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large volume pilot valve....CHEAP!!!

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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large volume pilot valve....CHEAP!!!

Unread postAuthor: jeepkahn » Fri Jan 09, 2009 1:41 pm

I been watching this forum for a few weeks, just registered today...

What I'm using on my 1" coaxial gun is a high quality garden hose sprayer slightly modded since I'm not worried about spray patterns, it's rated at 150psi and I mean to tell you there is NO piston honk on my gun... now to use a sprayer like this you can get a 3/4"npt to 3/4" garden hose adapter for like 2 bux usd... It flows so well that if you use a t fitting and a quick release you can leave it hooked to your compressor tank and it will still fire...

Anyone else ever used these???

BTW, my gun is 66"x1" barrel, and a 33"x2" chamber, barrel sealing piston valve, with an ultra lite piston about 3/4"oz, and after pressurizing it has zero leakdown after 30 minutes... I've got a coupla others and I'll give specs on them later, I do have a 1.5" barrel gun that with a 11oz homemade "missile" will shoot over 1/2 mile, and with vacuum assist will probably go at least double that, with vacuum assist and a 2oz lo density projectile it'll go supersonic... :D
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Unread postAuthor: jrrdw » Fri Jan 09, 2009 2:32 pm

I've heard talk of using these, but don't myself. If this is a completed cannon you should post it in the showcase section with pictures and details. Damage pictures go a long way around here, so do video clips. :D

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Re: large volume pilot valve....CHEAP!!!

Unread postAuthor: jimmy101 » Fri Jan 09, 2009 3:24 pm

jeepkahn wrote: NO piston honk on my gun...

So? In many cases "honking" has nothing to do with the performance of the gun. The "honk" only occurs after the ammo has left the barrel.
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Re: large volume pilot valve....CHEAP!!!

Unread postAuthor: jeepkahn » Fri Jan 09, 2009 3:31 pm

jimmy101 wrote:
jeepkahn wrote: NO piston honk on my gun...

So? In many cases "honking" has nothing to do with the performance of the gun. The "honk" only occurs after the ammo has left the barrel.


I was refering to the fact that it doesn't honk even when I have active supply still hooked up... before I was using a blowgun for the pilot and even without the active supply still hooked up it would honk from not enough pilot flow and the piston would struggle to open properly and "honk"...

I may try to design a self loader for it so that it would reload after each shot, with it hooked to my bigtank compressor I can fire it every 3 seconds...


I need to get a video camera, I'm going to try and get my daughters digi cam to post some pics though...
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Unread postAuthor: starman » Fri Jan 09, 2009 4:25 pm

How about just a regular still pics of your setup. That will be helpful until you can throw us you honkless video.... :wink:

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Unread postAuthor: PVC Arsenal 17 » Fri Jan 09, 2009 5:07 pm

Here is a picture of my second [DWV-ridden] pneumatic.

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I used a garden hose. The thing worked great.
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Unread postAuthor: D_Hall » Sat Jan 10, 2009 12:56 am

I'm just trying to figure out WTF "vacuum assist" is.
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Unread postAuthor: JohnnyBOOM » Sat Jan 10, 2009 1:58 am

D_Hall wrote:I'm just trying to figure out WTF "vacuum assist" is.


Maybe you place 15 psi "burst disks" at both ends of the barrel and pull a vacuum in the barrel just ahead of the projectile. When fired, the projectile would break through the first burst disk and enter a vacuum barrel and thus, not only have no air resistance, but also be pulled along with the added 14.7 psi of the vacuum, while the chamber air pushes it.

That might be how it works in my head though. :D
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Unread postAuthor: jeepkahn » Sat Jan 10, 2009 9:29 am

D_Hall wrote:I'm just trying to figure out WTF "vacuum assist" is.


the gun referenced is a 72"x1.5" barrel attached by a 1.5" high pressure butterfly valve to a 5gal 200 psi rated steel tank.... when firing with vacuum assist, I use a "burst disc"(actually it's the bottom from a plastic cup with sealing grease where it meets the barrel), at the exit end of the barrel I have a vacuum port, where I attach an industrial vacuum pump that pulls between 26 to 28 inches of vacuum between the butterfly valve and the sealing disc(72"s between the 2)...

