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  HAPTER 3

WATER TREATMENT

DAB 30102ENVIRONMENTAL TECHNOL

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OBJECTIVE

In the end of this chapter the student shouldto :

•Identify the water supply sources

• Explain the main principles of water supwater treatment processes

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3! "#TE$ %'IT(

•#s consumers) we expect our water to be besthetically pleasin* and safe to drin+

• "ater that does not impart a taste or odor therefore) pleasant to drin+) is called palat

• "ater that is free of chemicals) microor*anand other contaminants) and is) therefore) drin+) is called potable.

• "e expect our water to be both palatable apotable

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•  The followin* four cate*ories are used to ddrin+in* water ,uality:

! -hysical : -hysical characteristics relate to,uality of water for domestic use and are associated with the appearance of water) or turbidity) temperature) and in particulaand odor

. Chemical : the chemical characteri/ation odrin+in* water includes the identi0cation ocomponents and their concentrations

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3 1icrobiolo*ical : 1icrobiolo*ical a*ents areimportant to public health and may also be

si*ni0cant in modifyin* the physical and checharacteristics of water

2 $adiolo*ical : $adiolo*ical factors must beconsidered in areas where the water may ha

in contact with radioactie substances The

radioactiity of the water is of public health c

Conse,uently) in the deelopment of a water ssystem) it is necessary to examine carefully al

factors that mi*ht adersely a4ect the intende

water supply source

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3. "#TE$ $E5O&$CE51.Su!a"e #ate 6 water in a rier) la+e or fresh water w

5urface water is naturally replenished by precipitation naturally lost throu*h dischar*e to the oceans) eaporaeapotranspiration and *roundwater rechar*e

•. #lthou*h the only natural input to any surface water syprecipitation within its watershed) the total ,uantity of that system at any *ien time is also dependent on ma

factors•. These factors include stora*e capacity in la+es) wetland

arti0cial reseroirs) the permeability of the soil beneathstora*e bodies) the runo4 characteristics of the land inwatershed) the timin* of the precipitation and local earates #ll of these factors also a4ect the proportions of loss

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THE $ATER CYCLE AND GRO%ND$ATER

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• 8atural surface water can be au*mented by importin* suwater from another watershed throu*h a canal or pipelinalso be arti0cially au*mented from any of the other sourhere) howeer in practice the ,uantities are ne*li*ible 9

also cause surface water to be lost ;ie become unusabthrou*h pollution

D&'t&but&o( o! Eat)*' $ate

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2. Gou(+#ate , =roundwater is fresh water located in the

subsurface pore space of soil and roc+s It is also water that is >o

a,uifers below the water table 5ometimes it is useful to ma+e a

between *roundwater that is closely associated with surface wat

*roundwater in an a,uifer ;sometimes called fossil water

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GRO%ND$ATER -LO$ ROCESS

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33 "#TE$ T$E#T1E8T

• "ater treatment describes those processes used to ma+e water more ac

desired end6use These can include use as drin+in* water) industrial procmedical and many other uses The *oal of all water treatment process is existin* contaminants in the water) or reduce the concentration of such so the water becomes 0t for its desired end6use One such use is returninhas been used bac+ into the natural enironment without aderse ecolo*

• The processes inoled in treatin* water for drin+in* purpose may be so

separation usin* physical such as settlin* and 0ltration) chemical such aand coa*ulation

• Biolo*ical processes are also employed in the treatment of wastewater aprocesses may include) for example) aerated la*oons) actiated slud*e o0lters

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$ATER TREATMENT ROCESS

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Ob?ecties for the @eelopments of a " Treatment 5ystem

• -roduction of 5afe@rin+in* "ater

• 1inimi/e the cost ofsupply of safe drin+in*water

• Brin* water to ruralcommunities

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Aactors considered at the treatment prselection

• %uality of raw water• &se for the processed water

• Treatment and ,uality desired for the

• 5i/e and capacity of the system

• Cost of processes

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 -rocesses for "ater Treatme

&/STORAGE•) $ate &' pla"e+ &( a "lo'e+ ta( o e'eo& "alle+ a "lea #ell to allo# t&

")lo&(e to & t)ou4)out t)e #ate &( o+e to +&'&(!e"t &t. T)e #ate t)et)e +&'t&but&o( '6'te.

