Module 4 - Construction of a gravity fed system

- Pipe laying
If the bottom of the trench is not flat or if there is a risk that the ground can damage the
pipes (weathered rocks), a layer of sand must be installed in the bottom of the trench. If
there is no sand, sieved soil can be used.
Lay the pipes and assemble them with care. Be careful to the pipe expansion phenomenum,
particularly during the installation of important length PE pipes in a hot weather. Once
covered with ground, concraction will occur. It is thus important to let some slack to the PE
pipes during its installation in order to avoid problem during backfilling (see figure 19).
The PE pipes are generally bought in rolls of 100 meters that are unrolled as shown on figure
20. Pipes are joint with sockets or unions.
Before joining the pipes permanently, it is necessary to wait until water flows out to
prevent the formation of air plug during the first time water is flowing in the pipes.
Another method to avoid the formation of air plug during the network commisioning is to
start running water in the pipes after the completion of each section: for example, build
the header tank – storage tank pipeline, then run water. Then build the storage tank –
break pressure tank pipeline, run water etc…running the water progressively can also be
useful to make water available for the construction works downstream.
Fig.19: PE pipes laying in the trench
Fig.20: Unrolling PE pipes
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