Crown Sheets

As everyone knows the old time steam boilers, the ones made from sheets of iron riveted together with large coal fires under them, have crown sheets held in place by stay bolts.   When the water level in the boiler gets low the crown sheet no longer has water on top of it and thus has a hot fire under and hot steam above and thus it gets red hot which both weakens it and stores up a lot of specific heat so whenever water is either pumped into the boiler or sloshed around in the boiler much water flashes into steam such that the safety valves and fusible plugs cannot handle the load and so the boiler blows up and kills people.

Several years ago I had a personal traumatic experience with an engineer who had not done any research into steam generators, monotube boilers, or Field Tube boilers and who was in charge of the safety inspection at a small time alternate energy vehicle meet.  As an indication of how small time this was the runner up to my wood fired steam vehicle was a little tricycle glued together from PVC tubing with a couple of scuba tanks filled with 4500 psi air bungee corded to the back running an air impact wrench hose clamped to the frame that hammered away at one stub axle so one of the rear wheels turned.

The purpose of the meet was to drive for 5 miles through a small town and get publicity and a prize and start the process of saving the world using renewable clean energy to provide transportation.  The safety engineer took his work seriously and while he was comfortable with 4500 psi air tanks precariously tied to a vehicle that would have traveled through several buildings if they had fallen off and the valve broken off he was greatly afraid of modern steam power because he had heard about boilers blowing up.  Therefore I was made to set the safety blow off valve at 100 psi and much precautions were in place for my run and much tension and unhappiness was present.

The safety guy was not swayed by the National Board Synopsis of Boiler and Pressure Vessel Laws, Rules and Regulations that I was showing him about the law in the State of Indiana.  For background there are the ASME codes for boilers and pressure vessels that control every possible metal container with pressure in it.  Every state and province in Canada has adopted the ASME code and then made exceptions to it and the code is enforced by the National Board of Boiler and Pressure Vessel Inspectors out of Columbus, Ohio and this synopsis can be obtained off the internet.  It is quite complex.

The only thing the engineer safety guy knew is that when the crown sheet in a boiler was exposed due to low water level bad things happened and so his only concern was how to measure water level.  I happened to have a Field Tube boiler with a fire underneath it and thus when the tube went dry there was no water anywhere around to explode.  Logic and common sense did not work on the engineer as he was ahead of us steam nuts.  He wanted to see at least two water level sight glasses and was not amused when I told him that I did not have a sight glass because it was expensive to have one that would withstand 1000 psi.

That is why all of us sophisticated steam people do not make boilers, we make steam generators and about a quart and a half of water is in each one so blowing up and killing people is minimized.

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