Questions over safety regarding 12 grams Co2 & Steel Pip

[Blitzen]

Whats Up?!?

I am trying to build a "gun stock" ball valve launcher that is powered by 12 gram Co2 canisters. The whole purpose of this launcher is to fit it on top of an old rifle stock. Therefore the airchamber needs to be small and compact and I have decided to build it out of steel piping.
Here are some pics showing what I am going for:





(This one is the one that I would really like to try and copy)


However my main concern is that this steel piping might be too weak for the pressure let off by the 12 gram Co2 canister. From what I have heard on other forums, 12 Gram Co2 canisters let off around 800 PSI. My concern is that the steel piping will not safely hold this amount of pressure. This concern mainly comes from the fact that when I look for steel piping at Homedepot none of the pressure ratings are listed. Also, as stated above, I want the airchamber to be somewhat compact. I would prefer to have a small diameter piping (1") and just increase the length of the air chamber. Yet I am unsure if a 1" diameter steel piping would be safe to use with a 12 gram Co2 canister.


NOTE:I know that ball valves aren't the most effiecent/fastest/quickest valve. I have already built a sprinkler valve launcher, and now I want to try to build a ball valve launcher. So please do not tell me to build something else...

Thanks guys!

[Jared Haehnel]

That's a pretty sweet gun the SCH40 steel pipe should be fine for what you are using it for...I tried to do that with a small combustion but it didn't work so well...the combustion proved to be too finicky...

[spudman029]

I don't know the exact pressure rating of sch40 steel pipe, but i think it is somewhere around 2000psi? Someone correct that please.

Also, on the old forum, there used to be a chart that listed the pressure you would get in X chamber from a 12g CO2 cartridge. Is that chart still here anywhere?

If not, you can use Boyle's Law (i pay attention in chemistry):

P1V1=P2V2 where P=pressure and V=volume of the chamber and catridge. Use this equation to find out how much pressure you will be getting in X chamber with the CO2 and then you will know whether it is safe or not.


800psi*volume of cartridge = pressure of chamber(psi)*volume of chamber

or

800psi*volume of cartridge = pressure of chamber(psi).
Volume of chamber

Depending on the volume of the steel chamber you use, you will come up with different pressures. In my opinion, the pressure of your steel chamber will be quite high if you make it as compact as you suggested.

For example:

Knowing how big 12CO2's are, i can estimate that the cylinder has a legnth of 3" with a radius of .5" That being said:

Pi*.5"^2 * 3" = a volume of 2.36ci at 800psi.

Even if your chamber was double the volume, at 4.71ci, you would still be getting a pressure of 400psi.

And still, if your chamber had a volume of 10ci, you would still be getting a pressure of about 188.8psi, in my opinion too high for paintball.


Again, someone please correct me if i am wrong.

So really, you can make a chamber with a safe pressure (or one at least that you are comfortable with) by upping the chamber volume. Although, with sch40 steel being very resilient to high pressures, i am sure you will be fine with a small chamber. However, whatever you are using this for may require you to only have the launcher at a certain pressure. In this case, you would have no choice but to make the chamber bigger to reach the pressure required.

Also, take into consideration the volume i used for the CO2 cylinder was an estimate. The actual numbers will vary.

-Aaron


EDIT- i found the chart.

The equation is written on the wiki as:
4200/Chamber Volume In ci=Chamber Pressure in psi -OR- 4200/CV=CP

4200 must be the volume of CO2*psi of C02, so reverse math would give the CO2 cartridge a volume of 5.25ci, around twice what i estimated.

The chart also shows that a 30ci chamber would yield a pressure of 140psi, VERY safe for a steel chamber.

You said above that you would like to use 1" steel pipe. Use this equation to find out how long your pipe would need to be to be 30ci in volume:

30ci = Length * (Pi*.5^2)

30ci= Length * .7853

30ci \ .7853 = Length, and it comes out to 38.2" (hardly compact).

By the looks of the chambers in the pictures, i would say that they are using very high pressures, and should not be shot at other people. My only suggestion is either use a bigger diameter pipe, or resort to using a very high pressure that has the potential to do damage.

-Aaron

Again, corrections are appreciated.

[Fnord]

1" sch40 steel will take 800 psi like it's not even there. 2" and up is where your safety margin gets uncomfortable. 2" threaded has a theoretical burst pressure of ~1200 psi, but it's probably a little higher because of the thread geometry.

[bigbob12345]

1" sch40 steel will take 800 psi like it's not even there.

but the malleble iron fittings rated to 150psi wont

[Ragnarok]

@spudman: Your maths is perfectly accurate, however, in CO2 cartridges, it is partly stored as liquid (as CO2 liquefies under high enough pressures), which makes the molar quantity higher than the pressure and volume alone would suggest.

With liquid "gases", Boyle's law cannot be directly applied.

[Blitzen]

@spudman: Your maths is perfectly accurate, however, in CO2 cartridges, it is partly stored as liquid (as CO2 liquefies under high enough pressures), which makes the molar quantity higher than the pressure and volume alone would suggest.

With liquid "gases", Boyle's law cannot be directly applied.

So do you think that the steel piping is safe with Co2?

[judgment_arms]

This is a tricky question, you see, it worked fine for them, but being as how the threaded fittings are only rated to 150psi I don’t feel it advisable.

I believe wrought copper is rated that high, fittings included, but I can’t remember for sure at the moment.

[Blitzen]

This is a tricky question, you see, it worked fine for them, but being as how the threaded fittings are only rated to 150psi I don’t feel it advisable.

Yah thats sorta how I feel but its more like this:

This is a tricky question, you see, it worked fine for them, but will it one day blow up in my face, and kill me

[judgment_arms]

Indeed.
Here, take a look at McMaster-Car product number 50475K26, it’s 1 inch type K copper rated to 1000psi; should suit your wants nicely if you braze on the fittings right.

[Blitzen]

Where can I get a pipe section for the main part of the air chamber? I have tried homedepot and are any of their pipes (galvanized, and black pipe) acceptable? Once again I am worried since none of these pipes have the pressure ratings on them. The main problem is that I dont know what pressures different pipes can handle.

[Gippeto]

Look in your phone book for hydraulic supplies, farm supplies, welding shops, etc.

They will have pipe, fittings, and hoses that will do the job.

Just be sure you are in the hydraulics isle, (not plumbing) and the parts have a working pressure rating on them.


Also, according to the copper hand book, brazing copper actually lowers the safe working pressure. The heat needed actually anneals the copper.

http://www.copper.org/resources/pub_lis ... ndbook.pdf

[spudman029]

@spudman: Your maths is perfectly accurate, however, in CO2 cartridges, it is partly stored as liquid (as CO2 liquefies under high enough pressures), which makes the molar quantity higher than the pressure and volume alone would suggest.

With liquid "gases", Boyle's law cannot be directly applied.

If Boyle's law cannot be directly applied to CO2, the information on the wiki needs to be changed:



4200/Chamber Volume In ci=Chamber Pressure in psi -OR- 4200/CV=CP

[judgment_arms]

Also, according to the copper hand book, brazing copper actually lowers the safe working pressure. The heat needed actually anneals the copper.

http://www.copper.org/resources/pub_lis ... ndbook.pdf

Sorry, somebody on here once said that it worked better to braze the pipe as it made it one solid piece.

[Gippeto]

No worry's, we're all here to learn.