water distribution system updated on 210612

7/27/2019 Water Distribution System Updated on 210612

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WATER DISTRIBUTION SYSTEM

6/21/2011Lecture - S. Y. B. Arch (ID)


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STAGES OF WATER SUPPLY SYSTEM:


SOURCE

CONVEYANCE

TREATMENT

STORAGE

CONVEYANCE

DISTRIBUTION

DRAINAGE OF WASTE WATER

TREATMENT

SOURCE


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DISTRIBUTION SYSTEM ELEMENTS AND ACCESSORIES

The elements of a water distribution system include distributionmains, arterial mains, storage reservoirs, and system accessories.

1. DISTRIBUTION MAINS. Distribution mains are the pipelines thatmake up the distribution system. Their function is to carry waterfrom the water source or treatment plant to end users

2. ARTERIAL MAINS. Arterial mains are distribution mains of largesize. They are interconnected with smaller distribution mains toform a complete gridiron system.

3. STORAGE RESERVOIRS. Storage reservoirs are structures used tostore water. They also equalize the supply or pressure in thedistribution system.



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System accessories include the following: BOOSTER STATIONS. Booster stations are used to increase water

pressure from storage tanks or low-pressure mains.

VALVES. Valves control the flow of water in the distribution systemby isolating areas for repair or by regulating system flow orpressure.

HYDRANTS. Hydrants are designed to allow water from thedistribution system to be used for fire-fighting purposes.

METERS. Meters record the flow of water in a part of thedistribution system.

SERVICE CONNECTIONS. Service connections are used to

connect individual buildings or other plumbing systems to thedistribution system mains.

BACKFLOW PREVENTERS. A cross- connection is anyconnection between a potable and non-potable water systemthrough which a contaminating flow can occur. Backflowpreventers, such as air gaps and vacuum breakers, are used to

prevent flow through potential cross-connections. 6/21/2011Lecture - S. Y. B. Arch (ID)

4. SYSTEM ACCESSORIES.


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LOCATION OF MAINS

In general, mains should be located in such a way that

they are clear of other structures

should be adjacent and parallel to streets but not within roadways.

Mains also should be separated from other utilities to ensure the

safety of potable water and to lessen interference with other utilities

during maintenance.



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LOCATIONS OF VALVE

The purpose of installing shutoff valves in water mains at variouslocations within the distribution system is to allow sections of thesystem to be taken out of service for repairs or maintenance withoutsignificantly curtailing service over large areas

Valves should be installed at intervals not greater than 5,000 feet inlong supply lines and 1,500 foot in main distribution loops or

feeders. All branch mains connecting to feeder mains or feeder loops should

have valves installed as close to the feeders as practical.

In the areas of greatest water demand or when the dependability ofthe distribution system is particularly important, valve spacing shouldbe of 500 feet.

All buried small- and medium-sized valves should be installed invalve boxes.

For large shutoff valves (about 30 inches in diameter andlarger), it may be necessary to surround the valve operator or entirevalve within a vault or manhole to allow repair or replacement.



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Street intersections are the preferred locations for fire hydrantsbecause fire hoses can be laid along any of the radiating streets.

Hydrants should be located a minimum of 6 feet and a maximum of7 feet from the edge of paved roadway surfaces.

If they are located more than 7 feet from the edge of a road, thenground stabilizing or paving next tothe hydrants may be necessary to accommodate fire-fighting equipment.

Hydrants should not be placed closer than 3 feet to any obstruction

and never in front of entranceways.


LOCATIONS OF FIRE HYDRANTS


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GENERAL DISTRIBUTION OF WATER DISTRIBUTION LINES

The MINIMUM information that you should show on a waterdistribution plan is listed as follows:

1. Locations and lengths of mains

2. Sizes and types of piping materials

3. Locations, sizes, and types of all valves4. Location of fire hydrants; meter pits; outlets on piers; elevated,

ground, or underground water storage reservoirs; water wells; pump

houses; and valve boxes, vaults, and manholes

5. Capacities and heads of all water pumps in pump houses, including

minimum average and maximum residual pressures at points of

connection to municipal water systems

6. Exterior sprinklers or fire mains, including indicator and main

shutoff valves



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LAYOUT OF DISTRIBUTION SYSTEM

Depending upon their layout and direction of supply, distribution

systems are classified as

Dead End or Tree System

Grid Iron system

Circular and Ring System

Radial System



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DEAD END OR TREE SYSTEM

It is suitable for old towns and cities having no definite pattern ofroads.

