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Interesting valve

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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Interesting valve

Unread postAuthor: D_Hall » Thu Mar 05, 2009 11:42 pm

Just took delivery of a 1.5" Asco QEV. I'm liking it. Cv = 50. Best part? Right off the shelf it has a pilot valve built into it. That is to say...

...See the red cap on the top? That's a 1/8" NPT fitting. Put a blow gun on there and it opens up a small diaphram valve that dumps out of a 3/8" NPT fitting (the red cap just below the 1/8" fitting). This 3/8" valve, of course, in vents the primary valve and away we go.

A high-flow cascading system perfect for spudding with no work! :P


edit: And for what it's worth, GGDT is implying 650 fps for a golf ball.
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Unread postAuthor: LikimysCrotchus5 » Thu Mar 05, 2009 11:45 pm

Hey guess what i got the same thing!

Lol, this valve has been mentioned here a long time ago. I still have 2 of them and have not even used one of them. But soon i will cause it will be summer! Woo

What you gonna make?
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Unread postAuthor: D_Hall » Thu Mar 05, 2009 11:48 pm

Golf ball gun, of course.

I'm torn... I've decided that I want to go for Mach with a golfball. I'm pretty sure I can do it, but it'd be a hybrid and would require some help from a friend (I can't weld for sh*t!). But that got me jonesing for a new golf ball launcher....

...So maybe I can't break Mach, but I can still go pretty quick with very little effort.
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Unread postAuthor: LikimysCrotchus5 » Thu Mar 05, 2009 11:52 pm

Yea it sounds good. I wish i even experimented with a hybrid. But due to my procrastination, i still have to build a stirrup pump, fix up my big gun cause it has quite some leaks so i might just rebuild it better, i need to fix up my copper gun and finish my new combustion as well. Then, maybe ill get to a hybrid.

Huh, too much work :(
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Unread postAuthor: jackssmirkingrevenge » Fri Mar 06, 2009 1:08 am

D_Hall wrote:I've decided that I want to go for Mach with a golfball


With that valve and a long enough barrel and high enough pressure, I'm sure you can get pretty darn close. I'm guessing it would take 300 psi or so easily.
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Unread postAuthor: D_Hall » Fri Mar 06, 2009 1:11 am

jackssmirkingrevenge wrote:With that valve and a long enough barrel and high enough pressure, I'm sure you can get pretty darn close. I'm guessing it would take 300 psi or so easily.

Well, there is the whole problem of it being an unheated gas in there. Also, I'm not one to push valves much (if at all) beyond their ratings. This one is rated at 125. I won't go past 150 under any circumstances.

Nay, when I go for Mach... Well, I've got some 5" ID, 7" OD pipe lying around (yes, 1" wall) that I could really make one hell of a hybrid out of, but it'll take some welding. I don't weld and right now my honey do list is loooong. If I'm lucky, I'll get started on that a year from now. Good news is that I ought to be able to recycle the barrel from whatever I build right now (simple pneumatic).
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Unread postAuthor: starman » Fri Mar 06, 2009 2:21 am

Are you planning to use that cute stainless sched 10 3 footer you just picked up for your barrel?
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Unread postAuthor: IlovePsi » Fri Mar 06, 2009 10:53 am

i have a 1" qev thats a beast pilotet by a 1/2 qev with blowgun i use it at marble gun , at 100 - 200 psi . allways wear eye saftey , soory for my english
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Unread postAuthor: jeepkahn » Fri Mar 06, 2009 11:01 am

D_Hall wrote:Golf ball gun, of course.

I'm torn... I've decided that I want to go for Mach with a golfball. I'm pretty sure I can do it, but it'd be a hybrid and would require some help from a friend (I can't weld for sh*t!). But that got me jonesing for a new golf ball launcher....

...So maybe I can't break Mach, but I can still go pretty quick with very little effort.


D, Since I'm sure you've got a chrony laying around and access to a vacuum pump, how's about pulling a vacuum on the barrel and see what kind of measurable differance it makes, since we've just been theorizing about it up until now, look s like I'm a week or 2 away from a chrony of my own...
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Unread postAuthor: D_Hall » Fri Mar 06, 2009 12:01 pm

starman wrote:Are you planning to use that cute stainless sched 10 3 footer you just picked up for your barrel?

No.

