DESIGN OF DISTRIBUTION SYSTEM - Enginnering notes

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.