•) E7e"t' o! 'toa4e8

•))6'&"al8 Ga&t6 9 :0;'u'pe(+e+ &pu&t&e' 'ettle +o#( &( o(e +a6

  O&+&

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&&/ AERATION

• #eration is a unit process in which air and water abrou*ht into intimate contact Turbulence increase

aeration of >owin* streams• #eration as a water treatment practice is used for

followin* operations:

• carbon dioxide reduction ;decarbonation<

• oxidation of iron and man*anese found in mwell waters ;oxidation tower<

• ammonia and hydro*en sul0de reduction ;

• #eration is also an e4ectie method of bacteria co

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&&&/ SCREENING

• Initially) wood chips) leaes) a,uatic plants

>oatin* impurities are remoed by the screprocess

• #fter the screenin*) a more compact suspematerial will be remoed to allow water to throu*h the chamber in which it will settle bottom

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 The purpose of screenin* proce

• $estrict the entry of suspended solids sas *arba*e in the water treatment plan

• -reent pump) pipe and e,uipment fromclo**in* or dama*e

• 'aunched a water course for the nextprocess

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 Types of 0lters 

CO#$5E AI'TE$ To 0lter materials such as

the lar*er >oatin* *arba*e and twi*s

AI8E AI'TE$

 To remoe >oatin* materials such smalleer plants) leaes and so forth

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&/ SEDIMENTATION

• It is the process of remoin* solid particlesthan water by *raity force

• 5edimentation tan+s are desi*ned to reducelocity of water so as to permit suspendeto settle out of the water by *raity withouaid of chemicals

• -articles that will settle within a reasonableof time can be remoed usin* a sedimentatan+ ;also called clari0ers

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E>AMLE 1

# research6scale water treatment plant usesturbidity raw water and is desi*nin* its oer>weir at a loadin* rate of ! m3Ddaym If its>ow rate is 22 m3Ds) how many linear meweir is re,uiredF

5olution:

;22 m3Ds< x ;GH2sDday< o 22

  ! m3Ddaym

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E>AMLE 2

• @etermine the surface area of a sedimentatan+ The desi*n >ow is 22 m3Ds &se a oer>ow rate of .mDday Aind the depth ofsedimentation for the *ien oer>ow rate adetention time

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• 5olution:

! Aind the surface area

Airst chan*e the >ow rate to compatible units

;22 m3Ds< ;GH2 sDday< 3@01. 3+a6

 The surface area is 3G!H m3Dday

  . mDday

  1:0 2

Common len*th to width ratios for sedimentationbetween .:! and :!) and len*ths seldom exceed# minimum of two tan+s is always proided

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'ets continue with our desi*n) assumin* thacan use two tan+s ) each with a width of !. mtotal surface area of !K m. would imply a tlen*th of

'en*th !K m. D ;. tan+s

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. Aind the tan+ depth

Airst 0nd the total tan+ olume by usin* a detention

!. min ;assumed< based on the rule of thumb thatdetention time should be .62 hours ;minimum . ho

V ;22 m3Ds

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/ COAG%LATION -LOCC%LATION

• Coa*ulation and >occulation: turbidity and suspsolids ;55< remoal

•  @esi*n ob?ectie is remoal of colloidal particleto ! micron<

•  Can remoe bacteria) soil) sand and clay partic

•  5table particles in natural systems

•  -articles in natural waters ;*enerally in p9 ran*to G<

•  'i+e char*es repel each other and remain suspsolution ;stable particles and no a**re*ation is

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• Coa4ulat&o( e")a(&''

• Char*e neutrali/ation: #ddition of #l or Ae salts and or*aniproides hi*h concentrations of counter ions that neutrali/

surface char*es of particles

•  $educes electrostatic repulsie interaction forces) and interaction ener*y becomes attractie ;mainly Van der

forces<

•  8et attractie forces lead to a**re*ation) and settlin* a**re*ates or >oc formation