I've got a 3/4" QEV (you know, a McMaster special) that I'll be using that with. Velocities will be pretty low (300 fps), but it'll be a cute little gun to tinker with.

For the 1.5" QEV, I'll be getting a 6' sch 10 piece of stainless. :)
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Unread postAuthor: D_Hall » Fri Mar 06, 2009 12:10 pm

jeepkahn wrote:D, Since I'm sure you've got a chrony laying around and access to a vacuum pump, how's about pulling a vacuum on the barrel and see what kind of measurable differance it makes, since we've just been theorizing about it up until now, look s like I'm a week or 2 away from a chrony of my own...


No idea. It's not an experiment that catches my eye, per se. I've worked with powder guns that had barrels under vacuum. It's a royal PITA. Unless I've got a very good reason, that's just something I won't be doing for "fun" because there's absolutely nothing fun about it.
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Unread postAuthor: jeepkahn » Fri Mar 06, 2009 12:25 pm

D_Hall wrote:
jeepkahn wrote:D, Since I'm sure you've got a chrony laying around and access to a vacuum pump, how's about pulling a vacuum on the barrel and see what kind of measurable differance it makes, since we've just been theorizing about it up until now, look s like I'm a week or 2 away from a chrony of my own...


No idea. It's not an experiment that catches my eye, per se. I've worked with powder guns that had barrels under vacuum. It's a royal PITA. Unless I've got a very good reason, that's just something I won't be doing for "fun" because there's absolutely nothing fun about it.


I was just thinking that it may make mach more easily attainable, I've run the theory past some physics buffs I know and they seem to think that it will make a much larger differance in velocity and acceleration because the projectile will accelerate as if it was zero mass up to a point and by the object accelerating that quickly it will create a circumstance that will "trick" the pressured gases into behaving as they would in a vacuum, ie, increased mach #...
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Unread postAuthor: mark.f » Fri Mar 06, 2009 12:56 pm

I believe Velocity's "Midsize Pneumatic Launcher (Original)" used a similar valve. I'm going to be putting the same concept to use on a piston valve I'm designing right now as well. If you can get the valve cheap it's definitely an advantage over having to buy a separate quick-exhaust or build a separate pilot.
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Unread postAuthor: jimmy101 » Fri Mar 06, 2009 1:27 pm

jeepkahn wrote:I was just thinking that it may make mach more easily attainable, I've run the theory past some physics buffs I know and they seem to think that it will make a much larger differance in velocity and acceleration because the projectile will accelerate as if it was zero mass up to a point and by the object accelerating that quickly it will create a circumstance that will "trick" the pressured gases into behaving as they would in a vacuum, ie, increased mach #... (emphasis added)

I think you should find some "physics buffs" that actually know something about physics. :D

A vacuum in the barrel in front of the ammo does fairly little for a reasonably powered gun, be it a combustion, hybrid, or pneumatic.

If you are talking subsonic speed then all the air in the barrel does is add a tiny bit of mass that needs to be accelerated. The density of air is only about 1.3mg/L. The density of a spud is about 800,000mg/L. The density of most metals are about ten times greater than a spud. So, figure it out. In a typicall largish barrel that is 2"ID x 10'L the mass of the air in the barrel is ... not even worth doing the calculation. Since the density of the ammo is roughly 10<sup>6</sup> greater than the density of the air the mass of the air is insignificant until it's volume is upwards of say 100,000 the volume of the ammo, and even then the mass of the air would only be about 10% the mass of the ammo.

Evacuating the barrel will boost the effective pushing pressure by 14.7 PSIA. Though that really isn't all that big of an affect compared to say a starting pressure of 120 PSIG. That's only a ~12% increase in pressure.

In a "vacuum-only" gun that 14.7 PSIA is all that is pushing the ammo. Even a basic combustion will outperform a vacuum-only powered gun.

For a supersonic gun an evacuated barrel has a small advantage since you don't have to heat the air in the barrel hot enough to get it's speed of sound to be greater than the ambient speed of sound. But even that is a fairly minor affect.
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Unread postAuthor: jackssmirkingrevenge » Fri Mar 06, 2009 1:36 pm

jimmy101 wrote:For a supersonic gun an evacuated barrel has a small advantage since you don't have to heat the air in the barrel hot enough to get it's speed of sound to be greater than the ambient speed of sound. But even that is a fairly minor affect.


What about the lack of air resistance in the barrel as the projectile accelerates?
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