Amazingly simple magnetic heat-switching valve

Energy & Sustainability Science
Amazingly simple magnetic heat-switching valve
Bahl-Erikson Valve.png

Here’s an interesting article about a very clever gizmo by two scientists at Denmark’s Risø National Laboratory for Sustainable Energy. It’s being hyped as a totally original invention, but the idea is so conceptually simple that I have a hard time believing it’s entirely new under the sun. Still, though–very cool.

So, quick science review: If you take a magnetic material and heat it up, eventually it stops being magnetic. The temperature at which this happens is called the “Curie temperature” (named for Monsieur, rather than Madame, Curie). The process is completely reversible: Cool the stuff down again, and its magnetism returns. And it turns out, with modern manufacturing, a very wide range of Curie temperatures is possible depending on the specific materials involved.

What Danish scientists Christian Bahl and Dan Eriksen have done is exploit the Curie effect to create a simple, heat-switching mechanical valve: At low temperatures, a magnetic attraction keeps the spring-loaded flapper in one position, but at temperatures above the Curie point, the magnetic attraction is annulled and the spring drives the flapper into the other position. Like other devices commonly called “magnetic valves,” the Bahl-Erikson valve has the advantage that it can be operated without introducing any holes into the valve case, which is handy if you’re working with nasty or delicate materials. Unlike other magnetic valves, however, it does not require any kind of external power to operate, and hence is more reliable as a failsafe.

18 thoughts on “Amazingly simple magnetic heat-switching valve

  1. Colecoman1982 says:

    I’m not, entirely, sure that this would be, necessarily, any better as a fail-safe than a powered valve. The whole point of a fail-safe valve is that, when the system fails, mechanical systems (often gravity, in particular) cause the valve to either slam open or shut (depending on which mode is declared to be safe). In fact, since electricity is, usually, not an inherent component of fluid systems I would say that the electrical system might even be considered safer as it is, completely, unrelated to the function of the material being used by the system where things like the ambient temperature on the outside of the pipes could, theoretically, be extreme enough to override the critical temperature of the fluid in the system.

    Of course, at the end of the day, terms like “better” or “worse” aren’t very good for defining something like a fail-safe system as, I would assume, it tends to be very situation specific.

  2. Colecoman1982 says:

    In any event, I forgot to mention that I think this is a very cool project. I can, definitely, see uses for this in things like un-powered thermostats and the like.

  3. Silverman says:

    I have a Weller soldering iron that controls its temperature using a switch that works just like this valve. It’s a great idea.

  4. Anonymous says:

    Maxwell’s Demon? Is this legal?

  5. Don Ellingham says:

    Clever, yes but here in the USA, a patent (if they got one over there) is not granted for an obvious extension of technology, under the new US patent rules. And yes, I too have one of those Weller irons that use the curie temperature magnetic tips. They’re pretty neat and available for several operating temperatures in the 6-800 degree F range (min. 300C), as I recall. Other thermostats have used curie mechanism too in the past but I’ll bet, under the old rules, Weller got a patent for it in their application. Whether the valve would be considered an obvious extension here now, would take several thousand dollars and 2+ years in the USPTO. This is a clever application for very hot fluids (oil in commercial solar collectors?)..

    I’m not sure if the curie temperature could be low enough for over-temperature “dump loads” for hydro solar thermal collectors, a new consumer volume safety application. In the summer overheating is an issue and those 2-way valves might provide alternate paths to a finned pipe or your hot tub or pool. However, these apps (near 100C) seem unlikely as most low-curie rare earth magnets or metals switch at above 300C, too hot for water even under pressure. Of course bi-metallic and nitinol both work in these lower ranges already for thermostats.

    Don Ellingham
    Energy Conservation Products

  6. Oleksiy says:

    I remember my father telling me never to clamp a magnet next to the pipeline. The tiny metal particles in the water will end up accumulating near the magnet, eventually blocking the line completely. Its probably only true for metal pipes, and not s much plastic.

    In any case, great idea. If the tension of the spring is controlled will make a nice passive controller for showers: I always wanted to have a controller for water temperature, but I guess nobody wants to make one because of the liability issues.

    1. Don Ellingham says:

      Good point about metallic particles and the material doesn’t matter, the particles will find the field.

      As I said earlier, most curie points (except some really costly exotic metals) are around 300C (ouch). Not useful for a shower.

      But do not despair, if your pockets are deep enough, there are thermostatically controlled showers from several hi-end fixture manufacturers. Find the most expensive plumbing fixture store in your area and they will have several.

      In the meanwhile, use a cheap low-flow shower-head and save the money to pay for your thermostatic control someday!

      Don Ellingham
      Energy Conservation Products

  7. Roh says:

    Seems like the Denmark’s Risø National Laboratory discovered that when you open up any cheap Chinese rice cooker, behold there is a magical switch. WHAT?!? Its a magnetic switch described exactly in this artice but, it uses a coil to heal up instead of water. Wonderful rediscovery.

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I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I am a long-time contributor to MAKE magazine and My work has also appeared in ReadyMade, c't – Magazin für Computertechnik, and The Wall Street Journal.

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