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.
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.
> 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.
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.
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.
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!)
OMG, I HATE HATE HATE those interviews. I call them "Magic Word" questions.
I was drilled for several minutes by an interviewer who was trying to get me to use the ONE PARTICULAR WORD out of the entire English language to describe something - something I had 100% already specified.
If his manager hadn't been present, it would have ended with me not getting the job (and potentially a homicide) (which a jury trial would have acquitted, after I let him cross-examine me).
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.
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.
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.
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 disagree, I think motor in this case only means “creating movement”. The motor is the thing creating movement depending on the ambient temperature.
Also you seem to have a miscommunication with the person replying to where they are talking about a special thermal gradient and you mean it in a temporal sense.
Apples and apple seeds to me. The way I see it, the thermostat contains the motor (EDIT deleted the rest of explanation).
EDIT: the way I see it, talking about gradients here is nonsense. The wax motor works by expansion/contraction due to point temperature. No gradient is involved. Gradients are thermostat-level thinking, and even then, in the greenhouse scenario, there is no gradient to talk about, because the whole point is just to vent the heat from inside to outside when inside crosses certain absolute value of T, and the only "gradient" that matters is the assumption that outside side is less than T at all times.
no the material inflates proportionate to absolute temperature, causing motion, iiuc
things lietrally change its volume maintaining mass when its temperature changes, due to atoms moving more energetically, like something be 4x4x4 inches at 40F, but 4 1/16 x 4 1/16 x 4 1/16" at 200F
this isn't a Stirling engine with a displacer, just a sealed off piston
> 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.
I had to replace about half of them within the first ten years of usage in our floor heating. It may have been a bad batch, but I would definitely not claim that the rarely fail. My car did not fail once during that time.
I bet poor manufacturer, or poor quality, or poor batch. Also maybe NC (normally closed) vs NO (normally open) behave differently? In any case, the ones we use are solid, especially given they are installed on damp AC ice-water circuits.
There are some lines of front load washers that use them as the door lock. And the ones they use have a habit of shorting out and taking the control board with them.
The idea is that so long as the washer is providing power the motor stays locked. But if you ever loose power within a few minutes you can open the door if you had to.
Similar to how wax works in thermostatic valves for faucets (to keep faucet temperature constant given variable hot and cold mains): https://rogerdickey.com/the-ideal-faucet/
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.
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.
Anyone who has handwashed many dishes could tell you that cold water will work, but hot water works faster and with less effort. It's no different for your hands. For best results use hot water to wash your hands and cold water to rinse them then put some lotion on them.
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
It doesn't maintain temperature at all; it maintains the hot/cold mix.
The problem is that the hot temp varies widely (and the cold temp varies slightly as you drain the house tubing reservoir and begin drawing ground-temp water).
Thermostatic mixers make sense for continuous flow applications - showers, filling a large bathtub for example. But I don't think they make sense for a kitchen tap - where you might be filling a small basin.
The goal is that the water in the basin is the correct temperature, not the stream filling it - which means you need to compensate every time based on how much cold is already there before the hot water arrives. And that varies seasonally.
The time it takes for hot water to arrive tends to be a big proportion of the total time the tap is running, so you actually don't want controlled 40C water once hot water arrives. Perhaps if you had instant hot water, this would be useful.
A solenoid is a coil of wire that functions as an electromagnet. Solenoid actuators are named after the coil. This device does not contain an electromagnet, so it would be inaccurate to call it a solenoid.
You're not OP, but I think it's obvious that the question wouldn't have been asked had the nomenclature been more precise (i.e., had the article been titled "wax linear actuator" rather than "wax motor"). Yes, it's "like" a solenoid in the sense that it uses electricity to move a plunger, but a solenoid is a very specific type that relies on electromagnetism. Linear actuators are also available in other forms -- geared and pneumatic ones immediately come to mind -- and I felt it was important to point out the distinction.
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.
"Just need some breakthrough materials to work" is the kind of "just" that stops things dead in their tracks.
So far, the game in town has been primarily hydraulics or electromagnetics, and the things that replace them are better hydraulics and better electromagnetics. Alternative actuators are either super niche or fail to leave the labs.
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.
In washing machine application the locking action is quite fast as the heating element is PTC connected more or less directly to mains, pretty substantial amount of energy gets dumped into the wax over few AC line cycles. In that application (and also in most industrial automation situations) ~100ms is more than fast enough because when most of the effector components are AC powered you end up with ~40ms worst case actuation delay just from the physics of AC electricity. On my washing machine it is quite noticeable that when you press "start" the door gets positively locked well before the capacitive sensing "button" finishes playing its haptic feedback non-sense. (the fact that front panel of cheap-ish toploading washing machine is actually a huge touchpad with haptic feedback that is designed to look and behave like five physical buttons says many things about economics of manufacturing stuff for that somewhat hostile environment at these scales)
oh interesting - I didn't realize PTCs can be used that way safely. I thought it hits a target temperature and then will continue heating at that temperature (which in your scenario would be unsafe). Maybe for my usecase it'll be hard to find a suitable actuator b/c I have a 5V system running of battery
> When a cycle is started, a wax motor is actuated pushing a pin outward and locking the door. This design has cost, reliability and safety advantages. In moist conditions a wax motor costs less for equivalent reliability than an electromagnetic solenoid or motor latch. It has a predictable passive release delay. If power is lost the door remains briefly locked, designed to be longer than the high speed spin cycle coast-down time, then reliably unlocks as the wax cools.
