The Origin of the Relief Valve

Published: January 24, 2010 - by Dan Holohan

Categories: History Lesson

denis papin

Meet Denis Papin

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 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, once you touch it, you own it. Unless you’re feeling adventurous, you’ll look at that lowly valve and hope that it does its job when and 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 in the first steam-pressure safety valve; then his machine could be utilized 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, Watt and other inventors made use of a similar apparatus utilized 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 relief valves. Isn’t that wonderful? There’s a sketch of the device in that old, yellowed magazine. The relief valve sits atop a big, closed kettle. The relief valve 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 jelly.

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. There are no 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. 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 fill 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. 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. Today, we have these wonderful, pressurized tanks that take up so little space in a boiler room, but as with relief valves, most of us take those tanks for granted. We see them on just about every job and don’t give them much thought.

I was doing some research for a book I’m thinking about writing. This one’s about the air that comes out of water when we heat it and gets stuck in radiators. There’s a lot to this subject and I’m having fun thinking about it. I wrote to the good folks at Amtrol® in Rhode Island and asked if they had anything of a historical nature that they would like to share with me about the company. I already knew that the first diaphragm compression tanks (the ones we 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 Ken Cerpovicz, Amtrol’s Director of Marketing. Ken told me that he was going to send me a package. He did, and it was a very big 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 have to explain these things to others from time to time.

The other thing in the box looked like a small barbeque grill. I e-mailed 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’s sitting on the floor in my office right now and it’s making 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 Dead Men 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.

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?

Here’s Ken again: “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 jelly.

“Finally, in the 1960's,” Ken 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 Amtrol’s Ken Cerpovicz was how generous he was with engineering information, company lore, and how he answered every single question I asked, no matter how tough. He told me straight up, without hesitating, and then he asked how else he could help me?

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.