Construction and maintenance of water distribution systemSunday, September 16, 2012 16:56
Construction and maintenance of water distribution system
Following factors are considered for the proper construction and maintenace of water distribution system.
Excavation and back filling in water distribution system
- Trench should be wide enough to allow good workman ship. Its width should be equal to external diameter of pipe and an additional of 40-50 meter.
- Extra excavation is done which is necessary at the bells or joints.
- Sufficient cover is necessary to protect the water pipes from the traffic load and to prevent freezing. Generally pipes are placed at depth of 0.8-2.0 m from top of pipe.
- Back fill materials should be free from debris, rock, stones bricks etc., and should consist of good soil.
- Back fill should not be done in freezing weather or with frozen material.
- Partially backfill should be done before leakage test and complete backfilling should be done after tests.
- Special bedding material support must be provided adequately at the trench bottom.
Pipe Handling and Laying in water distribution system
Following points should be kept in mind while pipe handling and laying in water distribution system.
- All pipes and fitting should be checked before unloading at the installation site.
- Pipes and fitting should not be dropped from the truck as they may get damaged.
- If the cable with hooks are used in unloading, then hooks should be covered with rubber.
- If a fork lift is used, care is needed to avoid damaging the exterior coating, interior lining or the pipe itself.
- In moving pipes and fittings they should never be rolled by bulldozer blades or any other equipment. Instead they must be rolled by hand.
- Pipes and fittings in trench should be supported properly.
- Jointing procedure should follow the recommendation of pipes and joints.
- Stones found in the trench should be removed for a depth of at least 6 inches below the bottom of the pipe.
- Bottom of the pipe should be levelled properly.
Submerged pipes in water distribution system
Occasionally pipe lines must run through streams. So it is necessary to place the pipes under water. Generally cast iron pipes are used for this purpose. To lay a pipe it is good to dig out a trench in the channel bottom. The channel will silt up.
Silt up is to become choked or obstructed with silt.
It gives the protection. A dredged bottom will be rather irregular and it may be necessary to furnish a suitable foundation.
Dredge is a machine for removing earth usually by buckets on an endless chain or a suction tube.
The use of highly flexible joints may make blocking un necessary.
Hydrant placement in water distribution system
If summits and valleys are necessary in the water distribution system, then it is suitable to place hydrants near them.
It will allow the escape of air at proper time intervals. And if hydrant is placed near valleys then sediments will be collected there and it will help in blowing out of sediments.
In fact it is placed between sidewalk and kerb.
Kerb is an edging made of concrete built along a street to form part of a gutter.
Or hydrant is placed between sidewalk and property line.
Placing the hydrants on the base of concrete prevents setting the branch from a main to hydrant. To prevent the hydrant from being displaced by water pressure, is should be braced on the side opposite to the branch entrance.
Maintenance of valves in water distribution system
Valves should be properly inspected and maintained regularly.
The main defects in the valves are
- InaccessibilityWhen bores are filled with earth or debris, then it is difficult to access the valves.
A valve may become inoperatable through corrosion. Pouring kerosene oil or diluted lubricating oil, will lubricate the joint between the stem and packing. Corrosion can be overcome by carefully operating the gate up and down and allowing increased velocity of water to sweep out the sediments.
- Closure of valves
Closure of valves occurs due to corrosion or silting. It can be removed by pouring kerosene or lubricating oil down the valve key and by allowing increased velocity of water.
Disinfection of pipes in water distribution system
Disinfection means killing of disease causing micro organisms.
In the process of handling and placing of pipes, pollution is not created.
The mains may become polluted
- During storage on the street by the mud in the bottom of the trench.
- By polluted water which may run into the trench.
- By the debris which workmen push into the open ends of the pipe.
The following steps are involved in disinfection
- Flush the pipe with water at 0.8-1 m/s .
- Fill the pipe with water containing at least 1 mg/L of chlorine. A free residual of at least 0.5 mg/L must remain after 24 hours.
- If the total bacterial counts exceed 500/ ml or any caliform bacteria are found, the pipe should be filled with water containing 50 mg/L which should not decrease below 25 mg/L in 24 hours holding period.
- Flush the pipe again with water.
Waste water surveys in water distribution system
Undiscovered breaks in mains, unauthorized users of water and unmetered customers which are the cause of wasting water are discovered by waste water surveys.
These surveys are carried on by means of pitometers which are places in the mains when flow is to be measured.
Instead of using pitometers, it is possible to close all the valves on the mains leading into the district and supply water through a hose connecting two hydrants and with a large water meter in the hose line,
Close all the valves on the mains, except the one which is entering the district. The flow is measured in the one main at night when domestic use is low. So the location of loss can be estimated.
Further restriction of the district by closing other valves and noting upon the inflow rate in the supply mains will locate leakage very closely.
Water surveys save enormous amounts of water. These surveys make it possible to account for at least 85% of the output in metered cities.
Cleaning of water mains in water distribution system
Water carrying capacity of the water mains is reduced due to the sediments which accumulate in the water mains. It is also reduced by rusting. To restore capacity of water mains, cleaning is required. Various types of scrappers are used for this purpose.
At the lower end of the pipe to be cleaned, the pipe is broken. A 45 degree branch is used to bring the end to the street surface where it is left opened. A special sleeve is inserted at the upper end after a small float with an attached cable is inseted. The upper valve is opened and the small float passes through it. A large cable is then drawn through and scrapper is inserted at the special sleeve. The water pressure is put on and the scrapper is pulled through by means of the cable. In this way the dislodged clogging matter escape from the open end with the flow of water. Recleaning may be necessary after 5 or 6 years.
Leak and pipe location in water distribution system
It is difficult to locate a leak exactly. Various investigations methods may be applied to our ease.
Presence of melted ice or green grass during a drought will indicate a leak.
A steel rod is thrust along with the pipe line into the grown. Then it is withdrawn to determine whether or not its end is wet. A metal rod may be driven into the ground to make contact with the main. The sound of escaping waeter may be discernible by placing the ear against the rod. The sound may be discernible by means of amplifying apparatus placed in contact with the rod.
Pipe Location in water distribution system
Sometimes it is necessary to locate the lost underground mains and services. Various electrical magnetic devices are used for discovering buried metallic structures. They are particularly useful when there are no other interfering conduits or pipes. These electrical devices may be of little value in the streets or large cities where underground pipes are numerous.