I’ve seen them on the “security group” for boilers in Europe as a pressure release valve. There’s a thick spring inside which is what makes it hard to turn. The instructions say to open that valve once a month and verify that water discharges. If no water discharges, then it means the pressure relief will not function when something else goes wrong and the pressure gets out of control.
I’ve not seen orange nobs anywhere else, but different regions may differ. Orange is just one color by one maker. I’ve noticed sometimes they are green, red, or yellow.
