3. Component of Water Supply System
3
(1). Source (2).Treatment plant
(2). StorageTanks/Reservoirs (3).WaterTransmission/distribution
4. Design of Water Distribution System
A municipal water distribution system is used to deliver water to the
consumer.
Water is withdrawn from along the pipes in a pipe network system
(for computational purposes all demands on the system are assumed
to occur at the junction nodes)
Pressure is the main concern in a water distribution system.
At no time should the water pressure in the system be so low that
contamination (e.g. contaminated groundwater) could enter the system
at points of leakage
The total water demand at each node/Junction is estimated from
residential, industrial and commercial water demands at that node. The
fire flow is added to account for emergency water demand
5. Water Demand Forecasting/Estimation
In the planning of municipal water-supply projects, the water demand at
the end of the design life of the project is usually the basis for design.
For existing water-supply systems, the American Water Works
Association (AWWA, 1992) recommends that every 5 or 10 years, as a
minimum, water-distribution systems be thoroughly reevaluated for
requirements that would be placed on it by development and
reconstruction over a 20-year period into the future.
The estimation of the design flowrates for components of the water-
supply system typically requires forecast of the population of the service
area at the end of the design life, which is then multiplied by the per
capita water demand to yield the design flowrate.
Whereas the per capita water demand can usually be assumed to be fairly
constant, the estimation of the future population typically involves a
nonlinear extrapolation of past population trends.
6. Domestic Population Forecasting
6
Design of water supply and sanitation scheme is based on the
projected population of a particular city, estimated for the design
period.
Any underestimated value will make system inadequate for the
purpose intended; similarly overestimated value will make it costly.
Change in the population of the city over the years occurs, and the
system should be designed taking into account of the population at
the end of the design period.
The present and past population record for the city can be obtained
from the census population records. After collecting these
population figures, the population at the end of design period is
predicted using various methods as suitable for that city considering
the growth pattern followed by the city.
7. Domestic Population Forecasting
7
Methods of population forecasting
Arithmetic increase method
Geometrical increase method
Incremental increase method
Graphical method
Comparative graphical method
Master plan method
Logistic curve method
Ratio method etc
8. Domestic Population Forecasting
Arithmetic increase method
8
This method is suitable for large and old city with considerable development.
In this method the average increase in population per decade is calculated
from the past census reports.This increase is added to the present
population to find out the population of the next decade. Thus, it is assumed
that the population is increasing at constant rate.
Hence, dP/dt = C i.e. rate of change of population with respect to time is
constant.
Therefore, Population after nth decade will be
Pn= P + n.C
Where, Pn is the population after n decades and P is present population.
9. Domestic Population Forecasting
Geometric Increase Method
9
In this method the percentage increase in population from decade to
decade is assumed to remain constant. Geometric mean increase is used to
find out the future increment in population.
Since this method gives higher values and hence should be applied for a
new industrial town at the beginning of development for only few decades.
The population at the end of nth decade ‘Pn’ can be estimated as:
Pn = P (1+ IG/100) n
Where, IG = geometric mean (%)
P = Present population
n = no. of decades.
10. Domestic Population Forecasting
Incremental Increase Method
10
This method is modification of arithmetical increase method and it is
suitable for an average size town under normal condition where the
growth rate is found to be in increasing order.
The incremental increase is determined for each decade from the past
population and the average value is added to the present population along
with the average rate of increase.
Hence, population after nth decade is
Pn = P+ n.X + {n (n+1)/2}.Y
Where,
Pn = Population after nth decade
X = Average increase
Y = Incremental increase
11. Domestic Population Forecasting
Graphical Method
11
In this method, the populations
of last few decades are correctly
plotted to a suitable scale on
graph.
The population curve is
smoothly extended for getting
future population.
This extension should be done carefully and it requires proper
experience and judgment.
