Water and Wastewater Engineering
Dr. B. S. Murty
Department of Civil Engineering
Indian Institute of Technology, Madras
Intake Structures and Pumping Installations
Lecture

# 40

In this lecturewe will discussaboutintake structuresand pumpinginstallationswhich are

an integralpart of any waterdistributionnetworkor they couldbe a part of sewerage
systems
also.The pumpingis requiredin watersupplysystems
to transport
waterfrom
sourceto the treatmentplant. Sourcecould be at a lower elevationand treatmentplant
couldbe at a higher elevation.So we needto lift the water from a higher elevationso we
need pumpingfor that. We also need pumpingbecausewe have to get over the frictional
lossesthat couldbe comingin the pipeline.
(Refer Slide Time: 01:40)

Many timesin waterdistribution
networkbecausethe pressures
couldbe very low and
we have to meet that minimum sevenmetersof head of residualpressureand we needto
boost up thesepressuresso the pumping is also requiredto boost up pressuresin water
distribution networks in certain cases. We also need pumping in water distribution

networksto transport
waterthroughtreatmentplantsbecausea lot of energylossoccurs

in pipingsowehaveto getoverthesefrictional
losses
andweneedto havepumping
for
transportingwater throughtreatmentplants.

(Refer Slide Time: 02:40)

Pumping is required in wastewater schemesalso to lift septic tank effluent from a lower

elevationto a higher elevation.Many times we have to lift sanitaryand storm sewerage
from underground drains to treatment plants which are above the ground. In sewerage

systemswe also needto lift water from a lower elevationto higher elevationif the drain
slope is much higher than the slope of the prevailing ground. In such a case over a

distancethe drain will be buried deepinsidethe groundbut that will be very economical
from the point of view of constructing and installation. Also it is difficult to maintain
such pipes so we have to bring the drains to a higher elevation. In such caseswe need to
lift water from a lower elevation to higher elevation in wastewater schemes.There also
we have the requirement of pumping.
Before we go and look at the pumping we look at the intake structures which are the first

part of any water supply scheme.Intake is a deviceor structureto be placedin a surface
water source to permit the withdrawal of water.

(Refer Slide Time: 03:55)

The intakes could be wet intakes or dry intakes dependingupon whether the water is
temporarily storedin that intake structureor not. Again intakes could be river intakes,
lake intakes or reservoir intakes or canal intakes depending upon the source from which
we are taking the water. For example, in this figure you see this is a river intake, here we
have a bank and this is the river here (Refer Slide Time: 4:20) so the intake is almost

inside the river and this is the high flood level, my pump or the pump houseshouldbe
above the high flood level to be protected from the ood damage.

(Refer Slide Time: 05:20)

I also have this low water level. My intake structureshouldbe able to draw water even
when water is at a low water level. So we have two different pipes here which can draw
water from the river to the intake structure that is a high level penstock and a low level
penstock and there is a screen here at the front of the penstock this screen is preventing
the debris from entering into the intake structure or entering into the treatment works.
There is a pump here, (Refer Slide Time: 5:10) the suction pipe of the pump is like this
and this is the screen here which is again having the function of screening the fine

material from enteringinto the suction pipe and consequentlyinto the pump and then
damage the pump. Now this level here the screen level or the bottom level of this suction
pipe should be below low water level and there should be some sufficient head available
here otherwise

there could be an air entrainment.

This is called an intake well (Refer Slide Time: 5:40) and the water level in the intake
well be slightly lower than whatever is the prevailing water level in the river. like for
example if this is a high flood level and the water level is at this location in the river then

the water level in the intake well will be slightly below that so that differencein the head
accountsfor the headlossin this piping system.
Now we alsohave a valve herewhich canbe usedto control the entry of water from the
river into the intake well and this is the pump houseand the delivery from the pump is
taken to the treatment works. So this is a wet intake well system for a river intake. You
seethe next type of river intake.

(Refer Slide Time: 07:05)

This is called a jack well and here we keep the pump housenot inside the river away
from the river on the banks not too far away but slightly away from the banks. In this

casehere you have this intake structure,now this intake structureis placedmuch below
the low water levels so that water can enter in the well even during the low flow season.
Here this is the intake pipe (Refer Slide Time: 6:50) and there is a screen here which
screens the debris from entering into the intake well or jack well and we have a pump

herewhich hasa foot valve. Basically this foot valve is requiredfor priming of the pump
and this foot valve or the low end of this suction pipe should be below the river water
level.

There is a valve here (Refer Slide Time: 7:15) which can be operated so that I can control
the amount of water coming into the intake well and the pump house is much above the
high ood level so that the flood damage to the intake structure is minimized and the

delivery from the pump is taken to the treatmentworks. This is anothertype of intake
structure

or river intake structure.

