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96
Часть IV.
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Supplementary reading
Boilers
The boiler may be one of a number of types. It may be a solid one-piece
casting, rectangular in form; it may be sectional; or it may be conical in shape
and wrought or cast iron. For smaller systems, the first and last-named types are
both cheap and suitable. The sectional boiler has the advantage of the possibil-
ity of added sections should more heat be needed subsequent to initial installa-
tion. Sectional and shell type boilers are almost invariably used for bigger in-
stallations. The former are cast iron and can be built up in site, whilst the latter
are usually of the "packaged" type, having all auxiliary components together
with the boiler assembled as one unit ready for erection.
In general, a heating system should be designed so that the water will
circulate by gravity. In some installations, circumstances are such that a pump
or accelerator must be used to achieve a satisfactory circulation. This should be
avoided if possible.
When designing a heating system for a large building, it is usual — in the
interests of economy and to ensure efficient heating — to first calculate how
much heat will be needed to maintain the building at the desired temperature.
Then the size of the boiler and the amount of pipe and radiator heating surface
required to give out this heat will be estimated. For small systems, "rule-of-
thumb" methods and past experience are generally a sufficient guide.
The overhead drop-feed system
shows how the hot water from the boiler
is carried as high as possible in the building, from where it falls in cooling,
through the various branch pipes and radiators, back to the boiler. In this type of
system, the maximum amount of "circulating head" or pressure would be ob-
tained.
Erecting and fixing boilers
No difficulties exist in the fixing of independent boilers. A good level
concrete foundation is needed, and common-sense fire precautions should be
observed.
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