Thanks. Yes I assume it should be fully closed unless there is a blockage and then it does what it is supposed to but I can hear the air coming through when it's just the Henry on. I'll see if I can find another spring and see if the extra tension helps.Just been to check out the one I fitted - only has 1 spring from what I can see.
I do find that the valve will open depending on what stage of operation I'm at when using it. I did find it a bit of a fiddle to adjust and may not yet have it set correctly. As it doesn't open when the Henry is switched on and *no* machine actually working on any wood - thicknesser or router, not planning or cutting wood - the valve is closed I'm assuming that's how it is meant to be!? Only opens fully if I block the inlet.
Hopefully others will also post - and I'll adjust mine more if I have to.