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Tennis ball gun progress

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: dewey-1 » Sun Jun 07, 2009 8:38 pm

I will ask again the same questions"

1) 2 inch Tee?

2) 2 inch porting to the barrel?

Answer these first, then we can work on the rest.
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Unread postAuthor: Kai » Sun Jun 07, 2009 8:40 pm

yes it is a 2" tee, not sure what you mean by "porting" but the barrel and pipe connecting the tee to the threaded female adapter are also both 2" pvc.
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Unread postAuthor: inonickname » Sun Jun 07, 2009 8:45 pm

The point is that a 2" tee does not have 2" porting, you generally need a larger tee than barrel otherwise you choke flow.
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Unread postAuthor: Kai » Sun Jun 07, 2009 8:46 pm

soooo, are you saying i have to start all over?
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Unread postAuthor: thedeathofall » Sun Jun 07, 2009 8:48 pm

So what is on the barrel side of the piston? how big is the opening that the piston will shut? is it 2 inch pipe? or is there a reducer somewhere in there?

-------EDIT

Didn't see inon's post.

Yes you will probably have to start over.

I would recommend a larger T if you still want a tennis ball launcher. At least you haven't attached the barrel and breach assembly yet.

If you want some other pointers, you can always PM me. I'm almost always on the comp. (at least during the mornings/night)
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Last edited by thedeathofall on Sun Jun 07, 2009 8:52 pm, edited 1 time in total.
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Unread postAuthor: Kai » Sun Jun 07, 2009 8:51 pm

2"pipe,,,,,,,,,,,,,,
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Unread postAuthor: dewey-1 » Sun Jun 07, 2009 8:52 pm

To use a 2 inch Tee with piston sealing barrel you need an 1.5 inch port for the barrel side.

That is why I said more research.

If I can locate the info, I will do so.

Otherwise look under piston valve.
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Unread postAuthor: Kai » Sun Jun 07, 2009 8:56 pm

sooooooooooo, is this the death sentence: i need to duplicate all i have exept for the barrel diameter? its not so bad considering that i spent 30 dollars on it and some of that went to 5' of 3" pipe and 10' of 1.5" pipe.
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Unread postAuthor: dewey-1 » Sun Jun 07, 2009 9:09 pm

Please read page 5 of this posting.

fireman565 wrote;

One thing I missed trying to build my own piston was 'frontal pressure' applied to the front of the piston when pressurized.

In Phase Three where it's stated, "Once the force pressing on the back of the piston falls below the force acting on the front of the piston, it begins to slide back. Suddenly there is more surface area exposed on the front of the piston, and the jump in force slams the piston back leaving an opening for air to flow into the barrel to accelerate the projectile. " I didn't quite pick up on this part of building a piston until after I had built one. Of course common sense says the piston front face has to be larger than the port to which it seals. From what I've discovered this frontal pressure is the 'pressure' that's on the residual area of the seal around the port.

Now, my piston still opened even though I built it with no area for frontal pressure. It wasn't performing at its best, even though it would fire a spud 150 yds, it was trying to suck the seal through the barrel nearly tearing it on every fire. I ended up painstakingly adding a sleeve that protruded into the chamber to give it this frontal pressure needed.

http://www.spudfiles.com/forums/piston- ... rt,60.html
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Unread postAuthor: Kai » Sun Jun 07, 2009 9:18 pm

im still confused about what you're telling me but what i believe you are trying to show me is that i need the extra room around my pistonfor that flashing yellow part in the diagram on page 5.
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Unread postAuthor: Kai » Sun Jun 07, 2009 9:31 pm

ok, i get it now. now i need som guidance as to building a better piston.
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Unread postAuthor: Gaderelguitarist » Sun Jun 07, 2009 10:15 pm

Try for a solid material for your piston. It won't be as light, but the trade-off is less pilot volume.

Always research thoroughly before starting a project.
Always have a diagram of what goes where.
Always measure twice, cut once.

Etc etc...
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Unread postAuthor: thedeathofall » Sun Jun 07, 2009 10:15 pm

Well depends on the size of your T. There are lots of ideas out there and dozens of topics related to pistons.

heres a few clues....

Endcaps (pvc fittings)
Solid plastic rod (machined)
aluminum cans (not soda cans but soup cans, deoderant cans or similar)
epoxy
Hot glue
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Unread postAuthor: dudeman508 » Mon Jun 08, 2009 9:03 pm

Kai wrote: also, the rear piston had about 2-3mm of wiggle room in the 2" pvc pilot chamber. .



To much. :D :D :D :D
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Unread postAuthor: Technician1002 » Mon Jun 08, 2009 11:00 pm

dudeman508 wrote:
Kai wrote: also, the rear piston had about 2-3mm of wiggle room in the 2" pvc pilot chamber. .



To much. :D :D :D :D


Way too much. To find the area of the leak the areas of the circles of the cylinder daimeter minus the piston OD will give the area of the space in between. Two inches is about 40 mm as a round figure. The circles would be 40 mm area - 38 mm area. Your pilot has to be about 5 X larger in area to drop the pressure low enough for the piston to unseat. A large leak will keep the piston from opening as it simply vents the chamber pressure through the equalization leak. Friction and too big of an eq port/leak are the 2 reasons piston valves fail to fire. Low friction and low leakage make them pop.
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