Novel Self-adjusting Bonnet Temperatue Control

Differential expansion is a common methodology in 'probe' style micro switch and thermostats.

Maybe start searching those.

What part of your response is OT? Ridiculous voting. I fixed it.

What part of bimetal differential expansion is novel?

I think the novelty is in the idea that the overall tube length would change over time (hundreds/thousands of cycles) but the coefficient of expansion would remain the same. Or, perhaps, this system is set to control a specific temperature differential rather than a specific temperature (in this instance the solution IS novel and even clever). So, rather than have the tip of the tube be the contactor, the tube essentially has a free end and the washer is the contactor. The reset height remains the same and the travel due to expansion remain the same, regardless of any change over time of the overall tube length.

I am always a fan of low-tech solutions that work well. However, I am not a fan of using a spring in an apparatus subject to heat cycling. I am sure there is an even simpler solution available. Pictures would help.

What was the old quote? Something about how a design is not complete when you can no longer add to it, but when you can no longer take any more away. . .

-A-

I haven't any idea why zeroing at the coldest it gets is a good idea except what you say about giving a differential from coldest. Perhaps it wants to signal when the bonnet rises 20F or something to show it is no longer in idle mode and turn on the blower.

But the QUESTION is "has anyone seen an example?"

Do you mean a picture of the 'cranking washer' application?

Most of these have a version.

Yes, cranking washer seems to be a good term, though it is the first I have heard it. So, who used this on a temperature control?

Your example is the first I've heard of that requires constant zeroing.

that diet your on seems to be really working out for you.

i remember the same type of control on my grandfather's coal furnance. a temerature sensor entended into the "bonnet" that actuated a 12 v motor. the motor had an adjustable setting. after a certain temerature, the motor that would open or close the draft door by a chain. . it also had boiler tubes that spiralled around the fire box and ran to a storage tank. it produced scalding hot water during the winter months.