•  5weep >oc formation: precipitation of salts at hi*h concen•  In settlin*) the precipitate Lsweeps colloidal particles a

itself 

•  Interparticle brid*in*: polymers attach to more than one leadin* to a**re*ation and >oc formation

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• -lo""ulat&o( o &&(4

•  $apid mixin*: for mixin* the coa*ulant

•  @etention time is approx min

•  5low mixin*: for >oc formation

•  Too fast will brea+ >ocM slow enou*h to manumber of particle collisions

•  Optimum speed has to be determinedexperimentally

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C)e"oa#lu;#luAer;ferAer

Coa-oly'imaddp9 sul

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&/ SO-TENING

•  "ater softeners will remoe nearly all the calcium a

ma*nesium from the raw water durin* the softenin*

•  =roundwater dissoles roc+s and minerals releasin*and ma*nesium ions that cause water to be hard Tdissoled ions *ie hard water its characteristics

• 9ardness N to characteri/e a water that does not latcauses a scum in the bath tub) and leaes hard) whdeposits on co4ee pots) tea +ettles and hot water he

• The failure to lather well and the formation of scum tubs is the result of the reactions of calcium and mawith the soap

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•  The ion exchan*e process is a common mewater softenin* process and illustrated in 0below

T)e #ate 'o!te(&(4 a(+ e")a4epo"e''

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• 5odium ions are supplied from dissoled sochloride salt) also called brine

• In the ion exchan*e process) sodium ions a

to coat an exchan*e medium in the softeneexchan*e medium can be natural L/eolitessynthetic resin beads that resemble wet sa

• Calcium ;Ca.< and ma*nesium ;1* .< io

cause water hardness can be remoed fairby usin* an ion exchan*e procedure

• "ater softeners are cation exchan*e deicCations refer to positiely char*ed ions

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• Cation exchan*e inoles the replacementhardness ions with a non6hardness ion "asofteners usually use sodium ;8a< as the

exchan*e• #s hard water passes throu*h a softener) t

calcium and ma*nesium trade places with ions 5odium ions are held loosely and are

replaced by calcium and ma*nesium ions• @urin* this process free sodium ions are re

to the water

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&&/ -ILTRATION

Ailtration: remoal of >occulated particles of smaller;those

that cannot be remoed by settlin*<

P $apid sand 0lters: hi*her throu*hput

P 5low sand 0lters: lower throu*hput

P #dsorption is another important mechanism for pa

remoal

P Bac+washin* of 0lters is essential to re*ain head lto

clo**in*

P =enerally with chlorinated water to disinfect 0lters

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SLO$ SAND -ILTER

Slo# 'a(used inwater purtreatin* rproduce a product typically !deep) canor cylindrsection anprimarily water Thbreadth odeterminerate desir0lters) whhae a loa! to .

https://en.wikipedia.org/wiki/Water_purificationhttps://en.wikipedia.org/wiki/Raw_waterhttps://en.wikipedia.org/wiki/Raw_waterhttps://en.wikipedia.org/wiki/Water_purification

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RAID SAND -ILTER

Enhance 0! timescompared0lter withof it see The mostthese fea!< # 0lte

*ranubeen more than tin nat

.< The ucoa*uprecowater

3< 1echa

hydra

Cleanin* is achieed by a*itatin* the bed either mechanically orwith compressed air and washin* water upwards throu*h the bedto the surface) from where it is decanted as wastewater This

Lbac+wash water is then wasted or return to the be*innin* plant

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&&&/ DISIN-ECTION

• @estruction of e*etatie patho*ens

• 8ot sterili/ation which implies destruction of all life fo;microbes) spores) cysts) iruses) etc<

• #utoclain*) membrane 0ltration

•  -hysical methods

• 1embrane Ailtration

• $adiation: &V) R6rays) *amma rays

•  Chemical methods ;disinfectants<

• Chlorinated compounds

• chlorine) chloramines) chlorine dioxide

•  O/one ;hydroxyl radical mechanism<

•  -otassium perman*anate

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C)lo&(e ea&(' t)e o't popula= #)6F

