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How To Design And Install Plumbing
Cold-Water Distribution Systems In Tall Buildings
In tall buildings which cannot adequately be served by the normal water pressure of the city mains, mechanical means for water distribution are employed. There are two types of water distribution systems which may be used to serve this purpose, namely, the pneumatic air pressure system and the overhead feed system.
PNEUMATIC AIR PRESSURE SYSTEM
The pneumatic air pressure system is an assembly of mechanical devices which elevate water, using compressed air as the delivery agent. This method of water delivery is rapidly superseding other installations because it offers many advantages. The pumping unit is compact and may be installed in a limited amount of space. A small basement room usually is adequate for this purpose. The water is confined in air-tight equipment, which makes the installation a sanitary one—it is impossible for dust and other objectionable materials to come in contact with the water. In a slight way the oxygen contained in the compressed air, which passes through the water, serves as a purifying agent and tends to make water palatable.
The pressure system offers an economic advantage in that the pipe diameters may be smaller than those of other installations, and the cost of the original equipment is materially less.
The working parts of a pneumatic air pressure system are few and operate efficiently. Only occasional maintenance, such as lubrication or minor repair, is required.
This method of water distribution may be adapted to a small rural residence as well as to the tallest urban building. In buildings of extreme height, air pressure systems serve zones of about ten floors. A thirty-story building may be provided with three distinct Units, each providing water supply for a ten-floor interval.
Principle of Operation. The scientific principle on which a pneumatic pressure system operates is the fact that 1 pound of air pressure elevates water approximately 2.31 feet under atmospheric conditions of about 14.72 pounds.
The mechanical devices which are used in this method of water supply and the pipe connection of the separate units are as follows:
Assembly of Mechanical Devices. There are four mechanical devices used on an air pressure system:
1. A large storage tank, with all tappings located on the underside.
2. A single or duplex centrifugal pump.
3. An air compressor.
4. An automatic pressure control switch.
Fig. 215 illustrates a complete pneumatic air pressure distribution system. The centrifugal pump is set on a concrete footing. It must be insulated against noises produced by vibration. The inlet side of the pump is connected to the water supply main and is equipped with a valve, A. The outlet or delivery side of the pump is connected to an opening in the tank and is equipped with a valve. Two check valves, B, placed between the pump and tank, prevent the increased pressure within the system from exerting itself on the supply main. Two pumping units are used on most installations, especially those for large buildings, to insure a supply of water should one pump fail.
