SpudFiles

The usual same problem, piston can't seal.

I've been reading, but then and again materials are much harder to find in my country, so I can't use some of these solutions listed up there. Besides, all the neoprene rubber that I know of in my country is hard (around 75% hardness) and isn't exactly good for sealing stuff.

I'm thinking of a multi-layered thing as shown in the diagram.

Any comments?

Thanks.

Limbeh

Have you tried just the neoprene rubber? That is what I use and it doesn't leak. It would help to see pictures of your valve set up and piston.

3mm thick neoprene rubber, 70% hardness, 3mm thickness.

Air always seems to leak whenever I pump it up. The leaks are quite significant, can't get a decent pressure anyway.

The barrel isn't perfectly straight either - I tried sanding it out by placing sandpaper on the piston (as suggested by someone here some time ago), but the problem still stays.

Do you have a center bolt holding the seal to the piston? Might be leaking around that. I used JB Weld to seal my center bolt. Some pictures would really be helpful.

I think your uneven barrel porting is causing it.
Sand it some more, or, if possible take the porting out and cut it straight (and sand it)

I think I'll do that, then I'll report to you all any changes.

Thanks.