The interior of a drinking water treatment plant._DW Treatment Plant siurce: Flickr
Have you ever thought about the transmission and distribution of water from the water station to different areas in our cities? What about household water distribution to different apartments?
The dynamics behind it is very broad. In this study, i will be discussing mainly on the engineering aspect or constructional aspects. From the pipe works to the distribution systems as well as fire hydrants and valves. Let me start with pipes and the general requirement for pipe work. But before then it is needful we understand the concept of water transmission and distribution systems.
The water transmission works, form the connection between the water works and the distribution system. Water transmission is usually achieved through canals, aqueducts, tunnels and pipelines.
Whereby water distribution systems is all about the distribution of water from treatment plants to industries, houses, offices and other users. It includes different facilities for storage of water, water measuring meter (To check water use) as well as other fire fighting equipment like hydrants. Water distribution systems is made up of pipes, valves, and pumps.
Pipes are usually constructed with different materials such as cast iron, steel, PVC, cement-asbestos, pre-cast or in situ reinforced concrete. Steel and cast -iron pipes are usually protected against corrosion by bituminous or cement lining.
Obviously, pipes made of the above materials have different properties. A pipe is selected based on the carrying capacity which is measured by the Hazen-William's coefficient, and decreases as the pipe deteriorates, on the ability to withstand both internal pressures and external loads, its degree of ease of transportation, handling and laying, the safety economy and availability if manufactured sizes, availability of appropriate skilled labour and the extent of maintenance required.
The general requirement for pipe work is that the mains should be laid in sections with gate valves in each, so that any section may be subjected to operation for repairs without disrupting the whole system, the dead ends should be avoided. However, where this is unavoidable, a hydrant should be provided for cleaning. Air valves should be installed in drains at summits and at low points to remove air so that it will not reduce the effective area of the pipe, blow-off valves or scour valves should be installed at low points for discharging accumulated sediment.
The transmission pipes are usually big because they carry a large quantity of water from the source to the treatment plant or power station
plant for treatment, after then it passes through the distribution pipes. These pipes supplies the water to our communities both rural and urban areas. There is what we call service lines. It is this pipes that is been connected to different houses for usage. Let's discuss about the distribution systems.
In the distribution system, a network of pipes is used to distribute water to a community. There are different distribution systems which are used depending on street plan, topography and location of supply works and service reservoir.
There are several types of distribution systems which include branching pattern with dead end distribution system, grid pattern distribution system, and also direct feed and indirect feed distribution systems (in building).
When we talk about branching pattern with dead end distribution system, what it means is that flow is one - directional and water is supplied to an area by a single pipe.
In the case of grid pattern distribution system, all the pipes are interconnected without dead ends such that water can reach any point from more than one direction. There is also grid pattern with loops. The loop can be provided in a grid pattern to improve water pressure in portions of a city (industrial, business and commercial areas). Loops should be strategically located so that as the city develops, the water pressure will be sustained.
The direct feed distribution system (in buildings) is used when pressure is enough in the municipal main to supply all fixtures inside the building. While the indirect feed distribution system (in buildings) is used when pressure I insufficient to supply water to the fixtures at all times of the day.
Another factor we have to look into is the pipe network analysis, which is an important aspect of distribution system. Distribution systems are often complicated systems comprising of several pumps, reservoirs, valves of different kinds and other equipment used for specific task.
The design of distribution system in building is aimed a estimating the resistance to flow and the selection of adequate pipes. The water pressure is usually expressed as static head which is the vertical distance between the source, the water storage cistern and the tap (or outlet) pipe resistance to flow is expressed as loss of head per unit length of pipe. The frictional resistance of fittings (elbows, tees, valves and taps) to flow is expressed as length whose resistance to flow is equivalent to that of the fitting.
Also note that the rate of flow in a pipe is equal to the accumulation of all the rates in all the appliances it is serving. This brings us to the next lesson, which is dual supply system.
The benefits of the dual system are that there is no risk of health hazards from poorly treated water, and potable water for uses demanding less quality will be conserved for potable uses only.
As a safety specialist, I can tell you that the next lesson which is "hydrants" can not be over looked. The significance of hydrants is to fight fire outbreaks. So let's look at it briefly and move on.
Valves are simply mainly flow control devices. There are different types of valves from gate (sluice or scour) valve, butterfly valve, penstock valve, reflux valve, needle valve and air valve.
The gate valve is used for isolation of a section of the pipeline. It works by lowering a gate into the water channel of the valve which forms an integral part of the pipeline.
The butterfly valve is used in treatment works and rarely in pipelines.
The penstock valve is used at the ends of the pipelines.
The reflux valve is another terminal valve which by allowing water to flow in one direction, is used to prevent back flow when the pressure of the pipe falls.
The needle valve is a high precision flow control device, it is used in dosing chemicals at water plants and finally the air valve is fitted in pipelines to allow air bubbles entrained in the transported to escape from the system.
Water distribution systems are complex because of its multiple components. This article is more like an insight of what it is all about.
The complete water supply system includes all the system components to develop drinking water and distribute it to the users (customers) .
The most essential requirement of the distribution system are that it supplies each user with an adequate volume of water at enough pressure, it delivers safe water that satisfies the quality expectations of customers and also provides two main purposes
which are for usage and fire protection.
[1] Drinking water supply sanitation
[2] Introduction to water Distribution Systems
[3] Water transmission
[4] Water Transmission and Distribution System Solutions for Regional Coordination and System-wide Optimization of Water Supplies
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