Gravity Flow Water Systems重力流供水排水系统 2

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GravityFlowWaterSystems重力流供水排水系统2

r,-13-cussedbelow.4.4.3.EkceesiveHeadIndesigningthepipelineitisneceesarytoensurethatthepressureorheadexertedonthepipelineandfittingedoesnotexceedacceptablelimits.Thisieaccomplishedbybreakingthecontinuityinthepipelineatappropriatepointa.A1m3concrete-breakpressuretankdividedintotwocompartmentsisnormallyusedbutinmmecasesadistributionreservoircanalsoservethisfunction.Themaximumallowableheadwilldependonthetypeofthepipeusedendthefittingsinvolved.Thefollowingarerecommendedguidelines:a.Forsteelpipewithnovalvesinthelowerendamaximumheadof200metersisallowablealthough100metersismorereason-able.Acutoffvalveormean6ofdivertingthewaterisnecessaryatthetopendtopreventflowinthepipeincaeeofrepaire.Becausetherearenomeanstostoptheflowatlhelowerendthefullstatichead*of200meterswillne-verbeattained.b.Forsteelpipewithvalvesandotherfittingsitisbesttolimitthemaximumetaticheadto50meters,Thatisifallvalvesareclosedandwaterwereetationaryinthedie-tributionpipethenthelowestpointineachsectionshouldhavenomorethan50metershead.cmForPVCthemaximumallowableheadisthemanufacturersstandardforwhichthepipeisguaranteed.Ifthisexceeds50metersthancaremustbetakentoavoidaxcessivepressureonanyfittingsintheline.Theaboverecommendation8shouldbeviewedasapproximateandcanbeadjustedtoconformwithfieldconditiona,Forexample,ifthetotalheadwere65meter8itwouldnotbeabeolut-tlynecessarytoinstallapressurereleasetank.Similarlytheplecementoftanksonalonglinewouldnotbeatexactly50metereintervaleofheadbutwoulddependuponthetopographyandthelandavailableforthetankThereaxealsoiaetancelrwhereconformancetotherecommendedguidelinesianotpossibleordeairmble.Forexample,ifthepipelinedescendedsteeplyfromthesource150metersdownintoavalleyandthenroee100metersontheothersidetoreachthevillagethewashoutvalveatthelowpointcrossingthevalley4.4.4.ThrHydraulicGradeLine(HGL)4.4.5.TheDydraulicGradeLine(HGL)iodefinedbythedifferencebetweentheheadlossinthepipelineandtheetatichead.ThedifferencebetweenthegroundprofileandtheHGLiethepressureinthepipelinewhilethewaterizflowing.IfanopeningweremadeinthepipelineandatubeconnectedtoitthenthewaterwouldrisetotheleveloftheHGL.TheHGLshouldalwayslieabovetheprofile.Ifitdoesnot,thenthewatermaystillflowbutateectionewheretheprofileliesabovethegradientthereieanegativepressurewhichcancauseairorpollutiontoenterthepipeline.Thosesectionsofthepipelinewherenegativepreesureeoccurshouldberedeeignedtoeliminatethem.Figures2Aand2Billustratethis.PipelineDesignExamplee-14-wouldbeunderaheadof150meter8underetaticconditions.However,theuseofpreesurereleaeetank8wouldprobablymeanthatthewaterwouldnothaveenoughheadtoreachthevillage.Insuchcasesspecialeffortshouldbemadetoueethebestqualityfittingsavailableandtominimizethechancesofattainingthefullstatichead.Oncetheapproximatelocationofthebreakpressuretankshaabeendecideduponthencalculationstodeterminepipesizecanbecarriedoutforeachcontinouaeectionofthepipeline(wherenobreaksinpressureoccur).Itieimportanttolookatthetotalsectioninvolvedandnotjustthesectionabetweenwith-drawalswherechangesinflowoccur.Example1Aspringwithaflowof0.5l/eie1,OOGmetersfromthevillageandthedifferenceinelevation(availablehead)ia20meters.Itieplannedtoconveytheentireflowtoasmallreeervoirinthevillage.Whatsizepipeisrecommended?Onthewaterflowcalculator(oreimilarcharts)aflowof0.5l/eandalength1,000metersusing1.5inchpipeindicatesaheadloseof11meters.ForI.25inchpipetheheadloseis26meters.Thustherequiredflowwillnotbeobtainedwitha1.25inchpipeanda1.5inchpipeistoolarge.Themosteconomicalsolutionisacombinationoftwopipesizee.Bytrialanderroritisfoundthat500metersof1.5inch01pipewithaflowof0.5l/shasaheadlossof6mdtereand500meter6of1.25inchGIpipehasaheadlossof13meters.