03 water supply system

8/10/2019 03 Water Supply System

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Water supply system

Source

Drawing of waterfrom the source,known as intake

Leading water fromintakes to

purification plantsPurification plant

Storage reservoir

leading the treatedwater to consumersthrough distribution

pipes


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Pumps

Mechanical device or arrangement by whichthe water is caused to flow at increasedpressure

Purposes Increase pressure Raw water from source to treatment plant Clear water to elevated storage reservoir Throw water directly to distribution system


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Types of pumps

Air lift pump for pumping water from deep wells For lifts about 60m

Centrifugal pumps - Used in water supplyschemes

Displacement pumps Reciprocating pump and Rotary pump

Hydraulic ram lift of about 30m

Jet pump

deep wells of about 50 ltrs/second


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Conveyance of water Through gravity conduits or pressure conduits Gravity conduits

Open channels

Considerable loss of water due to evaporation,percolation, etc. Chance for contamination

Pressure conduits Form of pipes Size of pipe (A) is determined by considering two

factors Discharge through pipe (Q) Permissible velocity of flow in pipe (V)


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Pipes

Pipe material is selected depending on forcesto be resisted, type of water, durability etc

Usual stresses Change of direction Internal water pressure Soil above pipes Water hammer Yielding of soil below pipes Temperature stresses


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Types of pipes

Asbestos cement pipes Cast-iron pipes

Cement concrete pipes Copper pipes Galvanized iron (GI) pipes Lead pipes Plastic pipes Steel pipes


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Asbestos cement pipes

Advantages Inside surface is very smooth Joints are easy Anti-corrosive and cheap Light weight and easy to handle Suitable for small size


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Asbestos cement pipes

Disadvantages Brittle Cannot stand impact forces Cannot resist traffic vibrations under roads Not durable Cannot be laid in exposed places Can only be used for very low pressures


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Cast-iron pipes

Extensively used Available in diameter about 1200mm or more

Inner and outer surfaces are given anti-corrosion treatment Classified into four categories based ability

to withstand pressure


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Cast-iron pipes

Advantages Moderate cost Easy to join Not subject to corrosion Strong and durable Life time of about 100 years


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Cast-iron pipes

Disadvantages Breakages are common Carrying capacity is seen to decrease with time Not used for pressures greater than 0.7N/mm 2

Heavier and uneconomical at larger diameters


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Cement concrete pipes

May be plain, reinforced or prestressed Diameters 500mm to 2500mm


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Advantages Inside surface can be made smooth Low maintenance cost Durable Can be cast at site Can be used under water, not affected by

buoyancy Does not require expansion joints


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Disadvantages Heavy and difficult to transport Likely to crack during transport and handling Affected by acids, alkalies and salty waters Can cause leakage due to porosity


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Copper pipes

Used in conveyance of hot water in buildingsand steam boilers

Do not sag or bend due to hot water Not liable to corrosion Can be bent easily

Very costly Not used for water distribution


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Galvanized iron pipes

Widely used for service connections Diameters 6mm to 75mm

Cheap, light weight, easy to handle Easy to join Affected by acidic and alkaline water Short life 7 10 years


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Lead pipes

Not adopted for conveying water leadpoisoning

Easily bent less number of fittings required React with acidic water Used for apparatus required for alum or

chlorine dosages Sag and bend due to heat


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Plastic pipes

Various types of plastics available Low density polyethylene pipes are flexible

High density polyethylene pipes are tough Black in colour and resistant to most

chemicals

PVC pipes are three times as rigid as PE Used in water mains


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Plastic pipes

Advantages Cheap Durable, enough strength to resist impact,

sunlight and atmospheric conditions Flexible, lightweight, easy to bend join and handle No corrosion Electric insulators


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Plastic pipes

Disadvantages Co-efficient of expansion is very high Difficult to obtain uniform composition Less resistant to heat May impart taste to water


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Steel pipes

Made from mild steel Diameters greater than 1200mm

Surfaces are generally galvanised


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Intakes

Structure constructed across the surface ofwater so as to permit the withdrawal of waterfrom the source

To be constructed watertight, and be designedfor all forces likely to come upon it

Four types: Canal intakes, reservoir or lakeintakes, river intakes, portable intakes