(Refer Slide Time: 08:05)

Now we will look at the intake structure the kind of intake structure we adopt when we
want to take water from

a reservoir.

Here we have the reservoir

and this is the earthen

dam or embankmentthat is basically containingwater in the reservoir.We want to take
this water to the treatment works and here we put this intake structure, this is the intake
structure (Refer Slide Time: 8:10) and the water can enter into this intake structure
through the inlet ports shown here which are placed at three different levels. So water can

enterinto the intake structurefrom any of theseinlet ports and then the control flow into
the intake structureis doneby thesegateswhich we call the gatehouseandwe needa foot
bridge from the embankmentto the gatehouseand water which entersinto the intake
structure is carried through this particular pipeline to the treatment works. Either, I can

have a pump here if I need to lift the water or it can flow by gravity to the treatment
works. Sothis is an intakewith entry ports at different levels.

(Refer Slide Time: 09:30)

This is anothertype of an intake.Herethereis only one entry port and not too many entry
ports. The water enters the intake structure and then it goes through the conduit to the
treatment works. I can have a pump house here if it is required. but the main point is

water entersinto this conduit or into this intake structurethrough only one port and we
have a trashrack structureherewhich will preventthe entry of debrisinto this conduit or
into this intake structurehere and this entry port is kept at the bottom of the reservoirso
the water can enter into this conduit even when the water level in the reservoir is very
low.

(Refer Slide Time: 10:30)

We haveanothertype of intake structure.This is what we call a dry well intake structure
or dry intake. It is dry intake becausethe water is never storedin this intake structure
itself. I havethis outlet pipe here which is coming and then entry into this outlet pipe is
through this vertical riser and there are multiple entries into this vertical riser which take
water

from

the reservoir

and then there is a strainer

and all the fine

material

and the

debris is not allowed to enter into this pipe. The ports are at different levels so water

entersinto the riser and then directly ows throughthis outlet pipe. That way thereis no
which

is stored in this intake structure

at all. We have a valve rod here to control

the flow

into the outlet pipe. Therefore,this is completelya dry well or a dry intake structureto
take water from a reservoir. We may also have a reservoir where the water is stored
behinda gravity dam.
(Refer Slide Time: 10:50)

So, if I have a gravity dam like this then I can have one pipe the intake pipe which is
going throughthe body of that gravity dam and thereis a bell mouth here so that thereis
a smoothentry into this intake pipe and at the entranceto the bell mouth we have this
trashrack structurewhich preventsthe entry of debrisandthen suspendedmatterinto this
inlet or intake pipe and the flow into the intake pipe itself can be controlled by a gate.
This is the hoist cable for the gate (Refer Slide Time: 11:30) and the gate itself can be
controlled from the top of the dam.
We also need an air vent here that is meant for expelling air during the maintenance

period. Again we can also have anothertype of intake for gravity dams or to take the
water from the reservoirsbehind a gravity dam. In this fig. a there is only one port of
entry and it is kept at the bottom of the reservoir. Here we havemultiple entriesand one
entry is below the low water level, one entry at the middle and anotherentry is below the
high water level maximum water level and this water enters into this intake well, this is
the intake well I am showing so this intake well is always full of water so its a wet
intake, water is entering through these inlet pipes into this intake well and outlet pipe
goes from this intake well and the ow in the outlet pipe can be controlled through the

valve and flow into the intake well can also be controlled through thesecontrol valves

andthis is basicallythemasonryabutment
section.
So, for taking water out of a reservoir behind a gravity dam either I can follow this
particular arrangement (Refer Slide Time: 12:51) for intake or this particular arrangement
for the intake.
structure

We can also have what we call a lake intake

we take the water from the bottom

(Refer Slide Time: 13:50)

of the lake.

structure.

In the lake intake

This is the suction pipe and the suction pipe is the one which joins the suction side of the

pump and this is the lake bed and thereis a bell mouth entry for this suctionpipe so that
the water enterssmoothlyinto this suctionpipe. Herethereis plankingand over that there
is a CI grating. These are the ones which are preventingthe entry of debris into the
suction pipe and this whole intake is protectedfrom any damagefrom the sidesand top
using this plank as well this rock fill here. This intake (Refer Slide Time: 13:40) should

be operatedin such a way that there is a minimum water level abovethis suction pipe
otherwisethere could be air entry. That is a very important point in the design of this
intake structures

which

we will

(Refer Slide Time: 15:20)

discuss in detail little later.

We can also have an intake

structure

or this nature.

This is what we call a canal intake

structure. In the canal intake structure you put the intake structure on the canal bank.

Thesecanalintake structuresare normally usedfor water distribution systemswhich are
cateringto a small community. Here we have this outlet pipe which is supportedon a
thrust block like this and the top of this outlet pipe we have the screenwhich will prevent

the entry of debrisinto this outlet pipe andthereis a control valve herekept on the top of
this intake chamber which we can accessfrom the canal bank to this bridge and we can
operate this control valve and then control the amount of water that is owing into the
outlet pipe.

