Here is a compilation of essays on ‘Distribution System of Water’ for class 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Distribution System of Water’ especially written for school and college students.
Essay on Distribution System of Water
Essay Contents:
- Essay on the Meaning of Distribution System
- Essay on the Classification of Distribution System
- Essay on the Design of Distribution System
- Essay on the Layout of Distribution System
- Essay on the Pressure in the Distribution System
Essay # 1. Meaning of Distribution System:
After complete treatment of water, it becomes necessary to distribute it to a number of houses, estates, industries and public places by means of a network of distribution system. This process is called as distribution system of water. The distribution system consists of pipes of various sizes, valves, meters, pumps, distribution reservoirs, hydrants, stand posts etc.
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The pipe lines carry the water to each and every street, road. Valves control the flow of water through the pipes. Meters are provided to measure the quantity of water consumed by individual as well as by the town.
Hydrants are provided to connect the water to the fire-fighting equipment’s during fire. Service connections are done to connect the individual building with the water line passing through the streets. Pumps are provided to pump the water to the elevated service reservoirs or directly in the water mains to obtain the required pressure in the pipe lines.
The following are the requirements of a good distribution system:
(i) It should convey the treated water up to the consumers with the same degree of purity,
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(ii) The water should reach to every consumer with the required pressure head,
(iii) Sufficient quantity of treated water should reach for the domestic and industrial use,
(iv) The distribution system should be economical and easy to maintain and operate,
(v) It should be able to transport sufficient quantity of water during emergency such as fire-fighting,
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(vi) It should be reliable so that even during breakdown or repairs of one line water should reach that locality from other line,
(vii) During repair work, it should not cause obstruction to the traffic,
(viii) It should be safe against any future pollution. The pipe lines as far as possible should not be laid below the sewer lines,
(ix) The quantity of the pipes laid should be good and it should not burst,
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(x) It should be water-tight and the water losses due to leakage should be minimum as far as possible.
Essay # 2. Classification of Distribution System:
For efficient distribution it is required that water should reach to every consumer with required rate of flow. Therefore, some pressure in pipe line is necessary, which should force the water to reach at every place.
Depending upon the methods of distribution, the distribution system is classified as follows:
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(i) Gravity system,
(ii) Pumping system, and
(iii) Dual system or combined gravity and pumping system.
(i) Gravity System:
When some ground, sufficiently high above the city area, is available, this can be best utilized for the distribution-system in maintaining pressure in water pipes. This method is also much suitable when source of supply such as lake, river or impounding reservoir is at sufficient height than city. The water flows in the mains due to gravitational force. As no pumping is required, therefore it is the most reliable system for the distribution of water.
In this system usually pumping is not required at any stage. In case the source of water supply is lake situated at the hill, low lift pumping may be required to lift the water up to the water treatment units. The water will flow under gravitational force in the treatment units, and will be finally collected to the town again under gravitational force.
The designs of the distribution system pipes are done in such a way that water head available at the consumer’s door is just minimum required, and the remaining head is fully consumed in frictional and other losses. This will reduce the leakage and wastes to the minimum. But in this case the water will have to be pumped during fires.
(ii) Pumping System:
In this system water is directly pumped in the mains. Since the pumps have to work at different rates in a day, the maintenance cost increases. It is preferred to have number of pumps and only the required numbers may work at various times to meet the varying demand, in place of providing pump of variable speed. High lift pumps are required and their operations are continuously watched.
If the power fails, the whole supply of the town will be stopped. Therefore, it is better to have diesel pumps also in addition to the electric pumps as stand bye. During fires, the water can be pumped in the required quantity by the stand-bye units also. But this system is not preferred than other systems. The required pressure maintained in the pipe line is by direct pumping as shown in Fig. 18.2.
(iii) Dual System:
This is also known as combined gravity and pumping system. The pump is connected to the mains as well as to an elevated reservoir. In the beginning when demand is small the water is stored in the elevated reservoir, but when demand increases the rate of pumping, the flow in the distribution system comes from both the pumping station as well as elevated reservoir.
As in this system water comes from two sources one from reservoir and second from pumping station, it is called dual system. This system is more reliable and economical, because it requires uniform rate of pumping but meets low as well as maximum demand. The water stored in elevated reservoir meets the requirements of demand during breakdown of pumps and for fire fighting.
Fig. 18.3 shows this system with hydraulic gradient lines for minimum and maximum draft. This system is usually adopted everywhere.
Following are the main advantages of this system:
(a) The balance reserve in the storage reservoir will be utilized during fire. In case the fire demand is more and if required the water supply of few localities may be closed.
