Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Air and Steam are very different things to be sure, but if it does run on air okay, then the slide valve must be seated in the correct position and maybe okay. The jam nuts are supposed to be jammed against each other, but in such a way as to allow the actual valve the slightest amount of free movement to let it "seek" its seat on the port face. At least that is how I've always understood slide valve theory. Steam admission does change temperature of the metal drastically, and could change a slip fit to an interference fit under some conditions. But if the slide can in fact "float" some, then expansion of a rigid setup should not be a problem.