Here (Refer Slide Time: 15:00)the water entry into the intake chamberitself takesplace
from this side. From the canal the water enters like this to this intake

chamber

and there

are coarsescreensherewhich will preventthe entry of large particlesor large debrisfrom
entering into the intake chamber. This is a fine screenwhich will prevent the entry of fine

materialinto the outlet pipe. Now the coarsescreenor the total depthof this entry is kept
such that the top of this entry point is above the low water level so that water can ow
into this even when we have minimum

amount

of water in the canal. This is what we call

a canal intake structure.

There are certain points that we should consider while designing these intakes. First of all

we shouldworry aboutwherewe are going to placetheseintakes.So the intake location
is an important consideration in the design. We should locate these intakes wherever best

quality of water is available.We cannotlocatethe intakeswhere we dont havethe best
quality or the water quality is very poor.

(Refer Slide Time: 16:35)

The location where we install these intakes should be such that it is protected from the

damagingwater currents.Water currentsshouldnot be very swift suchthat the water load
or the dynamic load from the water on the intake structureis significant and it can get
damaged during floods. Also it should be located in such a place there is no formation of
shoals

and sand bars because

if shoals

and sand bars form

in and around

the intake

structuresthen the working of the intake structureis affectedsignificantly. The entry of
water into the intake structure is not going to be very smooth and sometimeswhat
happens is the shoals and bars form around the intake structures then the river can tend to

meanderand then we will not haveany water nearthe intake structureparticularly during
low season.So we shouldnot locate the intake structureswhere there is a possibility of
formation

of shoals and sand bars.

We also have to locate these intake structures away from navigation channels. becauseif
the intake structure is close to the navigation channel then the ships and other vessels

passingthroughthis navigationchannelmay go and then hit the intake structureand may
damageit. So we haveto placethis intake structuresor locatethis intake structuresaway
from the navigation channels. Again the location of the intake structures also depends
upon what kind of floods that are occurring in the river and what kind of ood damage

that could comeon the intake structurethis is very very important.
As we have seen earlier we may locate the intake structure right in the river or we can
locate the intake structure a little far away from the river. But if we locate the intake

structurevery far away from the river and my intake pipe is very long then whatever
variation that may come in, in the pumping operationthe river will not be responding
with very quickly becausethe river is now quite far away and there will also be energy
losses in this intake pipe so the water level in the intake well will be much lower than the

water level in the river which is not very good for pumpingbecausethe pumping costs
would be high. So the location of the intake structure as far as protecting them from the

flood damageis a very importantconsiderationin locatingthem.

Now, again wherever we put the intake structure we should be able to provide the power
for the operation of the pumps in intake structure. Thus, availability of power to the
intake structure is very important because if power is not available near the intake

structurethen we haveto operateit with batterybut that is not a very goodcondition.
Accessibility to the intake structure is also very important because if it is not accessible

then certainlythe maintenancewill be very bad. So accessibilityand availability of power
arevery importantconsiderationsin locatingthe intake structures.
Distance from pumping location: Sometimes the pumps cannot be placed within the

intake structureitself asthey haveseenin someearlierdiagrams.If the pumpingis a little
far away from the intake structureit hasto be consideredbecauseof the hydraulicsof the
flow, how much of friction loss will be occurring in the intake pipe and so on.
What are the design considerations for these intakes?

First of all we have to provide for withdrawal from more than one level, this is very
important. In some of that I have shown earlier we have the multiple entries. This will
help in proper operation of these intake structures during the flow variation. Sometimes

the water level in the sourcecould be very high, sometimesthe water level in the source
could be very low that hasto be taken into considerationand that is why we provide for
withdrawal

from more than one level.

We also have to provide under sluices to release less desirable water. under sluices are
the ones which are provided almost close to the bottom of the reservoir or bottom of the

canalor the river and they shouldbe placedvery closeto the intake structuresand these
under sluicesshouldbe usedfor removingundesirablewater so that only a good quality
of water enters the intake structure and the pumping installation.

Intake: If we haveto locateneara navigablechanneland we cannotavoid it lets saythen
we haveto protectit againstblows from the shipsby providing clustersof piers. So even
if the ship comes very close to the intake structure it hits against these piers but the intake
structure

itself is safe.

(Refer Slide Time: 21:40)

Underminingof foundationsdue to scourshouldbe avoided.This is very very important.
becauseif you have locatedthe intake structureinside the river like the first option first
intake structure that I have shown so in such a case during oods what happens is

becausethe velocity is very high the sedimentthat is sitting on the bed can get scoured
and if the sediment gets scoured during the high flood flows then the river bed level itself
is going to go down. If the river bed level goes below the foundation level of the intake

structurethen the intake structurecan get washedaway very easily. So, underminingof
foundations

due to scour should be avoided.

