Letters
of enquiry to the Website |
Enquiry to
Webmaster
10th November 2004
Your
webpage
on
the Perkins family
and their inventions is fascinating. I have always
admired the elegant
simplicity of the Perkins heating system and I share
your interest in
the
reasons for its demise. The pressure points quoted
in your paper speak
of the
system dangers due to the high pressure of operation
and cite examples
of
occurrences of explosions and of fires started by
allegedly excessive
pipe
temperatures. The allegations of fires started by
Perkins systems is
curious. I
can accept that an explosion of the pressurised pipe
occurring within
the
furnace would tend to scatter coals and cause a fire
but I question the
contention that the pipes could ever get
sufficiently hot to start
combustion.
Indeed pipes are reported to have become red hot.
Surely impossible if
they
contained water or steam, and impossible if they
didn’t unless of
course they
happened to be in the furnace!
As
to the
temperatures
necessary
to cause singeing and fire, what is the required
temperature I wonder
to cause
paper or timber to char, and what would be the
corresponding steam /
saturated
water pressure at such temperatures? Surely
the system would have exploded before these
temperatures
necessary to cause fire were reached? If
the system has been correctly designed with the
appropriate ratio of
tube length in the furnace to tube outside, the
system must work
safely,
unless, of course some of the external tube is
inadvertently smothered
in
insulation, or perhaps the water level falls so
preventing or hindering
circulation. In this situation the result would be
excessive pressures
and
explosions rather than fire, I suggest.
If
the furnace were lit in mid
winter with part of the
circuit frozen solid [an ever present danger in
churches heated only
one day in
seven] pressure would rise excessively and again lead
to an explosion
rather
than fire. Indeed this occasionally happens at the
present time in
houses with
a back boiler fitted.
All
food for thought,
but I
definitely remain sceptical
about fire occurring without a preceding explosion!
Also any explosion
would
tend to occur in the furnace where the iron/steel
tubes, in a fault
situation,
would be subjected to excessive temperatures and so
be critically
weakened
relative to the rest of the system.
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REPLY
TO
THE QUERY ABOUT PERKINS
The
Perkins HPHW heating
system
according to its inventor A M Perkins, was meant to
operate at
temperatures of
up to 300ºF, but the system could be used for
purposes other than
space
heating, for example it was used as the heating
source for baking
ovens,
enamelling stoves and roasting ovens with
temperatures of up to
600ºF.
The
Perkins system
was designed
as a hermetically sealed system so when the
distribution pipework was
full of
water and had been fully air vented, there could
only ever be water
inside the pipework.
The
expansion vessels were sized to suit the volumetric
water content of
the system
and to absorb the increase in water volume, so
steaming could never
occur. To date no type of safety valve has been seen
on a Perkins HPHW
system. As
the water
content of the pipework system is small it didn’t
need much of an
increase
in the
intensity of the furnace fire to raise the
temperature of the water
dramatically.
Every
Perkins system
seen in
either
Churches or Chapels have all had their pipework
virtually
touching
the base plinth of the wooden pews, so scorching of
the timber could
occur if
the
system temperature was allowed to increase
substantially. It would be
interesting to know at what surface temperature wood
will spontaneously
combust.
When the Perkins systems were first being installed in the 1830's there was no form of temperature control so the water temperature was dictated by the intensity of the furnace fire, and totally dependant upon the stoker who fired the furnace. Talking
to the people who
operated
the systems when they were solid fuel fired, the
furnace fire was
banked down
during the week (especially during periods of zero
ambient temperature)
and not allowed to be extinguished, as other church
services
were held during the week.
The
distribution
pipework was
all heavy
quality hydraulic tubing and bursts due to excessive
pressure didn't
occur,
when fitted with a correctly sized expansion vessel.
The only bursts in
the
pipework known about occurred in severe weather
conditions due to
frost
damage. When the furnace fire was banked down, the
gravity
circulation could
become sluggish and some of the longer pipe circuits
could even have
stopped
circulating altogether.
Written
articles
about the
Perkins system state that as the
water content of the system was so low it did not
take much
overheating within
the furnace to raise the water temperature to 600ºF.
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