(b) This system is overall best system. It is economical, efficient and reliable.
(c) This system has the advantages that during power failure, the balance water stored in the water will be supplied to the town.
(d) The pumps have to work at constant speed, without any variation in their speed. This increases the efficiency of the pumps and reduces the wear and tear of the pumps. The supervision, operation and maintenance of these pumps is much less as compared with the pumps working at variable speed.
Essay # 3. Design of Distribution System:
First of all the layouts of the distribution pipes are prepared and the position of valves, fire hydrants etc., is also marked on it. The reduced levels of the town at various points are also marked on the plan. The total population to be served with the pipe line is also marked on the plan. The minimum water pressures required at the tail end and near the highest buildings of the city are also determined and noted on the plan.
After completing the above work, now the main work is to determine the sizes of the distribution pipes which will be capable to carry the required quantity of water at the desired pressure.
Till date no direct methods are available for the design of distribution pipes. While doing the design, first of all the diameters of the pipes are assumed, the terminal pressure heads which could be made available at the end of each pipe section after allowing for the loss of pressure head in the pipe section when full peak flow discharge is flowing, are then determined. The determination of the friction losses in each pipe section is done. The total discharge flowing through main pipes is to be determined in advance.
The Hazen-William formula is widely used for determining the velocity through pipes. This formula has also been used in the design of pipe lines.
It states:
The values of CH are given in table 8.1.
The head loss due to friction can be determined by the formula
The head loss in the assumed pipe diameter is determined by formula 20.2. After deducing the head loss the pressures at the terminal points are determined.
Since the design work involves the method of trial and error by assuming various diameters of the pipes, it is very cumbersome and tedious work.
To reduce the tedious calculations, the Hazen-Williams nomogram is used. Fig. 20.1 shows Hazen-William’s Nomogram for cast iron pipes. In this nomogram CH= 100 has been used, because usually in practice C.I. pipes of standard diameters are used.
Hazen’s William’s charts for various materials of pipes are available in the Public Departments of the State Government, and are widely used for the design of pipe lines. The method to use the chart is very simple. A straight edge is placed on any two known values, such as discharge and velocity, and the values of two other unknowns such as loss of head per 1000 in and the diameter of the pipe can be directly read out.
The loss of head per 1000 m when multiplied by the length of pipe in thousand meters will give the total head loss in the pipe line. The values so obtained are used in the design work. If the terminal pressure in any particular zone is found to be more or less than the minimum permissible, then the size of the pipe can be suitably decreased or increased, and the whole distribution system can be accordingly analysed. The process is continued on trial till the required pressures are obtained.
The permissible velocities are kept between 0.9 to 1.8 m/sec. With increased diameters of the pipes, i.e., lower values for smaller pipes and higher values for bigger pipes as per Table 20.1.
The approximate values of the velocities of the pipe diameter from 10-40 cm (diameter not given in table 20.2) may be suitably assumed in between.
The distribution mains should be designed for the maximum hourly demand of the maximum requirement day, its value is about 2.7 times the average daily. It should also be checked for the maximum fire demand. Usually the pipe lines are designed for 3 times the average demand. In the distribution system the minimum size of the distribution pipe is kept as 10 cm and service pipe is kept as 10 cm and service pipe of 20 mm is used for giving house connections.
Essay # 4. Layout of Distribution System:
Generally in practice there are four different systems of distribution which are used.
Depending upon their layout and direction of supply, they are classified as follows:
(i) Dead End or Tree System
(ii) Grid Iron System
(iii) Circular or Ring System
(iv) Radial System.
(i) Dead End or Tree System:
Fig. 18.4 shows the layout of this system. It is suitable for irregular developed towns or cities. In this system one main starts from service reservoir along the main road. Sub-mains are connected to the main in both the directions along other roads which meet the main road.
In streets, lanes and other small roads which meet the roads carrying sub-mains, branches and minor distributors are laid and are connected to sub-mains. From these branches service connections are made to individual houses.
The main advantages of this system are cheap in initial cost and easy determination of pipe diameters, valves, size etc. But the main disadvantage of this system being formation of dead ends and if pipe breaks down or is closed for repair, the whole locality beyond the point goes without water.
Since the water is reaching at each point from one side only, it cannot meet the fire demand, nor the supply can be increased or diverted from other points. This causes serious handicap and limits the fire-fighting capacity.