Its very similar to designof brick piers. The foundationlevel for the brick piers should
go below the maximum scour that is expected during the high floods. Same kind of
principle one should use for finding out what should be foundation level or what is the
maximum

scour level

and the foundation

level

should

be below

this maximum

scour

level that can come during high oods, that is very important otherwise the intake
structurecan getwashedawayvery easilyduring high floods.
The other important point is the overturning pressuredue to slit deposition. Whenever we
have an intake structure it is creating an obstmction to the flow. This is particularly
important when the intake structure is located within the river or within the canal itself.
Now, on one side of this intake structure there could be deposition or sand and slit
deposition and on the other side there could be little scour so there will be differential
earth pressure that is going to act on this intake structure and that can result in
overturning pressures. When we design intake structure or when we do the structural
design of this intake structures these overturning pressuresdue to slit deposition should
be given due consideration.
The other important parts of the intake structures are the coarse screens. These coarse
screens should prevent entrance of large objects into the intake structure and into the
pumping scheme. The fine screens are also used and the purpose of fine screens is to

excludesmall fish and small objectsfrom enteringor preventthe entry of small fish and
small objects into the pumping scheme.
(Refer Slide Time: 24:30)

The areaof openingof thesescreensshouldbe suchthat the entrancevelocity is lessthan
8 m per minute. If the entrancevelocity is very high then large objects also could be
suspendeddue to the turbulence and these materials can easily enter into the intake
structure.So the entrancevelocity shouldbe lessthan 8 m per minute so that the entry of
settleablelmatterinto the intake pipe is avoided.And when we havesubmergedportsthen
the depth of water over the port should be more than three times the diameter of opening.

What happensis we have submergedports which are very similar to what you seein a
sink.

In your kitchen sink if there is not enoughdepthabovethe bottom openingof your sink
then you will seethis air code that is forming and then air can get suckedinto the inlet
pipe. So, to prevent that vortex formation to prevent the air entry into the inlet pipe if
there is a submerged port then the depth of water above the port should be a minimum of

threetimes the diameterof opening.This is very very importantbecauseair entry into the
inlet pipe or intake pipe and subsequent transmission of this entering air through the
suction pipe to the pump can cause damage to the pump in no time so we should avoid
this.

The other important designconsiderationsare if you have underwater conduitsthen we
shouldusea standardcastiron pipe, steelpipe or a concretepipe andthe velocity of these
conduitsshouldbe about 60 to 90 cm per second.We shouldnot allow a higher velocity
throughthe ports. In fact the velocity throughthe ports shouldbe lower than the velocity
in the conduit and that is the reasonwhy we always have a bell mouth entry into these
conduits.Again the velocity in the conduit shouldbe around60 to 90 cm per second.

(Refer Slide Time: 27:05)

The area of suction well or the suction well is providing some kind of a temporary
storage. So the cross sectional area of the suction well is another important consideration
in the design. This should be around three to five times the area of intake conduit. The

intake conduit itself shouldbe continuouslyrising or falling, it shouldnot haveany bends
becauseany bendswill causeflow disturbanceand it will increasethe head loss. That
way the water level for a wet intake will be much lower than the water level in the river

and that is not what we want. So the intake conduit shouldbe either continuouslyrising
or continuously falling.

(Refer Slide Time: 27:55)

Now let us look at the next part which is the pumping station. In the design of pumping
stations few things have to be given due importance. The first part is the selection of the

pumps.Then we have the sump designwhich is very very important,how do we place
thesepumps in the sump. In fact many of the pump manufacturersinsist that a model
study should be conductedwhile designingthe sump and only if the sump design is
satisfactorythe pump manufacturerwill give you guaranteesregardingthe performance
of the pumpsbecausethe performanceof the pump as far as the efficiency is concemed,

thelife of thepumpis concerned
is integrallydependent
on thedesignof thesum.So
th.eseftwofisf
whatwerlofokfapt
in Ithispparticularg
lecture.
The other important points in the pumping station design are the layout of the pipes
within the pumping station, how do we install these pumps and how do we operate these

pumps.But we look at in this lecture mainly on the selectionof pumps and the sump
design.

