shouldbecontrolledbyavalvewhichisspringbiased(mono-stable)tothe
safeposition.
115 Ifthemachineistobeprovidedwithanemergencycontrolitshould,without
delay,stoporsetmovingpartstowhicheverpositionprovidesmaximum
safety.Theemergencycontrolshouldbeofthemushroomheadtype,
colouredred,prominentlylocatedandreadilyaccessibletotheoperator.
Whereanoperatorhastoworkfrommorethanonepositionitmaybe
necessarytoprovideadditionalemergencycontrols.Operationofthe
emergencycontrolshouldnotofitselfcreateahazard.
116 Whereairisdischargedtotheatmosphereduringthenormalcourseof
operationofthemachine,andthiscausesworkerstobeexposedtohigh
levelsofnoise,somemethodofreducingtheworkersexposureshouldbe
considered.Componentsshouldbelocated,orshielded,sothatoperatorsarenotsubjectedtoairblastfromexhaustports.Ifsilencersarefitted,
theseshouldbedesignedtocreateminimumbackpressureandshould
becompatiblewithwaterandanylubricantsused.Alternativelyanexhaust
hosecanbefittedsothattheairisdischargedwellawayfromworkers,for
exampleunderafactoryroof(seeHSEGuidanceNotePM56Noise from
pneumatic systems).
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Actuators
Hazards
117 Wherelinearactuatorsareused,specialattentionshouldbegiventostroke
length,loadingandthemethodsofmountingthecylindertoavoidbuckling
ofthepistonrodandexcessivesideloadingwhichcouldleadtopistonrod
bearingandsealwear.Whereshearforcesonfixingscrewsarelikelyto
beexcessive,thecylindermountingshouldalsobekeyedordowelledin
position.Alternatively,fittedboltsmaybeused.
118 Repeatedshockloadsoncylinderendcapscaneventuallycauseeitherthe
cylinderorthepistonrodassemblytofail,whichcouldleadtoseriousinjury.
Mostcylindermanufacturerscansupplycylinderswithbuilt-incushioning
designedtoreducespeedatstrokeextremities,thusbringingthemachinecomponenttoashocklessstop.Equallyhazardousisthepotentialforpiston
androdtoseparate.Cylindermanufacturersshouldensurethatpistonsare
positivelylockedtothepistonrod.
General information and advice
119 Thefunctionoftheactuatordeterminestheprecautionsnecessaryfora
safedesign.Ifthepurposeistoimpartmotiontoaloadwhichisotherwise
supported,theproblemwillbedifferentfromthoseforanactuatordesigned
toliftorloweraload.Cylindersdesignedtoclampposeyetanotherproblem.
Precautions
120 Foranyactuatorsimpartingmotion,smoothactionispreferableand
cushioningisdesirable.Ifthecylindersaredouble-actingtheremaybe
occasions,egatstart-uporfollowinganemergency,whenthecylinderis
pre-exhausted,causingtheactuatortoacceleraterapidlywhenairisfirst
introducedtothecylinder.Wherethisislikelytocauseahazardasoftstart
arrangementshouldbeintroducedinthesupplylinetothemachine.Thiswill
initiallyrestricttheflowrateuntilacertainpredeterminedpressurehasbeen
reached.
121 Linearactuatorswithmagneticpistonsandintegralmountedreedswitchesorproximityswitchesforsignallingcontrolvalvesarenowpopular.This
islargelyduetothecomparativecheapnessofusingelectricormicro-
electroniccontroltogetherwithcostandspacesavingsfromnotneedingto
installindependentmechanicallyactuatedtrips.Safeguardingpneumatically
poweredmachineswherethecontrolcircuitiselectricalrequiresextracaution
toensurethattheriskofinjuryisminimisedifeithertheelectricorpneumatic
powersupplyfails.Reedswitchesmaymalfunctioninareassubjectedtohigh
vibrationlevelsorelectromagneticfields.
122 Actuatorsdesignedforliftingorsupportingloadsmaycollapsedangerously
ifthesupplyfails.Themachineshouldhavespring-appliedmechanical
scotchestosupporttheloadwhenevermovementisnotrequired.Incertaininstancesmechanicalscotchesmaybeimpracticable.Asasafetybackup
anormallyclosed,airtoopen,springreturnvalveinthecylindersupplyline
couldbeused.
