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chamber size (approx)

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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chamber size (approx)

Unread postAuthor: kpotmake » Thu Apr 09, 2009 11:57 am

Hello, I'm new into spud / air guns, and i want to be making one. I'm actually making plans to make a semi auto from scratch (I'll be making everything myself, that includes the valve, chamer, barrel etc.). What I need to know is what is a recommended chamber size. I will be using 2 chamber, one for temporaraly (spelled it right?), and one main chamber, the main chamber wil keep te main pressure, and when i will pull the trigger, my valve will get air from the main chamber into the teporaraly chamber, and then into the barrel (so it doesnt release ALL the air from the main chamber at once, so i can do multiple shots).

So heres the actual question: how many times (estimated) should i make my main chamber bigger then my temporaraly chamber? I know i cant ask the size of my chamber, but im just asking for a rough guess, because right now i have NO idea.

and sorry for the poor spelling, im from holland
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Unread postAuthor: Carlman » Thu Apr 09, 2009 12:07 pm

depends on how often you want to shoot, at least the same size
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Unread postAuthor: kpotmake » Thu Apr 09, 2009 12:12 pm

lets say about 5 to 10 shots, is this a verry high amount of shots and almost impossible to acchieve or is this reasonable?
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Re: chamber size (approx)

Unread postAuthor: Technician1002 » Thu Apr 09, 2009 12:16 pm

kpotmake wrote:Hello, I'm new into spud / air guns, and i want to be making one. I'm actually making plans to make a semi auto from scratch (I'll be making everything myself, that includes the valve, chamer, barrel etc.). What I need to know is what is a recommended chamber size. I will be using 2 chamber, one for temporaraly (spelled it right?), and one main chamber, the main chamber wil keep te main pressure, and when i will pull the trigger, my valve will get air from the main chamber into the teporaraly chamber, and then into the barrel (so it doesnt release ALL the air from the main chamber at once, so i can do multiple shots).

So heres the actual question: how many times (estimated) should i make my main chamber bigger then my temporaraly chamber? I know i cant ask the size of my chamber, but im just asking for a rough guess, because right now i have NO idea.

and sorry for the poor spelling, im from holland


If you study the expansion of gases, with a little math the volume of expanded gas can be calculated for a given working pressure.

How much pressure is remaining and therefore wasted is often a topic for hot discussions, but having the tank pressure fully depleted at the end of the launch is generally not a great idea because the last bit if barrel length is not providing any meaningful acceleration and with friction by be reducing speed.

A quick Google search for Gas Gun Design Tool will pull up an excellent software program that can be used to design an air cannon to meet your needs.

For good performance, having about 50 % of the initial tank pressure remaining at the end of the launch is a good starting point. Larger tank = less pressure drop in the shot and more wasted energy, so it's an art of science, not a fixed rule.
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Unread postAuthor: Carlman » Thu Apr 09, 2009 12:17 pm

oh your not going to have this continously hooked up to an air source?

in that case i would recomend alot bigger chamber than your main chamber as pressure will drop...fast.

how about running it on a 2kg tank of bbq propane, works a treat for my 3" porting cannon
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Unread postAuthor: kpotmake » Thu Apr 09, 2009 12:27 pm

Carlman wrote:oh your not going to have this continously hooked up to an air source?

in that case i would recomend alot bigger chamber than your main chamber as pressure will drop...fast.

how about running it on a 2kg tank of bbq propane, works a treat for my 3" porting cannon

sorry, but im not really following you now, bcause of my lack of english :roll:

your saying i need a bigger temporaraly chamber then my main chamber? i dont really understand you there because i think the exact opposite. I think we dont understand eachother in my meaning of the chambers. What i mean with temporaraly chamber is the chamber in where the air is kept for a short while, and this is used to proppel my bullet, my main chamber will be used for filling up my temporaraly chamber.

therefore i think i need a much bigger main tank then my "temporaraly" tank, because i use my main tank to fill up my temporaraly tank, which then propells the projectile. After the projectile is propelled, there is no pressure left in my temporaraly tank, and i use my main tank to fill it up again. Therefore, i need to have pressure left in my main tank, and it has to be bigger then my temporaraly tank (right?)
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Unread postAuthor: Big-E » Thu Apr 09, 2009 12:35 pm

I have built a pneumatic that does this. I've been experimenting with this sort of setup. There's a trick to doing it.