(Refer Slide Time: 29:30)

What are the different types of pumps available and which of these pumps are more
commonly used in the water supply schemeand then seweragesystems.The types of
pumps are centrifugal pumps, positive displacement pumps, for example, reciprocating
pumps, the screw pumps, gear pumps etc are all positive displacement pumps, then

buoyancyoperatedair lift pumpsand sometimeswe also have Hydraulic Rams.Among
all thesetypes of pumps the centrifugal and reciprocatingpumps are more popular in
water supply schemesand seweragesystems.
The first thing is we have to discuss regarding the criteria for pump selection. what kind
of a pump we should select, what should be its size, should we select a reciprocating
pump or should we select a gear pump or shall we go for a positive displacement pump or

a reciprocatingpump. This selectionof type of the pump dependsupon the natureof the
liquid. It dependson whether we are pumping raw water or treated water whether we are
pumping water for a water supply scheme or a waste water scheme or waste water
collection scheme, if we are pumping in a wastewater collection scheme then we have to
ask the question whether it is meant for pumping sanitary sewage or storm sewage. The

natureof liquid is an importantparameterin the selectionof the type of the pump.

(Refer Slide Time: 30:40)

Thenwe havethe operationof the pumpor what we call the duty whetherwe are going to
operate the pump continuously or intermittently or in a cycle fashion so the pump
selection depends upon that factor also. The size of the pump depends upon what is the

demandwe are going to meet.We are going to designthis pumping systemnot for the
presentuseonly but this pumpingsystemshouldbe ableto meetthe demandsevenin the
future. So the projected demand is another important factor in the criteria for pump

selection.So,over a period of yearsasthe demandis increasingthe pump shouldbe able
to operateand should be able to give samelevel of efficiency even when the demand
increases in the future.

The pump selection depends upon what is the head over which the pumping has to be
carried

and what is the amount

of flow

rate that we want to realize.

The head and flow

rate requiredalso affect very significantly the pump selection.The most importantpoint
is the efficiency of the pump. We are going to have this pumping operation over a long

period of time may be for twenty yearsor thirty yearsandwe may be operatingit for may
be twelve hours a day or even twenty four hours a day. In such casesthe power is
requiredto operatethesepumpsand not all the electricpowerthat we supplyto the pump
is convertedand is hundredpercentusedin lifting the water so the efficiency comesinto
the picture.

The efficiency of the pump shouldbe very high so that the power consumedduring the
pumping operations is minimized. Again whenever we have a pumping station or
pumping installation we may not be using only one single pump.
Let us say we want to lift the water over a small lift may be two meters or three meters

but our demandor the pumping rate is very very high. Now we can do this with one
single large pump which givesthat very high dischargeor we can do the sameoperation
by using three or four more pumpswhich are used in parallel so that the head the lift
givenby all theseindividual pumpsis samebut when you addthe dischargefrom eachof

these pumps the total discharge meets our demand. That means we are operating these
pumps in parallel. That is also an important consideration in selection of the pump

particularly the numberof pumpswe needto have,what shouldbe its size and so on and
so forth.

In somecaseswe needto have for the samedischargethe delivery point could be at a
muchhigher level comparedto the water level in the sumpor the lift is very high. In such
a case I can use a single pump which gives the required discharge as well as it is able to
lift the water to a much higher elevation. Or I can use three or four more pumps in a
series operation. That is the first pump will lift the water by a certain amount then the

secondpumptakesover and for the sameamountof dischargeit lifts the waterby another
amount and so on and so forth. So whenever we are selecting the pumps and whenever
we are doing this design of a pumping installation the number of pumps is important.
Whether these pumps are operating in parallel or whether they are operating in series is

anotherimportant considerationwhich we needto decideright away before we go and
select the pump.
The other important considerations in pump selection are what are the different modes of
installation, how are we going to install these pumps, what kind of space is available for
us in the pumping station to install these pumps, how we are going to move the
equipment and so on and so forth. Hence, these are also important considerations while
selecting the pump.
(Refer Slide Time: 35:34)

Finally we have the easeof operationand maintenance.The pumpinginstallation should
be such that we can maintain these pumping installations easily. We also have to know

the kind of operationwhetherit is easyor difficult becausemany times the operatorsare
not well qualified to be able to implement very complex operating scheduleso the
operationshouldbe suchthat it is easyto operatethe pump and it is easyto maintainand
pump selectionmanytimes is basedon that criteria.
In the pump selection one single most significant factor or significant parameter or

number whateveryou call is the specific speed.Just like for flows in pipes Reynolds
number is the most significant parameter or significant number or in open channels
Froude number is the significant number. Whenever we talk about pumps pumping
operations or pumping selection specific speed is a significant number that we have to
consider.