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123 Supplyfailuretoclampingcylinderscanleadtoahazardbyreleasingthe
componentprematurely.Thiscanbeovercomebyusingsingleacting
cylinderswherethereturnspringappliestheclampingforce(seeparagraph
127),ortheuseoftwocontrolvalveswilltemporarilykeepthecylinder
pressurised(seefigures4and5).Butcareshouldbetakeninusingthis
designasevenasmallleakcouldaffecttheintegrityofthesystem.
Figure 4 Singlecontrolsysteminterlockingwithpistonarrestandhold(guardopen)
Note:Figures 4 - 19 illustrate principles only, and they are not intended to provide all the
information needed to construct a safe working system.
124 Machinesincorporatingseveralactuatorsmayrequirethemtobesetina
certainpositionbeforethemachineisfirstused,andsubsequently,afterthe
emergencycontrolorinterlockingguardshavebeenoperated.Re-positioningmaybepossiblewithoutre-establishingthepneumaticsupply,butthese
caseswillbeintheminority.Inallothercasesre-positioningisbestachieved
byprovidingmanualoverridecontrols.Suchcontrolsshouldbeofthetwo
handtypeiedesignedsothatthetwocontrolsareplaced,separatedand
protectedtopreventspanningwithonehandonly,beingoperatedwithone
handandanotherpartofthebody,orbeingreadilybridged.Itshouldnotbe
possibletosettheactuatorsinmotionunlessthetwocontrolsareoperated
withinapproximately0.5secondsofeachother.Movementoftheactuators
shouldbearrested,orwhereappropriatereturned,immediatelyoneor
bothcontrolsarereleased.BSEN574Two Hand Control Devicescovers
functionalaspectsandprinciplesfordesignofthistypeofcontrol.
Cylinder
Stop
valve
Guard
(a) Interlocking
valves(b) Control
valves
(c) Power control valve(Air operated)
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Interlocking methods and circuit
designGeneral information and advice
125 Themethodusedforinterlockingshouldbecommensuratewiththerisk.The
highertheriskthehighertheintegrityoftheinterlockingsystemshouldbe.
126 Principlesfordesignandselectionofinterlockingdevicesassociatedwith
guardsaregiveninEN1088andBS5304.Generalprinciplesforapplication
aregiveninBSEN983Safety of Machinery-Safety requirements for fluid
power systems and their components-Pneumatics.
127 Onpneumaticmachinery,becausethepowermediumiscompressible
andnormallyexhaustedtoatmosphere,thesafetycircuitdesignisnot
straightforwardasforotherpowermedia.However,thebasicaimsfor
interlockingremainthesameand,wherepossible,thepowersupplyshould
beinterruptedbytheguardoperatedinterlockingdeviceandanyresidual
systempressureexhaustedtoatmosphere.Inthisconditionanycylinders
willbepre-exhaustedandalternativearrangementsinthesystemdesignwill
benecessarywhereanycylindersarerequiredtobeunderconstantload
(seeparagraph122).Inaddition,particularprecautionsmaybenecessary
whenreinstatingthesupplytopre-exhaustedcylindersifrapidacceleration
isundesirable.Toavoidtheneedtomaintainsupplypressuretocylinders
requiredtobeunderconstantload,suchasthoseoperatingclampsor
supports,alternativefeaturesshouldbeconsidered,suchassingle-acting
cylinders,orspringappliedmechanicalscotches.Cylindersfittedwithrod
locks,thelockingactionofwhichistriggeredbylossofairsupply,mayalso
beusedtopreventuncontrolledmovement.
128 Signalairlinesshouldbekepttoaminimumlengthtofacilitaterapidexhaust
pressuredecay.Wherethisisnotpracticableandpilotsignalsexhausting
totheatmosphereretainsufficientpressurelevelstooperatemaincontrol
valves(evenafteraguardhasbeenopened),additionalinterlockingdevices
shouldbeprovidedwhichpreventopeningoftheguarduntilitissafetodo
so.When3-positionvalvesareusedinsafetycircuits,wherepracticablethe
centrepositionshouldprovideasupply-sealed-onlycondition(outletsvented)
becauseanall-ports-sealedcentrepositioncanresultinstoredenergyintheactuator,leadingtounintendedmovementifpipingisdisconnected.
