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Lowest Pressure to break SOS?

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: psycix » Tue Nov 24, 2009 2:06 pm

HA I bet you guy's forgot about that one, hehe beat you all to it

No it was common knowledge and not worth posting. :wink:
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Unread postAuthor: iknowmy3tables » Tue Nov 24, 2009 3:28 pm

Ragnarok wrote:
iknowmy3tables wrote:but it was probebly with hydrogen or helium, HA I bet you guy's forgot about that one, hehe beat you all to it

Damn, one and a half hours after I said "or have used other gases", you beat me to saying it.

dang it,
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and yeah your probably right, I posted comment an hour before the time says and after a night with no sleep so my wits are at an all time low
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Unread postAuthor: jackssmirkingrevenge » Tue Nov 24, 2009 5:10 pm

I've given my burst disk design a go at 800 psi, power seems lower than the original but I lost the washer I was using so the disks aren't performing as before, not giving up yet though :)
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Unread postAuthor: ohspyro89 » Thu Dec 03, 2009 1:58 am

I've figured that unless the projectile is very light, and the acceleration is huge, Mach is really out of reach.

When using a heated air, which would be less dense, or helium or hydrogen, you can achieve Mach a lot easier.

A few things you may want to consider is the amount of compression that the projectile would cause just inside the barrel in front of it. The pressure would be fairly substantial at those speeds.

A very light projectile also wouldn't carry that amount of energy for very long. You may get a HUGE velocity, but the energy would dissipate fairly quickly.

Firearms can reach Mach because they use a super heated gas. Also, hybrids shoot insane velocities because it's just very hot gas escaping very quickly. Hell, jets work the same way.
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Unread postAuthor: CpTn_lAw » Thu Dec 03, 2009 4:47 am

A combination of pressurized air and water perhaps? Heated until water boils into the chamber? Water would boil at much higher temperature giving possible mach results...
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Unread postAuthor: inonickname » Thu Dec 03, 2009 5:31 am

CpTn_lAw wrote:A combination of pressurized air and water perhaps? Heated until water boils into the chamber? Water would boil at much higher temperature giving possible mach results...


GGDT has a steam 'working fluid' if you want to experiment. Note that water (and steam) will be rather dense, so extreme temperatures are required.
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Unread postAuthor: Ragnarok » Thu Dec 03, 2009 12:40 pm

ohspyro89 wrote:Firearms can reach Mach because they use a super heated gas.

Afraid not. I'm going to be pedantic here and say that there's a specific meaning to the word superheated, which isn't met.
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Unread postAuthor: kenbo0422 » Thu Dec 03, 2009 1:23 pm

Superheated steam is steam above the temp/pressure relationship of saturated steam (like the steam in a tea kettle). Superheating will lower the density quite a bit, but the water content makes it really powerful stuff. They drive ship's turbines with that stuff. Our efforts to produce superheated steam in a spud gun would be difficult to say the least.
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Unread postAuthor: Ragnarok » Thu Dec 03, 2009 1:41 pm

kenbo0422 wrote:Superheated steam is steam above the temp/pressure relationship of saturated steam (like the steam in a tea kettle).

Yes, but superheated steam is not the only option.

Superheated can also refer to liquid water under pressure at over 100 <sup>o</sup>C.
A superheated liquid (which may include water) is also a liquid in a metastable state above its boiling temperature at the given pressure, but which aren't boiling.

The latter is mostly due to a lack of any nucleation sites for vapour bubbles to form. In this way, it's somewhat related to supersaturated solutions (where a liquid contains more of a solute than it should be able to, usually caused by dissolving the solute at a higher temperature), in that those don't start to crystallise out until there's a nucleation site.

Cool example: Supersaturated Sodium Acetate, sometimes known as "Hot Ice"

Nucleation is a reasonably interesting subject, because it's possible to make pure water freeze at -42 <sup>o</sup>C rather than 0 <sup>o</sup>C if there are no particles to act as ice nuclei.

Superheating liquid is also the reason why it's dangerous to heat water in a microwave without stirring. It can easily pass beyond 100 <sup>o</sup>C, meaning that it will suddenly and very rapidly boil up if disturbed. It's a very easy way to get injuries.

Still, I'm wandering off topic.
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Unread postAuthor: kenbo0422 » Thu Dec 03, 2009 1:48 pm

You can also have superheated water (liquid water under pressure at over 100 oC) and other superheated liquids (liquids in a metastable state above their boiling temperature at the given pressure, but which aren't boiling).


Yes, that's the idea in a water cooled reactor as well. Put a couple thousand pounds of pressure on it, and it won't boil around the delicate fuel rods.
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Unread postAuthor: ohspyro89 » Sat Dec 05, 2009 2:33 am

Ragnarok wrote:
ohspyro89 wrote:Firearms can reach Mach because they use a super heated gas.

Afraid not. I'm going to be pedantic here and say that there's a specific meaning to the word superheated, which isn't met.


Take a chill, sit down, take off your badge and gun, and relax kid.

Super and heat, are two separate words. Using them in a row doesn't automatically mean that I have to be talking about a liquid beyond it's boiling point.

Regardless of how smart you are, I would say steam is the wrong application for hitting the speed of sound. I think you'd be better off, OP, to just use heated air or helium.
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Unread postAuthor: Ragnarok » Sat Dec 05, 2009 10:55 am

ohspyro89 wrote:Super and heat, are two separate words. Using them in a row doesn't automatically mean that I have to be talking about a liquid beyond its boiling point.

Separate, maybe - but I know enough people that do write superheat as two words.

Either way, little is going to stop "super heated" being interpreted as "superheated" on a regular basis. Personally, I'd just write "high temperature" (adding a "very" if necessary), because then no-one's about to misinterpret that.
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Unread postAuthor: Brian the brain » Sun Dec 06, 2009 9:18 am

It might be easier to go with a vacuume barrel..

BTW:
some would say liquor is two words...
Not something to get superheated about...
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: jackssmirkingrevenge » Sun Dec 06, 2009 9:22 am

Brian the brain wrote:some would say liquor is two words...


In a bar sign "liquor in the front, poker in the back" kind of way ;)
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Unread postAuthor: Brian the brain » Sun Dec 06, 2009 9:32 am

I love the recent hit single " pokerface" for that same reason..

But let's not go into that here...
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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