Advantages:

1. Relatively cheap.

2. Determination of

discharges and

pressure easier due

to less number of

valves.

Disadvantages

Due to many dead ends, stagnation of water occurs in pipes.



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GRID IRON SYSTEM:

It is suitable for cities with rectangular layout, where the watermains and branches are laid in rectangles.

Advantages:

1. Water is kept in good

circulation due to theabsence of dead ends.

2. In the cases of a

breakdown in some

section, water is available

from some other direction.

Disadvantages:

Exact calculation of sizes of pipes is not possible due to provision ofvalves on all branches.



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CIRCULAR OR RING SYSTEM

The supply main is laid all along the peripheral roads and sub mainsbranch out from the mains. Thus, this system also follows the grid

iron system with

the flow pattern similar in

character to that of dead

end system. So,

determination of the size

of pipes is easy.

Advantages:

Water can be supplied to any point from at least two

directions.



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RADIAL SYSTEM

The area is divided into different zones. The water is pumped into the

distribution reservoir

kept in the middle of

each zone and the

supply pipes are laid

radially ending towards

the periphery

Advantages:

1. It gives quick service.

2. Calculation of pipe sizes is easy.



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METHODS OF SUPPLYING SYSTEM:

Water can be supplied to the consumers by the following twomethods.

Continuous System

Intermittent System

Continuous System:

This is the best system.

Water is supplied for all the 24 hrs.

The system is possible when there is adequate quantity of waterfor supply.

Water is always available for fire fighting.

Due to constant circulation water always remains fresh.



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Intermittent System: If plenty of water is not available, the supply of water is divided into

zones and each zone is supplied with water for the fixed hours in aday.

As the water is supplied after intervals, it is called as intermittentsystem

This system can not continue on long term policy due to followingdisadvantages:

Consumer have to store the water for non supply hrs andstored water may get contaminated, or insufficient quantity ofwater stored may lead to insanitary conditions.

In case of fire during non supply hrs, non availability of watermay lead to sewer damage.

Consumers leaves their taps open for every time, whichcauses much wastage of water.

Bigger diameter pipes required to supply water required forwhole day in limited period.



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If more water stored during non-supply period it is thrown off

causing wastage of water. During non-supply period, the pressure in water mains falls

below atmospheric pressure, thus create vacuum, which mayinduce suction of soil particles in through joints.

Large no. of valves are required in maintaining this system,because they are to be properly operated while closing for

maintenance This is system causes great inconvenience to the consumers, as

they have to remain alert to collect the water during supplyperiods, especially from street stand posts or taps, where longqueues is formed for this.

This system dose not save water as requiredAdvantages:

In this system water can be supplied in the high level localitieswith adequate pressure, by dividing cities into zone.

The repair work can be easily done in the non supply hours.



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PRESSURE IN THE DISTRIBUTION SYSTEM:

When water enters in the distribution mains, the water head islost due to friction in pipe, at the entrance of the reducers, dueto valves, bends and meters etc. till it reach to the consumerstap.

The effective head available at the service connection to abuilding is very important , because the height upto which thewater can rise in the building will depend on this available headonly.

In multistory structures the following pressures are consideredsatisfactory.

Upto three storey: 2.1kg/cm2

From 3 to 6 storeys: 2.1 to 4.2 kg/cm2

From 6 to 10 storeys: 4.2 to 5.27 kg/cm2

Above 10 storeys: 5.27 to 7 kg/cm2



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While designing Distribution systems the following points should be

considered The main line should be designed to carry 3 times the average

demand of the city

The service pipes should be able to carry twice the average demand.

The water demand at various points should be noted.

The lengths and sizes of each pipe should be clearly marked on thesite plan along with the hydrants, valves, meters etc.

