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Valve upgrade

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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Valve upgrade

Unread postAuthor: omgimonfrie2 » Fri Sep 21, 2007 11:37 pm

How is a piston valve made? And it it cheaper than buying a sprinkler valve and modding it? Which one is more efficitive?

Right now I have two 3in by 5ft air tanks to a 1 1/2in ball valve and barrel. The barrel is only 10 feet. I plan on extending the barrel to atleast 20feet. But I will have to devise a way to hold it up. I'm also interested in a 2 1/2 in barrel for tennis balls. Any way I'm interssted in a valve upgrade.
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Unread postAuthor: homedepotpro » Sat Sep 22, 2007 12:23 am

first of all your fittings are dwv. there are also tons of posts about piston valves. they are no too hard to make but they aren't exactly as easy as a ball valve. A piston valve will open faster but with a 20' barrel that is not as important. you should first get rid of those dwv fittings, they're dangerous.
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Unread postAuthor: Killjoy » Sat Sep 22, 2007 12:31 am

If you don't want to change the fittings, then keep the pressure below 70 psi and don't go banging on it or moving it around when its pressurized.

If you have no experience with piston valves, then it will probably end up being more expensive then a modded sprinkler valve. I'd say go for the modded spinkler valve first, then a piston valve later on.
Good cannon by the way.
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Unread postAuthor: omgimonfrie2 » Sat Sep 22, 2007 2:46 pm

What's wrong with the fittings? And with a 2.5in barrel it will be much shorter so I decided to start looking into different valves now. I did not think to check this site for piston valve info *smacks self*
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Unread postAuthor: jackssmirkingrevenge » Sat Sep 22, 2007 2:52 pm

What's wrong with the fittings?


they're not pressure rated.
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Unread postAuthor: jrrdw » Sat Sep 22, 2007 2:59 pm

Killjoy wrote:If you don't want to change the fittings, then keep the pressure below 70 psi and don't go banging on it or moving it around when its pressurized.

If you have no experience with piston valves, then it will probably end up being more expensive then a modded sprinkler valve. I'd say go for the modded spinkler valve first, then a piston valve later on.
Good cannon by the way.


Thats a great plan of attack! Wait untill he figures out that piston valves can be opened with modded sprinkler......opppps! Did i just let the cat out of the bag???
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Unread postAuthor: Hubb » Sat Sep 22, 2007 3:01 pm

All of your fittings (at least the ones that are visible) are DWV. Like jack said, they are not pressure rated, which means they will hold just enough pressure to cause the pvc to shatter when you're least expecting it, sending shards into your innards, causing massive trauma and...well, you get the idea.

Anyway. With a 20ft barrel, you would be fine leaving the ball valve, however, you may want to think of a way to add a spring or something to assist in the opening. You may end up with even better performance with the ball valve (having a 2.5" barrel that is 20' long) than you would with a sprinkler valve anyway.

Just keep the ball valve until you decide to upgrade, in which case, you build a piston valve.
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Unread postAuthor: DYI » Sat Sep 22, 2007 9:48 pm

With such a long barrel, the high flow of the ball valve means that it could outperform a restrictive sprinkler valve, even with slower opening time. Your first concern should be to use pressure rated fittings, because PVC pipe shatters, and apparently doesn't show up on x-rays.
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Unread postAuthor: chaos » Sat Sep 22, 2007 10:30 pm

x-ray myth is a lie, it shows up, just like glass does.
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Unread postAuthor: meatballs » Sat Sep 22, 2007 11:02 pm

a piston valve would be your best bet here. a ball valve is better than a sprinkler valve becuae of the value of high flow over fast opening with the long barrel. a piston valve combines these benefits and can be triggered with a small ball valve or a sprinkler valve. this would open fast and the flow would be good. they aren't too hard to make, i made one for my first pneumatic cannon and it worked great.

and chaos, how do you know that? im not saying i think your wrong or anything im just curious how you know.
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Unread postAuthor: omgimonfrie2 » Sat Sep 22, 2007 11:05 pm

Really? Well its too late now. There already pvc glued together. A fews days ago My friend had it at 40 and one of the air tanks came flying off the side. We just glued it back on. Every time I fill it after a day or two of not being used you can hear the base creaking. It, for some reason, has a leak some where between the t connecter and the valve. The air tanks do say non-pressure on them. I figure it just means they have not been pretested, and since rated 3in pvc is at 240 I think we are fine. Our normal operating pressure is 35psi or 60psi. Are we safe? And I've never seen presure rated fittings. Spudtech said that fittings are higher than the pipe its self. And thanks for all the help.
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Unread postAuthor: Killjoy » Sat Sep 22, 2007 11:12 pm

Umm...i would suggest scraping it. because the pressure tanks say no pressure they are most likely cell core pvc, which means your basically holding pressure in a giant styro foam tube. It may just be best to start over for your own safety.
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Unread postAuthor: meatballs » Sat Sep 22, 2007 11:32 pm

yeah if the pipe itself says something like NOT FOR PRESSURE on it that means you should not use it for pressure. if it is pressure rated the pipe will say NSF-pw and have a pressure printed on it in PSI. i would agree, start over and use a piston valve and pressure rated pipe and fittings, its worth it for the safety. you should never, ever, use cell core pvc for pressure.
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Unread postAuthor: omgimonfrie2 » Sun Sep 23, 2007 12:40 am

Well where do I find the rated connectors?
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Unread postAuthor: Killjoy » Sun Sep 23, 2007 3:03 am

If your chain hardware stores don't have them (home depot, lowes, etc). Try small business plumbing stores, they should have prssure rated parts or be able to order them. You could also order off the internet.
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