WDS

REQUIREMENT OF A DISTRIBUTION SYSTEM:1. The should convey the treated water up to consumers

with the same degree of purity 2. The system should be economical and easy to maintain

and operate 3. The diameter of pipes should be designed to meet the

fire demand 4. It should safe against any future pollution. As per as

possible should not be laid below sewer lines. 5. Water should be supplied without interruption even

when repairs are undertaken6. The system should be so designed that the supply should

meet maximum hourly demand. A peak factor 2.5 is recommended for the towns of population 0.5. to 2 lakhs. For larger population a factor of 2.0 will be adequate.

LAYOUTS OF DISTRIBUTION SYSTEM:

Generally in practice there are four different systems of distribution which are used. They are:

1. Dead End or Tree system

2. Grid Iron system

3. Circular or Ring system

4. Radial system

DEAD END OR TREE SYSTEM:

• This system is suitable for irregular developed towns or cities. In this system water flows in one direction only into sub mains and branches. The diameter of pipe decreases at every tree branch

Main

Sub main

Branches

Branches

Cut off valves

Sub main

Branches

Branches

ADVANTAGES

• Discharge and pressure at any point in the distribution system is calculated easily

• The valves required in this system of layout are comparatively less in number.

• The diameter of pipes used are smaller and hence the system is cheap and economical

• The laying of water pipes is used are simple.

DISADVANTAGES

• There is stagnation water at dead ends of pipes causing contamination.

• During repairs of pipes or valves at any point the entire down stream end are deprived of supply

• The water available for fire fighting will be limited in quantity

GRID IRON SYSTEM• From the mains water enters the branches at all

Junctions in either directions into submains of equal diameters. At any point in the line the pressure is balanced from two directions because of interconnected network of pipes.

ADVANTAGES

• In the case of repairs a very small portion of distribution will be affected

• Every point receives supply from two directions and with higher pressure

• Additional water from the other branches are available for fire fighting

• There is free circulation of water and hence it is not liable for pollution due to stagnation.

DISADVANTAGES

• More length of pipes and number of valves are needed and hence there is increased cost of construction

• Calculation of sizes of pipes and working out pressures at various points in the distribution system is laborious , complicated and difficult.

CIRCULAR OR RING SYSTEM

• Supply to the inner pipes is from the mains around the boundary. It has the same advantages as the grid-Iron system. Smaller diameter pipes are needed. The advantages and disadvantages are same as that of grid-Iron system

RADIAL SYSTEM

• This is a zoned system. Water is pumped to the distribution reservoirs and from the reservoirs it flows by gravity to the tree system of pipes.

• The pressure calculations are easy in this system.

• Layout of roads need to be radial to eliminate loss of head in bends.

• This is most economical system also if combined pumping and gravity flow is adopted.

Methods of supplying water

• Continuous system

– This is best system and the water is supplied all the 24 hours

– This system is possible when there is adequate quantity of water for supply

– In this system water is available for fire fighting

– Due to continuous circulation of water always remains fresh

• Intermittent system

– This system is suitable when plenty of water is not available

– Supply is divided into zones and only on fixed hours in day

– This system should not be for long term because– No water for fire demand

– Contamination will be there because of storage

– Larger number of pipes and values are required

Pressure in DSHead :- head can be measured by the height to which water rises

in a column when directly open to the water

Head loss :- water head lost due to friction in pipes , at entrance of reducer ,

Due to valves bends , meters etc . Till consumer tap .

The static head of a pump is the maximum height (pressure) it can deliver

Velocity head is due to the bulk motion of a fluid (kinetic energy).

Elevation head is due to the fluid's weight, the gravitational force acting on a column of fluid.

Pressure head is due to the static pressure, the internal molecular motion of a fluid that exerts a force on its container.

Resistance head (or friction head or Head Loss) is due tothe frictional forces acting against a fluid's motion by the container.

