cve 471 - 5. water supply 2 - deukisi.deu.edu.tr/gulay.onusluel/water supply 2.pdf ·...

CVE 471 Water Resources Engineering 1/58

WATER SUPPLYWATER SUPPLY


55. WATER SUPPLY. WATER SUPPLY

Overview

Elements of Municipal Water Supply SystemsDistribution ReservoirsPipesPumps and Valves

Hydraulics and Operation of Gravity PipelinesDesign of Transmission Lines

Gravity LinesPumped LinesMixed Lines

Construction and Maintenance of Municipal Water Supply Systems



Elements of Municipal Water Supply System

Water is conveyed from a source or combination of sources to community in mainly closed conduits.

pressurized flow is possiblepollution control

Possible element of a water transmission system:canals and flumesgrade aqueductsgrade tunnelspipelinesvalvespumpspressure reducing chambers etc….

1915-19 Winnipeg, Manitoba, Canadahttp://www.mhs.mb.ca/docs/pageant/24/winnipegaqueduct.shtml




Transmission pipelineshttp://www.wau.boku.ac.at/fileadmin/_/H81/H811/Skripten/811356/05_Supply_Storage_distribution.pdf




Typical arrangement of a municipal water supply system

Distribution reservoirs are designed to meet the hourly variations in water demand and to store extra water for fire fighting and emergencies.




A water distribution network is normally composed of pipes, valves, hydrants, and pumps. Distribution of water is possible by

gravity (storage reservoir is required at a sufficient altitude)pump without storage (may be required during any emergency), andpump with storage (the most common way).

Types of distribution systems depends on street plantopography,location of supply works,level of service dictated.




Types of distribution systems: a) a branching pattern with dead ends,b) a gridiron pattern,c) a gridiron pattern with central feeder.

A branching pattern with dead endssuitable for strip-shaped districts where water flow in one directionduring any repair downstream of the section cannot take water

A gridiron patternpreferred for flat and wide terrains

A gridiron pattern with a central feederpreferred as the auxiliary main is in a looped pattern



Overview








Distribution ReservoirsIn large cities (population > 100,000) pumping stations and distribution reservoirs are operated in conjunction with each other.Pumping stations usually pump the average daily demand to distribution reservoirs during the minimum demand hours of the day.Distribution reservoir release the water when the demand is above the average daily demand to meet the fluctuations in use.Location: as close as the center of use as possible.Water Level: high enough to permit gravity flow at satisfactory pressure.




Distribution Reservoirs (con’t)May be located in critical points in the city in such a way that the hydraulic grade line is still above the highest storey buildings.Elevated tanks: circular cross-section (cylinder gives a max. volume).Buried reservoirs: rectangular

cross-section (easy to construct)Small: concrete or stone masonryLarge: reinforced concrete with dividing walls

Cylindrical Reservoirs: reinforces concrete or steel




Distribution Reservoirs (con’t)A fill layer of about one meter thick is placed.Lower temperature in summer (better quality and taste)

Buried distribution reservoirhttp://www.wau.boku.ac.at/fileadmin/_/H81/H811/Skripten/811356/05_Supply_Storage_distribution.pdf




Distribution Reservoirs (con’t)

Buried distribution reservoirhttp://www.wau.boku.ac.at/fileadmin/_/H81/H811/Skripten/811356/05_Supply_Storage_distribution.pdf




Distribution Reservoirs (con’t)The capacity of a distribution reservoir is determined by the summation of the following components:

Storage to meet hourly fluctuations,Required storage to put out a fire with certain duration (Cfire)Storage to meet emergencies



Overview








PipesPipes materials:

reinforced concrete (no corrosion problem),asbestos cement (limited use cancerous effect of asbestos fibers),ductile iron (corrosion problem interior is coated with cement),steel (good for large diameter and high pressure, buckling under high negative pressure)plastic (widely used, highly smooth, light, easy to install and remove)

The minimum pipe size required in a distribution network is dictated by the population.



