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some questions about my first pneumatic sniper.

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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some questions about my first pneumatic sniper.

Unread postAuthor: Bullit » Thu Nov 22, 2007 2:33 pm

Ok ive made a combustion gun , its cool its fun and its easy. Thats where it goes wrong it was easy. I impress my friends and having a great time shooting everything we can think of, but the next week they all have one themselves because its so easy.

so i decided to take it 1 step further, into a pneumatic sniper rifle:

this is what i had planned:

http://www.instructables.com/id/25MM-Pneumatic-Sniper-Rifle

With an added touch of myself ofcourse. But when i was gathering the components. The so calld "solenoid sprinkler valve" is completely unfindable where i live (the netherlands) most likely cause it isnt usual to dig in your sprinklers in your lawn, but just spray over it with a water hose.

so i decided to go another step further, id make my own piston valve

http://www.instructables.com/id/Golf-Ball-Gun!!!-How-To-Make-One-That-Can-Shoot-40/

ok but when i found out he is using deodorant as piston i was like WTF, so i decided to use my dads "Lathe" (i hope i translated right), but when i told him what i was planning he laughd at me and said it was a no go, so when i was googling for another solution.

my dad came along with this:

Image


And once again i take it one step further, I am gona make it all copper. tin-soldent.


But first i maded a test-setup, because i didnt understand what type of valve i was dealing with, it seems to be a Quick-exhaust valve though, it has a circular rubber flap inside and works just as the schematic you have on wiki about it.

Image


now the questions i have:

1- What would be a good chamber to barrel ratio ? i am thinking about this :

15mm barrel 1meter long
22mm chamber 60-80 cm long

other options are :

12mm/1m
22mm/60-80cm

15mm/1m
22mm/1.5m (2 times 60-80 cm)

2- what would be a safe operating presure?

i know the test-setup handled with 4-6 bars (60-90 psi) (i dont believe the meter is that acurate so thats my gues)

i got a compressor that goes up to 10 bars (150 psi) though, and im planning on using that, is it safe for all copper ?

3 would you recomend to use a ball valve for filling , or the kind that you can rotate slowly. and would it be wise to put one on my gun to ?


I think i bored you enough already, but when its finishd i will show off in the right section. thanks in advance btw.

EDIT: i think the pictures are verry unclear , i will see if i can do better tomorow.
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Attachments
spudgun 007.jpg
a fast release valve
spudgun 004.jpg
the test-setup for my fast release valve
(hence my basic combustion gun in the back)

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Unread postAuthor: Infernal Maveric » Thu Nov 22, 2007 4:45 pm

The valve you have is most commonly known as a QEV ( Quick exhaust valve) and has previously been used (quite a lot) by European spudders because they are easier to get than sprinklers.

To answer your questions:

1: a 1:1 volumes ratio is normally the best option for pneumatics, but if you use high pressures (200+) then a smaller chamber volume can be used (effectively).

2: As long as your fittings are all pressure rated (if they are copper, then YES) and have been connected properly, then the valves han handle pressures up to, and past 300PSI. I am not saying it is safe, but I have not have one failure (yet) at pressures of 400PSI.

3: To fill, a schrader (bike) fill-valve is best used in combination with a ball valve to prevent the valve from actuating. The best way to actuate the valve would be with another ball valve used as a trigger, or a blowgun.

Hope that has helped a bit, if more questions are required about QEVs, feel free to PM me.
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Unread postAuthor: jrrdw » Thu Nov 22, 2007 4:48 pm

I don't think you'll need the ball valve. That does look like a QEV, and it would make a great pilot valve for a piston valve. I see your dad said no??? For the ratio, i'm not good at math, but the chamber should deffently have more area then the barrel. Hang in there the anwsers to your questions will get answered. Welcome to Spudfiles.

