Unit 4

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 undertaken
6. 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 DS
Head :- 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 to
the 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 Storage
It 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 Storage
Sometimes 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 Storage
The 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)T
5 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

• 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 nutating
disc 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.

• 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

• Flow in each pipe must satisfy the head loss
equation (Darcy – weisbach equation )
gD
fLV
hf
2
2

2
4
D
Q
A
Q
V










 42
2
16
2 D
Q
gD
fL
fh


hf = head loss due to friction (m)
f = coefficient of friction
L = 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
fLQ
fh 
2
kQhf 

Hazen- william equation
• He gave head loss as
n=2 for turbulent flow
n vary from 1.
n
f kQh 

• 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
n
f kQh 
n
f QQakh )( 

• Expanding
hf=K.[Qa
n + n.Qa
n-1 ΔQ+ .........negligible terms]
hf=K.[Qa
n + n.Qa
n-1 ΔQ ]
• Now, around a closed loop, the summation of
head losses must be zero.
n
f QQakh )( 

• ΣK.[Qa
n + n.Qa
n-1ΔQ] = 0
• Σ K.Qa
n = - 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.Qa
n = - ΔQ Σ Kn Qa
n-1
1-n
a
n
a
nQK
QK
Q




• Final equation
hf is the head loss for assumed flow Qa
• n= 1.85 for hazen williams formula



Q
h
Q
f
n
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
f
n
hf

Unit 4

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