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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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Unread postAuthor: c11man » Sat Mar 28, 2009 8:09 am

so i think i have ruled out co2 as a pressure source.

how would a HPA work. would it only fill the gun a couple of times?


WOW that is a very big pressure difference
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Unread postAuthor: john bunsenburner » Sat Mar 28, 2009 8:33 am

HPA is ussually at about 4500psi so it would need to be regged down, this ussually already happens in the tank but it may not, in that case you need a regulator, i am not sure about the exact price but I would perusme 200-300$ for the tank and reg are probablbe. I would recomend you use either a fridge compressor or a scuba tank as your air source. Scuba tanks(or just plain compressed air) are often up for rent along with a regulator and do not cost alot(i paid 40$ for 30L of 3000psi air, with a tank and reg rented that for nearly 3months). I would stay away form paint ball gas and tanks as this is ussually expensive and not ment for the chamber vaolumes you are using. As mentioned before try not to jusm in at the deep end of the pool in terms of pressure, and by all means. Fro your first few guns 100-200psi will seem amasing, matter of factly, it IS amazing. Most members on here who use these pressures have several years of experience and even then are very catious. You have to able to comprehend what kind of power a cylinder of 800psi CO2 or 4500psi HPA has, something which is ver hard to do, and once you do understandt the power, then you will need to slowly work your way up with pressures, being careful all the time and starting to feel a bit more confortable around these pressure. Dont understand me wrong, you need to respect the power but if you are scared then you should stop, if you are nto scared you should also stop.

When BTB, Larda or any one else on here shoot even 200psi they will be careful, if they shoot 2000psi then they will make sure NOTHING can happen. Its not like you can mess around with anything over 50psi, and the experienced memebers here know that, that is one of the things that makes them so experienced.
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Unread postAuthor: c11man » Sat Mar 28, 2009 8:55 am

of course i would NOT start out at 500psi. i would probably start at like 50psi and work my way up over along period of time to a higher pressure so i would know what happens as the pressure increases. also when i worked my way up to 500psi i would not want to shoot at those pressures very often because of the long fill time.

does anyone have a clue as to the time it would take a fridgy to fill a 48 cubic inch chamber with one fridge compressor.

also did anyone figure out what pressures a air conditioner compressor can produce?
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Unread postAuthor: spudtyrrant » Sat Mar 28, 2009 9:57 am

c11man wrote:so a 1/2in qev from fastenal could handle 500psi?

i know they can "handle" far above 500 psi. i know for a fact btb has used a 12g unregulated co2 on a half inch qev. i am not saying it is stronger i am just saying they can handle those kind of pressures. But i strongly recommend that you find parts rated for the intended pressures, you might spend a little more money but its not worth taking the risk.

edit: sorry for the double post
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Unread postAuthor: c11man » Sat Mar 28, 2009 1:32 pm

oh that is good that it can handle the pressures.

i have not found one that is made for high pressure that is not overy exsessive at like 150bar. so if someone else has found one that would be great if they could post a link.

does ANYONE know how long a fridge would take to pump up a 48cubic inch chamber to 500psi?
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Unread postAuthor: jeepkahn » Sat Mar 28, 2009 1:41 pm

c11man wrote:oh that is good that it can handle the pressures.

i have not found one that is made for high pressure that is not overy exsessive at like 150bar. so if someone else has found one that would be great if they could post a link.

does ANYONE know how long a fridge would take to pump up a 48cubic inch chamber to 500psi?


I got 56in3 when I calculated 1" at 6ft... is it a coax, and if so what size barrel, and what length chamber are you gonna run...
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Unread postAuthor: c11man » Sat Mar 28, 2009 1:46 pm

first 60inches is not 6 feet it is 5 so it is 48cubic inches and i want to have dual 2.5ft chamber each hooked up to a 1/2inch qev and i am not sure of the barrel yet. will probably be around 1/2inch

is this a good design?
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Unread postAuthor: jeepkahn » Sat Mar 28, 2009 1:55 pm

Have you run the #'s through ggdt yet, because with hipressures, you can shrink your chamber WAY more than you realize without a noticeable loss in performance... I'll crunch some #'s and get right back to you...

If you run a 6ft barrel by .50", with a 60inch chamber you get 837fps, with a 48" chamber you get 830fps, and with a measly 24" chamber you get 797fps... so you only lose 10% or 40fps if you cut your chamber down to 24inches long(18in3)...

these figures were for a 15 gram projectile, but you should get the point...
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Unread postAuthor: c11man » Sat Mar 28, 2009 2:09 pm

wow that is not much of a preformance drop

what weight of a projectile was that with

so i might just cut the design down to a total of 36 in incase i want to run larger diameter barrels
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Unread postAuthor: jeepkahn » Sat Mar 28, 2009 2:17 pm

c11man wrote:wow that is not much of a preformance drop

what weight of a projectile was that with

so i might just cut the design down to a total of 36 in incase i want to run larger diameter barrels


That's one of the reasons to run Hi pressure, you can run smaller chambers, the biggest performance diff between hipress 400+ and lo press 60-175 is the initial push on the projectile to get it moving... even an 8" chamber is going to give you 660 fps.....
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Unread postAuthor: c11man » Sat Mar 28, 2009 3:19 pm

i think i will go with a so i think i will go with an overal chamber length of 30~36inches.

do you guys think that a 1inch fastenal qev could handle 500psi?
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Unread postAuthor: daberno123 » Sat Mar 28, 2009 3:30 pm

Probably, but a 1" QEV is outrageously expensive.

3/4" QEVs have been used at 500 psi before, but I'll let you decide how "safe" that is. The piston will be the first thing to fail, so make sure to always keep the gun pointed in a safe direction.
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Unread postAuthor: c11man » Sat Mar 28, 2009 3:43 pm

oh i guess i forgot to look at the price on the 1inch...

so i will stick to 3/4inch qev's

maybe even go with THREE of them...

ggdt says that with 3 qevs and helium i could get a golf ball going 1034fps :D

so i think a airconditioner compressor and 2 3/4inch qevs and an undicided chamber will be my final design
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