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My first 2" cannon (just something little) :)

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: Technician1002 » Tue Oct 12, 2010 6:30 pm

Here is a chart of some globe valves at various percentages of opening.
Image
It is great, but not as good as a butterfly, ball, gate, or coaxial piston.
It good as a fast opening valve, but not the highest flowing when open.
More info is here;
http://www.cheresources.com/valvezz.shtml

CV values for 2 inch butterfly valves is typically 175.
Reference is here;
http://www.pro-techvalve.com/TLBV.pdf
Look on page 6 of the PDF
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Unread postAuthor: High-PSI » Tue Oct 12, 2010 7:21 pm

Great. Thanks for the information. :)

These valves do open lighning fast when pilotted. So, that is good. I am glad the flow rate is still quite good, though obviously not the best around.

Question, I know a butterfly valve has high flow rate (that is obvious by the simple fact that it is a straght shot into the barrel when open), but how do you open one fast enough? Same for a ball valve.........

At any rate, I can run higher pressure than most 2 inch cannons (PVC cannons). So, the high pressure will make up for lack in flow rate. Of course, this thing will probably bruise me and do some serious damage to anything I aim it at anyway!

Matt
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Unread postAuthor: Gun Freak » Tue Oct 12, 2010 7:22 pm

Spring load the ball valve to make it open faster, or some people have used a pneumatic ram to open it.
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Unread postAuthor: Technician1002 » Tue Oct 12, 2010 7:26 pm

Piston valves are often used due to their fast operation and excellent flow. They are slightly slower than a diaphragm. Without the 2 internal 90 degree bends and the 180 at the seat, they flow better in the transonic range.
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 12, 2010 11:06 pm

High-PSI wrote:Anyway, I may start selling two stage 2 inch pilotted valves if this one proves to be what my 1-1/4 inch valve is. Of course, these things are so freakin expensive, I am not too sure how many others would have any interest in one. But, I am open to it. I know I have access to equpiment that others do not. So, I am not against helping others out if they are interested.


I don't think it would make sense commercially, a self made piston valve would be infinitely cheaper with likely better performance, even a pre-made one as offered by LaunchPotatos.com will set you back less than $100.

You do of course have the advantage of running at higher pressures but at these dimensions, typical compressor pressures (110-150 psi) usually suffice.
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Unread postAuthor: High-PSI » Wed Oct 13, 2010 7:08 am

jackssmirkingrevenge wrote:
High-PSI wrote:Anyway, I may start selling two stage 2 inch pilotted valves if this one proves to be what my 1-1/4 inch valve is. Of course, these things are so freakin expensive, I am not too sure how many others would have any interest in one. But, I am open to it. I know I have access to equpiment that others do not. So, I am not against helping others out if they are interested.


I don't think it would make sense commercially, a self made piston valve would be infinitely cheaper with likely better performance, even a pre-made one as offered by LaunchPotatos.com will set you back less than $100.

You do of course have the advantage of running at higher pressures but at these dimensions, typical compressor pressures (110-150 psi) usually suffice.


That is my perspective as well. :)

I want to thank you guys for all the useful information. I am still new at this. Fabrication is not big deal for me. Finding useful information is another.

Matt
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Unread postAuthor: Technician1002 » Wed Oct 13, 2010 11:00 am

When trying to model my 2 inch QDV in GGDT against my muzzle velocities and in barrel acceleration, I found I had to use a valve CV of at least 80 to start matching the acceleration on a 4 inch 2 oz Poof brand foam ball. Lower CV values simply could not reach the velocities I was measuring. This is for a cannon using a 2 inch piston valve feeding a 4 inch diameter barrel.

It takes high flow to exceed 500 FPS at 100 PSI. I exceeded 450 FPS at 60 PSI. The thread with the results is here;
http://www.spudfiles.com/forums/ggdt-and-in-tank-quick-dump-valve-performance-t18090.html

Have you picked up a copy of GGDT? It is fantastic for modeling these launchers.
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Unread postAuthor: High-PSI » Wed Oct 13, 2010 4:41 pm

I understand you need HUGE CV numbers when feeding a 4 inch barrel with a 2 inch valve. However, my 53cv valve is feeding a 2 inch barrel. That should be plenty of flow, shouldn't it?

Oh, lastly, I would guess a fast acting valve is great for a shrt barrel and a slightly slower reacting valve with higher flow rate would be better with a longer barrel. Does that sound right?

Matt
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Unread postAuthor: Technician1002 » Wed Oct 13, 2010 6:46 pm

You will be impressed with it. That valve is very fast and has great flow for a 2 inch barrel. With heavy (slower) projectiles, it will provide lots of kick. The valve will work great for launching spuds. I would guess it would do fine punching holes in plywood with spuds. 500-600 fps should be in reach.

Slower vales work well with longer barrels and heavy projectiles. Butterfly valves are the most common valve used in pumpkin chucking. Faster valves are needed for short barrels, smaller chambers, and higher pressures.

With your 4 foot barrel, the fast valve is a good choice.

Since the barrel screws on, I still recommend making a tennis ball / soda can barrel for it. That size is great for very fun ammo. Rolled T shirts work much better in a TB size barrel than a 2 inch.
You should be able to pancake soda cans like this.
Image

With that valve i would not bother with a barrel larger than 3 inch.
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Unread postAuthor: High-PSI » Wed Oct 13, 2010 7:48 pm

Gotcha. Sounds good to me. :)

As I mentioned before, I can give more pressure than most 2 inch guns typically run. So, that can make up for a bit of flow loss.

Oh, I am not launching potatoes. This gun is for firing non-organic amo only.

Matt
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Unread postAuthor: High-PSI » Thu Oct 14, 2010 5:57 pm

Here are some pictures of the progress so far.

I installed the pilot valve and began the frame spar. The spar will hold the two grips and shoulder stock. The pinch clamps we made at the shop on the big CNC. :)

I will post more pictures as I have them.

Matt
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Unread postAuthor: BeaverRat » Thu Oct 14, 2010 11:31 pm

Very cool! I want to see this thing in action.
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Unread postAuthor: High-PSI » Sat Oct 16, 2010 11:51 am

Here are a few pictures of the grip. I have about 5 hours of time spent machining this from a block of 1 inch 6061.

You can see its orientation on the gun along with a very rough version of the shoulder rest/stock. Both parts are just resting there. Neither is installed. I am just holding the shoulder rest in place to give an idea of the layout of the gun. That rest will be very solidly braced and padded with 1/2 inch thick Neoprene.

Matt
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Unread postAuthor: jackssmirkingrevenge » Sat Oct 16, 2010 12:28 pm

Impressive, how long before you have it ready for firing tests?
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Unread postAuthor: Technician1002 » Sat Oct 16, 2010 12:32 pm

I really like this. The trigger guard is a nice touch. I'm impressed.

May I come and play in your shop?
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