Exploring capillary thermostats

That was probably a thermocouple that generates enough current to hold the gas on magnetically.

Big Clive

Very interesting.. One time our gas boiler stopped working because the pilot light wouldn't stay lit. There's what looks like a copper capillary tube with one end in the flame and the other presumably connected to a gas valve which cuts the supply if the flame goes out. Once the repair technician removed the tube, the pilot light end had eroded away and what looked like a thin wire protruded from it. Does this work by expanding the inner wire and transferring this motion up the tube to a cut-off valve, like a bicycle brake cable in reverse?

Gordo

I see Big Clive also had a sister who rode horses and left "reading material" in the bathroom - we're guys, we gotta find something to distract us while taking a dump..

Gordo

the stat with grey body is a freezer stat the contacts 1 is for a red neon that switches at -15c, the other is adjustable from -18 to about - 24c this warns you if the temp rises

Just found out who Big Clive's grandpappy was. Here's a home movie of grandpappy's first ever job as an electrician, in 1922. You can see that his talents have been passed down the generations! https://www.youtube.com/watch?v=me-zbnHNwcU

Ymir the Frost Giant

Our fridge thermostat died some ancient French thing. Could not find a thermostat that would fit so I bit the bullet and got a 240v Chinese mains powered stat that is outside by the compressor. It has a thermocouple and mains relay for the compressor.

Nuts 'n' Proud

It's survived so far. I didn't want to make the video too long.

Big Clive

Did the eBay -30 to +30 one survive or is it my YT player?? Interesting, I pulled many fridge ones apart years ago as a child, pretty much the same experience as the second one (without a bulb) I suspect gas to give greater change over a smaller temperature range as all I pulled apart did the same thing, instantly deflated the bellows.

Anton

I’m pretty sure that’s the intended use case for the one without the bulb. Perhaps the use of gas gives it greater expansion/contraction within a smaller temperature range?

Anton

Will they be using a gas, because a liquid will freeze at very cold temperatures, whereas a gas needs to be supercooled to change state?

Mike Hughes

Really interesting - I never realised some used an oil type material, always had assumed they were gas ( of some type ) or a volatile and used blends for specific ranges due to vapour pressure differences.

RDM

I had some surprises watching this video! I cut the capillary of one many years ago and it discharged a drop of a low boiling point liquid that immediately evaporated (a freon perhaps) and assumed that they all worked from vapor pressure of the fill material. The occasional unit with the large bulb had confused me but I never had one to sacrifice and never suspected the use of oil working fluid. I sincerely doubt use a pure gas fill would work, since the very small volume of the capillary would not provide sufficient change in pressure to operate the bellows.

HarveyB

Was about to pull apart my old fridge thermo. just for a look, replaced it last week. is almost identical to last one. except mine was -9to+9C, There is no need for a sensing bulb or insulation on capillary, as the entire unit is inside the cooling compartment.

I am proud to be "people like us" and glad to belong someplace

Michael Thompson

Haha, I actually wondered why you wrote "Nowis" on the device when it's from someone called Simon. Then I realized... :D But interesting stuff, as always! ;)

In depth explanation. Thanks BC 👍❤️

Cerity

I've just noticed again that Clive's "so let's ah" triggers my nearby Alexa device!

Dr Andy Hill

very interesting indeed. I almost went off and described how to make thermocouples but it a complacently different subject, So I wont bore you.

DC Allan