I think rather than use a tube inside the valve to "direct" air towards the poppet.... I would simply make sure the inlet to the valve is unobstructed (eg. no piercing pin) and larger in diameter than the valve throat ID.... If the valve inlet is smaller than the throat, you will get a larger pressure drop than you should if the inside of the valve and the reservoir (that replaces the CO2 cartridge) acted as one....You can use the Delrin poppet from a Disco to get rid of the soft poppet seat in the 22XX valves.... Even better, bush the rear valve stem hole in the valve down to 1/8" and use the poppet from an MRod….Bob
Bigger is better on the intake side of the valve.... but 0.010" larger than the smallest port should keep the pressure inside the valve as high as possible, IMO....Bob
I'd be tempted to just use an O-ring, providing it is contained on all 4 sides.... Without knowing what you're trying to seal it's a bit hard to recommend anything....Bob
Once the air turns the corners past the poppet seat there will be no laminar flow.... That means through the valve throat, the exhaust port, the transfer port, barrel port and bore.... Once flow trips from laminar to turbulent, it never goes back to laminar.... It is doubtful there is even laminar flow into the valve from the reservoir or plenum.... Bob
How about machining a "spigot" on the front of the cartridge replacement reservoir.... A flat face with a piece of "tubing" sticking out of it in the middle, drilled to 0.165" with the thinnest possible wall.... It should be possible to have the OD of the spigot about 0.195", maybe smaller.... Stretch a 3/16" ID O-ring over it, that would be 5/16" OD.... That might fit inside the neck of the valve?.... If not, use a smaller cross-section Metric O-ring.... You get the idea, contain the O-ring on the valve on the back and outside.... and on the reservoir on the front and inside.... Just don't overtighten it against the valve and crush the thin wall of the spigot....I have drilled Crosman steel transfer ports to as large as 0.166", which leaves a VERY thin wall, but they survive.... I think the OD may be as small as 3/16".... Bob
They work fine.... but don't try and go to 11/64" (0.172")…. they buckle.... …. You do have to drill them out ONE number drill at a time, tho…. Bob