Is it safe to use hydraulic fittings for air?

Hi all,

Just thinking about the spud gun design. The pipe leaving the extinguisher says "1/4 IN BORE WORKING PRESSURE 4250 PSI" on it. It looks a lot like a hydraulic hose. I could do with a longer pipe and a quick disconnect fitting. I know I can get these things easily for hydraulics, but is it safe to use them for gases? Any thoughts?

Best wishes,

Chris

Reply to
Christopher Tidy
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Um, the title should have said "carbon dioxide" or "gases" to be more accurate.

Chris

Reply to
Christopher Tidy

Pressure is pressure so you should be ok. The only concern I have is the temperature and that would probably only be a concern if you did a lot of rapid fire and chilled down the rubber line to the point of freezing and had it crack on you.

Reply to
Roger Shoaf

Yes, I was wondering about temperature. The only other difference I guess is the viscosity. I won't be doing rapid firing as it will be a muzzle loader. I want the quick disconnect so that you can quickly look at the setup and see if it's safe to load via the muzzle.

I'm guessing hydraulic fittings will be okay.

Best wishes,

Chris

Reply to
Christopher Tidy

On Mar 3, 5:41 pm, "Christopher Tidy" wrote: ...> I know I can get these things easily for

In a word: No.

For those wanting a longer explanation. You should you use teflon hoses and only connectors offering a metal on metal seal. Backup o- rings should be teflon. Don't let the teflon hoses scare you; they are not that expensive. The cold environment that the expanding CO2 creates can crack the hoses and will cause any o-rings to stiffen such that they don't seal. Concentrated CO2 is corrosive and can attack the nitrile rubbers (Buna-N.) Interestingly the older butyl rubbers are a better choice for handling CO2.

That having been said; the hydraulic quick disconnect fitting use a metal on metal primary seal and only use the o-rings for backup. I really couldn't hazzard a guess as to their perfomance with CO2.

Your local specialty gas supplier ( welding store ) will have fittings and hoses for CO2. Be safe.

Bud

Reply to
starbolins

Thanks, Bud. I'll check with the welding store. I hadn't thought of trying them.

Chris

Reply to
Christopher Tidy

I'm not sure corrosive is the word I would have used. High pressure CO2 will dissolve into many rubbers, and when you release the pressure the rubber may develop internal cracks owing to stresses if the gas comes out of solution faster than it diffuses back out. It all depends on the gas, the rubber, the temperature, the thickness....As Bud says, some rubbers are worse than others. We have a code of practice in my industry, I don't have it to hand but will try to look it up and post it.

Reply to
Newshound

Yes, I didn't have the right the word. A much better explanation. Thanks!

Bud

Reply to
starbolins

I'd use the CO2 hose that the extinguisher comes with - it is made to handle high pressure sub-zero liquid CO2 coming through to the horn (where it expands into gas and dry ice), so it should work just fine for handling the short squirts of liquid CO2 needed to toss a baseball over a tree.

And note that there is a siphon tube in the fire extinguisher valve that is sending Liquid from the bottom of the tank up the discharge line, they want the bulk of the CO2 to leave the cylinder as liquid.

Otherwise you'd lose the tank pressure. The liquid has to boil off to vapor to pressurize the tank, which takes a few seconds to happen, and that boil-off chills the liquid - and when it reaches temperature equilibrium it stops vaporizing until the liquid warms up.

Step One: Get a small length of loop chain, sash chain, or 1/8" (3mm) nylon rope, and make a leash for the fire extinguisher safety pin.

Step Two: Before muzzle loading, make sure the pin is in. Treat it just like the safety on a gun.

Step Three: Always check that loading is completed and everyone is clear of the muzzle and clear downrange before you remove said pin. Again, treat it like the safety on a gun.

That way they can't fire it with any body parts in the way.

Oh, and bring along a fairly accurate parcel scale - CO2 in the tank is liquid and easily weighed. You will have to adjust the tare weight of the cylinder for not having the CO2 horn attached, but it will quickly tell you when you are approaching empty.

That would be my suggestion - but be sure to get fittings (or adapters) that match the right SAE flare or NPT threaded fitting on the horn and hose end.

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Reply to
Bruce L. Bergman

You're not doing rapid fire, buy you will use large volumes. Expect to blow dry ice out your barrel. It will probably look like fog.

I would rather go with solid lines, but I don't see why hydraulic lines would give you troubles.

Reply to
Dave Lyon

Paintball shops are a good source too. But, they probably won't have fittings as large as you're needing.

Reply to
Dave Lyon

I was thinking of having a quick disconnect fitting and a rule of only muzzle-loading when the cylinder is disconnected.

I don't think I can do that. The horn isn't easily removable from the hose.

Hydraulic fittings do seem to be much more readily available, but they do use nitrile rubber.

Best wishes,

Chris

Reply to
Christopher Tidy

If you could find that code of practice, I'd really like to see a copy.

Best wishes,

Chris

Reply to
Christopher Tidy

Just for the record....

Although I don't doubt what they're saying about CO2 impregnating certain rubbers, I used Buna-n O-rings in my gun without problems.

Reply to
Dave Lyon

Thanks for the advice, Bud. I made a few phone calls and found a supplier who will supply a teflon hose for only a little more than a hydraulic hose. It's rated at 270 bar and -70 C. He agrees with what you said.

Best wishes,

Chris

Reply to
Christopher Tidy

That's interesting, because at atmospheric pressure liquid carbon dioxide doesn't form. I assume that the extra pressure causes the liquid phase to form. I'll shake the cylinder and see if I can hear a liquid inside.

Best wishes,

Chris

Reply to
Christopher Tidy

Roll it slowly back in forth in your hand. You'll feel it slosh from one end to the other. The pressure in the tank is very dependent on the temperature. The warmer it is, the more CO2 will boil off, giving you higher pressure in the tank. At room temperature, it's going to be around 800 psi. The volume of the tank has little effect on the pressure as long as there is liquid in it.

Reply to
Dave Lyon

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