Get Compressed Air From Falling Water With The Trompe

If you’re like us, understanding the processes and methods of the early Industrial Revolution involved some hand waving. Take the blast furnace, which relies on a steady supply of compressed air to stoke the fire and supply the oxygen needed to smelt iron from ore. How exactly was air compressed before electricity? We assumed it would have been from a set of bellows powered by a water wheel, and of course that method was used, but it turns out there’s another way to get compressed air from water: the trompe.

As [Grady] from Practical Engineering explains in the short video below, the trompe was a clever device used to create a steady supply of high-pressure compressed air. To demonstrate the process, he breaks out his seemingly inexhaustible supply of clear acrylic piping to build a small trompe. The idea is to use water falling around a series of tubes to create a partial vacuum and entrain air bubbles. The bubbles are pulled down a vertical tube by the turbulence of the water, and then enter a horizontal section where the flow evens out. The bubbles rise to the top of the horizontal tube where they are tapped off by another vertical tube, as the degassed water continues into a second vertical section, the height of which determines the pressure of the stored air. It’s ingenious, requiring no power and no moving parts, and scales up well – [Grady] relates a story about one trompe that provided compressed air commercially for mines in Canada.

Need an electricity-free way to pump water instead of air? Check out this hydraulic ram pump that takes its power from the water it pumps.

23 thoughts on “Get Compressed Air From Falling Water With The Trompe

    1. The two are indeed working by similar means.
      The trompe though more or less uses the flow of water to bring with it air bubbles, though with a thin enough entry tube, the surface tension of the water would eventually be sufficient for it to work like the Sprengel pump.

      Though, this would then require a lot of entry tubes in parallel to get any meaningful pumping speed for compressed air applications. But I wouldn’t be surprised if it ends up more energy efficient compared to just using the flow of water to drag air with it. After all, a Sprengel pump is one of the more energy efficient vacuum pumps around, even to this day.

  1. “requiring no power” I don’t think so unless you have finally invented the perpetual motion machine. Probably what you meant to say was no electric power or something of the sort.

      1. Well, there’s also the reporters’ version, for example, “This wind turbine can power 100,000 homes”.

        Which means: the turbine will provide enough power to meet the electrical demand of 100,000 homes in a country that relies mostly on natural gas for heating, cooking, and hot water, at the average demand of the average home, at its peak output. The absolute amount of power divided by the given number of homes usually corresponds to the power demand of a hair dryer or a tea kettle.

    1. Requiring no power means you are allowed to use your own children to carry pails of water. Not using their energy would be a waste since you have to feed them in either case. Grad students are an even more reliable supply of free energy.

  2. I have always wondered how they did this before compressors this was one of the great mysteries of the Industrial Age for me.

    I immediately see the tie in with the hydraulic ram pump, but just as others said, this really is utterly brilliant. I get how it does it’s thing now and I get how they could be daisy-chained together.

    I know it’s mainly an electronics site, and I do read those articles too, but I love the range of hackaday and seeing lost technologies explained like this is deeply satisfying

  3. An early 60’s book, Tunnels by Gosta E Sandstrom illuminated me to this and many other Hacks that man has done to get at things underground and go places there too. I picked it up at a garage sale when it was10 years old. Air pressurized the works underground-underwater and one man was blown thru the roof and up into the lake being tunneled under! Hundreds killed tunneling under the Alps. Rocks & mud flowing like water and you got to dig thru them.14 inch timber crushed like matchsticks. Great reading when I was younger. The dream of the Chunnel.

  4. Interesting and great reference comments too. Primitive advanced technologies are always interesting to learn about. I was almost going to watch this video since Youtube AI showed… though was off in the world of getting back into electronics projects for the winter. Neat to see Dan pick this one up and the comments too.

  5. The pressure at the bottom of a column of water is about 1/2 psi per foot of height, so I would imagine that you would need about 5 or 6 feet of water head to achieve a pressure of 2.5 or 3 psi. Of course, that venturi also takes a little vertical height.

    How much air can the venturi entrain? It must be related to water flow rate and velocity, but I don’t know of any handy rules of thumb like 1/2 psi per foot of height. Sorry.

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