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.
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.