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Air Tank Help

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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Air Tank Help

Unread postAuthor: DerpWithAGun » Wed Nov 23, 2011 5:30 am

Hey guys,

I'm in planning stages of a new air rifle I want to make. I'm getting a lathe soon and I want some advice to help build a simple bolt action PCP air rifle. I will soon have access to a lathe and a mill.

I only want a small pressure chamber about 10cm long and 2.5 - 3cm in diameter. I need to have enough pressure in there to propel a 6mm or 5mm steel BB at 800 fps with a minimum of 8 shots before refilling with air again. Could someone please help me out I'm no expert with that program a lot of you use but all I want to know is how much pressure would I need and to reach that pressure what would be the safest wall thickness of my chamber.

Thanks guys I hope someone can help me! :)
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Unread postAuthor: Gippeto » Wed Nov 23, 2011 3:01 pm

To be honest, I haven't found ggdt to be all that helpful with pcp rifles.

The pcp rifle I built propels .22cal 15.8grain pellets at an average of 900fps over a 19 shot string. There is a 4% variation in the shot string (starting and ending are 4% lower than the maximum(middle))

It has a reservoir capacity of 135cc and I fill to 2700psi.

Out of time, will check in later.

Hey...it's later. :)

Why don't we start with "What do you have available for a pressure source?" We'll design around what you actually have available.
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Unread postAuthor: DerpWithAGun » Thu Nov 24, 2011 1:39 am

Alright then, I can probably get access to some hardened steel dowel. My dad told me there are specific shops that sell steel specially made for use with lathes.
I will have access to many sized drill bits and drill bits for making threads on the steel. The lathe I might be getting is the TL-5000, 7x14 mini metal lathe C3 on this website: http://users.tpg.com.au/users/p8king/tl4000.htm The maximum work area on the lathe is 350mm.
I would to create my valve similar to this one: http://www.youtube.com/watch?v=G6vr4QCIeH4 and I will have a pressure chamber maximum 20cm long. My design for this is that I want an over under type air rifle that have the pressure chamber on the bottom and the barrel on the top.
I want a small pressure chamber because I want it smaller than the size of my wooden stock so that I can carve deep into the wood and hide the pressure chamber inside.
I would probably have almost everything available to me material wise just tell me what type of steel is best and cheap to use and once I get the lathe I can go to the store and see if they have any of this metal in supply.

Thanks again :)
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 24, 2011 2:11 am

Have you considered a used 88g CO<sub>2</sub> capsule? Good for at least 1000 psi.

Image

Not sure what the thread size is, probably something weird but you can buyadapters.
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Unread postAuthor: DerpWithAGun » Thu Nov 24, 2011 2:19 am

I live in Australia mate it is only possible to get 8gram Co2. I haven't seen any Co2 cartridges above 8grams. I think it's possible to buy a bigger capsule from a paintball store but I think you need a license.
Anyway, compressed air is a lot cheaper and more efficient to use.
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 24, 2011 2:25 am

You can definitely get a 16 gram cartridge.

I didn't mean use CO<sub>2</sub> as a gas, rather use the cartridge as a chamber for air.
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Unread postAuthor: DerpWithAGun » Thu Nov 24, 2011 2:37 am

Oh i get it now lol.
So just buy a Co2 cartridge and then empty it out. Then somewhere put a schrader valve and pump it up with air. How much PSI can a 16g cylinder take?
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 24, 2011 3:07 am

DerpWithAGun wrote:So just buy a Co2 cartridge and then empty it out.


... or find an empty one, though a full one isn't too expensive.

Then somewhere put a schrader valve and pump it up with air. How much PSI can a 16g cylinder take?


That's the idea. If it's made for liquid CO<sub>2</sub>, it should be good for at least 1000 psi without problems.
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Unread postAuthor: DerpWithAGun » Thu Nov 24, 2011 3:16 am

Alright then thanks Jack.
Co2 cartridge is a choice but there are other things to consider as well.
A homemade chamber can take more pressure. If I could make a homemade chamber that can take 2000 psi then what tool is best to use that will reach 2000 psi easily? Even 1000 psi, how would I reach that?
And I've also heard that a schrader valve can only take up to 200 psi before it blows, whats the best way to create a fill valve?
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 24, 2011 3:42 am

DerpWithAGun wrote:Alright then thanks Jack.
Co2 cartridge is a choice but there are other things to consider as well.
A homemade chamber can take more pressure.


You need a 1000 psi plus pressure source though ;)

If I could make a homemade chamber that can take 2000 psi then what tool is best to use that will reach 2000 psi easily? Even 1000 psi, how would I reach that?


