How tight should a Maid-o-Mist steam valve adjustment screw be?
The particular model in the diagram should have the orifice hand tight. If the orifice is left loose it can vibrate loose and fall off. There are other models and other brands that are adjustable. By turning the cap you expose more or less of the orifice. The larger the orifice the faster the air is expelled. This allows the steam to enter the radiator at a somewhat controlled rate. This allows you to slow or increase the rate that the radiator warms to balance the heat from room to room.