If I could suggest a small variation, by matching the diameter of the stem to the housing you will trap air that will act as a cushion, removing the need for the bumper:
That would work if there wasn’t a vent to atmosphere. But then you’d basically have a cobra valve withought the air bleed.
Quote from: Hobbyman2007 on December 24, 2018, 09:19:11 AMThat would work if there wasn’t a vent to atmosphere. But then you’d basically have a cobra valve withought the air bleed.Perhaps you misinterpreted my suggestion, I'm talking about air trapped in the stepped portion as indicated in green:
I don't know how many balanced valves you have played with designing and building in PCPs, but they can do things that are quite unexpected, particularly during development, and destroy themselves in short order.... They can blow open with huge force if the vent is too small.... slam closed if it is too large (the Cothran will destroy the seat doing that)…. and machine-gun while emptying the reservoir if you get the wrong balance between the way the valve operates and the hammer strike.... All in all, development can be pretty exciting....
The bumper was to hopefully avoid such destruction by providing a resilient cushion, but with a VERY high spring rate.... I don't think the small amount of air trapped as you indicate would be capable of doing that job.... and it would require precision machining of two concentric bores in the thimble and concentric surfaces on the two diameters of the poppet.... Even then, I don't know if it would trap enough air to be useful without an O-ring.... However, thanks for the suggestion....
It will have a very narrow tuning field and no I dont think it will be capable of a bell curve other than the first initial shot being slightly slower than the rest.