Conveyance
There are two stages in the transportation of water:
•Conveyance of water from the source to the treatment plant.
•Conveyance of treated water from treatment plant to the distribution system.
In the first stage water is transported by gravity or by pumping or by the combined action of both, depending upon the relative elevations of the treatment plant and the source of supply.
In the second stage water transmission may be either by pumping into an overhead tank and then supplying by gravity or by pumping directly into the water-main for distribution.
Free Flow System
In this system, the surface of water in the conveying section flows freely due to gravity. In such a conduit the hydraulic gradient line coincide with the water surface and is parallel to the bed of the conduit. It is often necessary to construct very long conveying sections, to suit the slope of the existing ground. The sections used for free-flow are: Canals, flumes, grade aqueducts and grade tunnels.
Pressure System
In pressure conduits, which are closed conduits, the water flows under pressure above the atmospheric pressure. The bed or invert of the conduit in pressure flows is thus independant of the grade of the hydraulic gradient line and can, therefore, follow the natural available ground surface thus requiring lesser length of conduit. The pressure aqueducts may be in the form of closed pipes or closed aqueducts and tunnels called pressure aqueducts or pressure tunnels designed for the pressure likely to come on them. Due to their circular shapes, every pressure conduit is generally termed as a pressure pipe.
When a pressure pipe drops beneath a valley, stream, or some other depression, it is called a depressed pipe or an inverted siphon.
Depending upon the construction material, the pressure pipes are of following types: Cast iron, steel, R.C.C, hume steel, vitrified clay, asbestos cement, wrought iron, copper, brass and lead, plastic, and glass reinforced plastic pipes.
Cast Iron Pipes
• Cast – Iron Pipes are mostly used in water supply schemes. They have higher resistant to corrosion, therefore have long life about 100 years.
Cast Iron pipes are manufactured in lengths of 2.5 m to 5.5 m. The fittings of these pipes are also manufactured in sand molds having core boxes. These fittings are also weighed, coated with coal tar and finally tested. Cast-Iron pipes are joined together by means of Bell and Spigot, Threaded or flanged Joints.
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