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New Piston Cannon....Near Explosive Decompression

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 » Thu Jun 11, 2009 6:15 pm

Night Hawk wrote:
jimmy101 wrote:velocity3x
(It's a good thing most people on the forum live long distances from each other :D )


With cannons like the one above, im not sure if thats an issue any more. Atleast im over the pond. surely it cant reach -that- far?


Intercontinental ballistic spuds. Hmm, thanks for the idea for the contest.. :D :D
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Unread postAuthor: jeepkahn » Thu Jun 11, 2009 6:26 pm

BOT... You mentioned a second cannon??? Bigger than hungus, or are you gonna go for smaller package on the next one???
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Unread postAuthor: Night Hawk » Thu Jun 11, 2009 6:52 pm

jeepkahn wrote:BOT... You mentioned a second cannon??? Bigger than hungus, or are you gonna go for smaller package on the next one???

Nah i recon this time hes going for china ;p
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Unread postAuthor: jonnyboy » Thu Jun 11, 2009 7:17 pm

Wow :shock:

Do you have a high pressure source? This cannon could take some serious pressure if you replaced the pvc barrel with an aluminum one. For a first cannon this is definitely probably the best I've seen. What exactly does this "super" version improve upon?
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mobile chernobyl wrote:I can shoot a Canuter Valve off my '82 Chevy Ram F150 AT LEAST 3/4 Mile with 'ma cannon made of soup cans duct taped together, then I just squirt some bacardi 151 in the chamber and hold up my cigarrete lighta and WHOOSH! That thing flies at least 3/4 mile
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Unread postAuthor: velocity3x » Thu Jun 11, 2009 9:37 pm

Technician..."From what you are describing as symptoms indicate the valve seat is relatively small in relation to the OD of your piston. "


2 inch dia shuttle valve w/ 1.875" dia o-ring.
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Last edited by velocity3x on Wed Jan 13, 2010 4:31 pm, edited 1 time in total.
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Unread postAuthor: velocity3x » Thu Jun 11, 2009 9:54 pm

Jeep..."BOT... You mentioned a second cannon??? Bigger than hungus, or are you gonna go for smaller package on the next one???"
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Last edited by velocity3x on Wed Jan 13, 2010 4:32 pm, edited 1 time in total.
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Unread postAuthor: Technician1002 » Thu Jun 11, 2009 11:19 pm

velocity3x wrote:Technician..."From what you are describing as symptoms indicate the valve seat is relatively small in relation to the OD of your piston. "


2 inch dia shuttle valve w/ 1.875" dia o-ring.
<img src="http://i145.photobucket.com/albums/r240/velocity3x/44mm%20HUNGUS/44HUNGUSShuttleValve.jpg?">

I appreciate your thoughts but, the problem is as I stated in an earlier post. The piston to cylinder wall clearance is only .005". Because the piston seat is recessed .200" deep, a strong vacuum is formed as air escapes past the piston sides to the barrel. It's the same thing you'd experience if you tried to pull a rubber stopper straight up out of a drain from a laundry tub with 72" of water in it. The escaping water tries to hold the rubber stopper in the drain unless the plug is pulled quickly. It's just an oversight in my design and can be fixed with some simple machining. The reason I mentioned it in earlier post is to show that I didn't use a QEV because their not fast enough to "rip" the piston from the valve seat on this gun.

As for piston blow by.....very little of that happening in only .005". Seriously, this design doesn't have a breathing or any other problem. It's power is almost beyond evil. It's just a design glitch that is easily changed. Even with the glitch, it works exceedingly well.


Great analysis of the problem. I think you are on to it. A trip to the lathe for a face shave may fix it.

Dumb question, why does the air have to squeeze past the piston to get to the barrel? Isn't the chamber air fed directly to the area of the valve seat? If it feeds further back to where the waist is on the piston, that makes a ton a sense. Is there a way to machine ports past the face of the piston to eliminate that problem?

Very nice. It is possible to go too large in diameter on the seat. As the seat becomes larger, the force that initially cracks open the valve is very small. The pilot would need to drop to a very low value to crack it open. A fairly low pressure is required in the pilot to open it. Thanks for the great drawing. you may need a floating o ring to reduce the blow by even further is you wish to fire it with a QEV. From the ratio shown, that thing kicks when it fires. :shock: Nice job. Keep the big pilot valve and enjoy that thing.

1.875 O ring on a 2 inch piston. I'm impressed. It snaps to attention. Those close to 1:1 ratio valves can be tricky to get to work (I've done a few) but when they work, they can't be beat for power. :D
:wav:

That is an even tighter ratio than any of the ones I built except the QDV, and they require hand pulling.
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Unread postAuthor: Daltonultra » Fri Jun 12, 2009 4:48 am

Velocity, the valve I mentioned is insanely fast. It's not a diaphragm valve at all, it's a piston valve. It SNAPS open, INSTANTLY, and dumps fast enough to blow a steel dart completely through 1" of solid yellow pine and deep into a cottonwood stump behind that.

On recursion: In this case, it may make the firing process a few nano-seconds longer than a theoretically perfect valve, but it will be measurably faster than a spring-loaded ball valve.


And BTW, yes, i was complimenting your gun, highly. That thing is insane, way beyond anything I could put together.
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Unread postAuthor: Night Hawk » Fri Jun 12, 2009 5:12 am

velocity3x wrote:Jeep..."BOT... You mentioned a second cannon??? Bigger than hungus, or are you gonna go for smaller package on the next one???"

