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Piston Valves Explained Visually

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: BigDeutcher » Wed Sep 18, 2013 10:46 am

Okay, I am playing catchup with all this information. In the first shockwave file with the equalization hole, would there be any benifit to adding a light weight spring in the pilot area behind the piston to ensure quicker resealing?

Great illustrations!

Sorry about the bump had to ask the question .... my mind is reeling with ideas.
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Unread postAuthor: Gippeto » Thu Sep 19, 2013 11:19 am

Unless you're attempting a multi shot version...no benefit to the spring.

A check ball in the piston to prevent flow back to the pilot section would IMO be of benefit.
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Re: Piston Valves Explained Visually

Unread postAuthor: lonniev » Tue Oct 29, 2013 7:03 pm

The closed-cell foam used as a sealer on the inside and the outside of my piston valve cup compresses nicely to form a seal but it is a little fragile and gets torn by the air pressure. I am wondering what PSI is adequate to begin to experience the impulse effect: where the cup slides back and the pressurized air in the coax chamber rushes out the barrel rather than out the pilot/back valve.

At 50 PSI, I don't get the effect: the air still goes out the back.

On this first attempt cannon, the current piston is made with a durable, smooth plastic cup about 2.75" in diameter that fits over the inner 2" barrel and slides freely but not sloppily within the 3" PVC outer pipe. So, it is very light compared to a metal, epoxied plug.

Any clue on what PSI should be the transition region (yet won't shred the foam out of the piston cup?)
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Re: Piston Valves Explained Visually

Unread postAuthor: sharpshooter » Thu Oct 31, 2013 1:54 pm

Pics are broken now... perhaps on the forum change? Just in case some new guys need the info
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Re: Piston Valves Explained Visually

Unread postAuthor: jrrdw » Thu Oct 31, 2013 2:52 pm

These should open in IE8,9 or 10. I haven't tried with other browsers...Click on the file name, save as to a folder of your choice, open with IE.

chamberseal.swf [ 41.55 KiB | Viewed 868 times ]



barrelseal.swf [ 41.19 KiB | Viewed 868 times ]



coax.swf [ 40.96 KiB | Viewed 868 times ]

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Re: Piston Valves Explained Visually

Unread postAuthor: sharpshooter » Thu Oct 31, 2013 2:56 pm

Ahhh. I have only tried with chrome.
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Re: Piston Valves Explained Visually

Unread postAuthor: dart guy » Thu Oct 31, 2013 3:06 pm

Yea chrome doesn't get it but if i go to E 8/9 then i will get yelled at for bad spelling and punctuation.
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Re: Piston Valves Explained Visually

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Re: Piston Valves Explained Visually

Unread postAuthor: jrrdw » Thu Oct 31, 2013 3:10 pm

dart guy wrote:Yea chrome doesn't get it but if i go to E 8/9 then i will get yelled at for bad spelling and punctuation.


I was going to delete this but you seem to want to get complained about...BOOM!
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Re: Piston Valves Explained Visually

Unread postAuthor: calif94577 » Wed Jul 15, 2015 11:46 pm

Question, I am building my first spud gun and I had to already sledge hammer out my barrel because I accidentally shoved it in too far. Then when I re-set it, I thought I had it the right distance let it cure and found out that the barrel is now too far forward... sigh. How important is it to have the piston and the back of the barrel to meet in the middle of the T? Currently I have it quite forward of the middle, as in barely visible from the bottom of the T. Image attached with hand for size reference. Will this still work? I really don't want to have to re-sledge hammer it back out, I don't think it will come out now that it has cured almost completely...
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Re: Piston Valves Explained Visually

Unread postAuthor: matti » Fri Jul 17, 2015 3:50 am

calif94577 wrote:Question, I am building my first spud gun and I had to already sledge hammer out my barrel because I accidentally shoved it in too far. Then when I re-set it, I thought I had it the right distance let it cure and found out that the barrel is now too far forward... sigh. How important is it to have the piston and the back of the barrel to meet in the middle of the T? Currently I have it quite forward of the middle, as in barely visible from the bottom of the T. Image attached with hand for size reference. Will this still work? I really don't want to have to re-sledge hammer it back out, I don't think it will come out now that it has cured almost completely...


If your piston can reach the barrel and seal it then it will be ok. I think it's more a flow thing to have the port in the middle of the T fitting. But you can use it yes..
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Re: Piston Valves Explained Visually

Unread postAuthor: kitharington44 » Thu Jun 23, 2016 7:33 am

A device used to control the piston valve it's motion of fluid along the valve.If the tube or pipe means by the linear motion chamber.
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