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
Imagine if you will- a 3d sintered (https://en.wikipedia.org/wiki/Sintering) sand structure. Placed in it is heat collecting material- aka salty-brine- which stores heat as a kind of battery. Placed within it are waxmotors as actuators. Placed within it are nodes with https://en.wikipedia.org/wiki/Silica_gel - the whole thing is literally dumb as a printed rock, but also capable to do work powered by the sun.
It collects moisture from the air, distills the water out of the silica gel and stores it- then releases it in the evening to plants at the root. A terraforming rock, printed in-situ, with materials available in situ (well except silica gel, optical fibers and wax-motors).
I always wondered what the actuator in the exhaust air valve for my apartment ventilation was - now I'm pretty sure it's a wax motor! You can use a switch to increase the airflow, but it takes a few seconds to react and opens/closes very slowly and quietly.
Some of them are a sort of hydraulic one that uses a spring and some fluid to make the spring release slowly. No idea which you would have lol.
The slow closing prevents water hammer, at least in water systems. In air systems it might just prevent a blast of back pressure blowing all the dust out of your vents onto your carpet.
103 comments
[ 4.1 ms ] story [ 79.3 ms ] threadhttps://en.wikipedia.org/wiki/Wax_thermostatic_element
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.
https://en.wikipedia.org/wiki/Pneumatic_circuit
On the other hand one might as well associate it with “solar punk”, especially when powered by ambient temperature.
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 was drilled for several minutes by an interviewer who was trying to get me to use the ONE PARTICULAR WORD out of the entire English language to describe something - something I had 100% already specified.
If his manager hadn't been present, it would have ended with me not getting the job (and potentially a homicide) (which a jury trial would have acquitted, after I let him cross-examine me).
Thus moved solar-thruster
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.
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.
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.
Also you seem to have a miscommunication with the person replying to where they are talking about a special thermal gradient and you mean it in a temporal sense.
EDIT: the way I see it, talking about gradients here is nonsense. The wax motor works by expansion/contraction due to point temperature. No gradient is involved. Gradients are thermostat-level thinking, and even then, in the greenhouse scenario, there is no gradient to talk about, because the whole point is just to vent the heat from inside to outside when inside crosses certain absolute value of T, and the only "gradient" that matters is the assumption that outside side is less than T at all times.
things lietrally change its volume maintaining mass when its temperature changes, due to atoms moving more energetically, like something be 4x4x4 inches at 40F, but 4 1/16 x 4 1/16 x 4 1/16" at 200F
this isn't a Stirling engine with a displacer, just a sealed off piston
There are commercial thermostats where the wax element itself is both the temperature sensor and the actuator, eg Thera-100 T1002W0.
I had to replace about half of them within the first ten years of usage in our floor heating. It may have been a bad batch, but I would definitely not claim that the rarely fail. My car did not fail once during that time.
The idea is that so long as the washer is providing power the motor stays locked. But if you ever loose power within a few minutes you can open the door if you had to.
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
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.
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.
There's been studies demonstrating that soap is what matters.
Push/pull adjusts volume, rotation adjusts hot/cold mix
The problem is that the hot temp varies widely (and the cold temp varies slightly as you drain the house tubing reservoir and begin drawing ground-temp water).
The goal is that the water in the basin is the correct temperature, not the stream filling it - which means you need to compensate every time based on how much cold is already there before the hot water arrives. And that varies seasonally.
The time it takes for hot water to arrive tends to be a big proportion of the total time the tap is running, so you actually don't want controlled 40C water once hot water arrives. Perhaps if you had instant hot water, this would be useful.
It's a simple mechanism that used buoyancy to either open or close valves as water level changes in a container.
https://en.wikipedia.org/wiki/Ballcock
So far, the game in town has been primarily hydraulics or electromagnetics, and the things that replace them are better hydraulics and better electromagnetics. Alternative actuators are either super niche or fail to leave the labs.
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
Mayne you know, are the internal components already designed with corrosion in mind?
> When a cycle is started, a wax motor is actuated pushing a pin outward and locking the door. This design has cost, reliability and safety advantages. In moist conditions a wax motor costs less for equivalent reliability than an electromagnetic solenoid or motor latch. It has a predictable passive release delay. If power is lost the door remains briefly locked, designed to be longer than the high speed spin cycle coast-down time, then reliably unlocks as the wax cools.
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
It collects moisture from the air, distills the water out of the silica gel and stores it- then releases it in the evening to plants at the root. A terraforming rock, printed in-situ, with materials available in situ (well except silica gel, optical fibers and wax-motors).
The slow closing prevents water hammer, at least in water systems. In air systems it might just prevent a blast of back pressure blowing all the dust out of your vents onto your carpet.