Design of distribution system:
The following steps are involved in designing the distribution system.
1. Surveys and maps:
- Position of road, streets, lanes, commercial locality industrial area etc.
- Topographical map is also prepared.
2. Tentative Layout:
- Showing position of treatment plant, distribution mains, distribution and balancing reservoirs, valves, hydrants etc.
3. Discharge in pipe lines:
- Based on the density of population and other requirements, the pipes are designed for maximum hourly of maximum daily demand i.e, 2.7 times of average.
4. Calculation of pipe diameters:
- Flow velocity remains n pipes between 0.6 m/sec to 3 m/sec.
- The loss of head is calculated by William Hazen's formula ( nomogram formula) or by any other formula.
5. Computation of pressure:
- Analysis of pressure in the distribution system.
Equivalent pipe method:
A complex system of pipes is replaced by a single hydraulically equivalent pipe. The equivalent pipe is one which will replace a given system of pipes with equal head loss for a given flow.
Hardy cross method:
This is essentially a relaxation technique involving controlled trial and error. Following three laws are applicable.
- In each separate pipe or element comprising the system there will be a relation between the head loss in the element and the quantity of water flowing through it.
- At each junction, the algebraic sum of the quantities of water entering and leaving the junction is zero, i.e, sigma Q = 0.
- In any closed path or circuit, the algebraic sum of head loss in the individual element is zero i.e, sigma h = 0.
