Pmi USP

[Snowpuff]

I just bought this usp , fixed the 12gram co2 puncture oring and got it working then out of no where it started leaking down the barrel so I take out the valve and inspect the orings put new ones on and the cup seal looks fine I put it back together it leaks for one second then it hold air, it does this for one while 12gram charge then when I put another one in it leaks down the barrel and yes I cock it before putting in the 12gram,
so i figure i need a new cup seal so i buy this piranha for parts and shiny things , I put on the e grip cause why not, I also swap both valves and cup seals ,
I put in a 12gram it holds air , so i pit the hammer and bolt and grip on and it shoot 12 15 times cool...it runs out I recock the gun and insert another 12 gran and it blows through the barrel again... I know it's not the orings it's the cup seal I'm 95% sure but why??? Why does it work once then second time blow out the barrel,.... I'm going crazy here lol I wasted like 40$ worth of 12 grams trying to get this thing to work lol.
please any one any ideas? I must be doing somwtbing wrong.

When I tighten up the value set scrseti do it almost finger tight so I know it can't be that.


Also there the usp came with a bigger cup seal spring than the pirahana i tried the smaller one just for shits but same result.

[Ecapnation]

Could be aging out plastic parts.

[markdem]

I think old plastics get damaged very quickly. Ive had a couple similar situations where the valve lasts a few shots before springing a leak.

You can try buffing the cup seal with a drill and steel wool, but in my experience, the plastic just needs replacing

I would be tempted to try turning a new cup seal from a teflon rod. Chuck it in your drill and start filing it to shape