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Purification plants

Sedimentation tanks Coagulation

Filtration Disinfection Water softening

Miscellaneous processes


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Water softening

Water should not be very hard Affects dyeing systems

Causes corrosion of pipes More consumption of soap Makes food tasteless, tough and rubbery

Scales on boilers and water heaters


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Temporary hardness

Carbonate hardness Due to soluble bicarbonates of calcium and

magnesium Can be removed either by boiling or adding

lime Forms insoluble carbonates which can be

removed in sedimentation tanks


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Lime-soda process

Lime and sodium carbonate are used Hardness brought down to 3-4 degrees

By-products CaCO3 and MgCO 3 are separated by sedimentation Ca(OH)2 and Mg(OH) 2 are insoluble Na

2SO

4 and NaCl doesnt cause hardness


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Zeolite process

Base-exchange or ion-exchange process Compounds of aluminium, silica and soda Excellent property of interchanging base Naturally available zeolite green sand Most common artificial zeolite permutit

Hard water is passed through a bed of zeolite Ca and Mg are replaced by Na Hardness is reduced to 0


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Demineralization process

Deionisation process Similar to zeolite process Hard water passed through a bed of resin Ca and Mg are replaced by H

H2Y + CaCl2 = CaY + 2HCl

Acids can be removed by adding alkalinewater

Mainly used in industries


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DISTRIBUTION SYSTEM


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Methods of distribution

Gravity system Water is conveyed by gravity only Most reliable method Source of water supply is at higher level

Gravity and pumping system combined Treated water is pumped and stored in an

elevated reservoir Pumping system

Water is directly pumped into the mains leadingto the consumers


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Service reservoirs

To store clear, treated water before it isdispatched to the consumers

Serves as storage for emergencies such as

breakdown of pumps, heavy fire demand,interruption in power supply, etc.

Three types:

Surface reservoirs Elevated reservoirs Stand pipes


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Systems of supply of water Continuous system

Water is supplied to consumers for 24 hours a day Most ideal system of supply

Disadvantage - considerable wastage of water Intermittent system

Water is supplied during certain fixed hours of day Usual period is about one to four hours in the

morning and about the same period in the afternoon Main disadvantage - quantity of water available may

not be sufficient to meet with various demands forwater


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Dead-end method

Tree system One supply main Sub-mains are taken

from it Again divide into several

branch lines

Service connections aretaken from branch lines


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Grid iron

Interlaced system orreticulation system

Main, sub-mains and

branches areinterconnected


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Circular method

Ring system Ring of mains is formed around the

distribution area Distribution area is divided into rectangular

blocks Mains are laid on the periphery


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Radial system

Water is taken from themains and pumped intothe distribution

reservoirs which aresituated at centres ofdifferent zones

Water is supplied

through radially laidpipes


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PIPE APPURTENANCES Air valves Bib cocks Fire hydrants

Reflux valves Relief valves Scour valves Sluice valves Stop cocks Water meters


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Air valves

Air relief valves Air locking reduces discharge Provide exit for accumulated air in pipes Located at higher points


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Bib cocks

Water taps attached to end of pipes Operated by turning a handle Push type bib cocks close automatically


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Fire hydrants

Outlet provided for tapping water in case of afire

Generally placed at street junctions Flush hydrant and post hydrant


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Relief valves

Automatic cut-off valves or safety valves Located at points where pressure is likely to

be maximum When pressure exceeds a limit, valve opens

automatically and lets out the water or airuntil the pressure is normalised


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Sluice valves

Gate valves, shut-off valves or stop valves Control the flow of water and divides the

water mains into sections Placed at 150 200m intervals and junctions Opening and closing is done by rotating the

handle


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Scour valves

Blow-off valve, drain valves or washout valve Ordinary sluice valve at dead-ends or lowest

points To remove sand or silt deposited in the pipe Operated by hand and closed as soon as clear

water starts coming out


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Stop cocks

Small sized sluice valves, installed in servicepipes

Operate just like sluice valves Placed on water pipes leading to flush tanks,

wash basins, water tanks etc


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R f


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References:

Hammer, Hammer Jr. (2011). Water and Waste Water Technology. PHI Learning PrivateLimited.

Rangwala, S.C. (1998). Fundamentals of Water Supply and Sanitary Engineering .Charotar Publishing Company, Anand.

Panchdhari, A.C. (1993). Water Supply and Sanitary Installations. Wiley Eastern Limited.

03 water supply system

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