The best way of applying this method is to extend the curve by
comparing with population curve of some other similar cities
having the similar growth condition.
extrapolate
12. Example: Population forecasting
12
Predict the population for the year 2021, 2031, and 2041 from the following
population data using
Arithmetic increase method
Geometrical increase method
Incremental Increase method
Graphical method
13. Example: Population forecasting
13
year Population increment
1961 858545 -
1971 1015672 (1015672-858545)=157127
1981 1201553 185881
1991 1691538 489985
2001 2077820 386282
2011 2585862 508042
Arithmetic increase method
Avg. increment per decade, C, =345463
Population in year 2021 =P2021=2585862+345463 x 1= 2931325
Population in year 2031 =P2031=2585862+345463 x 2= 3276788
Population in year 2041 =P2041=2585862+345463 x 3= 3622251
14. Example: Population forecasting
14
year Population increment Geometric increase (rate of
growth)
1961 858545 -
1971 1015672 157127 (157127/858545)=0.18
1981 1201553 185881 (185881/1015672)=0.18
1991 1691538 489985 (489985/1201553)=0.40
2001 2077820 386282 (386285/1691538)=0.23
2011 2585862 508042 (508042/2077820)=0.24
Geometric increase method
Avg. Geometric mean per decade, IG, =(0.18x0.18x0.4x0.23x0.24)1/5
Avg. Geometric mean per decade, IG, =0.235
Population in year 2021 =P2021=2585862(1+0.235)1= 3193540
Population in year 2031 =P2031=2585862(1+0.235)2= 3944021
Population in year 2041 =P2041=2585862(1+0.235)3= 4870866
15. Example: Population forecasting
15
year Population Increment
(X)
Increment (Y)
1961 858545 - -
1971 1015672 157127 -
1981 1201553 185881 (185881-157127)=28754
1991 1691538 489985 304104
2001 2077820 386282 -103703
2011 2585862 508042 121760
Total 1727317 350915
Avg. 345463 87729
Increment increase method
Population in year 2021 =P2021=2585862+(345463 x 1)+(1(1+1)/2)x 87729=3019054
Population in year 2031 =P2031=2585862+(345463 x 2)+(2(2+1)/2)x 87729=3539975
Population in year 2041 =P2041=2585862+(345463 x 3)+(3(3+1)/2)x 87729=4148625
17. Domestic Population Forecasting
Comparative Graphical Method
17
In this method the census populations of cities already developed
under similar conditions are plotted.
The curve of past population of the city under consideration is
plotted on the same graph.
The curve is extended carefully by comparing with the population
curve of some similar cities having the similar condition of growth.
The advantage of this method is that the future population can be
predicted from the present population even in the absent of some
of the past census report.
18. Domestic Population Forecasting
Comparative Graphical Method
18
Example: Let the population of a new city X be given for decades 1970,
1980, 1990 and 2000 were 32,000; 38,000; 43,000 and 50,000, respectively.
The cities A, B, C and D were developed in similar conditions as that of city
X. It is required to estimate the population of the city X in the years 2010
and 2020.
The population of cities A, B, C and D of different decades were given
below:
(i) City A was 50,000; 62,000; 72,000 and 87,000 in 1960, 1972, 1980 and
1990, respectively.
(ii) City B was 50,000; 58,000; 69,000 and 76,000 in 1962, 1970, 1981 and
1988, respectively.
(iii) City C was 50,000; 56,500; 64,000 and 70,000 in 1964, 1970, 1980
and 1988, respectively.
(iv) City D was 50,000; 54,000; 58,000 and 62,000 in 1961, 1973, 1982
and 1989, respectively.
19. Domestic Population Forecasting
Comparative Graphical Method
19
Population curves for the cities A, B, C, D and X were plotted.Then an
average mean curve is also plotted by dotted line as shown in the figure.
The population curve X is extended beyond 50,000 matching with the
dotted mean curve. From the curve the populations obtained for city X are
58,000 and 68,000 in year 2010 and 2020.
Figure: Comparative graphical method
20. Domestic Population Forecasting
Master Plan Method
20
The big and metropolitan cities are generally not developed in
haphazard manner, but are planned and regulated by local bodies
according to master plan.
The master plan is prepared for next 25 to 30 years for the city.
According to the master plan the city is divided into various zones
such as residence, commerce and industry.
The population densities are fixed for various zones in the master
plan.
From this population density total water demand and wastewater
generation for that zone can be worked out. So by this method it is
very easy to access precisely the design population.
