Galvinised steel and brass

[Carlman]

hi all,

If i were to have 30cm of 20mm glavinised steel and a brass threaded end cap as well as a brass threaded reducer to fit a 1/4" ball valve and quick connect what kind of air pressure could that hold safely?

[ALIHISGREAT]

well you need to find the pressure rating on the ball valve and quick connect, which i would have thought would be the weakest parts although it wouldn't hurt to find out the pressure ratings for all the setup but i would guess it would be safe for at least 300psi.

[DYI]

Assuming that it is SCH40, 20mm galvanised steel is rated for over 1kpsi, and can likely hold well over 2k. If it is SCH 80 or 160 seamless, it will hold more pressure than than you can generate without an extreme high pressure (6kpsi+) pump. The end cap could be rated for anywhere from 125psi to 3000 psi, depending on what kind of brass it is. If the ball valve is a standard brass one, it is probably rated for 600 psi. If it is a high pressure ball valve, it's rating could range anywhere from 1kpsi to 4.5kpsi. If the quick connect is a standard air compressor one, it is likely rated for 150 psi. If it is a hydraulic quick connect like the ones I use, it will be rated for 3+kpsi.

[Carlman]

sorry i left out one part, a regulator, i want to regulate it down to 100psi, ill check ratings tomorrow i just though id may as well post this so see if there was a standard rating thanx to both of you.

[DYI]

Well, at 100 psi, none of those parts should have any problems. I have had hardware store ball valves rated for 600 psi develop bad leaks at 400 or so, because of the use of gas rather than liquid, but 100 will be fine.

[ALIHISGREAT]

100psi seems a bit of a waste for the fittings because they can tae so much more pressure unless you intentionally want to limit the power

[DYI]

Maybe that's all the pressure he can achieve?
1" galvanised steel fittings can take unregulated CO2, but cooling issues on firing could be a problem.
I don't think many people here actually want to limit the power on their cannons.

[Carlman]

no you dont understand me, i want to regulate down to 100psi but have the pressure in the pipe as like 300 odd

[goathunter]

i want to regulate down to 100psi but have the pressure in the pipe as like 300 odd

So in essence you want to create an expansion chamber, then regulate down from there?

In that case the only issue you will have is whether or not the pipe is welded or seemless(welded being bad),as well as the quick disconnect.The standard air compressor quick disconnects in my shop have all been used up to 200 psi. for long term and show no issues.Anything more than 220psi, and I'd be worried.I suggest for high pressure switch to a 1/8"(or whatever metric size is the equivalent) hydraulic quick disconnect.

And your fittings can be an issue too.I don't trust any of chinese manufacture.Too many have weak spots and bubbles.Complete junk.I suggest something Western manufactured.

[ALIHISGREAT]

ahh ok my mistake, what will you be using it for? and i asume you will be using co2?

[Carlman]

i will be using it for two things

1) to fill a small chamber of about one square inch for y brothers 'knex gun' (most are rubber band powered)

and 2) to use as a chamber for my 1/8" breech loaded bb gun ( at the moment it runs off my compresser that only goes to 110 so woth the aid of my mech shock pump after the compressor ill get more pressure thus more power.

[ALIHISGREAT]

woo knex guns, i used to make them 8) wouldn't it be abit hard to make a pnuematic knex gun? or is he making it out of something else to shoot knex?

[Carlman]

yea its only a knex gun because he is making the stock and the housing for this (basically a pnumaic cannon) out of knex and it fires knex lol, beat the crap out of all other knex guns lol, although some would consider it cheating lol.

EDIT: and merry christmas to all lol

EDIT EDIT: yay im now a Staff Sergeant woot 100 posts

[DYI]

I've used the crappy welded pipe and chinese/korean fittings at 500 psi, and I'm still living. Using them at 3 times their rating like I do obviously isn't recommended, but the SCTBDC would have cost $1k+ to build with properly rated pipe and fittings