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Brass Questions???....

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Brass Questions???....

Unread postAuthor: THUNDERLORD » Thu May 14, 2009 1:48 pm

So...
I was using a pressure washer and it was "3200psi"( water ),
most of the fittings on it were brass.

I have noticed several times that the fittings on high pressure welding tanks and helium (3000PSI+) etc. tanks are brass nipple pipe...

So I had assumed...

BUT I was in Harbor Freight yesterday and noticed that several of the packaged pneumatic brass fittings had pressure ratings that were pathetically 90-225 psi (stated "Up to 90" or "150" or "225" "PSI Working Pressure")...

There were many brass fittings with such low ratings. :(
I want to know if it's due to inconsistancies (from part to part) or that's all they can handle???

I have been designing a high pressure brass Blow- Forward Bolt/chamber and have a few of the components.
I was planning on hydro-testing them (homemade, but Gippetto style)
By shooting co2 from a bike tyre filler into a (rated) water tank going into the set-up with a pressure gauge.

This was a depressing find yesterday.
For example, I am wondering if my 3/4" brass T (from Home Depot) can handle high pressure after all this design work.

Seems more complicated than DWV Vs. NSF....

Any thoughts, ideas/ information appreciated. Thanks. 8)
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Unread postAuthor: thedeathofall » Thu May 14, 2009 2:02 pm

maybe it's because all the other parts are hydro rated, and these are pneumatic rated.

I think you will be safe with brass parts to at least 400 psi no matter what they are rated. Just check all your pieces for cracks and possible weak spots.
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Unread postAuthor: spudamine » Thu May 14, 2009 2:04 pm

Fittings are usually rated for a similar pressure to what they are intended to be used for, so pneumatic fittings usually have ratings a bit above your usual shop air pressure. There's no point in a company testing and rating a compoment to a high pressure that 99% of there customers don't need to use it at. Hydraulic components will have a much higher rating (200bar) but will be more expensive and only available in smaller sizes.
Personally I would rate a brass fitting better than a malleable iron one of similar dimensions, but I'd be interested if anyone disagrees with that.
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Unread postAuthor: THUNDERLORD » Thu May 14, 2009 7:29 pm

...I think you will be safe with brass parts to at least 400 psi no matter what they are rated...


I do too, But I am designing for unregged co2,
or to be exact, possible dry ice fill pressure (about the same).

Remember, pressure is pressure whether it's hydrualic or pneumatic....
It's just safer to handle in the hydraulic form is all
...that's why the (gippetto style) hydro testing I mentioned.
BTW, I agree with spudamine that brass fittings are preferable over malleable iron.
sad really, but brass is almost as strong as any steel, just heavier, in black powder guns for example, I hate brass, but in pneumatics... I love it.
8)
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Unread postAuthor: Gaderelguitarist » Thu May 14, 2009 7:50 pm

The inconsistencies also probably have to do with how the fitting was made, whether it was cast, forges machined, etc.

Generally cast fittings will hold the lowest pressure from what I've seen.

What was the look of the fittings on the welding tank? Where they smooth and ground down, or were they covered in very small bumps and pock marks the size of sand particles?
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Unread postAuthor: Gippeto » Thu May 14, 2009 7:57 pm

IMHO, it is dangerous to test with a gas as a pressure source. Period.

Get yourself a cheapo grease gun from HF, and use that to pressurize. MUCH safer. :D

Use motor oil, veg oil or similar as the fluid, and make certain to get as much of the air out as possible before pressurizing.

Brass (depending on specific alloy) has a yield strength of 19600psi.

You might want to do some research to narrow down the alloy and its yield strength.

Measure the diameter and wall thickness, and punch them into this calculator. Use a minimum of 3 for the safety factor.

http://www.engineersedge.com/pipe_bust_calc.htm
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Unread postAuthor: THUNDERLORD » Thu May 14, 2009 8:00 pm

What was the look of the fittings on the welding tank? Where they smooth and ground down, or were they covered in very small bumps and pock marks the size of sand particles?


That's what is p'ing me off.
The nipple pipe I am sure of,
but the 3/4" inch "T" (actually 1" + ID) is what I am wondering about.

My whole recent design revolves around it.
It would be easier to use a QEV.
But I want More pressure capability [moar]...
So anyway, with hydrotesting I will soon be certain.
But (if) upon failure, I will need a whole new design.
Hopefully I'll post some results soon. :roll: :wink: 8)

EDIT: Thanks Gippetto! (I type slow).
That's why I was thinking of a seperate (pressure rated) tank...To isolate the gas from the filler,going hydraulic. :) 8) Thanks.
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