It's name is "SUPER HUNGUS XL" .....if that's any indication of it's size.

Night Hawk...."Nah i recon this time hes going for china"

Not China.....North K. and that lil goofy dude, maybe.

Jonnyboy..."What exactly does this "super" version improve upon?"

400 psi Helium and pure brute horsepower, range and speed.....


Holy crap. These golf balls will be breaking the sound barrier with ease.

Strangely enough i was going to suggest koria, but i thought china was a bigger target. :p

Um could you explain how it works? I get certain parts of it but im not fully sure. Its barrel sealing yeah?
Thanks

NH
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Unread postAuthor: velocity3x » Fri Jun 12, 2009 8:51 am

Technician1002 wrote:Dumb question, why does the air have to squeeze past the piston to get to the barrel? Isn't the chamber air fed directly to the area of the valve seat? If it feeds further back to where the waist is on the piston, that makes a ton a sense. Is there a way to machine ports past the face of the piston to eliminate that problem?


Tech,
It feeds further back to where the waist is on the piston. The front portion of the 2.000" piston is essentially seated in a "counterbore" .200" deep x2.005". Thats why it creates a vacuum and needs so much power to retract. I can fix it by either step boring the cylinder from 2.005" to maybe 2.250 in only the area around the front portion of the piston. An easier fix would be turning a 45 degree angle on piston from just behind the o-oring rearward thus increasing the .005" clearance on the side of the piston. Then again.....I can leave it the way it is because it's 100% reliable and insanely powerful just the way it is. The only reason I'd ever need to change it is if I wanted to switch to a QEV on this gun. This gun is already built so I think I'll just leave it as is and not make this mistake on the next one.
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Unread postAuthor: velocity3x » Fri Jun 12, 2009 9:32 am

Daltonultra wrote:On recursion: In this case, it may make the firing process a few nano-seconds longer than a theoretically perfect valve, but it will be measurably faster than a spring-loaded ball valve.


Dalton,
I understand what you are saying about QEV's and recursion and I really like the idea. My original design intended to use a QEV but, the few nano second delay you mentioned were enough to prevent my gun from operating. I have many QEV's from aerospace manufacturers. They're high quality but.......they're diaphram style. Diaphram valves pull to slow and have a soft opening...also internal twists and turns which slow exhaust. On this gun....they just wouldn't work. I didn't try the type of QEV you suggested and maybe that style would have worked. My next build will DEFINITELY use a QEV...the type you suggested. QEV was and is my first choice but, on this gun I actually prefer the look of mechanical trigger linkage which is line with the WWII style. It's DEFINITELY harder to design and make the trigger linkage than thread on a 3/4 npt valve. I guess it all comes down to a matter of personal taste and preference.
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Unread postAuthor: velocity3x » Fri Jun 12, 2009 9:45 am

Night Hawk,
Yes...it's barrel sealing. It's like making a champaign bottle pull it's own cork to the inside of the bottle using it's own pressure by lowering the pressure on the inside end of the cork. A barrel sealing piston is the cork. The bottle opening is the barrel.
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Unread postAuthor: jeepkahn » Fri Jun 12, 2009 11:34 am

velocity3x wrote: It's DEFINITELY harder to design and make the trigger linkage than thread on a 3/4 npt valve. I guess it all comes down to a matter of personal taste and preference.


And on this cannon it is a nice added touch.... In fact, I think when I build the "Decimator" I'm going to use a mechanical valve, and it will probably be a "cockable" valve to make it more artillery like...Granted I'm ONLY gonna be running a 1" bore barrel, and 800psi....

And when dealing with HIGH POWER Large bore cannons, a mechanical valve also adds a level of safety/reliabilty that QEV and diaghram valves can't offer due to sensitivity and possibility of a ruptured diaghram or qev shuttle...
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Unread postAuthor: velocity3x » Fri Jun 12, 2009 2:22 pm

jeepkahn wrote:And when dealing with HIGH POWER Large bore cannons, a mechanical valve also adds a level of safety/reliabilty that QEV and diaghram valves can't offer due to sensitivity and possibility of a ruptured diaghram or qev shuttle...


When any devise becomes more automated or sophisticated, it also becomes more prone to failure. With mechanical trigger, you have less stuff (batteries) to tote along or be dependant upon just for a fun afternoon of blasting.
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Unread postAuthor: Daltonultra » Fri Jun 12, 2009 7:43 pm

velocity3x wrote:
jeepkahn wrote:And when dealing with HIGH POWER Large bore cannons, a mechanical valve also adds a level of safety/reliabilty that QEV and diaghram valves can't offer due to sensitivity and possibility of a ruptured diaghram or qev shuttle...


When any devise becomes more automated or sophisticated, it also becomes more prone to failure. With mechanical trigger, you have less stuff (batteries) to tote along or be dependant upon just for a fun afternoon of blasting.


My piston QEV uses no batteries. It's piloted by the small push-button valve I linked to. For safety, you can simply use a button cover available through any number of electronics hobby sites.
As for the piston breaking, it would take FAR more the 400psi to do so. I believe several people here have taken that model of QEV up over 600psi without consequence. The button-valve is also rated for 300psi, but it could be replaced by any number of other valves that are rated for much more.
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