So, you want two chambers. I tend to call them the firing chamber and the reserve chamber. The Firing chamber does just that: it holds the air you are using to push your projectile out the barrel. The reserve chamber holds the air supply for the launcher, and is what charges the firing chamber.

For your firing chamber, I suggest at least 1:1 ratio with the barrel, with 1:1.5 CB ratio at most.

For your reserve, In my opinion, you will want a chamber that is 3:1 of the firing chamber. That's if you're running 250-300 psi. The more pressure, the smaller the reserve needs to be. Low pressures will need a bigger reserve. this is not a rule, if you want more shots, or more powerful shots, you will need more air, so the chamber will need to be made larger. you need to experiment a little to find what works for your application. I tried several sizes of chamber before I settled on my design.

Now, I use a ballvalve the same ID as my chamber piping for the charging valve. This is so I can either plink off the small chamber, or use all the chamber space for a single, powerful shot. But, if you're regulating the flow, here's a trick (I'll be using it on my next gun)

I suggest you use a gate, screw, or air compressor regulator valve between the reserve and the firing chamber, and putting a gauge on the firing chamber. You can turn the knob on the valve slowly and fill your chamber more accurately, and conserve air. When pressurized for firing, you just turn the valve off.

one option would to be to use a regulated CO2 tank as your reserve, and put a manual valve on the tank to fill the firing chamber. I've been considering this lately too.

Another idea is to use a hammer valve and forget the firing chamber all together, but that's a subject for another post :)

BTW, I suggest adding a shock pump to the firing chamber. A few strokes on it will bump up your pressures quickly (so long as you're operating at a minimum of 50 PSI. You fill the entire chamber with a compressor, and can top off the gun with a few pumps as the reserve gets low on pressure.
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Last edited by Big-E on Thu Apr 09, 2009 12:42 pm, edited 1 time in total.
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Unread postAuthor: kpotmake » Thu Apr 09, 2009 12:39 pm

Big-E wrote:I have built a pneumatic that does this. I've been experimenting with this sort of setup. There's a trick to doing it.

So, you want two chambers. I tend to call them the firing chamber and the reserve chamber. The Firing chamber does just that: it holds the air you are using to push your projectile out the barrel. The reserve chamber holds the air supply for the launcher, and is what charges the firing chamber.

For your firing chamber, I suggest at least 1:1 ratio with the barrel, with 1:1.5 CB ratio at most.

For your reserve, In my opinion, you will want a chamber that is 3:1 of the firing chamber. That's if you're running 250-300 psi. The more pressure, the smaller the reserve needs to be. Low pressures will need a bigger reserve.

Now, I use a ballvalve the same ID as my chamber piping for the charging valve. This is so I can either plink off the small chamber, or use all the chamber space for a single, powerful shot. But, if you're regulating the flow, here's a trick (I'll be using it on my next gun)

I suggest you use a gate, screw, or air compressor regulator valve between the reserve and the firing chamber, and putting a gauge on the firing chamber. You can turn the knob on the valve slowly and fill your chamber more accurately, and conserve air. When pressurized for firing, you just turn the valve off.

one option would to be to use a regulated CO2 tank as your reserve, and put a manual valve on the tank to fill the firing chamber. I've been considering this lately too.

