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The Surprising Stories Behind Heating Inventions


Did you know that the first pressure relief valve was invented in 1681 because the King of England really liked jelly? And that the first gravity heating system was used to warm chickens? How about the expansion tank that was assembled using an overstock of baby carriage wheel rims? In this episode, Dan Holohan tells the fascinating stories behind inventions that paved the way for modern heating.


Episode Transcript

I was thinking about how the things we take for granted came to be and what life would have been like had they not appeared when they did. 

Take the lowly pressure-relief valve, for instance. I know it’s something you’d rather not touch when you’re on a job because, as with everything else in life, once you touch it, you seem to own it. Unless you’re feeling adventurous, you’ll look at that lowly pressure-relief valve and hope that it does its job if the boiler ever goes berserk.

I was reading a magazine that is more than 100 years old the other day and came across this little story, which I found delightful. Listen:

“The first safety valve was invented in 1681 by Denis Papin, a Frenchman, who was born at Blois, France in 1647. He commenced his experiments on the phenomena of steam in July 1676, at London, under Robert Boyle, the distinguished Irishman who founded the Royal Society of London.  About 1680, Papin brought out a little steam apparatus called, “Papin’s Bone Digester,” for softening animal bones for ‘cookery, voyages at sea, confectionary, chemistry, and dyeing.’

“England’s Charles II ordered Papin to make a digester for his laboratory at Whitehall, and the invention excited much interest. By means of this steam-pressure cooking machine, delicious jellies were made from beef, mutton and other bones. Enormous strength was needed in the machine to stand the high pressure generated, and Papin found that he could only make his machine successful by contriving a mechanical device that would release pressure at a certain point and thus prevent explosion.

“This he finally worked out during 1681 with the first steam-pressure safety valve. With this valve, his machine could be used without fear. A hundred years later, James Watt and others made use of his invention in connection with a steam-powered engine, and later in the 18th Century, James Watt and other inventors made use of a similar apparatus used for heating purposes.

“Papin was one of the great benefactors of the human race. Living in the age of Pascal, Newton, Boyle, and Leibnitz, he partook liberally of the spirit of progress, which was a work in those days to free the human race of its shackles imposed by ignorance of natural laws, and may well be said that Papin ‘builded better than he knew.’  He was both a prophet and executor of mechanical progress, and his memory is one of the sacred treasures of the power- and low-pressure, steam-heating industries.”

So, because the King of England liked jelly, we now have pressure-relief valves. Isn’t that wonderful? There’s a sketch of the device Papin invented in that old, yellowed magazine. The relief valve sits atop a big, closed kettle. It is a long lever attached to a pivot point. There’s a plug connected to the lever, very close to the pivot point, and this sits in a hole in the boiler. The lever reaches out several feet and had a movable weight near its end.
You could move the weight this way and that to adjust the relief pressure. 

And all for the sake of making meat jelly.

Let’s hear it for the inventors.

In my files, I have a sketch of the first hot-water heating system, which also has a neat connection to food. The man who first came up with the idea of central, hot-water heating was Jean Simon Bonnemain. The sketch I have is from 1777 and it shows a big, enclosed kettle sitting atop a fire. This was the boiler. Coming out of the top of the boiler there is a large pipe. It goes all the way up to the top of the building and then laces its way back and forth across each floor of the building and all the way back to the top of the kettle. The pipes are the radiators. The big pipe enters the top of the boiler through a dip tube, much like the dip tube that cold water uses to enter a water heater nowadays. There’s a second pipe that runs from the kettle to the top of the building, and at the top of this pipe there is a funnel. This is how you filled the system. Go get yourself a bucket and start climbing stairs. Oh, and one more thing, connected to the top of the main heating pipe, there’s a second pipe that rises up and then loops over into the top of an open tank. This gives the heated water a place to go, should it expand too much, a very simple relief point. Not a valve, but it did its job. This was the world’s first gravity system and Jean Simon Bonnemain used it to warm chickens for the Paris poultry market.

How about that?

Bonnemain’s open tank got me thinking about how far we’ve come, and all because of inventors. Today, we have these wonderful, pressurized tanks that take up so little space in a boiler room, but as with pressure-relief valves, most of us take those tanks for granted. We see them on just about every job and we don’t give them much thought.

I was doing some research for my book Classic Hydronics. It has a chapter about air and how that air comes out of solution water when we heat the water. The air often gets stuck in the radiators. There’s a lot to this subject and I had a lot of fun writing about it. I wrote to the good folks at Amtrol in Rhode Island at one point and asked if they had anything of an historical nature that they would like to share with me about their company. I already knew that the first diaphragm compression tanks (the ones we now take for granted) came from Amtrol, but I was curious about how that came to be.  A few days later, I got a note from their Director of Marketing. He told me that he was going to send me a package. He did, and it was a large box.

I opened it and found a couple of things that delighted me. First, there was a disassembled version of Amtrol’s popular Extrol compression tank. I had seen these parts at their factory years ago when I paid a visit, but it was great to have my own because I was doing seminars at the time and this helped me to explain these things.

Seeing is believing. And touching also helps.

The other thing in the box looked like a small barbeque grill. I emailed Ken and asked him what the heck it was. He told me that it was one of the first prototypes of today’s modern compression tank. They used it to prove the concept of a diaphragm compression tank. They had made it years ago by bolting together two streetlight blanks (imagine that). There is a sheet of rubber between the two halves, a pressure gauge on one side of the rubber, and a threaded female connection on the other side for the water. It made me smile.

Ken wrote, “The first commercially available version of the tank was the flying-saucer shape you see in the photos (he had sent those as well). This had a formed-rubber diaphragm trapped between two halves that we crimped to lock the tank together. This tank had legs welded to it so the contractor could screw it to the floor joists in place of the plain steel tank it replaced. As you know, our industry is slow to break tradition.”

For sure. If installers are used to hanging things on the ceiling, let’s go along with that.
He then told me that the early Extrol tanks didn’t use an air valve because they wanted to minimize the potential leak paths and speed production.

So how did they charge those tanks? They took a measured chunk of dry ice and put it inside each tank prior to assembly. Once the tank reached room temperature, the ice evaporated, releasing its gas and putting a 12-psi charge behind the diaphragm. 

I wouldn’t have thought of that. Would you?

He also wrote, “Our first cylindrical Extrols were manufactured using an overstock of baby-carriage rims. When the competition arrived, we found small holes drilled into their steel hoops, mimicking what they must have thought was a necessary feature.” I think that’s as delicious as Denis Papin’s meat jelly.

“Finally, in the 1960's,” He continued, “we developed the familiar deep-drawn version you know today, including the hoop-ring attachment method. When a flat disc of steel is drawn under hundreds of tons of pressure into the domes you see in the samples, the strength doubles as a result of cold working. This results in a lighter and stronger tank.”

I get to ask a lot of questions in my work, and the thing that struck me about this man was how generous he was with engineering information, company lore, and how he answered every single question I asked, no matter how tough it was.

He told me straight up, without hesitating, and then he asked me how else he could help?
I admire this guy and this company.

I admire his generosity, his honesty, his enthusiasm, and the pride he has in what his company is making.

Here’s to the inventors - then and now. Let’s go get some meat jelly!

Did you like that story? If so, please share it with your friends. And if you haven’t already, please subscribe to this podcast. I have many more Dead Men Tales to share with you.
And I appreciate your taking the time to listen. The listener is always more important than the storyteller. I already know what I know. And now you do too. Pass it on. Thanks.

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