Pressure in multistorage

• Upto 3 storeys :- 2.1kg/cm2

• Upto 3 to 6 storeys :- 2.1 to 4.2kg/cm2

• Upto 6 to 10 storeys :-4.2 to 5.72kg/cm2

• Above 10 storeys :- 5.27 to 7 kg/cm2

Designing • While designing

– The main line should carry 3 times the average demand

– Service pipe should carry twice the average demand

– The water at various points in city should be noted

– Length and size of pipe should be clearly marked along with hydrants , values and meters

– The pressure drops should be calculated

– Velocity should not be less than 0.6m/sec and max 3m/sec

Distribution Reservoir:

• A reservoir connected with distribution system a water supply project, used primarily to care for fluctuations in demand which occur over short periods and as local storage in case of emergency such as a break in a main supply line failure of a pumping plant.

• Classified as elevated or surface reservoir

Functions of Distribution Reservoirs: to absorb the hourly variations in demand.to maintain constant pressure in the distribution mains.water stored can be supplied during emergencies.Location and Height of Distribution Reservoirs:should be located as close as possible to the center of demand.water level in the reservoir must be at a sufficient elevation to permit gravity flow at an adequate pressure.

Storage Capacity of Distribution Reservoirs• The total storage capacity of a distribution

reservoir is the summation of:Balancing StorageIt is the quantity of water required for balancing the variations in the demand against the constant supply from treatment plant It is calculated by means of Mass curve or hydrograph of inflow and outflow , or by analytical methods using standard tables

Breakdown StorageSometimes there is breakdown in the pumps or power driving them. Therefore some quantity of water is required to be kept as reserve or breakdown time

Fire StorageThe quantity of water required to be kept as reserve for fire-fighting can be obtained by deducting the reserve fire pumping capacity “C” from the fire demand “F” and then multiplying it by the probable duration of fire time “T”

• 20Fire reserve =(F-C)T5 litres/capita

Reservoirs

• Earth reservoirs

• Masonry and R.C. reservoirs

• Elevated reservoirs

• Elevated reservoirs

– Stand pipes

– Elevated Tanks

VALVES

• Valves stop or open and regulate flow. Some of the basic valve types are gate, globe, check, Ball, Plug, etc.

• GATE VALVE: It is usually manually operated and is designed for open or shut operation. Flow can enter either end of the gate body.

• GLOBE VALVE: is for throttling. Good examples of globe valves are the faucets on washbasin which throttle or adjust the flow to suit a person’s needs. Flow must enter the valve and flow up, against the seat, and change the direction again to the outlet.

• CHECK VALVE: “checks” flow. It lets flow go one way and will not let it reverse. When you have a check valve in a line, you have made a one-way street. The flow can go one way.

When some fluid is flowing in a pipe we

may also like know the parameters like,

pressure, temperature, flow rate etc. of

the fluid.

Here are some of the pipe supporting

arrangements. There can be numerous variants.

All depend on piping designer’s preference and

judgement.

Valves

1. Gate Valves

– used to minimize pressure drop in the open position and to

stop flow rather than to regulate it.

Valves

2. Globe Valves - offer ease in throttling

Relief Valve

• A relief valve is an automatic pressure-relieving device actuated by the static pressure upstream of the valve, and which opens further with increase in pressure over the set pressure

• Used primarily for liquid services

• Rated capacity is usually attained at 25 percent over pressure

Relief Valve

Valves and fittings

• What are Valves?

Valves are mechanical devices that controls the flow and pressure within a system or process. They are essential components of a piping system that conveys liquids, gases, vapors, slurries etc..

Different types of valves are available: gate, globe, plug, ball, butterfly, check, diaphragm, pinch, pressure relief, control valves etc.

• Functions from Valves are:

– Stopping and starting flow

– Reduce or increase a flow

– Controlling the direction of flow

– Regulating a flow or process pressure

– Relieve a pipe system of a certain pressure

sluice valve

• A gate valve, also known as a sluice valve

• Most commonly used , valves are cheaper , offer less resistance to flow of water than other valves

• Gate values control the flow of water through pipes , and are fixed in main lines bring water from source to a town

• 3 to 5 kilometers intervals

• Gate valves are typically constructed from cast iron, ductile iron, cast carbon steel, gun metal, stainless steel, alloy steels, and forged steels.

• During repairs only one section can be cut off by closing the sluice valves at both ends

• It mainly consist of a wedge shaped circular disc fitted closely in a recess against the opening in the valve

• This connects to net and wheel above by means of thread spindle passing through a gland and suffixing box arrangement

• When wheel is rotated the spindle rises up , rising the disc along with it . Thus opening the valve

pressure relief valve

• The pressure relief valve (PRV) is a type of valve used to control or limit the pressure in a system or vessel which can build up for a process upset, instrument or equipment failure, or fire.