Interlocking systems
Single control system interlocking
129 Thebasicelementsofsinglecontrolsysteminterlocking(seeFigures4and5)
are:
(a) aninterlockingvalveorpositionswitchoperatedbytheguard;
(b) interposedcontrolvalves,electromechanicalrelaysand/orsolid-state
switchingdevices,ifany;and (c) anairoperated,solenoidoperatedorsolenoidactuatedairoperated
valve,controllingpowertothedrive.
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130 Anyoftheseelements,orthepipingorwiringinterconnectingthem,can
failandcausedanger,sotheyshouldbechosentoprovidethemaximum
degreeofreliability.Thegreaterthenumberofdevicesincorporatedinthe
system,theloweritsinherentreliability,sointerposingdevicesshouldbe
avoidedifpossible.
Dual control system interlocking
131 Thebasicelementsaresimilartothoseemployedinsinglecontrolsystem
interlocking.Wherethepossibilityofcommonmodefailureneedstobe
minimiseddifferentcontrolpowermediashouldbeusedandkeptseparate
exceptfornecessaryinterconnectionsforcrossmonitoring(whereprovided),
andconnectiontothesupply.
132 Suchsystemscanbeentirelypneumatic(seeFigures15and16),orhybrid
forexampleonesystem,pneumaticandonesystem,electric(seeFigures17and18).Thislatterarrangementmaybeparticularlyappropriatewhere
cylinderswithmagneticpistonsandintegralreedswitchesorproximity
switchesareused.Inbothsystemstheoutputofthepowercontrolling
devicesshouldbeconnectedsothateithercanstophazardousmovement
ofthemachinery,irrespectiveoftheconditionoftheother.Wherethecircuit
issuchthatasinglefailureisnotself-revealingegtheactuatorcontinuesto
operate,theintegrityofthedualcontrolsystemcanbeimprovedbycross
monitoring(shownalsoinFigures17and18).
Figure 6 Singlecontrolsysteminterlockingwithpistonarrest(guardopen)
Cylinder
Guard
(a) Interlocking
valves
(b) Controlvalves
(c) Power control valve(Air operated)
Note:
Manual reprositioning of thecylinder is possible with thistype of control valve.
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Figure 7 Singlecontrolsysteminterlockingwithpistonarrestandhold(guardclosed)
Figure 8 Useofanequalisingvalve-controlinterlocking(guardopen)
Cylinder
Guard
(a) Interlockingvalves
(c) Power control valve
(Air operated)
(b) Equalisingvalve
Cylinder
Guard
(a) Interlocking
valves
(b) Control
valves
(c) Power control valve
(Air operated)
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Figure 9 Useofanequalisingvalve-controlinterlocking(guardclosed)
Figure 10 Useofanequalisingvalve-powerlocking(guardopen)
Cylinder
Guard
(a) Interlocking
valves
(c) Power control valve(Air operated)
(b) Equalisingvalve
Cylinder
Equalising valve
(with power interlocking)
Guard
Control valve
(Air operated)
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Figure 11 Useofanequalisingvalve-powerlocking(guardclosed)
Figure 12 Useofareservoir-powerinterlocking(guardopen)
Cylinder
Equalising valve
(with power interlocking)
Control valve
(air operated)
Guard
Cylinder Guard
Reservoir
Power control valve
(Solenoid operated)
Interposedcontrol
valvesPower
interlocking
valves
Note
Cylinder returnsto instroke
position wheneverguard is open
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Figure 13 Useofareservoir-powerinterlocking(guardclosed)
CylinderGuard
Reservoir
Power control valve(Solenoid operated)
Interposed
control
valves Power
interlocking
valves
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Figure 14 Controlsysteminterlockingfromcomplexsequence
A B
D
C
Guard
Toclose
Springreturn
To portsmarked
Sequence
Closed guard
A+B+
C+ D+
A-
C- D-B-
Open guard
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Figure 15 Dualcontrolsysteminterlockingwithoutcross-monitoring,bothchannelspneumatic
(guardopen)