21. Domestic Population Forecasting
Ratio Method
21
In this method, the local population and the country's population for
the last four to five decades is obtained from the census records.
The ratios of the local population to national population are then
worked out for these decades.
A graph is then plotted between time and these ratios, and
extended up to the design period to extrapolate the ratio
corresponding to future design year.
This ratio is then multiplied by the expected national population at
the end of the design period, so as to obtain the required city's
future population.
Drawbacks:
Depends on accuracy of national population estimate.
Does not consider the abnormal or special conditions which can
lead to population shifts from one city to another.
22. Domestic Population Forecasting
Logistic Curve Method
22
This method is used when the growth rate of population due to
births, deaths and migrations takes place under normal situation and
it is not subjected to any extraordinary changes like epidemic, war,
earth quake or any natural disaster etc.
The population follows the growth curve characteristics of living
things within limited space and economic opportunity.
If the population of a city is plotted with respect to time, the curve
so obtained under normal condition will look like S-shaped curve
and is known as logistic curve.
24. Domestic Population Forecasting
Logistic Curve Method
24
McLean further suggested that if only three pairs of characteristic
values P0, P1, P2 at times t0 = 0, t1 and t2 = 2t1 extending over the
past record are chosen, the saturation population Ps and constant m
and n can be estimated by the following equation, as follows
25. Domestic Population Forecasting
Logistic Curve Method
25
Example: The population of a city in three consecutive decades i.e. 1991,
2001 and 2011 is 80,000; 250,000 and 480,000, respectively.
Determine (a)The saturation population, (b)The equation of logistic curve,
(c)The expected population in 2021.
27. Home Exercise
27
1. Explain different methods of population forecasting.
2.The population data for a town is given below. Find out the
population in the year 2021, 2031 and 2041 by (a) arithmetical (b)
geometric (c) incremental increase methods.
Year 1971: 1981: 1991: 2001: 2011
Population 84,000: 115,000: 160,000: 205,000: 250,000
3. In three consecutive decades the population of a town is 40,000;
100,000 and130,000.
Determine: (a) Saturation population; (b). Expected population in
next decade.
28. To properly design a water supply system, the engineer must evaluate the
amount of water that is required, known as the “water demand”.
Water demand is the volume of water required by users to satisfy their needs.
Types/Categories of water demand/uses
Domestic water demand
Public water use
Commercial water use
Industrial water use
Fire demand
Irrigation water demand
Losses and wastes
Water Demand Forecasting:
28
29. Typical Water Demands
There are usually several categories of water demand, that can be broadly grouped
into following categories
Domestic water demand also called Residential water use:
Domestic water demand represent the typical water use in houses and
apartments including use for drinking, sanitary, washing, bathing, and other
purposes such as private gardening.
Public water use:
It includes facilities such as government buildings, governmental schools, city
halls, and hospitals, etc. It also include many other use for public services such
as sprinkling, street flushing, public parks and gardening, etc. Such services
may consume water at about 10 to 15 gallons per capita
Commercial water use:
It is associated with retail businesses, offices, hotels, and restaurants.
(1 US gallon = 3.785 liter).
29
30. Typical Water Demands
Industrial water use: It is associated with manufacturing and processing
operations. Large industrial requirements are typically satisfied by sources
other than the public water supply.
Fire demand: Besides the fluctuations in demand that occur under normal
operating conditions, water-distribution systems are usually designed to
accommodate the large (short-term) water demands associated with fighting
fires. Numerous methods have been proposed for estimating fire flows
(AWWA, 1992), the most popular of which was proposed by the Insurance
Services Office, Inc. (ISO, 1980).
Irrigation water demand: It is associated with crop consumption and
irrigation processes. Irrigation water demand is typically supplied from surface
or ground water through a separate irrigation network system.
Losses and wastes: It is the amount of water lost from the water system
due to water leakage from the supply pipe network. In some countries
especially where water systems are old the losses can be as high as 40%.
30
33. FACTORS AFFECTING WATER CONSUMPTION
Climate conditions: Warm dry regions have higher consumption rates than
cooler regions. In addition, water usage is affected by the precipitation levels
in the region.
