I think the concentric stems to do away with the "umbrella" is a simpler and easier solution, IMO....Bob
That looks like a slide valve? Marko
Here is what I meant by concentric stems.... The concept is the same as your original idea, but IMO easier to make.... The idea is to use a smaller poppet (black) inside the main poppet (red), which opens first to equalize the pressure across the main poppet.... The small poppet stem is inside the main stem, which is tubular, concentric, and slightly shorter, so that the hammer first opens the small poppet, (which allows the pressure to equalize across the main poppet making it easier to open), and then the main one.... The green dotted line is the valve spring....I know of at least two guys who suggested or tried this, one was Travis (who built several working prototypes), the other one may have been Tim, but I honestly can't remember.... It is NOT my idea, but I don't see any reason it should not work as intended.... The key would be sufficient mechanical strength of all the components, and finding the optimum difference in the stem lengths.... If the small center stem is longer than needed, the pellet might start to move before the main poppet opened, and if it is too short, the pressure difference on the main poppet may not drop enough to reduce the opening force on it as desired.... My gut feel is that the stems only need to be 0.010" or less different in length, but I have never made one to test....Bob
I have only drawn the cross-section through the vents.... I would think 4 or 6 small drilled holes through the main poppet would be the right way to go, so that they would pass the same volume of air as the seat of the small poppet when opened 0.010".... I don't understand how you would have a one piece stem work to lift the inner poppet first, perhaps you could explain that?....Bob