• It essentially consists of a disc controlling by a spring which adjusted for any pressure

• When pressure in the pipe line exceeds the desire pressure , the disc is forced off from its seat and excessive pressure is relieved

check valve

• A check valve, reflux valve, non-return valve or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction and prevent it from flowing in reverse direction

• Check valves are designed to prevent the reversal of flow in a piping system. These valves are activated by the flowing material in the pipeline. The pressure of the fluid passing through the system opens the valve, while any reversal of flow will close the valve. Closure is accomplished by the weight of the check mechanism, by back pressure, by a spring, or by a combination of these means. The general types of check valves are swing, tilting-disk, piston, butterfly, and stop

Air Relief Valves

• When water enters in pipe lines , it also caries some air with it which tends to accumulate at high points of the pipe

• When the quantity of air increases it causes serious blockage to the flow of water

• Therefore it is most essential to remove the accumulated air from the pipe line

• Air – relief valves are used for this purpose

Air Release Valves, or Air Relief Valve

• function to release air pockets that collect at each high point of a full pressured pipeline.

• An air release valve can open against internal pressure, because the internal lever mechanism multiplies the float force to be greater than the internal pressure.

• This greater force opens the orifice whenever air pockets collect in the valve.

• Air Release Valves are essential for pipeline efficiency and water hammer protection.

• The valve consist of a cast iron chamber bolted on the pipe over the opening in the crown

• A weighted float and a lever in it are so adjusted that when the chamber is fitted with water pressure from the pipe line below, the float and liver remains released up preventing the flow of water through the valve.

• But when air goes on accumulating at the top , the float sinks down with the lever and opens the value

Drain valves

• In summits of main , it is possible that some suspended impurities may settle down and causes obstruction to flow of water

• In distribution system at dead ends , if water is not taken out it will stagnate and bacteria will be born in it

• To avoid all this difficulties drain- valves are provided

• Also called as scour valves or blow-off valves

Hydrants

• A fire hydrant is a connection point by which firefighters can tap into a water supply. It is a component of active fire protection.

• They also some times used for washing roads , drains , sewers etc..

Meters

• Water metering is the process of measuring water use.

• There are several types of water meters in common use. The choice depends on the flow measurement method, the type of end user, the required flow rates, and accuracy requirements.

• Water meters are important to a utility for several reasons:

1. They make it possible to charge customers in proportion to the amount of water they use.

2. They allow the system to demonstrate accountability.

3. They are fair for all customers because they record specific usage.

4. They encourage customers to conserve water (especially as compared to flat rates).

5. They allow a utility system to monitor the volume of finished water it puts out. 6. They aid in the detection of leaks and waterline breaks in the distribution system.

• Meters are classified into two basic types: positive displacement type and velocity of inferential type .

• Each of these meter types has variations, leading to the perception that there are several different kinds.

• Meters that feature both positive displacement and velocity are known as compound meters.

• The unit of measurement is usually in gallons but sometimes in cubic feet

Positive or displacement meter

• Displacement meters are primarily used for relatively low flows as for residential buildings

• In this meters , the quantity of water actually passing through it is measured by filling and emptying the chamber of known capacity

• Types of displacement meters in use include reciprocating , rotary , oscillating and nutatingdisc meters , depending upon moving parts

Velocity meters/ Inferential meters

• Inferential meters measures the velocity of flow across or cross-section whose area is known

• They are used only for high flows

• Common example == rotary and the turbine meters

Pipelines

Pipes, transmitting water from the

intakes to the service (distributing) reservoirs

Pipelines Kinds

I. According to the pressure

• Pressurised (gravity, pumping)

• Non-pressurised

• Slightly pressurised

• Combined

According to the branches

• Single

• Branch

Pipeline Appurtenances

(Auxiliaries)

Valves• Stop (gate) valve

• Air valve

• Check valve

Chambers (Shafts)• Water relieve chamber

• Air release/intake shaft

• Blow off shaft

Other facilities• Invert siphons

• Aqueducts (conduits)

