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Boilers are pressure vessels used to produce steam or hot water. They are different
from furnaces, a term usually used to refer to air heaters of any size. Boilers
come in a vast range of types and sizes.
The critical design factor is pressure. Boilers are fitted with safety valves
that release the steam or water if the pressure rises significantly above the
design pressure. The safety-equipment requirement and staff-monitoring
requirements are far less stringent for low-pressure boilers, so there is a
significant incentive to use low-pressure except where high pressure is
needed, or more economic.
A “low-pressure” steam boiler operates at a pressure of no more than
15 pounds per square inch, 15 psig, more than the local atmospheric pressure.
This means 15 psig as measured by a gauge exposed to the local atmospheric
pressure. In comparison, “low-pressure” hot water boilers are allowed up
to 160 psig. There is a good reason for the extreme difference in allowable
pressure:
When a steam boiler fails, the effect can be catastrophic: as the steam
expands uncontrollably, it is like a bomb going off. In comparison, when a
hot water system bursts, the hot water pours out, but there is no explosive
blast like there is with steam. For this reason, “low-pressure” hot water
boilers are allowed up to the higher pressure of 160 psig.
Boilers and system components are regulated by codes. These codes are generally
written, and updated, by practitioners in their geographic area. The main
codes in North America are those issued by the American Society of Mechanical
Engineers (ASME) Boiler and Pressure Vessel Code while the European Community
has their own, and in many areas, much less demanding set of codes. It is therefore
critical that a designer or operator knows the local code requirements, since
their experience from one place may not be relevant in another jurisdiction.
Read more ---> Boilers Design and Components
Commercial Boilers
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