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Comment by limaoscarjuliet

13 hours 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.

15 comments

limaoscarjuliet

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echoangle  11 hours ago

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?

  • jaggederest  7 hours ago

    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.

    • VygmraMGVl  5 hours ago

      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.

      4 replies →

croemer  8 hours ago

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.