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piston annoyance

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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piston annoyance

Unread postAuthor: lockmanslammin » Sun Apr 06, 2008 12:28 pm

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/lockmanslammin/?action=view&current=DSCF3161.jpg" target="_blank"><img src="http://i117.photobucket.com/albums/o75/lockmanslammin/DSCF3161.jpg" border="0" alt="Photobucket"></a>
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Unread postAuthor: jackssmirkingrevenge » Sun Apr 06, 2008 12:35 pm

Consider a bolt and washer along with the glue to hold the face in place.
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Unread postAuthor: Brian the brain » Sun Apr 06, 2008 2:24 pm

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


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

Don't fix it if it ain't broke...
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: lockmanslammin » Sun Apr 06, 2008 5:17 pm

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
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Unread postAuthor: Gippeto » Sun Apr 06, 2008 10:29 pm

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. :D
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Unread postAuthor: jackssmirkingrevenge » Sun Apr 06, 2008 11:26 pm

As I've pointed out before, the zirk setup is cool but unnecessary given the fact that your piston isn't 100% airtight.
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Unread postAuthor: Velocity » Sun Apr 06, 2008 11:33 pm

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?
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Unread postAuthor: lockmanslammin » Mon Apr 07, 2008 2:17 am

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-progress-update-pictures-new-damage-pics-t13286.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
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