Specific speedis defined as NQ which is equalto 3.65 multiplied by N where this N is
the operatingspeedof the pump in revolutionsper minute multiplied by squareroot of Q
or Q to the power 0.5 where Q is the discharge through the pump or the ow rate through

the pump shouldbe taken in units metercubeper seconddivided by the ratedheadH to
the power 0.75. This rated flow rate Q and rated head are the head end discharge that are

realized when the pump is operating at its maximum efficiency point. These values
(Refer Slide Time: 37:38) the rated head should be given in meters here and ow rate is

in meter cube per second.It is very important to notice here that this is not a non
dimensionalparameterand this 3.65 is basically that is a factor coming for the units that
we are using here.
(Refer Slide Time: 38:00)

So, if you seethe specific speedfor the samepump given by anothernumberyou should
understandthat the personis using a different unit system.this is the unit systemthat we
usefor defining specificspeedin our country or this is the onewhich is recommended
by
our water supply manual, our water supply and treatmentmanual given by the water

prevention and control of pollution act 1974 and the water prevention and control of

pollution rules 1975or it is given in the manualon water supplyandtreatment.
Specificspeed:you can know the specificspeedby knowing what is the ratedheador the
net pumpingheadthat you are going to haveand what is the rateddischargeand you can
put this operatingspeedthat is lets say around 1200 RPM and so on. Then once you
know the specific speedthen you can selectthe type of the pump. For example,as the
specific speedincreases,in this diagram you can see, what is the efficiency that is
achievable for different pumping rates.
(Refer Slide Time: 39:15)

Here (Refer Slide Time: 39:16) this is the curve for 6.3 liters per second, this is the curve

for 12.5 liters per secondand so on and so forth. So the efficiency of your pump depends
upon the amountof water you are pumpingas well as the specific speed.This efficiency
that is achievableor the maximumefficiency that is achievablefor a given specific speed
dependsupon the design of the impellor which is shown in the next figure.

Here the impellor is called a radial ow impellor, the water flows radially on the
impellor. On the other end it is called a propeller, here the ow takes place along the axis
of the pump so this is the axial flow machine and this is the radial flow machine and

typically if the specific speedsare low one should go for radial flow machines.The
reasonis one can achievemaximum efficiency by designinga radial flow machineas
comparedto the efficiency that can be achievedby going in for an axial flow machine.
Thus, as the specific speed increasesfrom 35 to 75 then to 130 where we go for a mixed

flow impellor wherethe entry is radial andthe outow is in the axial direction.Or we can
go for a diagonalwhen the specific speedis 350 and for very high specific speedswe go
for a propeller pump.
(Refer Slide Time: 40:55)

Here in this figure therearethreecurves.On the x axis we actually plot the dischargeand
on the y axis we plot the first curve which is for the head, this curve is head versus
dischargecurve (Refer Slide Time: 40:56) for a typical pump which has a specific speed
of 35 and this is power versusdischargecurve and this one is the efficiency versusthe
dischargecurve. Thesecurvescanbe plotted for any type of impellor or any pump.You
can see, when the specific speed is low the power increases with the discharge, the

dischargeis on the x axis. So if I want to pump morewater and I openmy delivery valve
then I will be increasingthe load on the motor. This hasto be consideredproperly while
selecting the motor and designing the motor.
Whereas in this figure here when the specific speed is 350 the power consumption

reducesas the dischargegoesup. That meanswhen I if I selectthe motor for very high
dischargesand then when I operatethe pump at very low dischargesby throttling the
valve then there will be more power when I throttle the valve or when there is a shutoff

condition there is overloadon the motor. So such pumpswhen we operatewe actually
should start the pump with the valve open. Whereas in this particular casewhen I operate

the pump or when I startthe pump operationI shouldkeepthe delivery valve closed.So
how the motor gets selected and what is the power consumption etc depends upon the
specific speedwe have. The other important point to be considered from this figure is the
maximum efficiency. For any given pump the efficiency is maximum at particular
discharge value and corresponding the head value. That is what we call the maximum

efficiency point or the dischargeand head correspondingto the maximum efficiency
point is what we call the rated conditions.
(Refer Slide Time: 43:10)

The other important point to be considered while designing these pumps or while
selecting these pumps or designing the pumping installations or operation of the pumps is

what kind of pressureswe have on the suction side of the pump. Lets say this is the
pump here, this is the sump, (Refer Slide Time: 43:08) this is the water level in the sump,

this is the water level in the delivery reservoirso now at that water level in the sumpthe
pressure is atmospheric whereas on the suction side of the pump pressure will be below
atmospheric. This is because as the water goes from this level to this level there is a

changein the headso correspondinglythe pressuredecreases.
And alsothereis headloss
in this suction pipe. Becauseof that on the suction side you always have negative
pressures. If the pressure is below the vapor pressure of water then vaporization takes
place. That is what we call cavitation.
Cavitation means the bubbling will

start occurring and when these bubbles get

transportedthrough the pumping systemthey could reach the regions where pressure
could be very high. In sucha situationbubbleswill collapsethis is what we call pitting. If
the cavitationoccursin the operationof any pump life of the pump can comedown very
significantly so a cavitation shouldbe avoidedlike a plague.If the pressurehere or the
below atmosphericpressurehereitself is very low (Refer Slide Time: 44:30)then one can
expect a more significant below atmospheric pressure in the pump. So each pump

manufacturertells you what we call a NPSH requiredthat is Net Positive SuctionHead
required at the suction side. If the actual pressuresare not meeting this minimum NPSH

required then the cavitation is likely to occur so pump manufacturerswill insist the
installation of the pump or the design of the pumps or the design of the suction side such

that this NPSH requiredis alwaysmet that is actual net possiblesuctionheador the net
positive head should be more than the minimum net positive suction head or the NPSH
required.

