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question on diaphram in a "Supah valve" design

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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question on diaphram in a "Supah valve" design

Unread postAuthor: sgehring » Sun Nov 26, 2006 1:40 am

I am new to this forum and need your help. I have build combustion guns before but am building my first air cannon. It has a 48 inch by 4 inch chamber and has a 72 inch by 2 inch barrel. All parts are PSI rated schedule 40 PVC. I am using a diaphram valve design found at he following link; www.geocities.com/advancedinventions/plansspv.htm
the chnages I have made is that rather than using the 1/8 inch hose fitting I have plumbed in 1 inch pipe back to a one inch modded sprikner valve that will be activated with a blow gun. I am using 1/8 inch rubber for the diaphram from a mud flap. It has a 2 3/4 aluminum disc on the back side. My question is the positoning of the barrel outlet to the diaphram. Once the glue sets there will be no moving it! I believe that this is how to postion the barrel outlet; I am guessing there needs to be enough spring pressure againest the diaphram at rest that it seats againest the barrel so it needs to be bowed out slightly and againest the barrel. When I activate the spinkler valve the change is pressure will pull the diaphram back away from the barrel and the air will shoot up the barrel outlet. Am I right? Other than postioning the barrel outlet and picking the spring the cannon will be ready. Because of the 1 inch outlet behind the diaphram I have to find a spring a little over an inch in diameter and as of yet have not found one. Any advice or comments will be apreciated, this site/forum has already answered alot of questions for me.
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Unread postAuthor: Scope » Sun Nov 26, 2006 8:34 am

Ok, Isnt that a barrel sealing valve while the actual supa is a chamber sealer??

What you said seemed right. Good luck man!!
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Unread postAuthor: sgehring » Sun Nov 26, 2006 3:13 pm

thats the problem I really don't know. I've built combustion guns and they are a lot simpler. This is my first air one. I think I have th right way to do it. Problem now is finding a spring to push the rubber againest the barrel when theyre is no pressure. Did you checl out the link for the design I am using in the tee? i am hoping that when I activate the blow gun the rubber will be pulled from the barrel to allow the air to go in. I used a slip in cap in the 4" tee I'm using. It is adapted to accept 1 inch pipe which leads to the modded sprinkler valve. Thus the spring needs to be a larger diameter that the hole in the slip in cap or it will fall into the pipe. I know some oil filters have a larger diameter spring inside of them that might work. I am going to cut one up later today. Once that is installed I can do some testing. It ought to have some power; :!: the chamber is a 4ft by 4 inch piece of pvc and the barrel is 6 foot of 2 inch.
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Unread postAuthor: PVC Arsenal 17 » Sun Nov 26, 2006 4:51 pm

seems like you're building a similar cannon as I am.

you shouldn't need springs. Air from behind the piston will push it against the barrel and then pressure will hold it there.
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Unread postAuthor: jrrdw » Sun Nov 26, 2006 6:17 pm

Where did you get that diagram? Did Joel let that out? Or is that what someone else thinks?
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Unread postAuthor: PVC Arsenal 17 » Sun Nov 26, 2006 8:24 pm

that is not Joel's diagram...

It someone elses idea for a barrel sealer, Joel's is a chamber sealer.
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Unread postAuthor: sgehring » Sun Nov 26, 2006 9:43 pm

If I don't use a spring do I glue my barrel in place flush with the rubber? It is backed with a piece of alumunum to make a good flat seal, will the action of triggering the blow gun cause the seal to pull free of the barrel and allow the air, on the resivior side, to escape up the barrell outlet? Another thought I had was to have two diaphrams with a spring between them. I took the spring out of a oil filter from my harley. It is about an inch high and and an inch wide. I was wondering if I put an equalization hole in each piece of rubber, with the spring between them, that when I released the pressure if the one sealed againest the barrel would pull more completly free and let the air in faster up the barrel outlet.
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Unread postAuthor: jrrdw » Mon Nov 27, 2006 11:27 am

Most of the pistons/seals i see here are long, (kinda), so i personaly can't tell you the answers to your questions. That being said here is what i would do if i where you -- assemble your valve without glueing/solvent welding it together, for a sort of test run. That will give you a good idea of how it's going to act, you can actualy wrap some tape around the outside to hold it together good enough to test at low pressure, like 5 to 10 psi tops. As for the spring i used a peice of wood inbetween my sprinkler valve and piston to adjust the tension, the longer the wood the stronger the spring, and vice versa. Sounds to me like it's time to build and see what happens!!
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Unread postAuthor: sgehring » Mon Nov 27, 2006 1:19 pm

kool. yea I am going to put the diaphram/valve together tonight when I get off work and try some tests shots. I have come up with some good springs. The ones out of oil filters are from 1 tto 1 1/2 inch long and diameter wise 3/4 to 1". I also have one from a chevy starter solinoid spring that is about 2 1/2 inches and reasonablely soft that I think will work great. I like looking around the garage and making something work that is not designed for what I want to use it for. Got use to doing that when I built my bike. thanks again.
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