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Author Topic: Air pressure in a cylinder  (Read 288 times)

Aerotulz

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Air pressure in a cylinder
« on: August 05, 2017, 02:28:20 PM »
Hi Bob, I got to wondering if you could divide the air blast from propelling a bullet in two opposite directions, so they ended up running into each other, would they cancel each other out?
Curious, John Hagan


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rsterne

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Re: Air pressure in a cylinder
« Reply #1 on: August 05, 2017, 04:07:39 PM »
ummmmmmmmm.... no, because there isn't really a "blast" of air, it is a pressure rise behind the bullet.... it is the pressure that does the work....

If you fired air into both ends of a barrel, when they met in the middle the entire barrel would be at reservoir pressure....

Bob
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Alan

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Re: Air pressure in a cylinder
« Reply #2 on: August 05, 2017, 05:29:14 PM »
That is to say.... The pressure rise behind the bullet becomes far greater than the atmospheric pressure in front of the bullet. Makes one think about the G forces applied to the pellet or bullet?
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Alan

I have an Omega compressor. If you're a fellow Guild member, and you pass through Roswell, NM, I'll fill your portable tank as a courtesy.

Aerotulz

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Re: Air pressure in a cylinder
« Reply #3 on: August 05, 2017, 07:43:55 PM »
Bob, I should of been more specific. Thinking of venting the air after exiting the muzzle, in two opposite directions to collide into each other to try and expend the energy to quiet the blast once it finally leaves the shroud.
John
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rsterne

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Re: Air pressure in a cylinder
« Reply #4 on: August 05, 2017, 08:14:02 PM »
Not sure how that would work.... You are dealing with a residual pressure, and a gas that is moving at virtually the velocity of the projectile.... If the passage ways are long enough to drop the pressure a LOT, then the two moving masses of air would tend to collide, mix, and lose some energy in that collision.... However, if the passages are short (as they most likely would be in that circumstance), then the air would meet, and the pressure in the entire system would still be quite high.... That residual pressure will still have to vent out the muzzle, where the bullet left.... Remember, air is not a solid mass, it consists of tiny molecules, with huge spaces between them.... The molecules have to hit each other randomly to cancel out each other's momentum and energy....

Some PCPs (notably lower power, running on high pressure) are naturally quiet, because the residual muzzle pressure is low.... Others, where it is high, tend to be loud, and require a lot more suppression.... Suppression is not something I play around with, being Canadian, those items are considered Prohibited Weapons (yeah, like a machine gun) up here.... but my understanding is that they work by two methods.... They need enough volume to reduce the pressure to a much lower value.... and they twist and turn the gas, and bounce the sound waves (and the gas molecules themselves) around (which is quite different from just the pressure) to hopefully cancel each other out to some degree....

Short answer to your question is.... I don't know....

Bob
« Last Edit: August 06, 2017, 08:33:51 AM by rsterne »
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Alan

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Re: Air pressure in a cylinder
« Reply #5 on: August 06, 2017, 06:06:55 AM »
I hope this is the place to bring this up....

Until recently (≈10 years), not a whole lot of work has been done with respect to suppressors. Most followed variations of the original Maxim design which ONLY dealt with the pressure wave. As Bob alluded to, later designs also undertook suppressing the sound signature caused by the escaping gases. One example is the OSS design, but it isn't the only one. Aren't computers wonderful?
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Re: Air pressure in a cylinder
« Reply #6 on: August 06, 2017, 08:27:14 AM »
My (very limited) understanding is that with no suppressor, there is no "sound" produced until the gas escapes the muzzle.... The molecules of high velocity gas exiting hit other (stationary) molecules, causing the sound wave.... Once you install a suppressor, where the gasses expand at the end of the barrel, there would be a sound wave generated inside the suppressor.... In addition to providing a volume for the gasses to expand into (and therefore a lower pressure at the exit of the suppressor), there should be an ability to reduce that sound wave as well.... This is where baffles and multiple chambers come in..... If the pressure was the only issue, a big empty can would have more volume than the same size can with a bunch of stuff inside.... The baffles would also, of course, help disperse the kinetic energy of the molecules between the muzzle and the exit, which would reduce a second sound wave produced at the eventual exit....

So perhaps there are actually three (or four) sources for the report.... pressure, kinetic energy, and the resulting sound(s).... It is the kinetic energy component (the actual movement of the gas molecules) that might potentially be cancelled out by routing the gas in two directions which ultimately collide head on with each other.... Perhaps that is what the OP was asking about?....

Bob
« Last Edit: August 06, 2017, 08:37:15 AM by rsterne »
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