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my first pneumatic cannon

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 cannon

Unread postAuthor: geardog32 » Mon Jun 22, 2009 9:44 pm

so i am designing my first pneumatic cannon and i have decided on a simple sprinkler valve design. my question is what size my chamber should be i plan to make it so that i can have several barrel sizes up to a two inch diameter. im not sure how big i should make the pressurized chamber i was thinking a 22 inch by 3 inch cylinder which would give me a little over 622 cubic inches. i not asking that someone spend alot of time working out all of the physics, im just asking for someones experience and whether it is big enough.
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Unread postAuthor: twizi » Mon Jun 22, 2009 9:50 pm

how big is the sprinkler valve and is it modded
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Unread postAuthor: geardog32 » Mon Jun 22, 2009 9:56 pm

yes it will be modded and it has 1 inch openings
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Unread postAuthor: twizi » Mon Jun 22, 2009 9:57 pm

then your chamber should work fine
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Unread postAuthor: Technician1002 » Mon Jun 22, 2009 10:57 pm

May wish to recheck your math on the chamber.

Volume is the cylinder area X length.

Area of a circle is Pi X Radius Squared.

3 inch chamber is 1.5 inch radius (nominal, actual slightly larger)
1.5 squared is 2.25. Multiply pi time the radius squared value of 2.25 to get area and then times length 22 inches to get cubic inches.

I had my doubts on volume. My t shirt cannon is only 700 cubic inches.
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Unread postAuthor: geardog32 » Mon Jun 22, 2009 11:34 pm

wow ok sorry you are right, i mistakenly used 3 inches as the radius which is not the case it is 1.5. which gives me a little over 155.
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Unread postAuthor: Technician1002 » Tue Jun 23, 2009 3:24 am

geardog32 wrote:wow ok sorry you are right, i mistakenly used 3 inches as the radius which is not the case it is 1.5. which gives me a little over 155.


Your chamber is about 3X bigger than my little cannon which also has a 1 inch valve. You will like the results. I even stuck a tennis ball barrel on mine and get 100 yard tennis ball launches at 100 PSI.
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Unread postAuthor: spudtyrrant » Tue Jun 23, 2009 10:15 am

Technician1002 wrote:
geardog32 wrote:wow ok sorry you are right, i mistakenly used 3 inches as the radius which is not the case it is 1.5. which gives me a little over 155.


Your chamber is about 3X bigger than my little cannon which also has a 1 inch valve. You will like the results. I even stuck a tennis ball barrel on mine and get 100 yard tennis ball launches at 100 PSI.

well yours also has your precious qdv which has about double the flow coeffeciant of a sprinkler valve so even with a chamber that large i think it should have similar performance
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Unread postAuthor: geardog32 » Tue Jun 23, 2009 10:45 am

well i seem to have run into a problem. i went to get supplies today nut all the 3 inch pvc i could find was cell core no pressure stuff. so i think im going to use two 24 inch chambers with 2 inch diameter which will get me about 150 cubic inches. would i get a performance decrease if i where to connect the two with a U fitting and the valve connected to one of them, rather than connecting the valve to a T fitting leading to both the cylinders?
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Unread postAuthor: Technician1002 » Tue Jun 23, 2009 12:21 pm

geardog32 wrote:well i seem to have run into a problem. i went to get supplies today nut all the 3 inch pvc i could find was cell core no pressure stuff. so i think im going to use two 24 inch chambers with 2 inch diameter which will get me about 150 cubic inches. would i get a performance decrease if i where to connect the two with a U fitting and the valve connected to one of them, rather than connecting the valve to a T fitting leading to both the cylinders?


Cell core PVC is not recommended. A better option is the same size in PVC electrical conduit. It's built the same as Sched 40 water pipe, but grey for electrical use. Cell core ABS may split under pressure, but doesn't shatter into shards like PVC. Safety first.

I'm not sure how much difference a U or T will make. In theory the T is better for short distance, but has a bend right before the valve that a U at the other end of the chamber won't have, so the U may be better. If either is better, is it enough to matter?
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Unread postAuthor: jmeyer1022 » Tue Jun 23, 2009 1:01 pm

Technician1002 wrote:
geardog32 wrote:well i seem to have run into a problem. i went to get supplies today nut all the 3 inch pvc i could find was cell core no pressure stuff. so i think im going to use two 24 inch chambers with 2 inch diameter which will get me about 150 cubic inches. would i get a performance decrease if i where to connect the two with a U fitting and the valve connected to one of them, rather than connecting the valve to a T fitting leading to both the cylinders?


Cell core PVC is not recommended. A better option is the same size in PVC electrical conduit. It's built the same as Sched 40 water pipe, but grey for electrical use. Cell core ABS may split under pressure, but doesn't shatter into shards like PVC. Safety first.

I'm not sure how much difference a U or T will make. In theory the T is better for short distance, but has a bend right before the valve that a U at the other end of the chamber won't have, so the U may be better. If either is better, is it enough to matter?



Electrical Conduit is usually not pressure rated, if pressure rated at all. I used 2.5" conduit for a tennis ball barrel on my 2" piston valve the conduit didn't hold very well. Look around the forums, I'm sure you'll see other examples, maybe I was just unlucky. Your best bet is googling "Plumbing supply warehouse in (state you live in). Find one, even if it's over an hour the prices are far cheaper than if you bought it at home depot and they have an enormous selection
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Unread postAuthor: geardog32 » Fri Jun 26, 2009 9:54 pm

just wondering is there a program that is common for designing your cannons on the computer. i think i have what i want design wise but it would be nice to make it 3d on a compute. ohh... and off topic but i am new to these forums and i was wondering what spud bux are?
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quick sketch in paint

Unread postAuthor: geardog32 » Fri Jun 26, 2009 11:58 pm

Image

Image
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Unread postAuthor: geardog32 » Wed Jul 01, 2009 8:41 pm

where has anyone bought schrader valve's? because i seem to be having trouble finding them at lowes and home depot.
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Unread postAuthor: mark.f » Thu Jul 02, 2009 3:44 am

I have found small steel schraders for air tanks at Lowes near the pumps. They do a good job of hiding so you should look carefully.

You should also be able to find rubber ones at any store which sells auto parts.

Also, nice avatar, but a little too simple to deduce. :P
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