Evanix sniper valve redesign

Had an issue with the poppet vavlve of my evanix sniper recently, found a solution, which even might be an improvement and thought I’d share for you to benefit from my findings…
First of all and before starting, a big “thanks” to Wingman NZ for his advice concerning material choice. You made my day, week, month, my friend!

Ok, issue description: basically, after 500 or so rounds downrange, the Sniper had a slow air leak, loosing around 100 psi over night. After 20 more rounds, it became something like 100 psi a minute and 10 more rounds later the last 100 left the tube whithin a single second. Hisssssssss…..
Well, decided to tear down the rifle and found the reason quite quickly – poppet valve plastic rim seal worn out. Due to the construction of the valve, the metal ring touches the (also metal) valve seat.

Metal on metal, that ain’t sealin’ nothing…

Well, next step was to get rid of the worn plastic rim seal in the valve body and replace it with something else, better or at least equal.
As the stem wouldn’t move, I heated it up as I remember having read somewhere that it is locktited. Managed to get the stem screwed out (use a cloth when doing that, otherwise you damage the stem and valve body with your pliers and vise) and of course the plastic didn’ like the heat treatment too much.
Ordered Delrin and PEEK rods and new valve stem material and thought about a redesign with a complete plastic valve body, equal to Wingman’s pistol valves. Simply ordering a new valve wasn’t a solution as I believe that after a few hundred rounds the new one will have the same issue. Same for just making a new plastic rim seal insert of the Evanix design.
I then stumbled over a site in the UK selling delrin balls for ball bearings, 11mm diameter, perfect.

With these, the complete redesign was not necessary anymore, I changed plans towards adapting the balls (well… one of them) to the current valve body. Doing this, the outer rim of the valve body had to undergo a little modification as well, I wanted it to center the plastic part, but to have it less high so that part of the delrin seal covers the metal part (seen from the sealing side), in a way that even when worn, there was no chance for metal touching metal again.this way, even with the valve rod going through the Delrin, I have multiple surfaces for sealing and a maze/meander effect, making other sealing like o-rings unnecessary.

Ground down the rim of the valve body, but left 2 mm height for the maze and centering of the Delrin.
Lathed down the Delrin ball to shape so that it fits the new body, covering the outer rim.
Some pictures say more than a thousand words, I guess? OK, here we go…

Why using a ball shape by the way? Well, conic or ball- shape helps center the valve on the valve seat.

Cleaned the valve stem threads and polished the stem itself, as well as the metal part of the valve body. Then put everything together by screwing the stem in its original positon with the Delrin (ex-)ball in between.
Before assembling everything back, I also replaced the stem o-ring with resine material, this is a test how well this will work.

Looking at the ends of the valve return spring, I saw grinding marks and as everything was torn apart, I did some basic polishing, that can’ be bad anyway. At least it will prevent unneccessary marking on the valve body and tube outlet.

Reassembled the tube and valve and started pumping (yes, manual filling, great workout), and … hisssssss…, panic…
Told myself that this is due to the fact that the Delrin seal is not yet perfectly fitting the valve seat and would most probably have to wear in under pressure. While some air was still hissing out, I turned the valve stem a little, until the hiss got to the weakest possible point. Then started pumping again and somewhere in between 10 and 15 bar, the hiss stopped. Pumped up to 50 bar and decided to look into the other issues of this rifle before reassembly.

This resumes to changing all o-rings because all of the ones I saw during disassembly were damaged. Reason is that al drilled holes and threads have not been deburred by Evanix, therefore damaging the o-rings when passing in front during assembly. Deburred all holes, slipped on the new o-rings and assembled the whole thing.

After 24 hours, the whole 50 bars were still in, pumped up to 100 and dared some shots. Perfect sealing after every shot, no hisses. Shot until 90 bars and left the gun alone again. After another 48 hours, still 90 bars in, topped up to 200 and waited.

Well in the end, it’s shooting again, no leak at all since 2 weeks and some 100 rounds. As far as I can see things now, accuracy seems to have improved, as well. This remains to be proven on bigger distances (waiting for the wind to calm down to test and chrony).

Hope that gives some inspiration for similar issues.
Thanks for reading. Cheers