Brass and copper

[Crawdigger]

When I first pulled this out of the ground at the base of a 200 year old oak tree, I thought it was a wheel. After cleaning and further inspection I am positive it's not a wheel. Inside is a type of butterfly valve which, when manipulated, opens and compresses what seems to be some type of bellow. The entire piece is brass except for the bellow which I think is copper. Any ideas??

 

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[bravowhiskey]

It is some kind of thermostat. When water runs through as water temp changes it would expand or contract the "bellows" opening or closing the valve at the other end. There by shutting off or opening the water flow to where ever it was going.