check valve effect in a piston valve using a rubber cap

[Gun Freak]

well washers would need to be bolted on which would add more weight than just dumping in some epoxy

That is true, but there should be another way to reinforce it without weighing it down too much.

[clemsonguy1125]

maybe super glue down plastic washers

[Gun Freak]

maybe super glue down plastic washers

Yeah or epoxy. There is still the hole in the middle that can blow out... but I think it will hold up just fine. We wil find out I plan on trying this wiht my next Co Ax or my tee piston valve.

[Hubb]

I don't see how the flexing of the sealing face would be a problem. If anything, it would help the seal. As the piston is pulled into the barrel, it will flex and shape itself around any imperfections that may be present in the barrel, forming a sort of dome. In order for the sealing face to be sucked into the barrel, the entire piston will have to either break apart (which would be unlikely seeing as how the rubber is fairly strong for one of these caps) or the entire piston would have to fold and go into the barrel (which is also unlikely, as it would take some pretty high pressures, which would probably be higher than what the PVC can support anyway).

If one does see, however, that it would be a problem, or they want to prevent the dome flexing, then why not just place a simple PVC disk into the piston? It is much lighter than the flat washer, and will probably be more supportive (and easier to get right) than the epoxy.