Size of the city. In small cities, it was found that the per capita per day water
consumption was small due to the fact that there are only limited uses of
water in those cities. Small cities have larger area that is inadequately served
by both water and sewer systems than larger cities.
Characteristics of the population. Domestic use of water was found to
vary widely. This is largely dependent upon the economic status of the
consumers, which will differ greatly in various sections of a city. In high-
value residential areas of a city the water consumption per capita will be high
and vice versa
33
34. Metering. Communities that are metered usually show a lower and more
stable water use pattern.
Water quality. Consumer perception of bad water quality can decrease the
water usage rate.
Cost of water. A tendency toward water conservation occur when cost of
water is high.
Water pressure. Rates of water usage increase with increases in water
pressure.
Water conservation. Public awareness and implementation of water
conservation programs by utilities tend to have an impact on the water usage
rate.
FACTORS AFFECTING WATER CONSUMPTION
34
35. Variations in Water Demand
35
Seasonal variation
Daily variation
Hourly variations
36. Water Demands: Terminologies
36
Average Annual Demand (AAD) - The total volume of water delivered to the system
in a full year expressed in litres. When demand fluctuates up and down over several years,
an average is used.
Average Daily Demand (ADD) - The total volume of water delivered to the system
over a year divided by365 days.The average use in a single day expressed in Litres per day.
Maximum Month Demand (MMD) - The litres per day average during the month with
the highest water demand.The highest monthly usage typically occurs during a summer
month.
PeakWeekly Demand (PWD) - The greatest 7-day average demand that occurs in a
year expressed in litres per day.
Maximum Day Demand (MDD) - The largest volume of water delivered to the system
in a single day expressed in litres per day.The water supply, treatment plant and
transmission lines should be designed to handle the maximum day demand.
Peak Hourly Demand (PHD) - The maximum volume of water delivered to the system
in a single hour expressed in litres per day. Distribution systems should be designed to
adequately handle the peak hourly demand or maximum day demand plus fire flows,
whichever is greater. During peak hourly flows, storage reservoirs supply the demand in
excess of the maximum day demand
37. Peak Water Use Estimation: Estimation of
Average Daily Rate Based on a Maximum Time Period
37
Goodrich Formula:
Estimates maximum demand (expressed as daily water demand based on
time period for which maximum water demand is desired) for community
when given annual average per capita daily water use rate:
where p = percentage of average annual rate (volume/day) used in period
of time of interest
t = length of period for which peak demand is required (days) (valid time
periods – 2/24 hours to 360 days)
**Daily rate based upon a maximum hour is approximately equal to 150
percent of average annual daily rate.
38. Peak Water Use Estimation
38
Consumption rate for max day = 180% of the annual average daily consumption
Consumption rate for max week = 148% of the annual average daily consumption
Consumption rate for max month = 128% of the annual average daily consumption
Consumption rate for max hour = 270% of the annual average daily consumption
or150% of the max day
39. Example
39
Estimate average and maximum daily demand/flow for a community
with a population of 22000 having an average consumption of
600litre/capita/day
40. Fire Demand
40
Fire flow is defined as the rate of water flow needed to control a fire
(AWWA, 2008).
Adequate fire flow is critical for the effective extinguishing of a fire.
If the fire flow is over calculated, there could be a negative impact on the
water distribution systems. If the fire flow is under calculated, a fire may
result in the loss of the building of lives.
41. Fire Demand: Some of the Methods
41
Building Planning Methods
1) ISO Method (US)
2) IFC/NFPA 1 Method (US)
3) NFPA 1142 Method (US)
4) IWUIC Method (US)
5) Ontario Building Code Method
(Canada)
6) FIERAsystem Method (Canada)
7) TP 2004/1 andTP 2005/2 Methods
(NZ)
Etc etc
On Scene Methods
12) ISU Method (US)
13) Särdqvist ,Thomas, and
Baldwin Methods (UK, UK, and
US, respectively)
14) IIT Method (US)
15) NFA Method (US)
16) 3D Firefighting Method
(UK/US/Australia)
For details: Matthew E. Benfer and Joseph L. Scheffey 2014, Evaluation of Fire
Flow Methodologies, Prepared for The Fire Protection Research Foundation,
WEB: www.nfpa.org/Foundation
43. Fire Demand
43
Maximum and MinimumValue of C:
The value of C shall not exceed
8,000 gpm (32000L/min) for Construction Class 1 and 2
6,000 gpm (24000L/min) for Construction Class 3, 4, 5, and 6
6,000 gpm (24000L/min) for a 1-story building of any class of
construction
The value of C shall not be less than 500 gpm (2000L/min).