The pressure drops at the end of each line should be calculated andmarked

Min velocity of pipe should not less than 0.6m/sec and max velocityshould not be more than 3m/sec

Diameter of Pipe Velocity

o 10cm 0.9m/sec

o 15cm 1.20m/sec

o 25cm 1.52m/sec

o 40cm 1.82m/sec



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GENERAL REQUIREMENT OF WATER STORAGE TANKS To store the treated water till it is distributed to the city

To absorb the hourly variations in the water demand and thus

allowing the treatment units and pumps to work at the average

constant rate. This will reduce operation & maintenance cost of

treatment as well as improve their efficiency For meeting the water demands during fires

In case of breakdown of pumps, repair the storage reservoir will

provide water



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STORAGE OF WATER IN BUILDINGSIn the buildings, the storage of water is required for the following purposes

1. For supplying the water to the consumers during non-supply hours

2. For reducing the maximum rate of demand on the water mains

3. For storage of watering during interruption due to damage, repair etc of

the water mains

4. When the available head is insufficient to supply the water in each storey

in multi storey buildings

The storage of water in buildings are constructed of cast Iron, wrought iron,

galvanized mild steel plates or R.C.C. storage tanks. Storage tanks may be kept

on the roof of the building or on the ground and should be water-tight. The tank

should be provided with overflow pipe and drain pipe near the bottom to clean

the tank. The storage tanks are provided with outlet pipes to draw the water.



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ESTIMATING STORAGE CAPACITYThe quantity of water to be stored depends on the following factors.

a) Rate of supply of water from water works

b) Type of building such as residential, public or industrial

c) Whether water supply is continuous or intermittent

d) Frequency of replacement of overhead tanks, during the 24 hours



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Domest ic Storage Capacit ies

Flush ing Storage Capacity

As per IS 2065-1963 the storage capacities are given in the tables below:


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STORAGE RESERVOIRS:

Underground Water Tanks: Storing and distributing clear water.

Constructed in stones, bricks, Plain or Reinforced cement concrete.

Side walls are designed to take the water pressure when reservoir is

full and take earth pressure when the reservoir is free. To obtain water tightness bituminous compounds are used in all

construction joints.

Should provide with RCC roofs.

For aeration in water and going inside for inspection, pipes andstairs are provided respectively.



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Overhead Tanks:

When water is to be distributed at very highpressure.

RCC elevated water tanks are very popular,because of

long life.

Requires less maintenance

Decent Appearance

Pre-stressed water tanks are economical.

All tanks are provided with

inlet, outlet, drain pipe,

overflow pipe, water level

indicator, manhole, ladder,

lightening conductor.

About 60 to 100cm wide balcony is providedaround the tank for inspection andmaintenance of the tank.



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ACCESSORIES OF RESERVOIRS:

Following are the various accessories which are commonlyprovided in the reservoirs

Inlet pipe - for the entry of water

Outlet pipe - for the withdrawal of water

Overflow pipe to prevent wastage of water the overflowpipe will be connected to drain.

Float switch - to stop the pump when the tank is full

Float gauge - to show the depth of water in the tank

Wash out pipe - for washing out the suspended impurities

in the tank Manhole for providing entry in the water tank

Ladder to reach the top and bottom of the tank

Vent pipe with steel mesh to allow fresh air circulationpreventing the entry of birds.



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TYPES OF TANKSa)

R.C.C TANKS: R.C.C tanks are very popular because1) They have long life

2) Very little maintenance

3) decent appearance

b) G.I. TANKS: G.I. tanks are generally rectangular or square in shape. Now a days G.I.

tanks are not preferred because1) Life of the tank is short

2) Corrosion

3) maintenance cost is more

c) HDPE (High-density polyethylene) TANKS: Now a days HDPE tanks are very popular forstoring less quantity of water and hence useful for residential purpose. The following

are the advantages of HDPE tanks

1) Handling is easy because of light weight

2) Cheap in cost

3) Maintenance cost is low

4) Cleaning of tanks are easy 6/21/2011Lecture - S. Y. B. Arch (ID)

water distribution system updated on 210612

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