•  -otent *ermicide

6 9i*h oxidation potential

6 $esidual in distribution system6 Chloramine can do the same but is a less powerful oxidant

•  Taste and odor control

- Oxidation of 8O1 and remoal of compounds causin* taste and odo

•  Biolo*ical *rowth control- =rowth of al*ae and bacteria in stora*e reseroirs and water supply

•  Chemical control

- Iron and man*anese remoal

- Oxidation of 5OCs

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oble' #&t) ")lo&(e•  9a/ardous material

- @iQculty in transportation) handlin* and stora*e

•  -un*ent compound

6 @isa*reeable taste and odor

- @ermal and eye irritation

•  1icrobial resistance to chlorine

- 1ore e4ectie a*ainst bacteria rather than spores) cysts and ir

•  @isinfection by6products ;@B-s< formation

6 -otential health ha/ard

•  Carcino*enic) muta*enic) terato*enic

•  8on6carcino*enic e4ects N little information or discussion in l

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32 "#TE$ @I5T$IB&TIO8 5(5T

•  The purpose of distribution system is to de

water to consumer with appropriate ,uality,uantity and pressure

• @istribution system is used to describe coll

the facilities used to supply water from its to the point of usa*e

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 The layout should be such that no consumewould be without water supply) durin* the

of any section of the system

#ll the distribution pipes should be preferabone metre away or aboe the sewer lines

It should be fairly water6ti*ht as to +eep losdue to lea+a*e to the minimum

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'ayouts of @istribution 8etwor+

 The distribution pipes are *enerally laid beroad paements) and as such their layouts*enerally follow the layouts of roads

 There are) in *eneral) four di4erent types onetwor+sM any one of which either sin*ly orcombinations) can be used for a particular

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 They are:

@ead End 5ystem

$adial 5ystem

=rid Iron 5ystem

$in* 5ystem

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1ethods of water distributionS

Aor eQcient distribution system ade,uate pressure re,uired at arious points

@ependin* upon the leel of source) topo*the area and other local conditions the watbe forced into distribution system by followways 6

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! =raity system

. -umpin* system

3 Combined *raity and pumpin* system

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GRAVITY SYSTEM 

5uitable when source of supply is

at suQcient hei*ht

1ost reliable and economicaldistribution system

 The water head aailable at the

consumer is ?ust minimumre,uired

 The remainin* head is consumedin the frictional and other losses

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%MING SYSTEM

 Treated water is directly into thedistribution main out storin*

#lso called pumpin* without stora*esystem

9i*h lifts pumps are re,uired

If power supply fails) completestoppa*e of water supply

 The method is not *eneral used

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COMBINED GRAVITY a(+ %MING S

1ost common system

 Treated water is pumped and stored in an eleateddistribution reseroir

 Then supplies to consumer by action of *raity

 The excess water durin* low demand periods *et storeseroir and *et supplied durin* hi*h demand period

Economical) eQcient and reliable system

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COMBINED GRAVITY a(+ %MING SYSTEM

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@istribution $eseroirs

@istribution reseroirs) also called serice

reseroirs) are the stora*e reseroirs) whicthe treated water for supplyin* water durinemer*encies ;such as durin* 0res) repairs)and also to help in absorbin* the hourly

>uctuations in the normal water demand

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-u("t&o(' o! D&'t&but&o( Re'eo&'

 to absorb the hourly ariations in demand

 to maintain constant pressure in the distribution ma

 water stored can be supplied durin* emer*encies

Lo"at&o( a(+ He&4)t o! D&'t&but&o( Re'eo&'

 should be located as close as possible to the centre demand

 water leel in the reseroir must be at a suQcient elpermit *raity >ow at an ade,uate pressure

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T6pe' o! Re'eo&'...