Figure 16 Dualcontrolsysteminterlockingwithoutcross-monitoring,bothchannelspneumatic
(guardclosed)
Guard openCylinder
(a) Interlocking
valves
(c) Power control valve(Air operated)
(b) Interposed
control valves
Guard closedCylinder
(a) Interlocking
valves
(c) Power control valve
(Air operated)
(b) Interposed
control valves
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Figure 17 Dualcontrolinterlocking,onecontrolchannelpneumaticandoneelectric,withelectriccross
monitoring(guardopen)
Figure 18 Dualcontrolinterlocking,onecontrolchannelpneumaticandoneelectric,withelectriccross
monitoring(guardclosed)
Cylinder Guard open
Interlockingswitch
(electric)
Interlocking
valve(Pneumatic)
Monitor
Control
valves
A B
Power
controlvalve
2nd channelinterposed powercontrol valve
Sol A
Monitor C
Cylinder Guard closed
Interlockingswitch
(electric)Interlocking
valve(Pneumatic)
Monitors
Controlvalves
A B
Powercontrol
valve
2nd channelinterposed powercontrol valve
Sol A
Monitor C
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Figure 19 Guardoperatedpowerinterlockingwithscotchtopreventdrillfallingundergravity.Alsofitted
withguardlocktopreventinadvertentopening
Power interlocking
133 Powerinterlockingisachievedbydirectmechanicalactionofavalveinthe
mainairsupplyinserieswiththeactuator.Themechanicalactionmaybe
directfromguardmovement(seeFigures10and11)viaalinkage,bya
captivekeyoratrappedkey.
134 Interlockingbymeansofairisolationandexhaustmaycausedifficultieson
machinerywhichreliesontheairsupplytokeepheavyarticlessuspended
orcomponentsclampedinposition.Similarly,wherecomplexmachinery
isdesignedtoperformaseriesoffunctionsinsequenceautomatically(see
Figure14),airisolationandexhaustinterlockingcouldleadtotheneedforpotentiallydangerous,extensivemanualre-settingofactuatorsand
sequencingvalves.Forthesereasons,powersystemmethodsofinterlocking
arenotnormallypracticableforcomplexairoperatedmachineryandhence
controlsysteminterlockingofthepilotsignalshastobeused.
135 Wherepracticable,however,powersysteminterlockingofcomplexsystems
isbetterthansinglecontrolsysteminterlocking,providedthepower
interlockingvalveandthearrangementsbetweentheguardandvalveareof
similarorhigherintegritythanthecontrolsysteminterlocking.Inaddition,any
machinerypartswhicharesupportedbycompressedairandwhichwouldfall
undergravitywhentheairisisolatedandexhaustedshouldbeautomatically
scotchedwhiletheguardisopen.
136 SuchprecautionsareshowninFigure19,thelayoutofwhichisinlinewith
BSISO1219-2recommendations.HazardsarisefromactuatorsAl,A2,
A3andA5,whichneedsafeguarding.Also,A3operatesverticallyandwill
V3
V2
V1
Run
Singlecycle
Clamp
A1
B11 Clamp
A2
B22 B21
Drill
A3
ScotchA4
B31
Drill
A5B52 B51
FeedA61
A62B62 B61
C6 C7C5C1 C2 C3
B72
B62B52 B11 B21 B31 B22
Guardlock A7
B72
Interlockingvalve
Guard
Toclose
To lock
A7
B61 B51
Single cycle sequence
Close guardScotch withdraws (A4 - )Operate V2
Guard locks(A7+)A1+A2+A3+A5+
A2 - A3 - A5.
Guard unlocks (A7 -)A61 & A62 -
Machine stopsOpen guardScotch engages (A4+)
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fallundergravitywhenairsupply,throughtheguardoperatedinterlocking
valve,isexhausted.Thecircuithasthusbeenarrangedsothat,withthe
guardopen,A3isscotchedusingasingleactingcylinder.Oncetheguardis
closedthescotchwithdrawsandtheguardislockedsothatthesequence
cannotbebrokenbyinadvertentlyopeningtheguard.Thecompletesingle
cyclesequenceisindicatedinFigure19,whereitcanbeseenthattheguard
unlockstoallowmanualfeedingifnecessary.Continuouscyclingcanbe
effectedbyoperatingthevalvelabelledrun.If,duringuse,amalfunction
occursrequiringtheguardtobeopened,thiscanonlybeachievedby
shuttingthestopvalveinthemainairsupplyline.