The NPSH available can be easily determinedusing the Bernoullis equation or the
engineering Bernoullis equation between the sump water level on the suction side of the

pump and accountingfor the difference in the elevationsand the energy loss in the
suction pipe. So that NPSHa should be greater than NPSH required. Typical NPSH
required curves are given in this figure for centrifugal flow pumps and mixed ow
pumps.

(Refer Slide Time: 46:15)

The NPSH required also dependsupon the specific speedand the head of pumping which

is given in units of meterhere. So, if I know what is my specific speedand I know what
is the head over in which the lifting is taking place then we can determine the minimum
net positive suction head required and then we make sure that pump is installed in a
manner that NPSHa is greater than NPSH required.
The other important factor in the pump selection is what we call the operating point. The

operatingpoint is the point wherewhen you take a pump and put it in a systemand start
the pump then (Refer Slide Time: 46:46) this is the operatingpoint which will tell you
what dischargeyou will get and what is the headdevelopedby the pump.Rememberthe
headdevelopedby the pump shouldbe suchthat it shouldget over not only the staticlift
but all the frictional lossesandthe velocity headat the delivery point.
Let us say your delivery pipe is discharginginto atmospherethen there is a certain
velocity with which water comesout so there is a velocity head.So the static headplus
the friction loss in the delivery pipe plus the velocity head is what we call the system
head.Now the systemheaddependsuponthe dischargewe havein the pipe andtypically
varies as the quadratic power of discharge or the total head is a function of Q square. So,
for different values of Q or for different values of Q we will find out what is the total

head in the systemand we can plot that curve and that is what we call the systemhead
curve as shown here.

(Refer Slide Time: 47:55)

The other curve I am showing in this figure is the pump curve. The pump curve is given

by the manufacturer.After designingthe pump and fabricatingthe pump one can conduct
a pump test. There are standard procedures available for conducting the pump test. And

this head developedby the pump which is equal to the delivery pressureminus the
suction pressurewhich one can easily find out during the pump test by installing a
pressuregaugeon the delivery side and pressuregaugeon the suctionside from this one
can find out what is the pump head developed. And one can take the flow from the pump
and then put it through a discharge measuring device and find out what is the flow that is

coming out of the pump during the pumptest and one canplot this headdevelopedby the
pump as a function of this Q. That is what we call the pump curve and wherethe system
head curve intersects the pump curve is what we call the operating point.
So this is the operating point (Refer Slide Time: 49:07). That means irrespective of what
the rated head is or what the rated flow rate is the pump will be operating such that this is

the dischargeyou get and this is the head developedby the pump. Now this operating
point shouldcoincidewith the best efficiency point or the ratedpoint if you haveselected
the pump properly of if you have designedthe pump properly to suit the given system.
During the life cycle of the pump the water level in the sumpcould be varying between
two limits; a low water limit and a high water limit.

(Refer Slide Time: 49:55)

When the water level in the pump is very low then the static lift increasesand when the
pump is operatingunder suchconditionsyou will get a low dischargeto balancefor the
high head. Whereas when we have high water level in the sump then the static lift is
reduced and to compensate for reduced total head the discharge will increase. So the
pump will be operating between this operating point and this operating point during the
operation corresponding to low water level and high water level.

Pump efficiency curve: We have seenthat the efficiency varies with the dischargeand
depending upon the specific speed of the pump. Now the pump should be selected or

should be designedor we should take such a pump such that the efficiency versusthe
dischargecurve (Refer Slide Time: 50:45) lets say this is the efficiency versus the
dischargecurve the efficiency is more or lessmaximumbetweenthe low water level and
high water level and that efficiency curve is more or less flat betweenthesetwo points
thats a very important point in the selection of the pumps.
The other important consideration is the sump design. Whenever we are designing the
sump the sumps should be designed in such a manner that it prevents vortex formation. If

vortex gets formed in the sumpsthen that vortex can entrain the air not only that the
turbulence that is created the disturbance that is created can have significant effect on the

pump operationor the ow structurewithin the pump and that affects the efficiency of
the pump. The other thing is if you are having more than one pump or three or four
pumps which is operating in parallel then we have to get a uniform ow distribution in
the sump.

