This is an air trap from an air bottle drain. The valve is levered down (open) when the water level in the chamber floats the float; when the float is not floating, it levers the valve up (shut), see? fine.
Now, have you seen a steam trap with the same design?
I swear that I did somewhere, but when I sketched it on an exam last year I was accused of inventing things and marked wrong. (I got partial marks because my drawing “could” work, but not full marks because I was being imaginative.) From time to time I do invent things, that’s a fact. But I always take credit for my inventions, and I’m quite sure I have never invented a steam trap. Its a cute little thing, and I wish I had invented it. The marks are done and dusted, but I still want some vindication.