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qev limitations and high pressure gas source questions

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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qev limitations and high pressure gas source questions

Unread postAuthor: c11man » Thu Mar 26, 2009 7:01 pm

i want to build a dual qev HIGH pressure cannon

i was wondering what qevs can handle what pressures. like i heard that the mcmaster qev is not as good as some others and will only survize around 250psi (correct me if i am wrong). if anyone has any advice on using qev with high pressure and where to get qevs that can handle the pressure it would be greatly appreciated.

i want to use 600~800psi and i dont want to use a fridge because of my proposed large chamber volume. i was thinking maybe unregged co2 which is 800psi right? or i was thinking a paintball tank but i heard that they have built in limiters on them that lower the pressure down to about 450psi. any suggestions as to witch gas source would be appreciated along with places to get paintball tanks with out this reggulator or with a reggulator that is around 800psi.

THANKS!!!

EDIT: i have once again dreamed way outside of my reasources so it will be about 500psi not the impossible figure of 800psi

i have succesufly made myself look like an idiot in my posts and the "paintball tank with out co2" i have been trying to descibe is a HPA (huge brain fart there).
do HPA's have a reg in the neck like i heard from somewhere?
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Last edited by c11man on Fri Mar 27, 2009 10:23 pm, edited 1 time in total.
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Unread postAuthor: mark.f » Thu Mar 26, 2009 7:08 pm

If you want to use those pressures, why not build a piston valve?
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Unread postAuthor: c11man » Thu Mar 26, 2009 7:31 pm

well i am also considering a piston but i want to cover all my options
also if a qev cant handle 800 then i will just use somthing like 600psi
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Unread postAuthor: mark.f » Thu Mar 26, 2009 7:35 pm

Well, the McMaster Q.E.V.'s I've had have been up to 300 PSIG before, but that's nothing to really go by.

If you want to build a launcher to go up to those pressures by design, then I would look for a Q.E.V. rated to those pressures, or build a piston valve.
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Unread postAuthor: c11man » Thu Mar 26, 2009 7:47 pm

ok i will look for a valve

any suggestions on the gas source?
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Unread postAuthor: mark.f » Thu Mar 26, 2009 7:50 pm

Well, I'm sure somebody else will say, but I'm fairly certain that paintball tanks don't have a built in regulator. The guns themselves (the better ones, anyways) have a built in regulator which reduces the gas pressure and (maybe) makes sure all the CO<sub>2</sub> is in the gas state.

However, depending on how large your chamber volume is, I don't even know if a 20oz paintball tank will fill it enough times to be cost effective.
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Unread postAuthor: c11man » Thu Mar 26, 2009 7:56 pm

realy? i always thought that a reg in the neck took the 4500psi in the tank down to 400psi

the chamber would be like a total of 6~10 feet of 1 inch copper pipe so that was why i was wondering about paintball tanks that are just compressed air not co2

again feel free to point all mistakes in my posts
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Unread postAuthor: psycix » Fri Mar 27, 2009 12:04 pm

Especially with a large chamber fridge compressors are advisable.
If you would use CO2 in a large chamber, you would soon be out of CO2 and that would cost alot of money every shot.
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Unread postAuthor: sniper hero » Fri Mar 27, 2009 1:18 pm

a fridgy is your best friend
you might want to use 2 :D
wow those pressures and a big chamber volume
8)
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Unread postAuthor: c11man » Fri Mar 27, 2009 1:30 pm

ok say i use a fridgy... what psi can these get up to?

also isnt there paintball tanks that DONT have co2 in them?
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Unread postAuthor: Brian the brain » Fri Mar 27, 2009 2:19 pm

You seem to be in the dark about the means to achieve the high pressures you want...

You should really build this up slowly and don;t just rush to the highest pressure currently used on this site.

None of the materials we use to make these cannons are meant to be used in this way.
You need to learn wich parts can safely take these enormous pressures.
I get the feeling you are not in the least bit experienced with building high pressure guns.

I'm a high pressure guy myself, but you should only try this if you truely know what you are doing.

If you are not at least a bit scared you probably don't.

