Wax motor
en.wikipedia.org350 points by mhb 2 days ago
350 points by mhb 2 days ago
Wikipedia page has a small error. It shows an actuator (i.e. wax motor) described as thermostatic radiator valve https://en.wikipedia.org/wiki/Wax_motor#/media/File:Thermisc...
These are two separate things: thermostat will close and open based on surrounding temp., the actuator on the other hand opens and closes based on energizing a heating element that is driven by a separate thermostat.
Wax motors are pretty cool things. They rarely fail and do their job even in damp environments. I take care of my better half's hotel with approx 100 of these installed and we replace one of these once every couple of years.
As you seem to know how to explain that would you mind fixing it? You don't even need an account.
Wouldn't the thermostatic radiator valves contain a wax motor? According to the definition in the article, using ambient heat as the energy source counts. Or are you saying it's only a wax motor if there's electric heating?
My understanding is that wax motors are based on actuation - they are intentionally and deliberately either heated to extend or cooled to retract, and if ambient temperature is used as one endpoint, the other will not be ambient (i.e. a heating element or cooling peltier).
Thermostatic valves are ambient at both sides - they expand and contract naturally with the existing temperature, so they are not motors per se, because there's no actuation beyond the temperature.
Why does there need to be a thermal gradient? It seems like the action driving the actuator is the expansion of the wax due to temperature. You don't need a persistent heat flux to get that, the wax just needs enough heat warm up and change phase.
Edit: also, the actuation from the wax motor only happens while it is absorbing (or losing) heat, even if it later ends up in a steady state with no heat flux.
There needs to be a gradient or the wax won't move due to temperature. The motion is the change in state, as you say, but it won't change state if you don't heat or cool it.
That's why it's a motor, like in dishwashers, not a thermostat like in e.g. greenhouse windows or radiators.
It doesn't need to be persistent, but without some way to create a state that is different than ambient, it's not a motor.
I'm not sure I get what you mean.
There are commercial thermostats where the wax element itself is both the temperature sensor and the actuator, eg Thera-100 T1002W0.
If you want to see one in action, I found this: https://www.youtube.com/watch?v=sApyrDEXGAI
Here is a timelapse of one opening a greenhouse window as it gets warm: https://youtube.com/watch?v=S-55VBYbbdo
It was so refreshing to see a video with a clear and direct title. In 2026 this would have been "We cracked open a motor. You won't believe what we found inside! <emoji>". Checking the channel, it seems they have succumbed to this for their latest videos.
I'm surprised this page doesn't mention the automotive thermostat which uses the same principle to control the flow of coolant between the engine block and radiator in an ICE vehicle.
Perhaps you would consider adding that information? That's would be an interesting addition!
The "See Also" has "Wax thermostatic element" [0] which seems focused on automotive applications, so perhaps it was there and grew large-enough that it got split off.
> Its principal application is in automotive thermostats used in the engine cooling system.
Big Clive took one to bits some years back: https://www.youtube.com/watch?v=uPuvhnIoz2g
What a treasure Big Clive is. Educational, entertaining, and zero of those YouTube cliches and clickbait that everyone hates. I don't think he's ever said "Like and subscribe" literally ever.
The expansion of paraffin wax is substantial. I have experience wax potting guitar pickups as well as bicycle chains. I use a skinny, tall tin can for this, placed in boiling water. When the liquid wax solidifies, it not only pulls away from the sides of the can so that the resulting ingot slides out freely, but a void forms in the center. The top surface has a depression and a deep hole in the center.
Using this as a greenhouse vent actuator is pretty cool. It just makes so much sense.
I love alternative types of actuators. Electromagnetic motors are great but they're pretty complex to make, require rare earth metals for best efficiency, and require gearing in most applications. I think in the far future most of our devices will be using other types of actuators, probably made mostly of organic materials. There are many concepts for alternative actuators that just need some breakthrough materials to work.
Seems this would make it possible to make a relatively cheap waterproof actuator if you made it out of something corrosion resistant?
I've been looking for actuators to use in damp/wet environments and sealed actuators are rather expensive and supposedly don't last too long
Some hot water radiator systems use wax actuated valves made from brass (Taco brand is common). They are extremely simple and robust.
thank you for the pointer!
I've struggled to protect eletronics. Waterproof enclosures all fail over time. Though I have some ideas for immersion in mineral oil. But finding actuators that could work has been a bit of a struggle. These look cool, though maybe not something one could run off 5V :) Ill keep looking around
This is why wax motors are used for washing machine door locks.
how does it work for a door lock?it seem it works pretty slowly.
Mayne you know, are the internal components already designed with corrosion in mind?
