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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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Tennis ball gun progress

Unread postAuthor: Kai » Sun Jun 07, 2009 3:07 pm

Ok, so here is an update on the progress i have made on my semi auto tennis ball launcher. I will have more done by tonight. im dying to tenst my piston valve now. you can see my pilot valve it a blowgun w/ a PVC grip.

I still have to:

-finish the 3" chamber
-build the entire blowforward, hopper, and barrel assembly


overview

Image

piston head in "cylinder area"

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piston and spring i got from a sprinkler head

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piston made out of a section of 1.5" PVC with a fish medicine bottle glued over it, a small hole drilled in the side and a gasket (cut out of rubber from home depot) bolted to the head

Image

rear of piston

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the small hole i drilled in it to equalize pressure w/ the pilot chamber

Image



Have any suggestions or problems with it that you see? Also, do you guys know of any type of piping that a tennis ball or a raquet ball can fit into w/ just a tad of wiggle room?
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Unread postAuthor: spudmanb3 » Sun Jun 07, 2009 3:16 pm

Yeah, the bell reducer and cleanout cap don't look presure rated, other than that nice
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Last edited by spudmanb3 on Sun Jun 07, 2009 8:27 pm, edited 1 time in total.
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Unread postAuthor: Kai » Sun Jun 07, 2009 4:21 pm

thanks, i just got back from the hardware store w/ some 3" PVC and im about to finish the chamber and then my piston valve will be ready to test!!! (after the glue sets for a few hours of cousre)
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Unread postAuthor: dudeman508 » Sun Jun 07, 2009 5:00 pm

THe pilot valve might be to small. It will work, but you could make it more powerful with a ball valve. If you want to keep the blowgun you could use a really small Qev or a REALLY small piston valve.
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Unread postAuthor: thedeathofall » Sun Jun 07, 2009 5:26 pm

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Unread postAuthor: thedeathofall » Sun Jun 07, 2009 5:30 pm

Yeah, that bell reducer doesn't look presure rated, other than that nice


I believe that bell reducer is pressure rated. I can tell because of the ridge on the side.

When people go on and on about bell reducers, it gets very annoying. I think we should start asking, before screaming DWV. When someone is involved with a gun that looks as nice and well thought out as this one, yelling NOOB at the top of our lungs is rather rude. Especially if the screamer doesn't appear to have much experience in this field either.

I would really like to see this finished. Good job man.


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Sorry bout the double post. I am trying to figure out how to delete the first. Just ignore it.
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Unread postAuthor: Kai » Sun Jun 07, 2009 6:12 pm

Thanks alot you guys, especially "thedeathofall". also, if i need a better pilot, i can put the blowgun back onto a 3/4" modded sprinkler valve. Also, remember that this is going to be SEMI-AUTO Anyway, this is how far i am now.

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Unread postAuthor: Kai » Sun Jun 07, 2009 6:28 pm

do you guys think 2 hours of letting the cement set is enough before giving it 150psi?


PS: never mind, my cement said 2 hours.
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Unread postAuthor: dewey-1 » Sun Jun 07, 2009 7:25 pm

Kai wrote:do you guys think 2 hours of letting the cement set is enough before giving it 150psi?


PS: never mind, my cement said 2 hours.



Allow 24 hours for a "curing/drying" time.

Always better to be safe rather than sorry.

Take your time and be patient.
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Unread postAuthor: Kai » Sun Jun 07, 2009 7:54 pm

oh, i already did it. My valve didnt fire though. Also, my piston eventually broke alfter i already tested it. Could you guys help me with a stronger piston? Also, can you help me figure out why my piston valve didnt work, here's a diagram of it.


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Unread postAuthor: thedeathofall » Sun Jun 07, 2009 8:08 pm

if i need a better pilot, i can put the blowgun back onto a 3/4" modded sprinkler valve


I have found that unless the piston is really tight (and i mean REALLY tight) you will probably need a better pilot. I know blowgun valves work for a lot of people, but i have never had good luck with mine. (maybe I should switch brands :roll: .)

This looks really great so far. It is extremely clean which gives huge bonus points in my book. One thing i am not liking so much, is the inlet tapped into the elbow. This may prevent you from going to 150 psi. I wouldn't trust a self tap in PVC anywhere above 100 psi, especially not in an elbow at that angle.

Secondly, double check the clean out cap. I find that most clean outs are not pvc. There is also another self tap there that i wouldn't trust. You should think about threaded bushings. I know they will give you a little more pilot volume, but they are definitely worth it safety wise. If you do find that the clean out is DWV not PVC, then you will need to buy something else anyway.

Overall, for someone as new here as you, (you have probably been lurking for a while anyway) this is a very clean, well thought out and ambitious project. I cannot wait for it to be finished, as i am planning a large bore blowforward breach semi myself.

Great Job
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Unread postAuthor: Kai » Sun Jun 07, 2009 8:12 pm

thanks. Ok, first of all, does the rear of the piston need to be sealed in the body of the pilot chamber?
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Unread postAuthor: thedeathofall » Sun Jun 07, 2009 8:17 pm

no. I think your biggest problem here is the spring. You should remove it. Secondly, how tight is your piston?
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Unread postAuthor: dewey-1 » Sun Jun 07, 2009 8:21 pm

If that is a 2 inch Tee with a 2 inch barrel you will have problems getting it to work.

Way to much dead space, Hollow piston also also causing to much dead space.

The diameter of the piston needs to larger.

You may need to review piston valves and construction before proceeding.

The give away hint of inexperience and insufficient research was
the "2 hours" remark.
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Unread postAuthor: Kai » Sun Jun 07, 2009 8:24 pm

well, first of all, know that the spring wasn't strong enough or even long enough to hold the valve shut, also, the rear piston had about 2-3mm of wiggle room in the 2" pvc pilot chamber. Also, remember that i need a new piston anyway because the end of that bottle broke.
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