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high pressure low volume vs low pressure high volume

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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high pressure low volume vs low pressure high volume

Unread postAuthor: streetfire » Wed Aug 17, 2011 12:17 pm

title says it all which is better for a 16 mm inner barrel diameter? its going too shoot spuds
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Unread postAuthor: nathanhd123 » Wed Aug 17, 2011 1:09 pm

I'm sure this isn't really the answer you are looking for but its all about finding somewhere in the middle that works for your gun and projectile. Heavy projectiles do require slightly more volume but that dosn't mean you should completly sacrifice pressure.
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Unread postAuthor: Gippeto » Wed Aug 17, 2011 1:36 pm

"title says it all" eh? Not really.

Although, the lack of capitalization leads me to believe you're under 15 and failing English. :lol:

If you're going to shoot spuds, stick with <150psi. I don't think they'll survive the accelleration provided by pressure much higher than that....feel free to try though. :)

Use ggdt to determine chamber volume.
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Unread postAuthor: streetfire » Wed Aug 17, 2011 2:40 pm

Gippeto wrote:"title says it all" eh? Not really.

Although, the lack of capitalization leads me to believe you're under 15 and failing English. :lol:

If you're going to shoot spuds, stick with <150psi. I don't think they'll survive the accelleration provided by pressure much higher than that....feel free to try though. :)

Use ggdt to determine chamber volume.
17 actually and my English is pretty good i think but my question leads too that i see a lot of pvc air guns that do some much with low pressure but a big tank. my gun uses a small chamber but high pressure so i was wondering if i wasted my time with pumping it up with a shock pump.
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Unread postAuthor: Brian the brain » Wed Aug 17, 2011 3:00 pm

Your English isn't bad considering it's not your native language.

Power has to do with a lot of factors.
Chamber size and pressure play a big role in it but of course so do barrel length and diameter and the valve set-up.

A large reservoir with relatively low pressure means that the initial force on the projectile is fairly low but it will be sustained for longer.

A small reservoir with high pressure means high force on the projectile but as it moves through the barrel that forces becomes smaller very fast.

This all sounds simple but your barrel can only be so long...so a very large reservoir is useless.
If you therefore also limit yourself to low pressure the results will be very...limited.

Putting a large PVC reservoir on a 1/2" metal QEV gun is not going to up your performance.
A metal reservoir running the full length of your barrel, with a diameter as large as you can get will serve you better.

I have found that 1.5" is the largest you'll ever need practically speaking, when using a 1/2 QEv and a 16 mm barrel.
Member Psycix used two sections of about 30cm coupled together wich was clearly overkill at 40 bar... :D
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Unread postAuthor: streetfire » Wed Aug 17, 2011 3:06 pm

Brian the brain wrote:Your English isn't bad considering it's not your native language.

Power has to do with a lot of factors.
Chamber size and pressure play a big role in it but of course so do barrel length and diameter and the valve set-up.

A large reservoir with relatively low pressure means that the initial force on the projectile is fairly low but it will be sustained for longer.

A small reservoir with high pressure means high force on the projectile but as it moves through the barrel that forces becomes smaller very fast.

This all sounds simple but your barrel can only be so long...so a very large reservoir is useless.
If you therefore also limit yourself to low pressure the results will be very...limited.

Putting a large PVC reservoir on a 1/2" metal QEV gun is not going to up your performance.
A metal reservoir running the full length of your barrel, with a diameter as large as you can get will serve you better.

I have found that 1.5" is the largest you'll ever need practically speaking, when using a 1/2 QEv and a 16 mm barrel.
Member Psycix used two sections of about 30cm coupled together wich was clearly overkill at 40 bar... :D
thx its just that when i upgrade the vss with a bigger chamber it takes too long to pump it up with a shocky so a normal pump is used which i can not take that high
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Unread postAuthor: Lockednloaded » Wed Aug 17, 2011 4:12 pm

Usually it just depends on your air source, but generally speaking low volume and high pressure performs better. Also depends on your gun's layout, more realistic looking replica guns can be made to look more like the real thing with a small HP chamber
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Unread postAuthor: ramses » Wed Aug 17, 2011 4:46 pm

Assuming the propellant never liquifies and the ammo never disintegrates, HPLV will always perform better than LPHV if the actual amount of air in the chamber is the same.

Think of comparing a 10bar absolute launcher with a 2l chamber to a 20bar absolute launcher with a 1l chamber. After the projectile has traversed 1l, the 2l chamber gun will have (roughly) 6.66bar in it. The 1l gun would have 10 bar in it at this point. Since e=integral(force*distance), the 1l gun performed more work on the projectile during the first length of barrel and has the ability to perform more work on the projectile for future lengths as well.
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Unread postAuthor: Mr.Tallahassee » Wed Aug 17, 2011 5:43 pm

Hehe, what about a HPHV setup? Maybe 300PSI in a 2 gallon(7.5L) tank? GGDT says that with a .25 pound(113 gram) projectile and a 12 foot barrel (2.5 inch porting) will punch with over 3000 ft-lbs (4100J) of energy. Tank turret! Definitely NOT handheld though. :twisted:
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Unread postAuthor: Hubb » Wed Aug 17, 2011 6:33 pm

Not one mention on GGDT? Every pneumatic launcher is going to have it's preferred ratio. For example, if you put a 2 kg projectile in a launcher, fill its 5 ml chamber up to 1000 psi, it's probably not going to do much. Likewise, if you place the projectile into a 50,000 ml chamber and fill it up to 1 psi, it's probably going to do about the same.

Of course, those are extreme examples, but you should get the point. What I would do is, instead of asking this question for a particular barrel size, I would use GGDT to get me where I want the launcher to go.

And take heed to what Gippeto said about using spuds.
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Unread postAuthor: Technician1002 » Wed Aug 17, 2011 6:35 pm

That is almost the spec for my very slow current build. Instead of 300 PSI at 2 gallon, it is designed for 200 PSI with a 3 gallon chamber. At full pressure, hand held would be totally dependent on the mass of the projectile and operator. :D
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Unread postAuthor: Mr.Tallahassee » Wed Aug 17, 2011 8:21 pm

Technician1002 wrote:That is almost the spec for my very slow current build. Instead of 300 PSI at 2 gallon, it is designed for 200 PSI with a 3 gallon chamber. At full pressure, hand held would be totally dependent on the mass of the projectile and operator. :D
So your not-so-little project should be a REAL treat. Really scary! :shock: That will be the real test for high pressure and volume.
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Unread postAuthor: Moonbogg » Wed Aug 17, 2011 9:44 pm

Whats wrong with high pressure high volume?
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Unread postAuthor: Technician1002 » Wed Aug 17, 2011 11:43 pm

In a hand held the recoil is pretty intense. The 2 inch valve with a 3 inch barrel and 3 gallon chamber at 100 PSI provides very respectable recoil with heavier projectiles. This video is only 100 PSI with a 2 inch valve and the 3 inch barrel. This shot bruised my leg.
[youtube]http://www.youtube.com/watch?v=XsSTxCP8rvY[/youtube]
A 2.5 inch valve and the chamber at 200-300 PSI would be a very serious recoil force.
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