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A few piston questions.

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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Unread postAuthor: evw2k » Tue Jul 15, 2008 9:07 pm

Oh, this is good news. Now all I have to work on is making the piston airtight on the outside so air from the chamber doesn't leak into the tee when its sealed.

Also, lets say I pump air behind the piston to 20 psi. From what I've read this should be enough to seal it. Air will then slowly fill up on the barrel end of the tee until both ends are at 20 psi. Once the two parts and the inside of the piston all are at 20 psi, and the chamber is at about 100 psi, won't the piston just slide back if the gun is pointed upward because of gravity?

And the sagging shouldn't be a problem, its just my bad microsoft paint skills makes it look that way. The real thing rests completely in the tee and isn't hanging down into the chamber. lol
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Unread postAuthor: iisthemuffin » Tue Jul 15, 2008 10:25 pm

From what ive read. If the chamber is at 100 psi so is the pressure in front of and behind the piston. Thats how it actuates. There is equal pressure infront of and behind the piston. When you release the air behind the piston the air in front of it forces it open.

I may be wrong about this part because im just going from logic. Someone please correct me if im wrong: Gravity wont let the piston slide back because the air behind the piston has more volume than the air in front of it, which will hold the piston tight against the barrel.
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Unread postAuthor: pat123 » Wed Jul 16, 2008 7:50 am

you let a little air out from behind the piston forcing it back, so that the air in the chamber can go out of the barrel

edit: have you seen this
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Unread postAuthor: evw2k » Thu Apr 23, 2009 8:57 pm

Okay, I know this has been a long time, almost a year, since I've posted on this topic. However, we ended up scraping the build for two reasons. The first was that out piston could not seal the chamber from leaking into the barrel. The reason for this is:

1: Our piston is in no way even or flush at all points in it's housing.
2: The T valve is tapered and has ridges on the inside!

Essentially What I am asking is this, does anyone know of purchaseable parts that I can use to make a working piston inside a 4'' T? The standard 4'' PVC one simply will not work as it is tapered on the inside. I have no means of machine making anything. No lathes, just PVC glue.

For example, hoarp001 seemed to have a T that was smooth on the inside, allowing for a T to move smoothly in it. Where did you get it? Hopefully I can resurrect this project over summer!
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Unread postAuthor: psycix » Fri Apr 24, 2009 1:55 pm

Use a pipe inside the T for the piston to slide in. You will need a slightly larger T or smaller piston for that though.
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