Overview








PumpsPumps: mechanical energy potential energyTypes of pumps are named according to the direction of the movement of water from the rotating element of the pump (impeller).The specific speed:

where Q: discharge (m3/s)N: rotative speed of impeller (rpm)Hp: Head (m)

2/3p

sHQN

n =




Pumps (con’t)Centrifugal Pumps:

For the requirement of high heads (low ns).Impeller in series having radial flow characteristics are adopted.

http://en.wikipedia.org/wiki/File:CetriFugal_Pump.jpg http://www.thomasnet.com/articles/pumps-valves-accessories/centrifugal-principles




Pumps (con’t)Axial-flow Pumps:

For greater flow rates under low heads (high ns).Having axial flow characteristics with respect to the pump axis.

http://en.wikipedia.org/wiki/File:Axial_2.png http://www.directindustry.com/prod/weir-minerals/axial-flow-pump-23306-376724.html




Pumps (con’t)Mixed-flow Pumps:

For medium head and discharge (medium ns).

http://www.shakthipumps.com/download/mixed-flow-pumps.pdfhttp://www.pattersonpumps.com/axial.html#




Pumps (con’t)Power of the pump:

where Pp: the power (kW).γ: specific weight of water (kN/m3)Q: discharge (m3/s)Hp: head of the system by the pump (m)ηp: the efficiency of the pump

p

pp

QHP

ηγ

=




Pumps (con’t)Multiple pump operations are often used to increase the discharge or head.

Pumps in Series: Increase the head

Pumps in Parallel: Increase in discharge




Valves Sluice or gate valves are used to isolate the flow especially during repair works.

http://en.wikipedia.org/wiki/Gate_valve




Valves Butterfly valves are widely used at the exits of distribution reservoirs for regulation or isolation purposes.

http://en.wikipedia.org/wiki/Butterfly_valvehttp://www.scanco.no/produkter_ventiler.php




Valves Check valves are used to stop flow automatically in the reverse direction.

http://www.checkall.com/valvestyles/un3/un3enlargedphoto.htm

http://www.spiraxsarco.com/resources/steam-engineering-tutorials/pipeline-ancillaries/check-valves.asp

http://www.checkvalves.co.uk/




Valves Hydrants are those appurtenances used for the withdrawal of pressurized flow from the network for fire fighting.

http://en.wikipedia.org/wiki/Fire_hydrant



Overview







Design of Transmission Lines

The pipe size should be determined to meet future requirements.The system should confirm to the required hydraulic performance:

velocity criteriapressure criteria etc…..

In this section design principles ofgravity lines,pumped lines, andmixed lined

are introduced.




Design of Gravity LinesFor a gravity pipeline, neglecting operating cost, the optimum diameter minimizes the capital cost of the pipeline.

The optimum diameter minimum diameter which can convey the specified design discharge with the available gravity head.

In gravity lines there are several design criterions:Velocity: 0.5 – 2.0 m/sPressure head: 3-5 m – 80 m



Overview








Design of Pumped LinesFor a pumped line, the economical diameter is the one which minimizes the total cost.

investment cost of pipes (placement and installation costs),cost of pump,energy cost of operation (operation and maintenance costs).

A small diameter reduces initial cost but increases pumping and energy costs.

For the most economical diameter:



Overview








Design of Mixed LinesA pipeline having both

gravitational and pumped flow rates.

Topographic elevation of point C is higher than the reservoir level.In such a case it is convenient to build a small reservoir at C.The pump may be

located at reservoir site A orlocated as a booster pump along the line.

Topographic elevation of point C is higher than the reservoir level.



Water Supply Systems

The selection of suitable route for a pipeline has an important bearing on the capital cost and operation cost.

A pipeline route is selected fromaerial photostopographic and cadastral planson-site inspections, andother data available on the terrain, obstacle, and local services.

For suitable route Jointly consider Cost and Practicality.

The general level of pipeline route should be as close to hydraulic grade line as possible to minimize pressures and hence pipe costs.

cve 471 - 5. water supply 2 - deukisi.deu.edu.tr/gulay.onusluel/water supply 2.pdf ·...

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