Профессиональное развитие будущих инженеров-строителей средствами иностранного языка: Лексический практикум по английскому языку. Трубникова Н.В. - 68 стр.

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sure within the bellows to exceed the pressure in the pipeline. The water quan-

tity that is passed can be adjusted to avoid wastage.

Low-pressure supplies

Static water pressures in tall buildings are reduced by storing water at

various levels. Sealed storage tanks are used for drinking water. Open water

tanks become contaminated with airborne bacteria and are only used for sani-

tary purposes. Cold-water services are taken to taps, WC ball valves, hot-water

storage cylinders and equipment needing low-pressure supplies. A separate cold

feed is taken to a shower of showers to avoid the possibility of scalding. Tanks

are sized to store the total cold-water requirement for a 24 h period.

The minimum mains water pressure available in the street is 100 kPa

(1 bar), which is 1 atmosphere gauge or 10 m height of water. The water

supplier may be able to provide 300 kPa, or enough pressure to lift water to the

top of a building 30 m high; however, allowance has to be made for friction

losses in pipelines and discharge velocity, which effectively limits the vertical

distance to between two and six storeys.

Separation of the contaminated water being used within the building for

washing, flushing sanitary appliances, circulating within heating and air-

conditioning cooling systems, evaporative cooling towers, ornamental foun-

tains, agricultural irrigation or manufacturing processes from potable mains wa-

ter is achieved by using the following:

1. a storage tank with ball valve (break tank);

2. a permanent air gap between the tap discharge and the contaminated

water level (e.g. wash basin);

3. a single-seat non-return valve (check valve);

4. a double-seat check valve.

The Water Byelaws 1989 classify the risk of contamination from the

building reaching upstream into the water main in three groups, each having its

own protection.

Cold-water storage tanks are expected to contain water of similar quality

to that supplied from the main and so must be covered to exclude foreign mat-