137 Alltheseproblemshighlighttheneedforthemachinedesignerto
considercarefullytheoverallsystemdesigntoensurethattheinterlocking
arrangementsareeffective.Althoughinmanycasesinterlockingthepilot
signalsratherthanthepowersupplymaybetheonlypracticalsolution(see
Figure14),thisshouldbealastresortonly.
Circuit design
Piston arrest
138 Whereitisnecessaryjusttoarrestthemovementofapistonwhenaguard
isopen,thiscanbeachievedbyusingeithertwothree-port,two-position
valves(seeFigures6and7)oranequalisingvalve(seeFigures8to11).Ifan
equalisingvalveisusedthepistonmaynotstopimmediately,butitwillseek
anequilibriumpositionwherebyforcesonbothsidesofthepistonareequal.
ThecircuitinFigure6willallowmanualrepositioningofthepistonwithout
disconnectingpipes(dependingonthefrictioninthesystem).Neitherofthese
techniquesissuitableforclampingorsupportingapplications.
Piston arrest and hold
139 Where,forsafetyreasons,thepistonmustbearrestedandheldinposition,
twotwo-portcontrolvalvescanbeused(seeFigures4and5).Thepistonwill
seekanequilibriumpositionbeforecomingtorest.However,ahazardcould
ariseifconnectionstothecylinderarebrokentosubsequentlyoverridethe
lockedposition.Airexhaustingthroughthebrokenconnectioncouldallowair
underpressureontheoppositesideofthepistontoexpand,therebycausing
movementwhichcouldleadtoinjury.
Overriding locked position
140 Wherethelockedconditionmustbeoverriddenwhiletheguardisopen,a
two-portstopvalvecanbeaddedtothecircuit(seeFigures4and5).Thiswouldnormallyhaveblockedportsbutbydepressingthestopvalveboth
sidesofthecylinderareopenedtoatmosphere,enablingthepistontobe
movedmanually.
Predetermined position
141 Itmaybenecessarytoensurethatpistonsadoptapredeterminedsafe
positionintheeventofpowersupplyfailing.Againtheuseofsingleacting
cylindersmaybepossiblebutanalternativeistouseareservoirand
nonreturnvalvearrangement(seeFigures12and13).Itisimportantto
ensurethatwherereservoirsareusedtheyareofsufficientcapacitytoensure
thatthepistondoesnotstallinanunsafeposition.
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Inspection and maintenance
Statutory requirements
142 Therearespecificstatutoryrequirementsfortheexaminationand
maintenanceofpressuresystemsincludingairreceivers(seeparagraph
30).Inadditiontothespecificrequirements,generalrequirementsareset
outinSection2(2)(a)oftheHSWActandPUWER:employersmustprovide
andmaintainplantandsystemsofworkthatare,sofarasisreasonably
practicable,safeandwithoutriskstohealth.Thefollowingadviceisaimedat
assistingemployerstocarryoutthisduty.
Hazards
143 Faultfindingonpneumaticmachinerycanbehazardousifitisnotproperly
planned.Themachinedesignshouldincorporatemeansofminimisingthe
needfortrialanderrormethodsoflocatingafault.Furtherassistancecanbe
giventofaultfindingbyincorporatingdiagnostictechniqueswhichindicate
theareaofafault(seealsoparagraph100).
General information and advice
144 Theefficientsaferunningofacompressedairsystemreliesoncleanliness,
filtration,coolingandlubrication.Thebestwayofachievingthesefour
conditionsistooperatetheplantinaccordancewiththeoperatorsmanual
andtodrawupandfollowawrittenscheduleofmaintenanceworkwhichcan
berevisedinthelightofexperience.Thisisaformofsafesystemofwork.