ISO rounds the calculated value of C to the nearest 250 gpm (1000L/min).
1gallon=3.79liter~4Liters
44. Fire Demand
44
Needed Fire Flow (NFF)
For 1- and 2-family dwellings not exceeding 2 stories in height, ISO
prescribes the following needed fire flows based on the distance between
buildings:
500 gpm (2000L/min) where the distance is more than 100 feet
750 gpm (3000L/min) where the distance is between 31 and 100 feet
1,000 gpm (4000L/min) where the distance is between 11 and 30 feet
1,500 gpm (6000L/min) where the distance is 10 feet or less.
ISO rounds the final calculation of NFF to the nearest 250 gpm
(1000L/min) if less than 2,500 gpm (10000L/min) and to the nearest 500
gpm (2000L/min) if greater than 2,500 gpm (10000L/min).
1gallon=3.79liter~4Liters
48. Fire Demand
48
Example-2: Estimate the flowrate and volume required to provide adequate
protection to 20 story non-combustible building. Let each floor has an area
of 1000m2.
The construction factor is calculated as F=0.8 for class 3 non-combustible
construction.
Floor area of building=Ai=1000+0.5(1000)x19=10500m2
Ci=220(0.8)(10500)0.5=16395L/min
The occupancy factor is 0.75 (C-1 non-combustible) and the (X+P)
is estimated using the median value of 1.4. Therefore the required
fire flow is
NFFi=Ci Oi (X+P) i=16395(0.75)(1.4)=17214=18000L/min
If the flow must be maintained for a duration of 4 hours, the total required
volume will be
=18000(4x60)= 4320000L=4320m3
49. Fire Demand: Fire Hydrants
49
A fire hydrant is an active fire
protection measure, and a source of water
provided in most urban, suburban and rural
areas with municipal water service to
enable firefighters to tap into the municipal
water supply to assist in extinguishing a fire.
Fire hydrant in
Charlottesville,Virginia,
USA
50. Fire Demand: Fire Hydrants Spacing and
Discharge
50
Guidelines are not uniformly defined and varies wide according to
municipality. Typical information on spacing and discharge are given below;
Capacity of a fire hydrant is 30 m3/h (500L/min) to 60 m3/h (1000L/min)
and should be within 40m (130ft) to 50m(165ft) from every object. This
results in fire hydrants every 80m (262ft) to 100m (328ft) in a distribution
network.
Looking at single- family houses with an average width of 4 (13ft) to 5
(16ft) meters, this means that for every 20 to 25 houses a fire hydrant is
needed.
Required fire flows, plus domestic demand, must be available within the
water system at a minimum of 20 psi (150kPa) residual pressure.
For details refer to guideline of fire hydrant spacing & fire flow
requirements issued by municipality
51. Design Flows
The required capacities consist of various combinations of
the maximum daily demand,
maximum hourly demand,
and the fire demand.
Typically, the delivery pipelines from the water source to the treatment plant,
as well as the treatment plant itself, are designed with a capacity equal to the
maximum daily demand.
The flow rates and pressures in the distribution system are analyzed under
both maximum daily plus fire demand and the maximum hourly demand, and
the larger flow rate governs the design.
Pumps are sized for a variety of conditions from maximum daily to maximum
hourly demand, depending on their function in the distribution system.
Additional reserve capacity is usually installed in water-supply systems to
allow for redundancy and maintenance requirements.