-15Figure2CHECKINGOFTHEHYDRAULICGRADELINEFigure2AIfthepipelinefollowedgroundprofileAthenthechoiceofpipewiththegive5HGLisacceptable.IfthepipelinefollowedgroundprofileBthennegativepressurewouldexistinsectionCsothepipelineshouldbere-designed.SeeFig.2BFigure2BThepipediametershavebeenchangedthuschangingtheHGL.Useofalargerdiameterpipenearthesourceensure8thattheHGLliesentirelyabovethegroundprofileandisacceptable.NotethattwopipediametersareAOVusedbetweenthesourceandreservoir.ForeachdiametertheHGLhasadifferentslope.Theslopeisdirectlydependentontheheadloss80:asmallerpipehasasteeperslope._-16-Thuethetotalheadlossforthe1,000meterpipelineis19meterrsvhichcloselymatcheetheavailablehead.ThepipelineprofileandHCLareplottedinFig.3.Figure3(Rample1)Example2Awatersourceis1,000metersfrom%pongKeringanditis1,000metersfurthertoKampungKeringSekali.ThedifferenceinelevationbetveentheBourceandKeringis20metersandbetweenKeringandKeringekaliitisalso20meters.Thedesignflovsare2.0l/sfromthesourcetoheringand0.5l/sfromKeringtoKeringSekali.Whataresuitablepipediametera?CalculatedHeadLossesforvariouspipeearea6follows:lengthflov(meters)(l/s)pipediameter(inches)headloss(meters)Availablehead(meters)l,W235.20l,O@J22.511201,ooo223320‘VW0.52.3201,m0.51.51120l,Q=0.51.252620Asuitableselectionofpipewouldbe2,5inchpipeforthefirst1,000metersand1.25inchpipeforthesecond1,000metem.Thetotalheadloeeiethen357meterswhichcloselyqatcheethetotalavailableheadof40meters.Note!thatthesecond1,000metershasaheadlossof26metersandanavailableheadofonly20meters.-17-Thisisallovablebecausethereisexce88headavailablefromthefirst1,000metersofthepipelineandtheHGLisalwaysabovethepipelineprofile.SeeFig.4.Rample3Aspringwithaflovof3l/eia500EYsrsfromthebathingareaandthemosqueis1,000metersfueher.Aflovof1l/swillbeusedtoservethebathingareaand2.0l/aforthemosque.Thedifferenceinelevationis10meter6betveenthespringandbathingareaand20metersbetveenthebathingareaandthemosque.Whatpipesizesarerecommended?Somecalculatedheadlorxesareaafollows:lengthflowpipediameterheadloss(meter-e)(l/e1(inchee)(meter61500335WJ32.5125003236l*fJOo2351,m22.5111,m223350022.565002216Availablehead(meters)101010202020If2.5inchespipeieusedfortheentire1,500metersthetotalheadloesie23meter6whichielessthanthetotalavailableheadoffometerrs.Tlnmthedesiredamountofwaterofmayflow,Hovever,theHCiLaeplottedinFig,5fallsbelowthepi-pelineprofileandthisienotallowable.-18-Figure5(Rmple3)500P-JO1,5m01sTRYCEAnacceptablealternativesolutionwouldbetouse500metersof3inchpipefollowedby1,000metersof2.5inchpipe.ThetotalheadlosswouldthenbeI6metersandexcessavailableheadwouldbe14meters.Amoreeconomicalsolutionwouldbe500meterseachof3,2.5,and2inchpipewhichwouldconveythefulldesignrlows.TheHGLforthesetwosolution6areplottedinFig.6Figure6(Example3)-19-5.SUMMARYOFSUGGESTEDESIGNGUIDELINES5.1.5.2.5.3.5.4.4.5.5.6.BacterialQuality:Nofecalcoliformsinanysamplefromtheproposed80urce.Ifthisisnotpossible,thenanaverageoflessthan50fecals/?OOmlforallsampleswithnosinglesampleexceeding100fecals/lOOml.Forlevelsabovethis,simpletreatmentisadvisablesuchasslowsandfiltration.DistancetoDistributionPoint:Nomorethan2096ofintendedu8er8towalkmorethan100meterstoobtainwater.NumberofUsersperWaterFaucet:Between30and100,lowerrangeformultipleuseandupperrangefordrinkingwateru8eonly.PerCapitaUsage:Multipleusesystem8ataminimumofb0l/daywithupto100l/daypreferredifsufficientwaterisavailable.Minimumof20l/dayforsupplyofdrinkingwateronly.StorageCapacity:Forstorageatthepointofuseonehalfoftheaveragedailyusage(ADU).Forstorageabovethepointofuse(standpipesonly)dependentupontheratioof8ourceyieldtoaveragedailyflow.ForaratiobetweenoneandtwothenstorageonehalfofADU;foraratiobetween2and3tnenstorageoneeighthofADU;foraratiogreaterthanfourthennostorage-required.DesignIizows:Ifstorageisatthepointofuse;usetheaveragedailyflow.