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My first pneumatic piston air cannon.....sadly doesnt work

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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My first pneumatic piston air cannon.....sadly doesnt work

Unread postAuthor: LikimysCrotchus5 » Wed Sep 19, 2007 8:22 pm

My cannon is leaking through the barrel and I am pretty sure that its because the piston is not working. I got pictures. Advice and anything?

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The whole cannon

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The trigger (modified sprinkler valve)

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4 inch T (looks different from other T's I know its different in some way)

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Schrader valve

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The piston (which im pretty sure is the problem)

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The sealing part of the barrel

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The bumper

I couldn't find Sheet PVC so i had to use sheet metal. I found this kind of design on one of the topics here in spudfiles. Also i couldnt really find a good rubber sealant so i will take any options on what else will be a good sealant. And i will most likely make a new piston that needs to be able to fit a 4 inch T. Post any ideas that will meet the requirement for my new piston. Thx for the help. Also tell me at what STORES i can find sheet pvc. And I tried home depot, the guy didnt know what the hell I was talking about.

EDIT: I got some inner tube and i put it on my piston and it does work better and i got it to 25 psi until it started to leak more. after that i get to 10-15 psi and it leaks but it does a better sealing job.

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And for you MrCrowley here is the pic of the inside of the 4 inch T

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So tell me if you can see why there might be something else wrong.
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Last edited by LikimysCrotchus5 on Sat Sep 22, 2007 3:47 pm, edited 1 time in total.
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Unread postAuthor: iPaintball » Wed Sep 19, 2007 8:25 pm

Nice gun, but the fittings are DWV, so they're not safe over like 70 psi.
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Unread postAuthor: LikimysCrotchus5 » Wed Sep 19, 2007 8:32 pm

Most fittings found in stores are DWV but some of the DWV fittings are also PVC because on one of my cannons i have a DWV fitting that says PVC too.
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Unread postAuthor: iPaintball » Wed Sep 19, 2007 8:36 pm

PVC is the type of plastic. DWV refers to the pressure rating. A pressure rated part will say NSF-PW on it
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Unread postAuthor: MrCrowley » Wed Sep 19, 2007 8:41 pm

Can you post some specs of the inside of the non-pressure rated tee?

Read up on pressure ratings and PVC, DWV is non-pressure rated PVC like ipaintball said, if you live in America look for NSF-PW XXXPSI @73F
Where the XXX will have a pressure rating number, e.g 260psi @ 73 Degrees
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Unread postAuthor: noname » Wed Sep 19, 2007 10:30 pm

You should thank whoever it is you worship (unless you're aetheist) for saving your balls, or at least your hands. The cannon doesn't work, oh no. Good! The think would have violently disassmebled itself eventually anyway. Rebuild it, using parts that say:
PVC I Sch 40 NSF-pw only. If they say NSF-dwv, DO NOT use them!
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Unread postAuthor: jackssmirkingrevenge » Wed Sep 19, 2007 10:49 pm

The sealing end of your piston should look more like this with a neoprene face. Also, I hope you've ensured that the breech end of your barrel is cut at 90<sup>o</sup> and sanded smooth and clean.

A little efficiency tip, cut down the link between the sprinkler valve and the endcap to the absolute minimum (ie valve touching endcap) to cut down on pilot volume.
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Unread postAuthor: LikimysCrotchus5 » Wed Sep 19, 2007 10:55 pm

ok well fixing the the fittings can be easily arranged but I need to fix or make a better piston valve. So can you help me on that. Well thx for telling me anyway. I also would like to know if they sell pressure rated fittings at homedepot.
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Unread postAuthor: LikimysCrotchus5 » Wed Sep 19, 2007 10:56 pm

To Jack - I tried using that side but the same was happening. It could be because that is made of a mousepad which i heard is somewhat porous.
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Unread postAuthor: jackssmirkingrevenge » Wed Sep 19, 2007 11:02 pm

Get yourself some car inner tube and cut a disk from that, you should be sorted :)

By the way, why the extra bit of rod protruding from the piston? cut it down, less weight -> faster opening time ;)
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Unread postAuthor: LikimysCrotchus5 » Thu Sep 20, 2007 5:05 am

ok that works what should i use to cut it cause i thought about that and i wasnt sure what should i use.
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Unread postAuthor: jackssmirkingrevenge » Thu Sep 20, 2007 5:08 am

'acksaw ;)

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Unread postAuthor: LikimysCrotchus5 » Thu Sep 20, 2007 1:48 pm

ok thx jack do have any comments on my piston cause i think it sucks and im probably gonna make a new one but also can you tell me at what store you can get sheet pvc? not an online store.
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Unread postAuthor: dongfang » Thu Sep 20, 2007 2:24 pm

Hi,

For cutting the rubber, you could also try sharpening the edge of a scrap piece of pipe, and use a vice and/hammer some board to press it...

Car inner tube? Haven´t tires been tubeless for decades? Well if it exists, no problem but I just wonder...

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Unread postAuthor: jackssmirkingrevenge » Thu Sep 20, 2007 3:45 pm

LikimysCrotchus5 wrote:ok thx jack do have any comments on my piston cause i think it sucks and im probably gonna make a new one


I think your existing piston can work, just make both sides like the bumper end of your current piston and have a disk cut from rubber (inner tube or similar rubber sheet) on the front of the sealing end, as I suggested earlier.

I don't know about sheet PVC, what do you need it for?

Car inner tube? Haven´t tires been tubeless for decades? Well if it exists, no problem but I just wonder...


They are normally tubeless to start off with but in the event of a puncture it's usual to add an inner tube for extra safety, at least that's what happens with my car hehe.
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