51
52. Methods of Water Transmission/Distribution
52
(pumping system)
(gravity flow)
(pumping system)
(Gravity flow and pumping system)
53. Methods of Water Distribution
53
Gravity flow and pumping with storage (Pumping with Storage)
Most common
Water supplied at approximately uniform rate
Flow in excess of consumption stored in elevated tanks
Tank water provides flow and pressure when use is high
Fire-fighting
High-use hours
Flow during power failure
54. Water Distribution System Components
54
Pumping Stations
Distribution Storage (reservoirs or tanks)
Distribution System Piping (transmission system)
Other water system components include water source
and water treatment
55. Distribution Reservoirs/Tanks
Reservoirs and elevated tanks in water distribution systems play an
important role to:
provide service storage to meet widely fluctuating demands imposed on
water supply distribution systems.
Accommodate fire-fighting and emergency requirements.
Provide, regulate, and equalize operating pressures.
Type of reservoir depend on service to be provided:
Surface Reservoirs: a ground level storage for large volumes
Standpipes: cylindrical tank whose storage volume includes an upper
portion (useful storage) – usually less than 15m high
ElevatedTanks : used where there is not sufficient head from a surface
reservoir – must be pumped to, but used to allow gravity distribution in
main system.
55
56. Location of water tanks
Fire water reservoirElevated water tank
Jumaira-UAE
Surface water reservoir
Elevated water tanks in
Kuwait
Underground reservoir (8m deep)
Dam reservoir
Water tanks must be designed:
At good enough elevation to develop adequate
pressures in the water system
In large metropolitan area, we might require more
than one
56
57. Elevated tank usage and properties
Influence of the tank location on the hydraulic gradient distribution
Pumping
station
Pumping
station
57
59. Storage Design Criteria
1. Adequate volume to supply peak demands in excess of maximum
daily demand (MDD) using no more than 50% of the available
storage capacity.
2. Adequate volume to supply the critical fire demand in addition to
the volume of MDD fluctuations.
3. Adequate volume to supply possible emergency (MDD for short
duration volume = average daily demand )
4. Where detailed demand data is not available, the storage available
to supply peak demands should equal 20%-25% of the MDD
volume.
59
60. Storage Design Criteria
5. The minimum height of water in elevated water tank is determined by
computing the minimum acceptable piezometric head in the service area
adding the estimated head losses between the tank and the critical service
location under the condition of the daily demand.
6. The maximum height of water in elevated tank is then determined by adding
the minimum piezometric head to the head losses to the critical point under
the condition of maximum hourly demand.
7. The difference between the maximum and minimum water levels is then
specified as the normal operating range.The normal operating range is usually
limited to 4.5 to 6 meters (keep pressure fluctuation between 35 to 70 kPa)
Upper half storage: operating range,
lower half : firefighting and emergency storage
60
61. Example
61
A service reservoir is to be designed for a water supply serving
250,000 people with an average demand of 600 L/day/capita and a
fire flow of 37,000 L/min.
Solution:
The required storage is the sum of:
(1) volume to supply the demand in excess of the maximum daily
demand,
(2) fire storage, and
(3) emergency storage
62. Example
62
(1) Maximum Daily Demand:
The volume to supply the peak demand can be taken as 25% of the
maximum daily demand.The maximum daily demand factor is 1.8
times the average demand.The maximum daily flow rate is
therefore:
63. Example
63
(2) The fire flow of 37,000 L/min (0.62 m3/sec) must be maintained
for at least 9 hours.The volume to supply the fire demand is
therefore:
(3) The emergency storage can be taken as the average daily
demand:
The required volume of the service reservoir is therefore:
64. Example
64
A service reservoir is to be designed for a water supply serving
100,000 people with an average demand of 600 L/day/capita and a
fire flow of 17,000 L/min.
Solve
65. Example
65
A water supply system design is for an area where the minimum allowable
pressure in the distribution system is 300 kPa.The head loss between the
low pressure service location (having a pipeline elevation of 5.40 m) and
the location of the elevated storage tank was determined to be 10 m
during average daily demand conditions.
Under maximum hourly demand conditions, the head loss is increased to
12 m. Determine the normal operating range for the water stored in the
elevated tank.
67. Water Transmission
(Distribution System Piping)
67
Water transmission refers to the transportation of the water from the
source to the treatment plant and to the area of distribution.
It can be realized through
free-flow conduits,
pressurized pipelines or
a combination of the two.
For small community water supplies pressurized pipelined (e.g.,
piping system) are most common, since they are not very limited by
the topography of the area to be traversed.