*fstorageisabovethepointofuse(standpipesonly)thenusefourtimestheaveragedailyflow.APPENDIXA1.-Al-GENERALEXPLANATIONFORFLOWANDHEADLOSSESINCLOSEDPIPESPressureExertedbyaColumnofWaterAcolumnofwatersxertsaforceduetotheweightofthewater,Thepre88ure,orforceperunitarea,iedependentontheheightofthecolumnofwater.orwaterpressureieu8uallyexpreseedinterm6oftheequivalentheightofwaterneededtoexertthatpres8ure.Thepreesureunderstaticcondition8ienotdependentonpipesize.SeeFig.A1.FigureA1Thepressureatthebottomofeachcolumnofwateristhesame.Itis10meter8ofheador10kg/cm2.Thepressuremidwayineachcolumnwouldbe5metersofheador5kg/cm2.2.PreeeureinaStaticSystemIna8yetemunderetaticcondition8thepressureatanypointisdependentonthedifferenceinheightbetweenthepointinquestionandthehigheetpointinthesystem,Ifanopeningismadeinthepipeinanypartofthesystemandatubeconnectedtoitthenthewaterlevelwillriseuntilitisthesamea8thehighestpoint.SeeFig.A2.F’gureA2Thesystemisstaticandnoflowoccurs.ThepressureorheadatpointsB,C,F,andHisFig.A2thesame,i.e.10metersyherressureorheadatpoint!Zis5metersofthedifferenceinheightbetweenpointsAandE.IfthepipelinewereopenedandatnbeconnectedtoitatpointCorFthenthewaterwouldrise10me-tersandbeatthesamelevelaspointsA,D,andG,3.PressureinaFlowingSystemWhenuaterinthepipelineisflowing,thenthepressureisnolongerdependeatsolelyontheknightdifferencewithrespecttothehighestpoint.Thereisalossofpressureorheadduetofrictionbetweenthewaterandthepipe.Thepressureorheadatanypointisequaltothestatichead+(relativeheightdifference)minustheheadloss+duetofriction.Becauseoftheheadlossthewaterwillnotrisetothesamelevelasthehighestpointbutonlyashighasthepressureorheadatthatpoint.Headlossoccursonlywhenwaterisflowing.SeeFig.A3Underflowingconditionsthepressureisno?:,;:\\longerthesameandthepressureatpointCOrGisnotsufficienttoraisethewaterleveltopointsDorF.Theheight_differencebetweenpointsDandEorpointsFandGistheheadlossduetofrictioninthepipeline.Iftheflowwerestoppedthewaterlevelwouldreturn.-A3-4.FactorsInfluencingHeadLossesTheamountofheadlossisinfluencedbythefollowingfactors:a.Thelengthofpipe.Thelongerthepipelinethegreatertheheadloss.Thislossisdirectlyproportionaltothelengthi.e.theheadlossfor200metersofpipewouldbetwicethatfor100metersunderthesameconditions.b.Thediameterofthepipe.Thesmallerwillbefortional.thediameterofthepipelinethenthegreaterthefrictionthesameflowofwater.Thedifferencesarenotpropor-c.Theflovofwaterinthepipe.Thehighertheflowofwaterinagivenpipethegreatertheheadlossduetofriction.Frictionincreasesasthesquareoftheve-locity.d.Thepipematerial.Thesmoothertheinnersurfaceofthepipethelowertheheadloss.Thus,eincePVCpipeissmootherthansteelorcastironithasaloverheadlossforidenticalconditions.e.Thenumberoffittingsorbendsinthepipeline.Astraightpipelinewouldhavealowerheadlossthanoneofthesamelengthwithfittingsorbends.Someofthepracticalconsequencesoftheaboveindesigningagravityflowt3ySteJIIare:a.Increasingpipediameterbetweenanytvopointswillproducealargerflowofwaterbetweenthosetwopoints.b.Addingmanybendsandfittingsreducestheflow.5.PipeDesignIndesigningagravity#l.ovpipelinetheavailableheadLobtainedfromfieldmeasurements.Fromthenumberofpeopletobeservedandthepro-jectedpercapitaconsumptionthedesiredflowofwateriscalculated.Apipesizeisthenchooeenwithaheadlosslessthantheavailableheadatthedesiredflowofwaterandpipelength.Theheadlossistakenfromchartsandtables.