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Hubb's 2" piston

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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Hubb's 2" piston

Unread postAuthor: Gun Freak » Sat Apr 24, 2010 7:11 pm

Here are Reedfe and I's dual 2" pistons, Hubb's design.

I blow through the back hole and air comes out the front ones, as expected.

But I blow through the front ones and air goes out the back holes, problem.

Hubb... I need you help. These pistons were 12 dollars each lol.

And I just ordered parts for the rest of our gun, only 20 each.

Pretty good, 35 dollar advanced mega piston valve :D

The two valves, in all their glory:
Image

Showing the front:
Image

Showing the back:
Image

Reed's piston says "Hey Hubb, I think this piston is sexy" :D
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Unread postAuthor: deathbyDWV » Sat Apr 24, 2010 9:28 pm

I'd guess air comes out the back because your breath isn't enough pressure...

I need to look at his piston design though. I never have...


Btw I like the new thing in your sig... Haha...
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Unread postAuthor: jor2daje » Sat Apr 24, 2010 9:51 pm

What type of one way valve did you build into it?
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Unread postAuthor: MrCrowley » Sat Apr 24, 2010 10:56 pm

I'm guessing there isn't enough pressure, assuming it is built correctly. Why is there no o-ring by the way?

edit: Is this for a tee valve? They look pretty long and heavy for a tee valve. Though you wanted it a little more compact.
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Unread postAuthor: jrrdw » Sun Apr 25, 2010 5:49 am

From the looks in those pictures, there is no check valve. There for air will go through the piston both ways unrestricted, period.
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Unread postAuthor: MrCrowley » Sun Apr 25, 2010 5:51 am

jrrdw wrote:From the looks in those pictures, there is no check valve. There for air will go through the piston both ways unrestricted, period.

If it is designed like Hubb's, there is a rubber gasket on the inside at the back which flexes forward with pressure behind it and flexes back when the pressure is trying to go the other way.
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Unread postAuthor: jrrdw » Sun Apr 25, 2010 5:56 am

MrC wrote:If it is designed like Hubb's, there is a rubber gasket on the inside at the back which flexes forward with pressure behind it and flexes back when the pressure is trying to go the other way.


If that's the case maybe there is a bur around the hole not allowing a complete seal?????
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Unread postAuthor: MrCrowley » Sun Apr 25, 2010 5:57 am

Yeah I can't imagine what else it'd be except that higher pressure is required to make it seal for whatever reason.
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Unread postAuthor: jrrdw » Sun Apr 25, 2010 6:05 am

Look at that second pic, it looks like a bur hanging out of the hole there, (top hole, near seal). Or it's a scratch. You can also see ridges around the holes, that could also create a weak seal...

Looks like he built in a hurry and missed the details.
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Unread postAuthor: Hubb » Sun Apr 25, 2010 8:12 am

Where is the o-ring. The built in check valve is useless without it.

As far as the check valve, if you have the rubber inside the piston, then it will work. It may need, as others have mentioned, higher pressure than what you can produce with your lungs, but it will work.

Suggestions: This piston is heavy. I'd drop the steel hardware and go with nylon hardware if possible. At least trim the bolt down on the front.

But, besides that, I think this piston is sexy :D
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Unread postAuthor: Technician1002 » Sun Apr 25, 2010 12:05 pm

Be sure the threads on the bolt through the rubber is sealed. That is another path through the seal.
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Unread postAuthor: Gun Freak » Sun Apr 25, 2010 1:53 pm

Hubb, O-rings are going on today. sorry.

Tech, they are epoxied.

MrCrowley, I think the low pressure is the problem too. It is for a tee valve, but not a compact design like Gipetto's.

jrrdw, it is all de-burred, trust me :wink:

jor2daje, check it out in the Hubb Library.

I added one o-ring on mine today, but I have to wait until my online-ordered parts to come in to find out where to put the second one so that it doesn't come out of the 2" pipe it slides in when sealing the barrel.
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Unread postAuthor: Hubb » Sun Apr 25, 2010 2:25 pm

I'm looking forward to it when the valve is complete.

Just remember that this is a heavy piston. This means that a light bumper will not do. I used aquarium tubing for the pumper in my first one and still cracked the valve (at 50psi). As far as performance goes, I was able to use just lung pressure to seat and unseat the piston.

And, just for reference, I've never glued any of the pieces in place. I just let the bolt pull the plugs into place so that I could fix the check valve if I ever needed to.
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Unread postAuthor: Gun Freak » Sun Apr 25, 2010 2:37 pm

Yeah I didn't glue either, I orignially planned to put o-ring grooves in the plug to seal but the o-rings I bought for that were too thick and it wouldn't really make a difference. I'm glad I didn't glue, because today I took it apart to fix the rubber washer check valve, it did a little better but still not perfect. What do you recommend for the bumper? A big spring? With some foam? I don't want to break any parts because I ordered them online. Rare fittings.
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Unread postAuthor: Hubb » Sun Apr 25, 2010 10:10 pm

What fittings were rare? Just curious, 'cause I'm able to get all these fittings locally quite easily.

As far as the check valve goes, try placing the holes as close to the edge of the washer as possible. If it's not already, the rubber washer should be the same size as the inside of the plug, and the washer holding it should be as small as possible. If necessary, get an oversized neoprene washer and trim it down.

Bumper: A pool noodle works. Thicker rubber hose also works.

Now, for the o-rings. I've got a technique that I've wanted to try, but haven't yet for this particular piston.

Trim about 1/8" from the coupling, then glue this piece onto the plug with the check valve. Allow the glue to completely dry, then slide the o-ring over the plug to rest next to the piece. From there, just slide the rest of the coupling into place and tighten down the bolt, which will squish the o-ring into place.

When choosing an o-ring, find one that has the same diameter as the coupling. I believe the e-book has the correct size, but it's still probably best to take the coupling to a hardware store to find one.

If you can't find an o-ring that's the right size, then look for o-ring stock. It is found on a spool and is generally thicker than regular o-rings. Simply by a foot of it, then trim it to size with a razor and super glue it together (<that's actually what I had to do on the last sprinkler valve I modded...had no problems).

Another option is to find a rubber gasket material and trim it to the right size.
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