Re: reastats and pressure points

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Posted by Carl Jones on February 26, 2000 at 16:03:04:

In Reply to: reastats and pressure points posted by synomen on February 17, 2000 at 14:08:52:

: What are outside reastats are used for what:
: a. starting and stopping modes
: b. ambulant outside air temps
: c. safety valve
: d. zone device
: ????
: What pressure point of a hot water boiler or vessel is considered dangerous?

: Thanx for your help!!
: Synomen

Agreeing with most of what I saw posted in regards to your question. However,
the American Society of Mechanical Engineers (ASME ) classifies both a low pressure
and high pressure type of Hot Water Boiler. The exact Code conditions are operating
at a pressure below 160 psi or 250 degrees F (Low Pressure) and above 160 psi and
250 degrees a high pressure unit. If you refer to standard properties of water
tables you will note that 250 degrees is for water at approximately 30.199 psia, or
another way to look at this is convert absolute pressures to gauge pressures,
30.199 (psia) - 14.7 (atm) = 15.499 psig. Also, interestingly enough if you
were to look at the steam tables at 15.3 psig or 30.00 psia you would the Code limit
for low pressure steam boilers. boilers at 250.33 degrees F. This then becomes the
limiting factor of Low Pressure Hot Water Boiler. equates to the 260 degree limit
for low pressure hot water boilers. Basically, if you are concerened with the point
they become dangerious, just consider any temperature above 125 to 135 degrees.
Above this temperature the heat contained in any water being released is high
enough to produce serious scalding. The violent rupture of hot water boiler can
produce serious physical and property damage. I would offer to you to contact the
National Board of Boiler & Pressure vessel Inspcetors at and
review some of the available articles contained in their on-line "Classic" serries

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