Another idea is to use a hammer valve and forget the firing chamber all together, but that's a subject for another post :)

BTW, I suggest adding a shock pump to the firing chamber. A few strokes on it will bump up your pressures quickly (so long as you're operating at a minimum of 50 PSI. You fill the entire chamber with a compressor, and can top off the gun with a few pumps as the reserve gets low on pressure.

thanks a lot, thats pretty clear to me, so if i fully understand you, you suggest i make my "reserve" chamber 3 times bigger then my firing chamber?

by the way, how do you get it up to 300psi? do you use your compressor? because i dont have a compressor thats capeable of that amount of pressure
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Unread postAuthor: Big-E » Thu Apr 09, 2009 12:59 pm

I have a small 12 volt compressor that gets to 250 psi. I also have a shock pump (used for putting pressurized air in mountain bike shocks) integrated into the gun. The shock pump goes up to 300 PSI.

Image

I would suggest a 3 or 4:1 ratio for your reserve (as you want about 10 shots per charge). But, like I said, you need to experiment with sizes to get the best results.

Remember, as you use pressure, it will drop, your shots will get weaker as you go. If you have a higher pressure to begin with, the effect will not be as noticable. The greater the ratio of reserve to firing chamber, the more shots you'll get between having to refill the gun.

BTW, I added that breech finally. Updated pics on my last write up on it here: http://www.spudfiles.com/forums/kopperbess-update-w-pics-4th-revision-now-has-a-breech-t17747.html if you wanted to check it out.[/url]
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Unread postAuthor: kpotmake » Thu Apr 09, 2009 4:09 pm

Big-E wrote:I have a small 12 volt compressor that gets to 250 psi. I also have a shock pump (used for putting pressurized air in mountain bike shocks) integrated into the gun. The shock pump goes up to 300 PSI.

Image

I would suggest a 3 or 4:1 ratio for your reserve (as you want about 10 shots per charge). But, like I said, you need to experiment with sizes to get the best results.

Remember, as you use pressure, it will drop, your shots will get weaker as you go. If you have a higher pressure to begin with, the effect will not be as noticable. The greater the ratio of reserve to firing chamber, the more shots you'll get between having to refill the gun.

BTW, I added that breech finally. Updated pics on my last write up on it here: http://www.spudfiles.com/forums/kopperbess-update-w-pics-4th-revision-now-has-a-breech-t17747.html if you wanted to check it out.[/url]

thank you all very much for your quick replys! its now all realy clear for me, thanks
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Unread postAuthor: POLAND_SPUD » Thu Apr 09, 2009 4:34 pm

@kpotmake
are you from europe ??
I suggest building a fridge compressor... they are better than emergency tire pumps and normal compressors

the best way to get many shots is to keep the gun hooked to air source all the time...whenever you want to fire just open the valve to fill the chamber and then close it and fire the gun
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Unread postAuthor: kpotmake » Fri Apr 10, 2009 6:30 am

POLAND_SPUD wrote:@kpotmake
are you from europe ??
I suggest building a fridge compressor... they are better than emergency tire pumps and normal compressors

the best way to get many shots is to keep the gun hooked to air source all the time...whenever you want to fire just open the valve to fill the chamber and then close it and fire the gun

Yes, I am from Europe, does a fridge compressor has so much capacity?
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Unread postAuthor: john bunsenburner » Fri Apr 10, 2009 7:27 am

Well you can always have a large reserve chamber, lets say 10Liters which you hook up to your fridge compressor, then you put the compressor on and wait 5-10minutes(I have not worked with fridge compressors myself so i cannot say how long it would take to get a 10L chamber to about 200psi) Then you leave the compressor ON and connect your gun. you can get as many shots as you like if you do not shoot too quickly as there is air in you reserve to fill up your fireing chamber. I hope you understand.

Oh and we have many Dutch members on here, maybe they can make things a bit more clear for you. Oh and, try to use the spell check button at the lower right hand corner of the quick reply box, it will improve your spelling and hep us understand what you want to say.
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Unread postAuthor: psycix » Fri Apr 10, 2009 8:38 am

5-10 shots with decent power? HA!
Your secondary chamber will need to be very very very very very large. Like 20 times the first one.
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