Edit: IM beat me to it, thats cool. :P
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Unread postAuthor: cwazy1 » Thu Nov 22, 2007 5:12 pm

im pretty sure that 1:1 ratio is not the case for pneumatics. its more like .25:1 for pneumatics and .8:1 for combustions.
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Unread postAuthor: Bullit » Thu Nov 22, 2007 5:26 pm

About the gun

About the pilot valve i am planning to use a blowgun, but the only blowgun we have is used for filling tyres ,yeah we have no bike pumps in our home we use a compressor :P , so what alternatives are there that look like a trigger. Definitly not a ball valve for pilot, that just ruins the sniper part.

My dad said no to a piston valve because i had to operate his "lathe" for the first time , not because he doesnt want me to fidle with deadly weaponary , he is just precious of his machenerie ^^

About the quick release valve , my dad calld it a : "snelontluchters klep", but my translation was bad and i calld it a fast release valve :P

Btw i have those cool click thingys that you pull back and pull to get off, nothing to do with bike pumps ^^.

About GGDT

Can some1 do me a favor, and take a gues what the values should be for my QEV, cause i dont realy understand it. At 10 bar (150psi) i get a speed of 50m/s (150ft/s) wich is just lame :? if you compare it to similair guns in showcase

some specifics about the QEV that i know:
3 times 1/2" threaded entrances
inside pilot diamater is around 1"
inside exaust diamater is around 1"
a round rubber flap of like 3" between pilot and exaust.

but then i have no idee what to fill in and where :S
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Unread postAuthor: MaxuS » Thu Nov 22, 2007 5:35 pm

cwazy1 wrote:im pretty sure that 1:1 ratio is not the case for pneumatics. its more like .25:1 for pneumatics and .8:1 for combustions.


If you're doing it in the ratio Barrel:Chamber, I think you might be slightly off. Ive always, or atleast tried to go with 1.5:1 B:C ratio.
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Unread postAuthor: DYI » Thu Nov 22, 2007 6:42 pm

For a pneumatic at 120 psi, the MOST EFFICIENT, and therefore MOST POWERFUL C:B ratio, for a given chamber size, is roughly 0.2:1.
This is not a guess. This is not something I have heard from someone else on the forum. This is pure fact, taken from experimentation with GGDT, the most accurate pneumatic cannon physics modeling program in existence. It is frustrating how many times I have had to write this in the past few days.

1.5:1 is an awful waste of air, as is 1:1. The ONLY time that you need a ratio bigger than 0.5:1 or so is when you can't make the barrel any longer. And C:B is normally used, Maxus, not B:C.

As for the other questions, the valve looks like a diaphragm QEV, what amounts to a more efficient and premodded version of a sprinkler valve.

We can't model it in GGDT without ALL of the specifications for the valve, but your design will be fine. Could use a bigger barrel though.

Also, I don't encourage this, but any copper pipe and fittings that are not for drainage only and under 5 cm in diameter can easily withstand well over 50 bar. Their safety factors are extreme, and they tend to burst at over 200 bar. You don't need to worry about over pressurising them unless you are dumping unregulated high pressure gas cylinders into them.
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Unread postAuthor: MaxuS » Fri Nov 23, 2007 2:31 am

DYI wrote:And C:B is normally used, Maxus, not B:C.


Ahh why thankyou, im always getting confused on that. I normally have my barrel so long for accurate shots.
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Unread postAuthor: Bullit » Tue Nov 27, 2007 2:30 pm

ok , ive made version 1 ( fotos are comming tomorow).

but i got 2 questions.

1 to open my QEV, will a blowgun be enough , or could i enhance performance with another QEV , and so yes how ? is there anny way of making your own triggers, that actualy look like a guntrigger ?

2 how to best create an lock and load with copper pipe , as i cant figure it out yet :S
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Unread postAuthor: BigGrib » Tue Nov 27, 2007 6:12 pm

Hey Bullit go down to your local hardware store and get a blowgun, that will definatley be ehough to trigger your QEV, and as far as your dad not wanting you to run his lather just give him your spec's and have him run it if you are dead set on a piston. as far as a c:b ratio a 1:1 is fairly normal, what are you gonna use for ammo? as far as a"bolt action" or lock and load as you refer to it umm i would get a coupler and do some modding so that it will slide fairly easily over your barrel maybe hell i dont know
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Yea, that's definitely going to get you at least a tazer.

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