Confused. Cylinder chamber to barrel ratio for compressed air.

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Doc j
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Tue Jun 30, 2020 7:16 am

Hi.
Got a cylinder volume to barrel ratio.
Want to use on diff build.
I got it from a AEG.
Crono found sweet spot.
For diff build using air pressure. Not spring.
If I up the psi, would that mean to use a smaller chamber./ cylinder.
Bare with me.
Worked out cylinder volume.
To Guestimate pressure
Going off 14.7 psi to 1 cubic inch atmospheric.
Convert that into metric (25.4mm in a inch)
Gave me 0.5787 psi per mm3.
@18.57cm3 cylinder gave me 10.74 psi cylinder atmospheric.
Then I added spring force of 4.9kg( used a jig and luggage hand held digi weight scale to work that out) /convert that to lbs, 2.2 in a kg.
=10.78 lbs + cylinder atmospheric. 10.74
Guestimate of 21.52psi.
Dunno if that right way to work it out.
But if myth busters launch a chicken 190fps in a Canon using 25psi air, thought it sounded
right ish.?
Say if I upped pressure to 3x (64.5psi)
Would it be logical to assume have a cylinder volume of 1/3 or 6.19cm3,
Because air volume same but compressed
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Moonbogg
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Tue Jun 30, 2020 6:17 pm

If you have the same air volume and the chamber is 1/3 the volume, the pressure will increase by 3x.

https://www.omnicalculator.com/physics/boyles-law
Doc j
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Wed Jul 01, 2020 6:25 am

Moonbogg wrote:
Tue Jun 30, 2020 6:17 pm
If you have the same air volume.

You mean same pressure.
That calculator shows if compress 21. 5 psi to
A third of its volume increases presurre x3
No you don't have same volume.
But Yes a higher pressure.

Thats where I get confused and was saying.
Regulate pressure at higher to compensate for loss of volume. Orig idea was 64.5 psi for the third.
Now had a rethink
Use volume of cylinder at atmospheric.
10.74. Psi start point. @18.56cm3 volume.
As volume of cylinder decreases, increase the pressure of regulator to match volume loss.
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Moonbogg
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Wed Jul 01, 2020 1:49 pm

It sounds like you are talking about chamber size when talking about volume. That's the volume of the container. People also talk about the volume of a gas, such as 5 cubic inches of gas at atmospheric pressure. So, if you have a big container and a small container, but the same volume of gas going into each of them, then the pressures will be different but still contain the same volume of gas. The volume of the containers is different though.

In addition, I may have dog sh*t for brains and be completely wrong.
Doc j
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Wed Jul 01, 2020 6:48 pm

Moonbogg wrote:
Wed Jul 01, 2020 1:49 pm
Talking about both volume and pressure.
For a determined Barrel to cylinder / chamber ratio. Without changing barrel volume.
Just working on cylinder and pressures to volume.
I could be wrong too, seen somewhere take 1 bar off regulated pressure gives actual reg pressure.
In that case suppose adjust for that.
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Moonbogg
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Wed Jul 01, 2020 10:18 pm

Doc j wrote:
Wed Jul 01, 2020 6:48 pm
Moonbogg wrote:
Wed Jul 01, 2020 1:49 pm
Talking about both volume and pressure.
For a determined Barrel to cylinder / chamber ratio. Without changing barrel volume.
Just working on cylinder and pressures to volume.
I could be wrong too, seen somewhere take 1 bar off regulated pressure gives actual reg pressure.
In that case suppose adjust for that.
I see what you're saying. For example "D", I think the psi would be as you show, 58.8psi. However, the psig would be 44.1 because that 1/4 section already has an atmosphere in it. So the regulator would be set to 44.1psi. That's my understanding of it. Are you working on something that you had a question about? I lost sight of what you were trying to do.
Doc j
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Wed Jul 01, 2020 11:07 pm

Are you working on something that you had a question about? I lost sight of what you were trying to do.
[/quote]

Yeah,
I posted "air stapler"
In another topic.

For simplistic sake it might end up manual bolt yet.
Might try blow forward later.
Doc j
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Fri Jul 03, 2020 8:43 pm

Moonbogg wrote:
Tue Jun 30, 2020 6:17 pm
If you have the same air volume and the chamber is 1/3 the volume, the pressure will increase by 3x.

https://www.omnicalculator.com/physics/boyles-law
Interesting to note.
Apllying my reasoning, punch into calculator.
As cylinder reduces in volume.
increases the pressure to compensate for
The loss of volume. (more like expanded volume)
Using the above, the barrel pressure is the same.

Then my question is.

Regardless of barrel pressure.
Projectile receives higher pressure.
Is a better outcome.

OR achieve same result if used lower pressure
And bigger cylinder/ chamber volume.
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farcticox1
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Sat Jul 04, 2020 8:52 pm

Higher pressure will always give better performance, you can use smaller chamber to get the same volume, and probably smaller valve, just that everything has to be rated for that pressure, that's why I stick to 150psi, materials are easy to get hold of.
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