Free-flow conduits (e.g., canals, aqueducts and tunnels) are preferred
in hilly areas or in areas where the required slope of the conduit
more or less coincides with the slope of the terrain.
68. The Pipe System
68
Primary mains
Secondary lines
Small distribution lines
Primary Mains (Arterial Mains)
Form the basic structure of the system and carry flow from the
pumping station to elevated storage tanks and from elevated
storage tanks to the various districts of the city
Laid out in interlocking loops
Mains not more than 1 km (3000 ft) apart
Valved at intervals of not more than 1.5 km (1 mile)
Smaller lines connecting to them are valved
69. The Pipe System
69
Secondary Lines
Form smaller loops within the primary main system
Run from one primary line to another
Spacing of 2 to 4 blocks
Provide large amounts of water for fire fighting with out excessive
pressure loss
Small distribution lines
Form a grid over the entire service area
Supply water to every user and fire hydrants
Connected to primary, secondary, or other small mains at both
ends
Valved so the system can be shut down for repairs
Size may be dictated by fire flow except in residential areas with
very large lots
70. Pipe Sizes in Municipal Distribution Systems
70
Small distribution lines providing only domestic flow may be as small
as 100mm (4in) but,
<1300 ft in length if dead ended or
<2000 ft if connected to system at both ends
Otherwise small distribution mains > 150mm (6in)
High value districts-minimum mains > 200mm (8 in)
Major streets - minimum size 300mm (12 in)
Fire fighting requirement >150mm (6 inch)
National Board of Fire Underwrites > 200mm (8inch)
71. Velocity in Municipal Distribution Systems
71
(McGhee,Water supply and Sewerage, 6th Edition)
Normal use <= 1m/s (3 ft/s)
Upper limit = 2m/s (6ft/s) may occur in vicinity of large fires
(Viessman and Hammer,Water supply and
Pollution Control, 6the Edition)
1≤V ≤ 1.7 m/s (3 ≤V ≤ 5 ft/s)
72. Pressure in Municipal Distribution System
72
AWWA recommend normal static pressure of 400-500kPa,
69-75lb/in2
Supplied ordinary uses in building up to 10 stories
Will supply sprinkler system in buildings up to 5 stories
Will provide useful fire flow without pumper trucks
Will provide a relatively large margin of safety to offset
sudden high demand or closure of part of the system
73. Pressure in Municipal Distribution Systems
73
(McGhee,Water supply and Sewerage, 6th Edition)
Pressure in the range of 150-400kPa (20-60 psi) are adequate for normal
use and may be used for fire supply in small town where building heights do
not exceed 4 stories.
75. Piping Network Elements
Controls
Check valve (CV)
Pressure relief valve
Pressure reducing valve (PRV)
Pressure sustaining valve (PSV)
Flow control valve (FCV)
Pumps: need a relationship between flow and head
Reservoirs: infinite source, elevation is not affected
by demand
Tanks: specific geometry, mass conservation applies
75
76. Check Valve
Valve only allows flow in one direction
The valve automatically closes when flow begins to
reverse
closedopen
76
77. Pressure Relief Valve
Valve will begin to open when pressure in
the pipeline ________ a set pressure
(determined by force on the spring).
pipeline
closed
relief flow
open
exceeds
Low pipeline pressure High pipeline pressure
Where high pressure could cause an explosion (boilers, water heaters, …)
77
78. Pressure Regulating Valve
Valve will begin to open when the pressure
___________ is _________ than the set point
pressure (determined by the force of the spring).
sets maximum pressure downstream
closed open
lessdownstream
High downstream pressure Low downstream pressure
78
79. Pressure Sustaining Valve
Valve will begin to open when the pressure
________ is _________ than the setpoint pressure
(determined by the force of the spring).
sets minimum pressure upstream
closed open
upstream greater
Low upstream pressure High upstream pressure
Similar to pressure relief valve79
80. Flow Control Valve (FCV)
Limits the ____ ___ through
the valve to a specified value,
in a specified direction
Commonly used to limit the
maximum flow to a value that
will not adversely affect the
provider’s system
flow rate
80
