SpudFiles

The back is taken off an old non working bike pump which after a little sanding was a perfectly fit
SIDE:



BACK:



Anyways, I'd think with the small holes on the back air could go under the O-ring and fill into the chamber but not back since the seal but I'm horribly wrong and it's not filling into the chamber at all. Any suggestions? I can take more pics if needed.

Looks like you have the "vents" on the pilot side.

If so, turn the plastic bit around.

Also, how tight is the o-ring groove? It should be a slightly sloppy fit if you're doing the "floating o-ring thing".

The groove itself is fine, the O-ring fits loose on the groove.


That's what happens to the O-ring if you squeeze it. I wish I could describe how loose it is.

That should be fine.

The vents are supposed to be on the chamber side. Turn the plastic piece around, and try it again.

Nice piston.

The bikepump piston is meant to act as a check valve, so the 4 holes are meant to let air through in one way. Because you want air to go from pilot to chamber and not in reverse, turn the thing around like gippeto said.

What pipe does this slide in?

Slides lovely in 2" pipe, I figured the vents acted as a check valve just my logic failed, I'll retest it in a little bit then edit my post.

EDIT:
So I went out and tested the new piston. Words can't describe how nice it is, It's actuating at 5 PSI maybe even lower. Right now I'm testing it on my old cannon with a 4' x 2" chamber. Once my 3" coupling/bushing/cap comes in tomorrow I'll test it on that(Saturday, for glue drying)
Highest I tested today was 80 PSI and it feels stronger than my old piston at 100+ PSI. When I fill at lower PSI the needle doesn't move for 8 seconds or so then it slowly, and I mean slowly works its way to w.e I have it set at. I'd recommend every1 try to make one using wood or w.e. I know mine was a lucky find but looking at it seems pretty easy with wood.

Glad you got it working.

Enjoy.