Ever Seen Bi-Metal Bellows?

Welcome to the learning corner....and if you've seen them, welcome to memory lane.

A bi-metal device works because two different metals are sandwiched together. One metal expands faster than the other and that causes movement with temperature change. Most of us have seen bi-metal springs that react with heat to open & close incoming air dampers, those spiral things tucked inside a housing and connected to a chain that goes to the air damper, but, have you ever seen bi-metal bellows? Here's a photo of a pair that are in a Jamesway coal heater. Those two disc looking things on the left, as they heat up, they expand from left to right, pushing the connecting rods that open & close not only the air inlet, but the exhaust. A cast iron flapper at the very top of the stove opens & closes to regulate outgoing heat & smoke. The bellows have much more power than a spiral spring, they obviously used them because of power needed to move the exhaust damper. I'd hate to have to find new bellows if these ever got damaged.Cool design!

Cool!

The coal domestic hot water "bucket a day" boiler I grew up with had a bi-metal disk device clamped to the vertical supply pipe. As the water heated up, the expanding bellows lifted a lever arm. The hinged coal feed door was connected to it by a chain. This reduced the draft through the coal bed by increasing the over the fire draft. Themostatic control! It worked well.

Neat Freddy,I always appreciate older designs that incorporate good quality materials,basic concept engineering and simplicity.Today we try to do too much with flim flam plastic inadequacies.Thanks for the picture. Mike