• Tunnels

Pipeline materials

• Concrete pipes

• Reinforced concrete pipes

• Steel pipes

• Cast iron pipes

• Asbestos-cement pipes

• Plastic pipes

Pipeline Foundation

• Strait pipeline - bed and supports

• Horizontal and vertical turns - supports

• Duff-end and branching supports

Pipelines Construction

Pipeline Lay Out Requirements• Water intakes and service reservoirs to be connected

in the shortest way• The pipeline permanent way must be laid out on

uniform and not very steep terrain• The pipeline permanent way must be laid out in

parallel with or close to roads• Crossing rivers, rail ways and roads must be avoid if

possible• Weak soils should be avoid• Minimum ecological deterioration

Pipeline Construction

• Pipeline trench digging

• Pipes foundation

• Pipes laying down

• Pipeline trench filling up

Pipes laying down

Before lowering of pipeline in the trench,

• To clear the trench of all debris, stones, pipe cut pieces, welding rods, hard clods, skids etc. before lowering of pipeline.

• To drain out water from the trench (if any) to avoid floatation.

• To carry out complete check by full circle holiday detector.

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Analysis of pipe network

• In any water distribution system , the pipe line conveying water generally branch out or form a loops of complex manner

• This complex layout of pipe is called as pipe network

• Determination of flow by simply observation is not possible

• The uncertainty about the flow direction makes the problem of flow more complicated

• The hydraulic analysis of a pipe network can be achieved by following conditions

Basis of hydraulic analysis

• law of continuity must be satisfied.

– The flow entering a junction must be equal to the flow leaving that junction

Q1 = Q2 + Q3

Q1 Q3

Q2

Basis of hydraulic analysis

• Flow in each pipe must satisfy the head loss equation (Darcy – weisbach equation )

gD

fLVhf

2

2

2

4

D

Q

A

QV

42

216

2 D

Q

gD

fLfh

hf = head loss due to friction (m)

f = coefficient of frictionL = length of the pipe (m)V = average velocity of flow (m/s)D = internal diameter of pipe (m)g = acceleration due to gravity = 9.81 m/s2

5

2

1.12 D

fLQfh

2kQhf

Hazen- william equation

• He gave head loss as

n=2 for turbulent flow

n vary from 1.

nf kQh

Basis of hydraulic analysis

• The algebraic sum of pressure drops around a closed loop must be zero, i.e. there can be no discontinuity in pressure.

• In a close loop , the head loss due to flow in clockwise direction must be equal to head loss due to flow in anti clock wise direction

Method of solving a pipe network problem

• This complicated problem of pipe network is generally solved by trail and error method

• Different methods have been developed

• Hardy cross in 1934 developed a method of successive approximation

• This method is quite convenient and widely used

Hardy cross method

Steps involved in Hardy cross method

• principle of continuity is satisfied at each junction.

• In this method hazen william method is used to determine head loss

• Clockwise flow and associated head losses are assigned positive sign where as anit-clockwise are negitive

• The algebraic sum of pressure drops around a closed loop must be zero, I.e = Σhf = 0

• In order to achieve Σhf = 0 , the flow is adjusted by a correction ΔQ

Hardy-Cross Method

• If Qa is the assumed flow

• Q is the actual flow in the pipe, then the correction

• correction ΔQ = Q - Qa

Q= Qa + Δ Q

Now head loss

Hazen william equation

nf kQh

nf QQakh )(

• Expanding

hf=K.[Qan + n.Qa

n-1 ΔQ+ .........negligible terms]

hf=K.[Qan + n.Qa

n-1 ΔQ ]

• Now, around a closed loop, the summation of head losses must be zero.

nf QQakh )(

• ΣK.[Qan + n.Qa

n-1ΔQ] = 0

• Σ K.Qan = - Σ Kn Qa

n-1 ΔQ

Since, ΔQ is the same for all the pipes of the considered loop, it can be taken out of the summation.

• Σ K.Qan = - ΔQ Σ Kn Qa

n-1

1-na

na

nQK

QK Q

• Final equation

hf is the head loss for assumed flow Qa

• n= 1.85 for hazen williams formula

Q

h Q

fn

hf

Consider the pipe network shown below. The friction factor = 0.2. Determine the flow rate in

each pipe.

• Consider loop 1 and calculate ΔQ according to

• n = 2. Consider anticlockwise flows positive

Q

h Q

fn

hf