(ii) Grid-Iron System:
This system is also known as reticulated system and is most convenient for towns having rectangular layout of roads. Actually, this system is an improvement over dead-end system. All the dead ends are interconnected with each other and water circulates freely throughout the system. Fig. 18.5 shows the layout of this system.
Main line is laid along the main road. Sub mains are taken in both the directions along other minor roads and streets. From these sub-mains branches are taken out and are inter-connected as shown in Fig. 18.5. This system removes all the disadvantages of dead end system.
Following are the main advantages of this system:
(a) As water is supplied from both the sides to every point, very small area will be affected during repair.
(b) Since the water reaches every point from more than one route, the friction losses and the sizes of the pipes are reduces.
(c) All the dead ends are completely eliminated, therefore the water remains in continuous flow and there is no stagnation and chance of pollution is reduced to minimum.
(d) In case of fire, more quantity of water can be diverted towards the effected area, by closing the valves of nearby localities.
Following are the disadvantages of this system:
(a) More number of valves and longer length of pipe is required in this system, thereby increase in the overall cost.
(b) If one section is to be repaired more number of valves are required to close,
(c) The design is difficult and costlier, as the accurate calculation of the discharge and pipes in various lines is tedious job, requiring the services of computers and expert designers.
(iii) Circular or Ring System:
This system can be adopted only in well planned locality of cities. In this system each locality is divided into square or circular blocks and the water mains are laid around all the four sides of the square or round the circle. The branches, sub-mains etc. are laid along the inner roads as shown in Fig. 18.6.
All the sub-mains and branches are taken off from the boundary mains and are inter-connected. In this way every point receives its supply from two directions.
This system is the best of the other systems but it requires many valves and more pipe length. But the design of this system is easier. The ring system is more suitable for towns and cities having well planned roads.
This system is sometimes used as ‘looped feeder’ and is placed centrally around a high demand area, along with the grid iron system. In such cases it increases the capacity of the grid iron system and also increases the water pressure at various points. The advantages and disadvantages of this system are also the same, that of grid-iron system.
(iv) Radial System:
This system is not adopted in India, because for this system the roads should be laid out radially from a centre. Actually this is reverse of ring system and water flows towards outer periphery from one point as shown in Fig. 18.7.
The entire district is divided into various zones and one reservoir is provided for each zone, which is placed in the centre of the zone. The water lines are laid radially from it. This system gives very quick and satisfactory water-supply and also the calculation of pipe sizes is very easy.
Essay # 5. Pressure in the Distribution System:
When the water enters in the distribution main, the water head continuously is lost due to friction in pipes, at entrance of reducers, due to valves, bends, meters etc. till it reaches the consumer’s tap. The net available head at the consumer’s tap is the head at the entrance of the water main minus all the losses in the way. The effective head available at the service connection to a building is very important, because the height up to which the water can rise in the building will depend on this available head only.
The greater the head the more will be the height upto which it will rise. If adequate head is not available at the connection to the building, the water will not reach the upper storeys (i.e., 2nd, 3rd. 4th etc.). To overcome this difficulty the required effective head is maintained in the street pipe lines.
The water should reach each and every consumer therefore it should reach on the uppermost storey.
The pressure which is required to be maintained in the distribution system depends upon the following factors:
(i) The height of highest building up to which water should reach without boosting.
(ii) The distance to the locality from the distribution reservoir.
(iii) The supply is to be metered or not. Higher pressure will be required to compensate for the high loss of head in meters.
(iv) The supply is to be metered or not. Higher pressure will be required to compensate for the high loss of head in meters.
(v) The funds available for the project work.
Sometimes the design pressure is determined from the fire-Fighting requirements. In some cities and towns the fire-Fighting squads are equipped with pumping sets fitted on their vehicles for lifting the water at the site itself.
At such places the design pressure may be determined by the minimum required by the consumers. But in most of the towns in India the people living at 2nd, 3rd or 4th storey face lots of difficulties due to non-supply of water in their storeys. At such places small lifting pumps may be individually used which directly pump the water in their water lines.
In multistory structures the following pressure are considered satisfactory:
While designing pipes of distribution systems the following points should be kept in mind:
(i) The main line should be designed to carry 3 times the average demand of the city.
(ii) The service pipes should be able to carry twice the average demand.
(iii) The water demand at various points in the city should be noted.
(iv) The lengths and sizes of each pipe should be clearly marked on the site plan along with hydrants, valves, meters, etc.
(v) The pressure drops at the end of each line should be calculated and marked.
The minimum velocity in pipe lines should not be less than 0.6 m/sec and maximum velocity should not be more than 3 m/sec.
For best results the velocities in different pipes should be as follows:
