What are the requirements of good distribution system?
Requirements of a good distribution system:
1. It should convey the treated water up to the consumers with the same degree of purity.
2. The water should reach the consumer with the required pressure head.
3. Sufficient quantity of treated water should reach for domestic and industrial use.
4. The distribution system should be economical and easy to maintain and operate
5. It should be able to transport a sufficient quantity of water during emergencies such as firefighting
6. It should be reliable so that even during breakdown or repairs of one line water should reach that locality from other lines.
7. It should not cause obstruction to traffic during repair work.
8. It should be safe against any future pollution.
9. The quality of the pipe should be good and it should not burst.
10. It should be watertight and the water losses due to leakage should be minimum as far as possible.
Discuss the methods of distribution system of water.
For efficient distribution the water should reach to every consumer with the required classified as follows:
rate of flow. Depending upon the methods of distribution, the distribution system is.
1. Gravity system
2. Pumping system
3. Dual system or combined gravity and pumping system.
1. 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 suitable when the source of supply such as a lake, river, or reservoir is at a sufficient height than the city. The water flows in the mains due to gravitational force. As no pumping is required it is the most reliable system.
2. 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 a number of pumps and only the required numbers may work at various times to meet the demand, in place of providing pumps of variable speed.
If the power fails, the whole supply of the town will be stopped. During fires, the water can be pumped in the required quantity by the stand-by units also. But this is not preferred than other systems.
3. Dual system: This is also known as the combined gravity and pumping system. The pump is connected to the mains as well as to an elevated reservoir.
In the beginning, when the demand is small the water is stored in the elevated reservoir, but when demand increases the flow in the distribution system comes from both the pumping station as well as the elevated reservoir.
As this system has two sources, one from the reservoir and the second from the pumping station it is called a dual system. This system is more reliable and economical because it requires a uniform rate of pumping but meets low as well as maximum demand.
Water Distribution System in Hindi |Part – 1 | Environment Engineering
Discuss the layout of distribution system.
Depending upon their layout and direction of supply distribution systems are classified as follows:
1. Dead end or Tree system
2. Grid iron system
3. Circular or ring system
4. Radial system
1. Dead end system: It is suitable for irregular developed towns and cities. In this one main starts from the service reservoir along the main road. Sub mains are connected to the mains in both directions along other roads which meet the main road.
In the street, 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.
This system is cheap in initial cost and easy determination of pipe diameters, valve size, etc., the disadvantage is that due to the formation of dead ends stagnation of water takes place, if the pipe breaks down or is closed for repair the whole locality beyond that point goes without water because water is reaching at each point from one side only, it cannot meet the fire demand, nor supply can be increased or diverted from other points.
2. Grid iron system: This is also known as a reticulated system and is used for towns having rectangular layouts of roads. This is an improvement over the dead-end system, all the dead ends are interconnected with each other and water circulates freely throughout the system.
The Mainline is laid along the main road, and sub-mains are taken in both directions along other minor roads and streets. From these sub-mains branches are taken out and are o interconnected.
All disadvantages of the dead-end system are eliminated. More number of valves and a longer length of pipe is required in this system, thereby increasing the overall cost.
3. Circular or Ring system: This is adopted only in well-planned locality of cities. In this, 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. All the sub-mains and branches are taken off from the boundary mains and are interconnected. In this way, every point receives its supply from two directions.
This 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 advantages and disadvantages of this system are also the same as that of the gridiron system.
4. Radial system: In this system, the roads should be laid out radially from a center. In this system, water flows towards the outer periphery from one point.
The entire area is divided into various zones and one reservoir is provided for each zone, which is placed in the center of the zone. The water lines are laid radially from it. This system gives a very quick and satisfactory water supply and also the calculation of pipe sizes is very easy.
What are the functions of distribution reservoirs ?
The main functions of the storage and distribution reservoirs are:
1. To store the treated water till it is distributed to the city.
2. To absorb the hourly variation in the water demand, and thus allowing the treatment units and pumps to work at the average constant rate
3. To maintain the constant pressure in the distribution main, because when the pressure in the pipelines decreases due to an increase in demand at peak hours, the extra demand of water is fed by these reservoirs, and the pumps continue their work at a constant speed.
4. Distribution reservoirs lead to an overall economy by reducing the sizes of pumps, pipelines, and treatment units.
5. By providing distribution reservoirs, the pumping of water in shifts is possible, because treated water will continuously flow in these reservoirs.
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