Thewrittenscheduleshouldidentifyareasforattention,howoftenattention
shouldbegivenandtheresponsibilitiesofthosewhocarryoutandsupervise
thework(seeparagraphs146and147).
145 Thefrequencyofinspectiondependsverylargelyonthecircumstancesand
environmentinwhichtheplantisused.ThefrequencystatedinthisBooklet
shouldthereforebetakenasaguideonlyandadjustedtosuitparticular
installationsinthelightofoperationalexperience.
Maintenance of compressors and ancillary plant
Supervision and procedures
146 Smallcompressorunitsareeasilyoverlooked,especiallyifsitedinaseparate
enclosureoutsidetheworkingarea.Particularcareisneededtoseethat
regularmaintenance,inspectionandtestingiscarriedout.Proceduresshould
belaiddownandrecordskept.
147 Theusershouldnominatearesponsiblepersontosupervisetheproper
operationandmaintenanceofthecompressorplantinlinewiththe
manufacturersinstructions.
148 Thispersonshouldregularlycheckthatallinstructionsregardingoperationandmaintenanceareproperlyfollowedandthatthecompressor,its
accessoriesandsafetydevicesarekeptingoodworkingorder.The
responsiblepersonshouldalsomakesurethatmaintenanceworkiscarried
outonlybyadequatelytrainedstaff.
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149 Althoughtherearestatutoryrequirementscoveringsomeaspectsof
maintenance,thefollowingadditionalmaintenanceproceduresare
recommendedtominimisethelikelihoodofhazardsoccurring.
Daily
150 Thecompressingplantshouldbekeptascleanandfreefromoildepositsas
possible.
151 Adailyroutinecheckshouldbecarriedoutonreciprocatingcompressors.
Thecheckshould,whereapplicable,includethefollowing:
(a) thecoolingwatershouldbevisuallycheckedtomakesurethatitis
circulatingproperlybyobservingtheflowoutletorflowindicator;
(b) theleveloftheoilinthecrankchambershouldbecheckedusinga
dipstick,levelgaugeorotherdevice.Anyexcessiveusageoflubricating
oilshouldbeinvestigated;
(c) theoilpressureshouldbechecked; (d) theoilfeedtothecylindersshouldbecheckedtomakesurethatit
isadequatebutnotexcessive.Oilconsumptionshouldberecorded,
asexcessiveconsumptioncanoftenleadtoexplosionsdownstreamof
thecompressor;
(e) theoutletairpressureandtemperatureshouldbechecked;
(f) thecompressorperformanceshouldbecheckedegbylisteningforany
unusualnoisesduringrunning;
(g) anydefectsfoundshouldberectifiedandarecordkept;and
(h) attheendofeachdayanyaccumulationofoilandwatershouldbe
drainedfromtheairreceiver,theintercooler,theaftercoolerandmain
supplypipes.
Checks mainly directed to reciprocating compressors
Weekly
152 Eachweekthesafetyvalves(wheredesignallows)shouldbecheckedby
easingthembyhand.
600 hours
153 Aftereach600hoursofrunning:
(a) thequalityofoilinthecrankcaseshouldbecheckedand,accordingto
themanufacturersrecommendations,replacedifnecessary;and
(b) theconditionoftheinletairfiltersshouldbecheckedandthoroughly cleanedorreplaced.Theintervalbetweensuccessivereplacements
willbedeterminedbylocalcircumstancesbutis,toacertainextent,
controlledbythecapacityofthefilterandthecleanlinessofthe
atmosphereinthevicinity.Whereoilwettedviscousfiltersareused,
spareunitsshouldbeprovidedandexcessoilshouldbedrained
fromthefilterunitsforatleastfourtoeighthoursbeforetheunitsare
replaced,exceptwherethemanufactureradvisesotherwise.
Six-monthly
154 Whereoilcokedepositsareliabletooccur,theexplosionriskcanbereduced
bycarryingoutsix-monthlyinspectionsofthedeliveryportsandpipework
andcleaningasrequired.Theperiodbetweeninspectionscanbemodifiedinthelightofexperiencegainedfromoperatingaparticularinstallation.
