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35 bar repeater ( new pics on page 4)

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: daxspudder » Wed May 07, 2008 1:29 pm

okay, im just gonna say you obviously know nothing about the physics of water vs. air under pressure. im a submariner, so i think i grasp the concept a little. 1 cubic meter of water is the nearly the same weight at 35 atm as at 1 atm, water is almost completely insusceptible to compression, but rather air weighs 35x its 1atm weight. think about it like this, why do hydraulic systems use hydraulic fluid rather that water(hydro-pneumatics are rated to under 500psi, standard hydraulics go well over 4500psi)? because water is unstable under pressure, therefore something rated to 250psi for water can sustain short moments of much higher pressures of air, i would say its fair to say several uses at 1000psi+ is possible, but the likelihood the other materials will hold up is null. the real issue is safety after multiple uses, if you use a compressor without a desurger the risk is even greater, as the pulsations in the air as pressure is increased add more strain than ever should be desired, ever second its like dropping your gun from 3 inches 5-6 times... i warn you going about rated pressure will work, but only for a finite time.
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Unread postAuthor: MrCrowley » Wed May 07, 2008 2:23 pm

daxspudder wrote:okay, im just gonna say you obviously know nothing about the physics of water vs. air under pressure. im a submariner, so i think i grasp the concept a little. 1 cubic meter of water is the nearly the same weight at 35 atm as at 1 atm, water is almost completely insusceptible to compression, but rather air weighs 35x its 1atm weight. think about it like this, why do hydraulic systems use hydraulic fluid rather that water(hydro-pneumatics are rated to under 500psi, standard hydraulics go well over 4500psi)? because water is unstable under pressure, therefore something rated to 250psi for water can sustain short moments of much higher pressures of air, i would say its fair to say several uses at 1000psi+ is possible, but the likelihood the other materials will hold up is null. the real issue is safety after multiple uses, if you use a compressor without a desurger the risk is even greater, as the pulsations in the air as pressure is increased add more strain than ever should be desired, ever second its like dropping your gun from 3 inches 5-6 times... i warn you going about rated pressure will work, but only for a finite time.

I said water is heavier then air, which it is.

1 cubic foot of air at standard temperature and pressure assuming average composition weighs approximately 0.0807 lbs.

One cubic foot of water weighs 62.38 lbs.

Even at 35atm, water is still heavier.

You said water is incompressible, now you change your mind yet you say I know nothing of the physics of water and air. Well obviously I do know something to get you to change your mind don't I?

And this isn't going from 250psi to 1000psi, it's only going to 500psi.

The only thing that will fail in the valve at the pressure is most likely the diaphragm, which isn't dangerous unless it ends up shooting the projectile when you're not ready.

And now your saying because it's rated for water pressure, it can actually sustain higher air pressure...

something rated to 250psi for water can sustain short moments of much higher pressures of air, i would say its fair to say several uses at 1000psi+


But I thought you said that air is more dangerous to use then water...
it might fire many times at such a high pressure, but its rating is low for a reason, its rating is based on constant strain from water...


because water is unstable under pressure
...Well you can still use it at over 2200psi to cool nuclear reactors... :roll:

only for a finite time.

And you'll find everything only lasts for a finite time. Not exactly the best description to give something for it's life expectancy.

Patient: Doc, how long do I got to live?
Doc: Doesn't matter, you'll die some time
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Unread postAuthor: daxspudder » Wed May 07, 2008 2:46 pm

again, im a submariner, required to know exactly how a nuclear reactor works, yes it is at a very high pressure in a nuclear reactor(dont ask, i wont/cant tell) but its steam, and a "dry steam" at that, essentially extremely dense air, but as primary (previous is known as secondary as it doesnt actually pass through the reactor) primary coolant is at a very high temperature (again something im not aloud to disclose) so since the molecule of the water are moving at a faster speed they create the pressure trying to expand, which is kept in check by itself by allowing a small chamber to let boiling water/steam keep the rest of the system at enough pressure to keep the water from exploding into steam, but anyway last time i checked there arent any guns made with nuclear grade piping... which is rated much higher pressures than it will ever be used.
But I thought you said that air is more dangerous to use then water...
it is, every atm of air in a container is adding a whole entire amount of the original volume, water on the other hand at 35atm is more like 1.08x the original amount so if say you had a rupture with water, the water would expand to 1atm very fast, which would change at a ratio of aprox 1.08:1 where as air will expand 35:1 meaning air at 35atm will expand 32.4 times more than water, which is why air is more dangerous than water, water will rupture something sooner, while air will rupture a material more violently, given pressure of course.
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Unread postAuthor: MrCrowley » Wed May 07, 2008 3:08 pm

I was taking the piss because you keep changing sides from air is bad to water is bad.

And...it's not steam, it's still a liquid:

Water is used as primary coolant in a PWR and flows through the reactor at a temperature of roughly 315 °C (600 °F). The water remains liquid despite the high temperature due to the high pressure in the primary coolant loop (usually around 15 MPa, 150 atm (2200 psig)).



