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Ball Valve Idea

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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Ball Valve Idea

Unread postAuthor: theepicmool » Tue Jul 21, 2009 3:53 pm

The problem with Ball Valve's is their slow opening, but what if he potato is loaded into the valve itself, instead of in front of it. As long as the hole in the ball is drilled out to be identical to the barrel size it should work, right?
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Unread postAuthor: skyjive » Tue Jul 21, 2009 3:58 pm

What's gonna happen is that your chunk of potato is gonna get smushed to pieces when the ball valve is partly open since the air will be pushing it through but it won't be able to make it intact. It could conceivably work with a rigid projectile. But why not just use a sprinkler valve or QEV?
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Unread postAuthor: theepicmool » Tue Jul 21, 2009 4:02 pm

I'm looking for something more efficient then a sprinkler valve, and cheaper then a QEV. On the surface the sprinkler valves are pretty cheap, but also require a bunch of fittings etc.

Edit: Would my ball valve idea be good for tennis balls? Even if they do squeeze out mid-turn the opening for air would still be much larger then if I used a sprinkler valve.
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Unread postAuthor: jor2daje » Tue Jul 21, 2009 4:10 pm

Just make a piston valve, they are easy, my 1.5" porting valve cost $13, cheaper than a ballvalve that would fit tennis balls, and it opens way faster.
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Unread postAuthor: Hubb » Tue Jul 21, 2009 4:12 pm

My god, man. You'd need a massive valve for a tennis ball, and ball valves have a nasty habit of getting very expensive.

I do think the original idea (although has been discussed) is a good idea, but would be better for hard objects, such as marbles or ball bearings. Whatever the ammo, though, it would probably need to be airtight to make sure no air leaks out before it is fully open.

If you are looking to open a ball valve faster than normal, put a spring on it. Otherwise, choose a different valve.
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Unread postAuthor: theepicmool » Tue Jul 21, 2009 4:18 pm

Yeah, the big price jump in ball valves is at the 2.5" mark, and i cant think of any good, rigid 2" projectiles. I wouldn't know where to start in machining a piston valve though.
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Unread postAuthor: Willdebeers » Tue Jul 21, 2009 4:24 pm

it might work...but you would need a hard projectile to make it work...
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Unread postAuthor: Hubb » Tue Jul 21, 2009 4:29 pm

theepicmool wrote:Yeah, the big price jump in ball valves is at the 2.5" mark, and i cant think of any good, rigid 2" projectiles. I wouldn't know where to start in machining a piston valve though.


Start with the search. Most piston valves on this site are not machined. In fact, I can only think of maybe two that are. Mr Crowley used a deodorant can for his piston in his launcher. Just be creative.
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Unread postAuthor: inonickname » Tue Jul 21, 2009 7:18 pm

This has been discussed in the ball valve breech topic.

Just go with a piston valve..
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Unread postAuthor: theepicmool » Tue Jul 21, 2009 8:09 pm

The more I think about it the more I think the potato would not be mushed while the ball valve is turned. It has no chance to gain momentum so the only thing pushing on the potato would be ~120 psi for about a half a second. Sure, if you put 120 pounds of pressure on a potato it will mush, but I'm not too sure that would be the case if its contained from all sides inside a ball valve. Kind of the idea of a burst disk: Do you think a whole potato is stronger then 5 layers of tin foil when under pressure?
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Unread postAuthor: Mateo » Tue Jul 21, 2009 8:20 pm

well if you feel the need to "machine" a piston then go buy a dowel rod from a hardware store and start workin at it wish some sand paper. but really you dont need to machine a piston. and that whole giant ball valve breach/confusion thing really is way more complex than a sprinkler which is plenty efficient.
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Unread postAuthor: spudtyrrant » Tue Jul 21, 2009 8:25 pm

Come on man you making this harder than it has to be just make a piston valve.

Its much easier to make a piston valve than to try to make a ballvalve/burst disk valve that may not even work at all, let alone as well , and to awnser your question we would need to know the exact barrel size you want but most likely the potato will try to escape before the valve is completely open resulting in mush as you said if you had a hard good sealing projectile it would be ideal
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 21, 2009 8:38 pm

I had proposed something similar to Brian back on spudtech while discussing an efficient design for a marble machinegun, it's basically a variation of the "valveless" idea where the ball valve replaces the detent:
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Unread postAuthor: theepicmool » Tue Jul 21, 2009 8:48 pm

@mateo
More complex? It's just a potato inside a ball valve. I am planning on making a 2" barrel and if i use a sprinkler valve I'm going to have to buy a bunch of couplers and loose efficiency that i would otherwise have if I had a ball valve the same size as my barrel.

@spudtyrrant
The barrel size would be 2" so theres a pretty big chunk of potato preventing squish-age. The way I see it is there are 3 possible outcomes:

1: It works fine

2. I have to use a piece of plastic to prevent squish-age

3. I'm stuck with a ball valve gun.

I'm thinking #2 is the most likely. If it works it would be more efficient then a sprinkler valve or a ball valve along, and maybe a piston valve.

@jackssmirkingrevenge
mmgdetail.JPG is similar to my idea, except the projectile would be inside the ball itself. This would remove one point of friction on launch.
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Unread postAuthor: Technician1002 » Tue Jul 21, 2009 11:33 pm

theepicmool wrote:@mateo
More complex? It's just a potato inside a ball valve. I am planning on making a 2" barrel and if i use a sprinkler valve I'm going to have to buy a bunch of couplers and loose efficiency that i would otherwise have if I had a ball valve the same size as my barrel.

@spudtyrrant
The barrel size would be 2" so theres a pretty big chunk of potato preventing squish-age. The way I see it is there are 3 possible outcomes:

1: It works fine

2. I have to use a piece of plastic to prevent squish-age

3. I'm stuck with a ball valve gun.

I'm thinking #2 is the most likely. If it works it would be more efficient then a sprinkler valve or a ball valve along, and maybe a piston valve.

@jackssmirkingrevenge
mmgdetail.JPG is similar to my idea, except the projectile would be inside the ball itself. This would remove one point of friction on launch.


Hint on this one.. Step on a raw potato. Now figure the valve size opening area and the pressure to find force. Notice anything close in the force? A 2 inch valve has a 3.14 square inch opening. At 100 PSI, the force is 314 lbs. I hope this helps the reality check. :D I predict mashed potatoes.
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