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2000 hrs or annually
155 Aftereach2000hoursofrunningorannually(whicheveristhesooner):
(a) inthecaseofoillubricatedcompressors,thedeliveryvalves,portsand
allthepipework,vesselsandfittingsbetweenthedeliveryportandthat
pointinthesystem
atwhichtheairtemperaturecanbeconfidentlyexpectedtobebelow
80C,shouldbeinspected.Anycarbonaceousdepositshouldbe
effectivelyremoved;
(b) fusiblepelletsorcompleteplugsshouldbereplaced;
(c) theconditionofprotectivedevicesshouldbecheckedandtestedto
determinethattheyoperatecorrectly;
(d) theintercoolerandaftercoolersectionsshouldbecleaned;
(e) theradiatorshouldbedrainedandwashedout;
(f) theoutputcontrolgearshouldbecleanedandinspected;and
(g) theairreceivershouldbethoroughlycleanedandexaminedinternally.
Precautions
156 Allmaintenancework,otherthanroutinecheckstofiltersdesignedfor
cleaningin-service,shouldbeundertakenonlywhenthecompressorhas
beenstopped,disconnectedandlockedofffromthepowersupplyandall
internalpressuredissipated.Otherprecautionsmayalsobenecessary:for
example,thecompressormayhavetobescotchedtopreventmovementof
themechanism.
157 Undernocircumstancesshouldflammableliquidsbyusedforcleaning.
Appropriatesafetyprecautionsshouldbetakenagainstanytoxicvapours
liberatedduringusageofanycleaningordegreasingliquids.
158 Anopenflameshouldneverbeusedforinspectingtheinteriorofa
compressor,pressurevesselorpipework.
Maintenance of air powered equipment
159 Dirtyandwetairandworncomponentsareamongthemostcommon
causesofhazardsassociatedwithairpoweredequipment.
Supervision and procedures
160 Theusershouldnominatearesponsiblepersontosupervisetheregular
inspectionandmaintenanceoftheequipment.Wheretheequipmentisextensive,someformofwrittensystemofplannedmaintenanceshouldbe
usedandrecordsoftests,repairsandmodificationskept.
161 Inadditiontoanymaintenancerequiredbystatutoryrequirements,the
followingmaintenanceproceduresarerecommended.
Daily
162 Thesystemshouldbecheckedforleaksandrepairscarriedoutas
necessary.
163 Attheendofeachdayanyaccumulationofwatershouldbedrainedfromthe
drainpoints.Thedrainvalvesshouldbeinspectedtomakesurethattheyarenotchokedwithsediment.
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Weekly
164 Attheendofeachweek,airlinelubricatorsshouldbetoppedupas
necessarywiththecorrectgradeofoilandcheckedtoensurethattheyare
providingadequatebutnotexcessivelubrication.Filtersshouldbechecked
andthosethatarecloggedorcausingunacceptableflowrestrictionsshould
bereplaced.
165 Similarly,onmachineswhichrequirepressureregulationbelowmains
pressure,thepressureregulatorshouldbecheckedtomakesurethatithas
notbeentamperedwithandthatthecorrectpressureismaintained.
Monthly
166 Allhoseswhicharesubjecttoflexingand/ormechanicaldamageshouldbe
inspectedforsignsofcrackingordeteriorationandreplacedasnecessary.
Particularattentionshouldbepaidtoareasadjacenttocouplings.
Three monthly167 Everythreemonthsmachineswithinterlockingguardsshouldbechecked
tomakesurethatallinterlockingvalvesarefirmlysecuredandoperated
positivelybytheircams.Checkthatwearinanylinkagesorvalveoperating
mechanismsisnotsoexcessivethatthevalveisindangerofmalfunctioning.
Six monthly
168 Everysixmonthsallstopvalvesshouldbechecked.Checkthataccessto
thevalvehasbeenmaintained,thatthehandleisinposition,thatitwillshut
offtheairsupplyandthatitwillopenfullyandoperatefreely.
Precautions
169 Beforeanypressurisedcomponentsaredismantledtheyshouldbeeffectively
isolatedfromallpressuresourcesandcompletelyventedtoatmosphere.
Precautionsshouldalsobetakentoguardagainstthepossibilityofinjury
throughsuddenreleaseoftrappedsprings.
170 Whencomponents,especiallyvalves,arefoundtobewornandservicekits
ofsealsareusedtorebuildthem,careshouldbetakentocheckthoroughly
thefunctionoftherebuiltvalvebeforeplacingitintheequipment.For
convenience,manufacturersofservicekitsoftenincludeenoughsealsto
servicearangeorfamilyofvalves,althoughnotallthesealsinthekitare
requiredforeachvalve.Incorrectsealreplacementcancompletelyalterthe
valvesfunctionandifreplacedintheequipmentcouldpresentaserioushazard.Manufacturersshouldsupplyclearinstructionsonhowtousesuch
servicekitsproperlyandsupervisorsshouldensurethatthisinformationis
passedontothepersoncarryingoutthemaintenance.
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Training
Statutory requirements
171 Section2(2)(c)oftheHSWActandManagement Regulations and
Regulations 8 & 9 of the Provision and Use of Work Equipment Regulations
(PUWER)requireseveryemployertoprovidesuchinformation,instruction,
trainingandsupervisionasisnecessarytoensure,sofarasisreasonably
practicable,thehealthandsafetyatworkoftheiremployees.Sections7and
8oftheHSWActplaceresponsibilitiesonemployeestotakereasonablecare
toco-operatewithemployersandnottointerferewithormisuseanything
providedfortheirsafety.
Hazards
172 Allthosewho,inthecourseoftheirwork,needtousecompressedair
mustbeproperlytrained.Manyaccidentswouldbeavoidedifadequate
trainingwasprovided.Itisprobablybecausecompressedairsuppliesare
socommonplace,beingfoundatmostgarageforecourts,forexample,that
employersfalselybelievethattrainingintheiruseisunnecessary.
Precautions
173 Supervisorsandworkersincludingmaintenancepersonnelmustbegiven
propertraininginsafeworkingpractices.Thetrainingshouldstressthe
hazardsassociatedwithcompressedair(seeparagraph2)andshould
highlightthefollowingpoints:
(a) compressedairshouldneverbeusedforcleaningclothing;vacuum
cleanerswithbrushtypeheadsarepermissible.Forothercleaning
operationsspecialnozzlesdesignedtoprovidelowpressure,high
volumemaybeusedwithcare(seeparagraphs96band104);
(b) horseplaywithcompressedairisextremelydangerousandisstrictly
forbidden.Employersshouldnotethatyoungpeopleinparticularmay
requirespecialsupervisiontomakesurethattheybehaveproperly;
(c) whenusingcompressedairtoolstheexhaustingairshouldbedirected
awayfromthebody;
(d) compressedairshouldneverbeusednearanakedflame; (e) anydefectsinequipmentshouldbereportedatonce;and
(f) safetyandmonitoringdevicesshouldneverbemisusedorabused.
Further information
ThefollowingfivepublicationsareproducedbytheEuropeanCommitteeon
ManufacturersofCompressors,VacuumPumpsandPneumaticTools(PNEUROP):
Safety recommendations for the use and operation of portable air compressors
London
Safety recommendations for the use and operation of stationary air compressors
London
Pneumatic tools - safety in operationLondon
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Health and Safety
Executive
Safety recommendations for the use and operation of portable pneumatic tools
London
Recommendations for the proper use of hand held and hand operated pneumatic
toolsLondon1986
BritishCompressedAirSociety(BCAS)produces:Guide to the selection and the
installation of compressed air servicesLondon,4theditionISBN090560802Xand
A guide to compressor noise reductionLondon,underrevision
EuropeanOilHydraulicandPneumaticsCommittee(CETOP)Hydraulic and
pneumatic systems circuit diagramsLondon
(PNEUROP,BCASandCETOPpublicationsareavailablefromtheBritish
CompressedAirSociety,33/34DevonshireStreet,LONDONW1N1RF)
RoyalSocietyforthePreventionofAccidents(ROSPA)Beware compressedairBirmingham,(IS303)(availablefrom:ROSPA,CannonHouse,ThePriory,
Queensway,BIRMINGHAMB46BF)
BritishAggregateConstructionMaterialsIndustryCompressed Air SafetyLondon
(availablefrom:BritishAggregateConstructionMaterialsIndustry,25Lower