I don't mean to put you down, I just express my concern to get you thinking about what you are trying to do.
It could turn very dangerous.Be safe!

A QEV piston could give out for example.And it won;t tell you when.
This would mean it could blow while filling.While you unplug the gun, while you walk around with it when you pick up the can you intended to shoot after it fell.

You will have to think about when you want to load it.In advance, before pressurisation will keep your hands out of the possible blast area, but will leave you with a loaded gun the whole time it's pressurised.

A QEv is basically a high pressure burst disk.It might give out, or it might not.A home made piston could be even more dangerous.

You get it now I hope.Every part has to be fullproof.
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Unread postAuthor: spudtyrrant » Fri Mar 27, 2009 2:37 pm

you have to specify how big you chambers are going to be, because the bigger the chambers the bigger the valves. the bigger the valves the lower the pressures. i have taken a 1/2 inch qev to unregged co2 pressures(about 800psi) they can handle them but i only took it that high one time and it was making noises that scared me. if your going to have very large chambers then i would suggest using a piston valve it will be much cheaper and more cost effective. for you air source i would suggest using compressed nitrogen they usually have built in reg's but they are quite expensive and you chaber must be able to withstand at least 3 times the pressure you plan on using even under cold tempertures(since co2 and nitrogen are both stored very cold)

edit: poland_spud; i dont know if your name insinuates your actually from poland or not but in the united states you can take a trip to a scrapyard and find a old helium or nitrogen tank for under 50 usd and i know most of them can handle above 4500psi safely. btw if you have access to a machine shop you can have a large hammer valve constucted for about 200-300 usd i dont know your budget but a hammer valve will get you the preformance you want even at just 200psi let alone 800+ psi
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Last edited by spudtyrrant on Fri Mar 27, 2009 4:19 pm, edited 2 times in total.
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Unread postAuthor: POLAND_SPUD » Fri Mar 27, 2009 3:48 pm

I'll just say it again...

you won't get much shots per tank and CO2 performs worse as a propelant than air.. so there isn't that much difference between 700 psi unregged co2 and 500 psi air

most fridge compressors should achieve 500 psi and I don't think you should ever go beyond that... I hope that AC compressors can provide more but as I already mentioned in several threads an average spudder doesn't have materials that can handle more than 500 psi safely

I don't know if you have any experience with pressures above 150 psi but even 300 psi is a lot at first... do as BTB says and increase it gradually


and finally, if you want to build a launcher operating at high pressures it isn't practiacal to stop at 800 psi since most commonly used/accesible parts can't handle such pressures safely....
however, parts that can be used safely at such pressures are usually rated to much higher pressures than that... so if you have to spend that extra $$$ on high quality materails and parts you can as well use 1500 psi

In other words - there is a gap between easily available materials (that are offically rated to 10-15 bar max) and high pressure parts (that can handle 100 bar or more)
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Unread postAuthor: c11man » Fri Mar 27, 2009 9:02 pm

ok thaks alot

sorry about the insane pressures in the OP. i have a habit of dreaming BIG and usualy end up going smaller. now that i have thought about it more i think a fridge and 500psi would be way more powerful than what i am currenty thinking it will be.

for the fittings and pipe i know to use quality parts and have a fairly large saftey margain. like for the chamber use mcmaster part number 50475K26 as a tank for the gun witch would be overkill in saftey for a 500psi gun

how long would a fridgy take to fill a 48 cubic inch chamber to 500psi?

so a 1/2in qev from fastenal could handle 500psi?

thanks again for all the help
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Unread postAuthor: D_Hall » Fri Mar 27, 2009 11:19 pm

psycix wrote:Especially with a large chamber fridge compressors are advisable.
If you would use CO2 in a large chamber, you would soon be out of CO2 and that would cost alot of money every shot.


50 pounds of CO2 costs $25.

If you've the budget to build a gun that would use a lot of CO2 ($$) per shot, you're not going to notice the cost of CO2.



edit: Oh, and unregulated CO2 pressure is *highly* dependent upon temperature. In reasonable scenarios it can very from as lot as 300 psi to as high as 1500 psi.
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