(seeSection4.4.andAppendixB)Landdistancele6.FactorsAffectingtheHydraulicGradeLine(HGL)InFigureA3thelevelofthewatersurfacedefinesthehydraulicgredeline(HGL).Theslopeofthislineisconstantforagivenpipediameterandgivenflowandisdirectlyrelatedtotheheadloss.ChangingthepipediameterortheflowwillchangetheslopeofthehydraulicgradelineasinFig.A4.ChangingtheamountofwaterflawinginthesystemalsoaffectstheHGLasinFig.A5.TheHGLiscomparedwiththegroundprofiletodetermineifthepressurein.apipelineisadequate.(Seeparapaph4.4.4.)FigureA4oftheHGLincreasesduetoanincreasedheadlossforthesmallerdiameterpipe.Theflowofvateristhemmeinbothpipediameters.FigureA5AtpointBaportionofthefloviswithdrawnfromthesystem.TheflowbetveenpointsBandCislessthantheflowbetweenpointsAandB.Thepipediameterremainsthe8eme80theslopeoftheHGLiareducedbecauseofthereducedheadloss,APPENDIXBTHEMEAPWATERFLOWCALCULATORTheMearwaterflowcalculatorisbaeedontheColebrook-Whiteformuiaforflowanpipes.Itprovidessolutionstotheequationforawiderangeofconditionswithoutthenecessityforcumbersomecalculation8.Inusingthecalculatorsthereare5variables,theyare:a.b.C.d.e.H=theheadlossinmillibars;98millibarsisequivalentto1meterofhead.Inpracticewhenreadingthecalculator100qillihar8canbeconsideredasequivalentto1meterhead.F=Coefficientoffriction.Thisisrelatedtothepipematerialandonthecalculatorthemostcommontypeeofpipearelisted.L=ThelengthofpipewhichonthecalculatorrangesfromI,5to150,000meters.D=theboreofpipe(pipediameter)whichonthecalculatorrange8from16to6,000mmttheflowwhichonthecalculatorrangesfromIl/sto1000m3/8Eunple2Awatersourceisl)0metersfromthemainreservoirinavillageisneceessrytooonveyaflowof2l/stoit,GalvanizedironpipebeUSThedifferenceinelevationis35meters+whatsizepipeianecessary?Ifanyfouroftheabovevariableareknownorfixedthenthevalueofthefifthvariablecanbefoundonthecalculator.ExampleIAsourceis2kilometersfromthevillageandthedifferenceinelevationis50meters.Uhatwilltheplowofwaterbeifa2PVCpipeisinstalled?Comparethisflowwiththeflowina2GIpipe.a.Settheboreofpipe51mmopposite2,000meters.b.Settheplasticpipearrowoppositethepreesureloseof#5bars(50meter81c.HeadtheflowforPVCpipeoppositetheflowarrow:2.3l/sd,Keeptheboreofpipe51mmopposite2,000meters.e.SettheGIpipearrowoppositethepressure1088Of5bar8f.ReadtheflovforGIpipeoppositetheflowarrow:1.8l/sitandmust-B2-a.Settheflowarrowat1l/sb.Setthearrowforgalvanizedironpipeat3.5bare(35meters)c.Readtheboreofpipeopposite1,500meters.Itis41.5mmorI,63inches.Thereisnopipeavailablewithadiameterof1.63inches.Ifweuse1,5inchpipetheflowwillbelessthan4l/eifweuse2inchpipetheflowwillbemore.Checka6follows:a.Settheboreofpipe51mm(2inchee)opposite1,500meters.b.Setthearrowforgalvanizedironpipeat3.5barsc.Readoppositetheflowarrow1.75l/sd.Settheboreofpipe38mm(I.5inches)opposite1,500meterse.Setthearrowforgalvanizedironpipeat3.5barsf.Readoppositetheflowarrow0.8l/sSince1.5inchespipeistoosmalland2pipeistoolangeacombinationofthetwocanbeused.Try750meters2pipeand750meters1.Ypipe:a.Settheboreofpipeofpipe51mm2opposite750metersb.Settheflowarrowopposite1.0l/sc.Readthepressurelossoppositethegalvanizedironarrow650millibarsor6.5meters.d.Settheboreofpipe38mm1.5opposite750meterse.SettheflowarrowoppositeI,0l/sf.Readthepressurelossoppositethegalvanizedironarrowat27bar6or27meters.Thetotalheadlossfort1?1,500metersthenequals27+6.5or33.5meters.Thismorecloselymatchestheavailableheadof35meters.TheHearWaterFlowCalculatorisavailablefrom:M.H.MearandCo.Ltd.56NettletonRoad,Dalton,HuddersfieldRngland.APPEDIXCCONSTRUCTIONOTES1.CAF’TRRING(SPRINGPROTECTION)NOTES1.1.‘rheconstructionofacapteringwilldependonthephysicalcbarac-terir-rticaofthespringandsurroundingarea.jeveralpossiblesitu-atiaredepictedinfiguresCl,C2,andC3.Inadditiontheconsi-derations