@ependin* upon their eleation with respe*round it may be classi0ed into

! 5urface reseroirs

. Eleated reseroirs

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5urface reseroirsS

 These also called *round reseroir

1ostly circular or rectan*ular tan+&nder *round reseroirs are preferred espe

when the si/e is lar*e

 These reseroirs are constructed on hi*h n

*rounds and are usually made of stones) bplain or reinforced cement concrete

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 The side walls are desi*ned to ta+e up thepressure of the water) when the reseroir iand the earth pressure when it is empty

 The position of *round water table is alsoconsidered while desi*nin* these reseroir

 The >oors of these reseroirs may construcwith $CC slab or s,uare stone bloc+s restcolumns

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 To obtain water ti*htness bitumen compouused at all construction ?oints

 #t the top of roof about Hcm thic+ earth deposited and maintained *reen lawns to pthe reseroir from cold and heat

Aor aeration of water and inspection) entipipes and stairs are proided

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Under Ground Reservoir 

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TYES O- TANJS

  R.C.C TANKS: $CC ;$einforced Concrete <

are ery popular because!< They hae lon* life.< Very little maintenance3< decent appearance

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G.I. TANKS: =I tan+s are *enerally in rectan

s,uare in shape 8ow a days =I tan+s arepreferrin* because!< 'ife of the tan+ is short.< Corrosion of metal

3< maintenance cost may be more

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9@-E ;)&4) +e('&t6 pol6et)6le(e/ T#85

days 9@-E tan+s are ery popular for stori,uantity of water and hence useful for resipurpose The followin* are the adanta*es9@-E tan+s

!< 9andlin* is easy because of li*ht wei*ht.< Cheap in cost3< 1aintenance cost is low2< Cleanin* of tan+s are easy

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Eleated 5tora*e $eseroirsEleated 5tora*e $eseroirs ;E5$s<

also referred to as Oerhead Tan+sare re,uired at distribution areaswhich are not *oerned andcontrolled by the *raity system ofdistribution

 These are rectan*ular) circular orelliptical in shape

If the topo*raphy of the town notsuitable for under *raity) the

eleated tan+ or reseroir are used

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 They are constructed where combine *rapumpin* system of water distribution is ad

 These tan+s may be steel or $CC

8ow $CC is commonly preferred

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 The accessories of E5$ are6

Inlet and outlet pipe) oer>ow pipe discharinto a drain

Aloat *au*e) indicatin* depth of water

#utomatic deice to stop pumpin* when this full

# manhole and ladder

Ventilator for circulation of fresh air

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S C & ! D& &b &

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Stoa4e Capa"&t6 o! D&'t&but&o(Re'eo&'... The total stora*e capacity of a distribution

reseroir is the summation of:Balancing Storage: The ,uantity of wate

re,uired to be stored in the reseroir fore,ualisin* or balancin* >uctuatin* demand

a*ainst constant supply is +nown as the bastora*e ;or e,ualisin* or operatin* stora*e

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Fire Storage: The third component of thereseroir stora*e is the 0re stora*e

 This proision ta+es care of the re,uiremen

water for extin*uishin* 0res

# proision of ! to 2 per person per day issuQcient to meet the re,uirement

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E>AMLE 1

"hen desi*nin* a booster pump to 0ll the an

eleated tan+ If the tan+ oer>ow is at !!Gfwill be the pressure at the *round leel in -5

!!G ft

Eleatedtan+

Booster

Solut&o(8

Conersion :! -5I ;pound per s,uare inc.3! ft

.3! ft ! -5I!!G ft !!G ftD.3! ft x ! -  K 1.1 SI

E>AMLE 2

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E>AMLE 2

# new house is bein* built at an eleation of H! ft "ith exboosters) you may pump up to an eleation of 2K ft if you

re,uired to proide a minimum pressure of 3 -5I to the howhat water eleation will the house hae the re,uired pressSolut&o(8

Conersion :! -5I ;pound per s,uare .3! ft

.3! ft ! -5I3 -5I 3 -5I x .3! ft  K :.3 SIT)e total eleat&o( )etuu' aa' la(4&t/ !o

Eleation that will proide 3-5I to the house

1aximum pumpin*eleation : 2K ft

9ouse eleation : H! ft