I'm pretty sure there are greater things than just the additional pressure diff. effecting the projectile, I just can't wrap my head around it totally yet(I don't work for NASA..LOL)... Such as when you apply thrust to an object in a vacuum I know it accelerates way faster than applying thrust to objects in the atmosphere, and my projectiles are accelerating in a vacuum for 72"s...

As a reference point, I can launch the above described projectile without the pressure tank attached, using only the butterfly valve, the disc, the barrel, and the vacuum pump, and the range is a hair over 200yds...

If anyone here has the physics background to help me figuring muzzle velocity and how the vacuum effects all of the other forces at work, please chime in..
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Unread postAuthor: jrrdw » Sat Jan 10, 2009 9:50 am

Once the projectile reaches the vacuum port, would it not hinder the projectile at that point in travel? Being as how the vacuum port is off the side of the barrel, instead of straight out of the muzzle.
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Unread postAuthor: jeepkahn » Sat Jan 10, 2009 10:42 am

jrrdw wrote:Once the projectile reaches the vacuum port, would it not hinder the projectile at that point in travel? Being as how the vacuum port is off the side of the barrel, instead of straight out of the muzzle.


the vacuum port is 3/64" located .5" from the exit end of the barrel, and I close the valve at the port fitting once I reach 26"InHg, so it is a static vacuum...

in short, it doesn't effect the projectile...
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Unread postAuthor: jrrdw » Sat Jan 10, 2009 12:49 pm

You should really get a video up of the operation in progress. I've been here 3 years and never seen anything like this yet. Very interesting concept.
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Unread postAuthor: JohnnyBOOM » Sat Jan 10, 2009 12:58 pm

jeepkahn wrote:
D_Hall wrote:I'm just trying to figure out WTF "vacuum assist" is.


I'm pretty sure there are greater things than just the additional pressure diff. effecting the projectile, I just can't wrap my head around it totally yet(I don't work for NASA..LOL)...


The added benefit is that you have no air resistance ahead of the projectile.
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Unread postAuthor: jeepkahn » Sat Jan 10, 2009 1:12 pm

jrrdw wrote:You should really get a video up of the operation in progress. I've been here 3 years and never seen anything like this yet. Very interesting concept.


I actually got the idea from my grade school son's science fair, if you google ping-pong cannon, you'll get the idea... it's a science project where they use a vacuumpump and a 10ft section of pipe with rupture discs on both ends to fire ping pong balls at about 300m/s...

I saw it and thought to myself, "hhhmm, what if I pulled a vacuum in my barrell, how much more velocity could I get."... the first time I tried it with a tite fitting homemade nerf ball, when it exited the barrel it made a very definitive "keeraack" that deafened me the rest of the day and this little liightweight foam ball put a huge dent in a industrial rollup service door... :shock:



And Yes, I gotsta get me a video camera... :D

JohnnyBOOM wrote:
jeepkahn wrote:
D_Hall wrote:
I'm just trying to figure out WTF "vacuum assist" is.


I'm pretty sure there are greater things than just the additional pressure diff. effecting the projectile, I just can't wrap my head around it totally yet(I don't work for NASA..LOL)...


The added benefit is that you have no air resistance ahead of the projectile.
And my question is how much does that affect acceleration???

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Last edited by jeepkahn on Mon Jan 12, 2009 12:39 pm, edited 1 time in total.

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Unread postAuthor: ALIHISGREAT » Sat Jan 10, 2009 1:20 pm

jeepkahn wrote:
JohnnyBOOM wrote:
jeepkahn wrote:
D_Hall wrote:I'm just trying to figure out WTF "vacuum assist" is.


I'm pretty sure there are greater things than just the additional pressure diff. effecting the projectile, I just can't wrap my head around it totally yet(I don't work for NASA..LOL)...


The added benefit is that you have no air resistance ahead of the projectile.
And my question is how much does that affect acceleration???


think of it this way.... try running with a mini parachute attached to your belt... because of air resistance, it slows you down... so the same applys if you are pushing a large surface area forward through the air, the air resistance slows you down.... so if you take away the air, there is no longer a force acting against you so you can go foreward faster.
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