Oh and BTB, very nice, just waiting for some pictures :)
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Unread postAuthor: daxspudder » Wed May 07, 2008 3:31 pm

but its steam, and a "dry steam" at that, essentially extremely dense air, but as primary (previous is known as secondary as it doesnt actually pass through the reactor)


allowing a small chamber to let boiling water/steam keep the rest of the system at enough pressure to keep the water from exploding into steam


i know very well how a reactor works, in fact at one point it was my job to put my nuts on a hundred or more different places in the engine room(yes my nuts, part of USN submarine qualifications, nuts arent a req. but its respected) primary is way hotter than that to, almost twice that, that is a bullshit number put out on the internet, to make my point clear again, water and air are both bad, materials have a greater tolerance for air, but failure is much more destructive, where as materials will fail at lower pressures with water but will cause considerably less damage.

he water remains liquid despite the high temperature due to the high pressure in the primary coolant loop

this is actually backwards, the water which is heated by "cooling" the reactor expands, as all things do with heat, which in turn creates the pressure through a component simply known as a pressurizer, with has liquid at the bottom, and an opening at the top where water falls through, but there is an amount of space which is intended to expand which keeps the whole system under pressure, based on its heat, not the other way around.

my use of the word finite is simply the easy way of saying that the material will fail sooner by over pressurization, all water rated materials will function with higher air pressures, anyways, i just think its dangerous to push it so far, chances are your diaphragm will fail first, which i believe i said in my first post (internal vs external failure), but if it fails otherwise, GL, GL...
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Unread postAuthor: MaxuS the 2nd » Wed May 07, 2008 4:46 pm

I think we're missing the big picture here..
You two are just about the only ones who know what the hell you are talking about..
Daxspudder, you're changing your mind with each and every reply MrC gives in return to your grammatically irritating posts.

Besides, I thought this topic was about BTB's new and upcoming beast of a creation, not something to do with '35atm'? (atm? atomic mass? a tall monkey?)

Be happy and remember, play safe.
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Unread postAuthor: Ragnarok » Wed May 07, 2008 5:14 pm

MaxuS the 2nd wrote:... not something to do with '35atm'? (atm? atomic mass? a tall monkey?)

How about:

ATM, I couldn't give a toss about this daft argument.

Air and water at 500 psi will put exactly the same strain on the valve.
Yes, different things will happen if it should fail, but 500 psi is 500 psi - guys.

Heck, I'm an engineer (well, a student one), and I cannot be arsed to read any of the techno babble that's being spouted, because I know if I do read it, I may comment on it, and then I'll risk saying something that could cause the thing to spiral out of control into the locked bin.

Brian the Brain doesn't deserve that guys, can't we just leave this alone?
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: daxspudder » Wed May 07, 2008 5:31 pm

i agree, but i would like to say i never changed my mind, but rather stated pros and cons of each, btw atm is also known as bar, or atmospheres, or multiples of 14 to equate to psi
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Unread postAuthor: Ragnarok » Wed May 07, 2008 5:37 pm

daxspudder wrote: btw atm is also known as bar

Not quite - 1 atmosphere is actually 1.01325 bar (about 14.7 psi), but unless you have to be really precise, the two units are indeed generally interchangeable.
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Unread postAuthor: DYI » Wed May 07, 2008 8:07 pm

I've read this discussion over, and it seems like there's quite a bit of questionable science spouted here. Pressure is pressure, and if the temperature is constant, the strain on the vessel will be constant as well.
That's really all there is to it.

As to BtB's repeater: I don't see any potential for dangerous failure as long as the gun is always pointed in a safe direction during charging (which it should be anyway), although using parts in excess of their rated pressure, in applications out of line with what they were intended for will almost always decrease their operational lifespan.
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Unread postAuthor: MrCrowley » Wed May 07, 2008 11:44 pm

Ragnarok wrote:Air and water at 500 psi will put exactly the same strain on the valve.
Yes, different things will happen if it should fail, but 500 psi is 500 psi - guys.

Brian the Brain doesn't deserve that guys, can't we just leave this alone?

Thank you, what i've been trying to say.

I agree also, BtB doesn't deserve this. Just passing time waiting for the pictures and *crosses fingers* videos. :)
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Unread postAuthor: OuchProgramme » Wed May 07, 2008 11:56 pm

Uhmm dax..why do you have to keep stating that you're a submariner?

Honestly, that is irrelevent to the discussion. We just need the KNOWLEDGE and INFORMATION about water and air
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Unread postAuthor: daxspudder » Thu May 08, 2008 12:28 am

well sorry to be a pain, i have to say DYI summed up my thought completely, thank you DYI, and ouch, when it comes to air and water as well as bringing up nuclear reactor knowledge i found it is relevant to state my profession. my apologies for the knowledge flame session. BtB GL i look forward to hearing of your success.
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Unread postAuthor: Brian the brain » Thu May 08, 2008 3:21 pm

well...That was all a load of...you know..

I tested the modded solenoid with a modest chamber and guess what?

It buried a .50 leadball into wood at a 45 degree angle.
The leadball was somewhat squashed.I elbowed the barrel over the valve, into a 3/4 T to use as breachloader, so there was a lot of dead space.

I then started thinking about making this whole idea even more compact, and decided to mod a QEV.I puched a hole in the phram ( holecutting device , basically a sharpened pipe, 2mm) and made that repeat.
I made my own poppet/hammer/pin valve, using the rubber washer out of a blowgun and a bolt with tapered head as the pin.
Threaded that right into the QEV.

When I depress the pin fully, it sets the QEv-piston to closed, to start filling.
From then on, I can hammer the valve ( with the fridgepressor running) and the QEV goes off and resets instantly WITHOUT THE USE OF A SPRING!

When I get the fittings, I'll connect my paintball tank as the reservoir, underneath the barrel.
Then I shall get to work building the trigger/ hammer and handle.
Last comes the breachloader.I'm leaning towards lever action, using a "falling block"system with ball reservoir at the bottom of the stroke.

Hammer shall have a halfcock safety.
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Unread postAuthor: MaxuS the 2nd » Thu May 08, 2008 3:53 pm

How are you planning on knocking open the hammer? This is where I've been stuck, the hammer in my design needs to be knocked open inside the breech...
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