39x valve to tube transfer gap

[antithesis]

I have been examining the concept of the potential losses in the gap between the valve body and tube wall in 39x guns, there being no form of seal around transfer region. Cartridge valves of course

Firstly, how much could theoretically be lost in this region?

Second, there are various potential approaches. Shim under the valve, closing gap where it matters, make an actual gasket around the transfer area, add a third oring to reduce the potential loss...or perhaps even find a way to pre pressurize this region.

Seems to me in this case one may be best off with as tight a valve as possible, but I'm no engineer (that's why we got rsterne hint hint)

[Psipumper]

I did the third oring and went from 720 to 737 fps. I think the gain would be more at higher power levels. I later soldered the outside diameter of the valve between the o rings and machined it to a few thousandths under the tube. I didn’t see any notable increase  with that. I like the way it keeps the valve centered in the tube when tightened though.

[Tack Driver 10]

I modded a 392 valve with a 1/8" Delrin valve stem and concave seat, third o-ring, ported, light valve spring, could even make it a FT.

Never tested is as I don't own a 392.

[antithesis]

Oh she's PERRRTY...I less than an hour ago did emergency surgery on my valve(impatience, wrong oring, and a hammer. I'm stupid sometimes). Had to hand cut rear o ring slot to accept a 111 oring, so far so good..if I get any dumber I may just try to cut another like that one...that's using a hammer and triangle file mind you. Miracle it worked maybe I'll not push it

Is that a all metal poppet?

Oh delrin...NVM. wonder if I could sleeve the stem hole and try a 13xx stem I'm curious...or maybe a mrod stem idk yet

[WyoMan]

Double O-ring mod:


Old photo (circa 2005), this mod has been around for a while.


TP gasket seal:


Done by fellow member Millipede. Only photo I've seen of this mod. And I'm not sure what size o-ring. Reported gain was 25 fps with 14.3gr.
This seems like the best approach and is a proven design...i.e. Crosman 600 uses something similar:



Wyo

[antithesis]

Wyo,

I've often considered this around the tp type mod . Only gripe from me is it looks like there is a tiny dead space created Making room for the o ring. If I had a mill I'd shave maybe a 16th deep square around tp and use a small Teflon sheet pressed into place by the tube wall. Gotta work within my means tho