- INTRODUCTION
The distribution system consists of a network of pipes with appurtenance, for transportation of water from the purification plant to the consumer’s tap. It also includes the design and operation of storage, service and balancing reservoirs. The requirement of a good distribution system are
(i) The water should be transported to the consumer’s tap at a reasonable pressure head.
(ii) It should be capable of meeting the fire demand simultaneously.
(iii) The distribution system should be completely watertight.
(iv) It should be easy to operate and maintain.
(v) Water should be available even during breakdown period.
(vi) It should be laid such that it does not cause obstruction to traffic.
(vii) The initial cost of distribution system should be as low as possible.
- TYPES OF DISTRIBUTION SYSTEM
There are three types of distribution systems
(i) Gravity Distribution System: In this system, water is distributed from high level to lower level by simple action of gravity.
(ii) Direct Pumping System: In this type of system, treated water is directly pumped to the distribution mains.
(iii) Combined System: In this type of distribution system, treated water is pumped and transported to an elevated reservoir and then fed to the distribution system under the action of gravity only.
- SYSTEM OF WATER SUPPLY
There are two system to supply water to the consumer
(i) Continuous System: In this system water is available to the consumer 24 hours of the day.
(ii) Intermittent System: In this type of system, water is supplied to the customer only during some fixed hours of the day. This is the most common system of supply in India.
- LAYOUT OF DISTRIBUTION SYSTEM
There are 4 methods of laying out of distribution system
(a) Dead end system
(b) Grid system
(c) Circular system
(d) Radial system
(a) Dead End System: In this type of system one main pipe line runs through the center of area and submains takes off from this to both the sides. From each submain, several branch pipes (laterals) separates which are used to supply water to the houses. This type of system is also known as tree system.
(b) Grid System: This system is also same as dead end system except the dead ends are interconnected thus, the water can freely circulate through the whole of the distribution system.
(c) Circular/ Ring System: In this system, the supply mains form a ring around the distribution system. The branches are connected cross-wise to the mains and also to each other.
(d) Radial System: In this type of system, the whole area is divided into several zones and a distribution reservoir is placed at the center of each zone
- ANALYSIS OF NETWORK OF PIPES
There are two major methods for analysis of network of pipes:
(a) equivalent pipe method
(b) Hardy Cross method
(a) Equivalent Pipe Method: In this system, a complex system of pipes is replaced by a single hydraulically equivalent pipe causing same head loss and having same discharge. This method is used for large network of pipes.
(b) Hardy Cross Method: This is an trial and error method in which flow in the system of pipes is assumed and resulting head losses are balanced. Successive corrections are applied until the network is hydraulically balanced. Two conditions must be satisfied in the analysis:
(i) At any junction, the quantity of water entering the junction should be equal to quantity of water leaving the junction.
(ii) In any closed loop, the algebraic sum of pressure drops should be equal to zero.
Steps for Calculation:
(i) Divide network in number of closed loops.
(ii) Assume flow in each pipe satisfying continuity equation. Take clockwise flow as positive and anticlockwise flow as negative.
(iii) calculate head loss in each pipe using the formula hf = rQn.
(iv) The modification in discharge is given by the following formula:
(v) ΔQ is added to the assumed discharge algebraically.
- DESIGN OF BALANCING RESERVOIR
A reservoir is designed such that it can meet the fluctuating demand with a constant rate of supply. The storage capacity of reservoir can be determined using the mass curve method.
6.1. Mass Curve Method
A mass curve is a plot of accumulated supply/demand with time. The amount of balancing storage is determined by adding the maximum ordinate between the demand and supply line.
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