I have this in the greenhouse that came with my house. Seeing its roof closed in fall after it had been open all summer made me question my sanity.
The greenhouse vents example reminds me a lot of a float valve (or ballcock).
It's a simple mechanism that used buoyancy to either open or close valves as water level changes in a container.
Huh. Do these work in a vacuum? Presumably if sealed right? I imagine there's a few space applications, particularly with solar panels.
Yeah, they are used in space. I don't work directly in this field, but have discussed wax motors with some newspace/smallsat folks, and get the impression they are popular for the same reason nitinol wire actuators are: few moving parts, no rotary bearings, resettable/multi-use unlike pyrotechnic actuators.
My old espresso machine had one of these, always amazed by the simplicity and robustness. Low-tech solutions often hit different.
Wax elements are also used in thermostatic valves for faucets (to keep faucet temperature constant given variable hot and cold mains): https://rogerdickey.com/the-ideal-faucet/
Moen figured out a good enough solution without wax called moentrol
Push/pull adjusts volume, rotation adjusts hot/cold mix
Hard disagree with that faucet design, but is a neat idea. I like my bathroom faucet as low maintenance as it already is.
The use case for the full unmixed hot tap is hygiene (usually washing face and shaving).
I also don't want any hot water mixed in when I'm washing my hands. The water coming out of the unmixed cold tap indicates the ambient temperature of the pipes. That's a feature, not a bug.
You should use warm water when you're washing your hands.
Why?
I'm already upset enough about what the water heater water is doing to my skin and am about to go tankless under my bathroom sink!
That's by far the more practical option anyway if we truly cared about the problem instead of fawning over engineer porn. The problem is solved. This is pointless engagement about temperature preference masquerading as something more interesting.
It used to be public health recommendation (bathrooms in commercial buildings will often only have warm water, for example, because code required it).
There's been studies demonstrating that soap is what matters.
at least in my home, both the cold and the hot water are very uncomfortable to wash my hands in, but mixing it right takes ~15s every time so i usually just accept the discomfort
there is this thing named "Single Lever Wash Basin Mixer Tap".
I think it takes time because the hot water line doesn’t immediately return hot water
I got one from a microwave, it opened vents. It is incredibly strong, also, takes soo much power and is so slow - although i suppose near heat it must work great.
Isn't this more like a solenoid than a motor?
Objects like this make me think of grimdark (steam|diesel)punk works like the video games Dishonored or BioShock. It feels like there's a touch of occultism or corruption whenever one creates a device that exploits analog side effects to create machines in a closed, black-box package.
I see what you mean, but it’s less the exploitation itself than its immediacy and legibility. It doesn’t vanish behind a million abstractions or complicated miniaturization processes but can be readily experienced and understood, like steam.
On the other hand one might as well associate it with “solar punk”, especially when powered by ambient temperature.
Yes, it seems generally *punk. It’s funny that steam, diesel, and solar punk have this association with immediacy.
Does the originator, cyberpunk? Lots of cyberpunk stories present us with a society that is dominated by a digital abstraction. But the protagonist is special, so, they might not be.
I think the “punk” in cyberpunk was about the AI having a gritty, streetwise protagonist to enable it/fight against it. Extremely immediate.
> Objects like this make me think of grimdark (steam|diesel)punk works like the video games Dishonored or BioShock. It feels like there's a touch of occultism or corruption whenever one creates a device that exploits analog side effects to create machines in a closed, black-box package.
The second sentence also fits for field effect transistors and solid state electronics in general.
In the spirit of grimdark steampunk, have you ever heard of pneumatic logic? I still see these systems operating normally in some older mechanical rooms, it’s cool to see them still working after 40-50 years.
My mini truck uses a couple of these with vacuum lines to control the choke and EGR. They are expensive to replace for obvious reasons.
Why is this obvious? Beeswax is not particularly expensive I think?
now go blow your mind with the first known conversion of electrical to mechanical energy via "Franklin Bells"
TWO HUNDRED SEVENTY FIVE years ago
in 1752, wow
(but they had no idea why it worked)
* https://en.wikipedia.org/wiki/Franklin_bells
Before the storm, the device would ring to remind Franklin, who had been obsessed with the study of lightning, urging him to chase the lightning
ha "chase the lightning" needs to be a catchphrase
We’ll circle back, launch our go to market strategy, and chase the lightning for a win…
I once had an interview at PA consulting where they asked one of those questions where they have "the answer" but their question isn't well specified enough to lead to that unique answer. They kept adding conditions, but I hadn't ever heard of wax actuators before. (I was like 19 or something - didn't get that job!)
...what is the point of starting this post with an egregious slop image?
