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Comment by limaoscarjuliet | Hacker News Reader

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.

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As you seem to know how to explain that would you mind fixing it? You don't even need an account.

Traditionally, Wikipedia encouraged you to "be bold", that is, if you think something is wrong, don't complain, don't ask for permission, just fix it. [1]

But now that Wikipedia is becoming more stable, I wonder if this policy is still pushed as much. My understanding is that on all articles there is an army of autistic and obsessive people who will make sure it stays clean (I mean it in a good way), so if you mess things up, it won't last long, as in, seconds.

[1] https://en.wikipedia.org/wiki/Wikipedia:Be_bold

Certainly not all articles; most edits I make stick. The problem is it sticks out as an extremely sore experience when it is the case, so that's what you hear about.

A dear friend of mine had a battle of sorts with a fan of mother theresa in the spanish version of her article.Of course the zealot maintainer won in the end, no place for evidence backed criticism in religious wiki articles.

Yeah I do this for the unicorns list typically. (I try to get my citations the best as possible, the UI for editing Wikipedia is modifying the actual text in the actual is it HTML or CSS, I have no idea I am a backend developer but it is difficult to keep up to date)

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.

The wax expands due to ambient (even uniform) temperature. It's a linear actuator, so warm -> expanded and cool -> retracted.

I think by thermal gradient they mean a change in temperature over time, not space.

Correct. Delta t

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 you where they are talking about a spacial 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.

But I'm betting you performed maintenance on your car in that period.

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.

I was quite amazed to find these when dismantling appliances.

Me too, took me some time to figure out what this thing does :-)

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.

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.

As the article stated.

Boy I really hope somebody got fired for that blunder!

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