SpudFiles

So, I thought this was kinda funny. The first piston I made for my copper cannon was made from one of those hard rubber things that you would put into a car cigarette lighter hole to plug it. Then I filled it with resin, and put a springless grease zerk in it for equalization. Then I decided to make a better piston so I cast one from solid epoxy and put the same grease zerk setup in it. BUT, the new better piston would leak air at about 200PSI. So I put the old one back in, which has survived numerous shots up to 350PSI. Meanwhile I put a new rubber face on the cast piston and re-installed it. One shot at 400PSI ripped a chunk off the sealing face. So...back out it came. Now I tried a different kind of glue on the epoxy one to get the sealing face on it, and ran a thin bead of CA glue around the outside of the rubber/epoxy connection point to hopefully keep the air from getting under the edge.

Anyhow I just thought it was silly that my upgraded piston has been nothing but a pain in the *ss. Maybe if this don't work I will just have to put the original back in and let it do its thing.

Here is a reference pic of the two pistons.

<a href="http://s117.photobucket.com/albums/o75/ ... CF3161.jpg" target="_blank"><img src="http://i117.photobucket.com/albums/o75/ ... CF3161.jpg" border="0" alt="Photobucket"></a>

Consider a bolt and washer along with the glue to hold the face in place.

That parrot isn't really him Jack...
That bird doesn't need a bolt to keep his face on anyway..


That upper piston looks better.
If it worked so well, why change it?

Don't fix it if it ain't broke...

nope the bird isn't me...He's my Mustache Parakeet named Billy Bob.

On a side note, that one dry fire at 400PSI.. The gun was laying flat on the concrete floor of my garage, and I triggered the ball valve with my foot. When it LOUDLY went of, sh%t went flying all over the garage. So I looked at what it was.... It was patch concrete that the muzzle blast peeled off the floor. LOL A patch about 4 inches wide by about 18 inches long and about an 1/8 or 1/4" thick got blasted off the floor. HAHA this thing is fun.

Also JSR, I'm afraid for the integrity of the epoxy if I were to drill and tap it again. It already has the 1/4 28 threads in the back end, and the equalization hole through it. I think the new glue will work way better anyways, I'll let you guys know on this thread after I test it again with the epoxy piston. I need to give the glue a little bit more time, this time, to cure though.

And yeah Brian, I hear ya about the "don't fix it if it ain't broke", I'm just bull headed, and the epoxy piston has less blow by when I open the pilot.

Lock

Lock, have you considered using a floating o-ring on the piston as a check valve? This would free up the room to bolt on the sealing face.

That is what I used with mine and it works great.

Congrats on the 400psi dry fire. I can only imagine how loud that was indoors.

As I've pointed out before, the zirk setup is cool but unnecessary given the fact that your piston isn't 100% airtight.

I agree with BtB...if your old piston was working well, no reason to change it.

Couple of questions...I have a vague idea what they are, but could someone please explain what a floating o-ring and a zirk are?

The floating o-ring and zerk are both just forms of a directional check valve. A zerk.. or grease zerk is a little directional nipple on a piece of machinery that is just the female side of a simple connector used to squirt grease into a bearing assembly or other frictional area. A floating o-ring is a popular design for use in the building or pistons for air pumps.

http://www.spudfiles.com/forums/ongoing ... 13286.html

There is a link to a thread about my cannon and pump with some pictures of a floating o-ring sealed piston. I'm sure with some sight searching you could find a lot more on floating o-ring pistons though.

And... Gippeto, yes I have thought about that, and I like the idea a lot however the piston won't fit into my "poor mans lathe" and I'm not sure how much I trust myself to carve the slot by hand. But I agree that it would be optimal.

Thanx for the replies guys.

Lock