If you're lazy and/or on a budget, a fridge compressor can take you to 600 psi or so happily, but if you want multiple shots from a small chamber you need to go higher than that.

Making your own stirrup pump is a good way to go higher (several tutorials on the site, such as this one by Gipetto)

You can also get yourself a SCUBA tank and decant from it.

And I've also heard that a schrader valve can only take up to 200 psi before it blows, whats the best way to create a fill valve?


Wrong, even an ordinary schrader needs thousands of psi before becoming unusable, much more to actually blow.

The problem is the threaded connection, therefore it's more recommendable to use QC fittings, easily available on eBay as well as other high pressure pneumatic accessories:

http://www.ebay.com/itm/Paintball-Quick ... 3a68f72e14

http://www.ebay.com/itm/Paintball-High- ... 3f0f07361f

http://www.ebay.com/itm/New-3000-PSI-Pa ... 3a697d224d
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Unread postAuthor: DerpWithAGun » Thu Nov 24, 2011 3:56 am

Hmm this is a hard decision. If I create my own air tank, maybe a 2000 psi tank that is 20cm long and 2 cm in diameter what would be the best way to reach 2000 psi? A fridge compressor wont take me that high, a scuba tank is expensive + needs refills every so often. Would a schrader valve go up to 2000 psi without blowing? And if I was to make that stirrup pump would it take my small pressure tank to 2000 psi? Lastly, how many shots do you think my chamber will be able to make before refilling?

BTW I have a small portable air compressor (one you take into your car that plugs into your car and used for pumping up tires) that can go up to 250 psi. It wont be much of help to me but if I was to pump up my chamber with it to 250 psi how many shots do you think it'll make? Remember I want to shoot 5mm or 6mm steel BB at 800 fps. What do you think would happen? Success or no success??

Thanks for the help so far jack!
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 24, 2011 4:22 am

DerpWithAGun wrote:Hmm this is a hard decision. If I create my own air tank, maybe a 2000 psi tank that is 20cm long and 2 cm in diameter what would be the best way to reach 2000 psi? A fridge compressor wont take me that high, a scuba tank is expensive + needs refills every so often. Would a schrader valve go up to 2000 psi without blowing? And if I was to make that stirrup pump would it take my small pressure tank to 2000 psi?


If you're not willing to go the SCUBA tank route, you need a stirrup pump. You can buy one that goes to 3600 relatively cheaply: http://www.ebay.com/itm/Benjamin-Hand-P ... 3f08a2de90

Barring some replacement seals, air will be free, and it will keep you fit ;)

Lastly, how many shots do you think my chamber will be able to make before refilling?


That depends entirely on your valve.

BTW I have a small portable air compressor (one you take into your car that plugs into your car and used for pumping up tires) that can go up to 250 psi.


It's rubbish, leave it in the car where it belongs and use it to pump tyres ;)

It wont be much of help to me but if I was to pump up my chamber with it to 250 psi how many shots do you think it'll make? Remember I want to shoot 5mm or 6mm steel BB at 800 fps. What do you think would happen? Success or no success??


Just to give you an idea, with this at 400 psi and using a burst disk valve (which is as efficient as it gets, and completely dumps the chamber) and a 37 inch barrel, I was "only" getting just over 700 fps with a 1 gram 5.5mm lead pellet.

To get such high velocity with a hammer valve, and get more than 2 or 3 shots, you're going to need very high pressure in your tank.

You might want to consider a slide valve/QEV arrangement, with a higher flow valve you don't need such high pressure.

There's no shame in having a bigger chamber and using that as a stock, some real world examples:

Image

Image

Image

Image
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Last edited by jackssmirkingrevenge on Thu Nov 24, 2011 5:38 am, edited 1 time in total.
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Unread postAuthor: DerpWithAGun » Thu Nov 24, 2011 5:04 am

Hmm, interesting.

I'm not really into having the air chamber as a but stock... it just doesn't appeal to me much...
Your link doesn't work btw.
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Unread postAuthor: Zeus » Thu Nov 24, 2011 5:18 am

First one fixed.
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Last edited by Zeus on Thu Nov 24, 2011 11:31 pm, edited 3 times in total.
/sarcasm, /hyperbole
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 24, 2011 5:39 am

Zeus wrote:http://www.spudfiles.com/forums/high-velocity-burst-disc-6mm-pneumatic-t10446.html

Fixed link.

That just blank posted, what the hell board software?


lol.

Original link fixed :)

edit: TROLOLOL blank post too :D

edit 2: unblanked! well spotted Tech.
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Last edited by jackssmirkingrevenge on Fri Nov 25, 2011 11:12 am, edited 2 times in total.
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