(Refer Slide Time: 51:50)

We also have to maintain sufficient depth of water in the sump to preventair entry. A
typical designfor a pump sumpis like this
(Refer Slide Time: 52:47)

This is my inlet pipe to the sump(Refer Slide Time: 52:02).This is lets saycomingfrom
the intake structure and we are operating four pumps in parallel. The sump should be

designedsuchthat the flow approachesall thesefour pumpsmore or lessuniformly and a
single pump is not stopped.Sometimeswe may have four pumpswe may be operating
only two pumps. In such a situation also the flow should be approachingthesepumps
more or lessuniformly. So the sumpdesignshouldbe suchthat evenwhen one or more

pumps are operating or lets say when not all the pumps are operating the ow structure

hereis conduciveto obtainmaximumefficiency.
There are limitations on the maximum angle you can take for this expansionhere and
lets say the preferred angle is ten degreeswhat should be the spacingbetween the
pumps, what should be the spacing behind the valve behind the pump the pump centre
line, what should be the spacing between the pump centre line and this place and what
should be distance between this inlet point here (Refer Slide Time: 53:15) and the pump
centre line and so on and so forth.

Guidelines available for this purpose: For example one should go for a sump design of

this natureor a sumplayout of this naturecomparedto this. This kind of a sumpdesignis
not recommendedat all. If you look at in the elevationthe water will be flowing in this
manner from this side to this side. Ahead of the pump we need to put a trash track. For

entry into the pump sumpwe needto havea trashtrack to eliminatelarge debris,then we
have this

screen here which

will

kill

lot of ow

disturbances

and the water

will

be

enteringor approachingthe pump more or lessuniformly, this screenhasto be there.and
we needto have enoughdepthof ow nearthe pump and that is the reasonwhy we need
to havethis sloping floor becausethe depthherecould be very low and if I take the floor
at this level then we would not haveproperentry into the pump.
(Refer Slide Time: 54:20)

There are conditions on;

0

How much of spacingshouldbe therebetweenthe bell mouth entry to the pump

and the oor

0
What is the minimum water level required for the submergenceof this bell mouth
when we get better efficiency

0

What should be the distance between the pump centre line and the trash track and

the screens and so on and so forth

In wastewater pumping the principles of pumping are very similar except that the nature

of water or quality of water is different and the kind of issuesthat one hasto consideris
the release of gasesfrom the wastewater. Particularly when we are talking about sanitary
sewerageor when we talk about storm seweragesystem the intermittency in the operation
is a important consideration. For example, here we are talking about a wastewater

pumping.one can have a dry well type of a design,this is called a wet well and this is a
dry well, the pumpsare locatedin the dry well, the sewagepipe or the drain pipe which is
delivering water into the wet well can have a high level or a low level but we dont put
the pump in the wet well itself.

In someinstallationswe can put the pump directly in this wet well and then pump the
wastewaterout. but herewe keepthe pumpin the dry well andtake the suctionpipe from
the pump to the wet well so that water entry from the wet well into this pump is through
this suction pipe. Here this is the motor and the power is supplied to the pump. This is the

pump centreline (Refer Slide Time: 56:11)andthis is the delivery pipe from the pump.
(Refer Slide Time: 56:10)

(Refer Slide Time: 57:10)

We can also have an installation of this nature where we have three pumps which are

operatingin parallel. This is what we have, a wet well and this is the dry well (Refer
Slide Time: 56:31).All the pumpsare locatedin the dry well and the suctionpipesfrom
theseare going into the wet well and delivery from the pumpsis taken through a check
valve and then put in a common header.All these delivery pipes are connectedto a
common header and this check valve is provided to prevent reverse flow when there is a
stopping of the pump. Here there is a bubble tube. This is an important feature that is

provided in sanitarysewagepumping.This bubble tube providesthe air to the water or
wastewaterin the wet well so that water quality is maintainedand ensuresthat septic
conditions

are not set in.

(Refer Slide Time: 57:32)

We can also have a wet well dry well type of an installation in this manner.This is the
wet well and the suctionpipe is going from the wet well to the dry well and the pump is
locatedhere.This is a factory assembledsewagepumpingstation.We canhavethis kind
of a pumping installation for pumping large storm water flows. Here the water is coming
from the storm water drain and there is a trash rack here and it enters through the trash
rack and we have a pump here, we have to maintain certain minimum depth of flow.
(Refer Slide Time: 58:00)

We also have a sump pit here so we have to provide a pump here also to drain for the
maintenance purposes.
In this lecture

we have seen what

are the basic considerations

or basic factors

that we

considerwhile designingintakesfor a water supply schemeand for designingpumping
installations for a water supply schemeor for a wastewaterscheme.As I mentioned
pumpingis requiredin water supplyschemesto maintaincertainamountof pressuresand
for lifting the wastewater whereas pumping is required in wastewater schemesfor lifting
the sewage from a low level drain to a high level drain. And we have seen where should
the intakes be located and how to design the sump and what is the main difference

betweenthe pumpingof a water supplyschemeandthe pumpingin a wastewaterscheme.