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High pressure flange question

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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High pressure flange question

Unread postAuthor: DYI » Tue Oct 23, 2007 5:50 pm

As some of you may have seen in my sig, I've come up with a solution to the severe sealing problems on my upcoming high-powered burst disk cannon.

The simple solution was to use a flange, providing the dual benefits of a flat sealing face, and a sealing face with a much larger surface area, and therefore a smaller chance of leaking. The problem was that the flanges at my hardware store were far too flimsy, and I can't order the heavy duty ones from Mcmaster due to my location. I decided, like all good spudders do when the right materials are too expensive or difficult to procure, to simply make my own.

The schedule for this project was accelerated when I found a leftover chunk of 1.5" thick plate steel lying around in my tech class.

Now, for my question: Due to the dimensions of the plate, the largest diameter circles that I can cut out of it are 5" in diameter, which the welding shop should finish cutting out tomorrow. Due to the pressure differential trigger design, at 500 psi, there will be approximately 715 pounds of force trying to rip apart the two halves of the flange, or a 350 psi pressure difference between the two sides. My original idea was to use 4 pieces of 3/4" threaded rod to hold the two halves together, and I was wondering; assuming that the rod and nuts are of the standard hardware store variety, will it be enough to withstand that kind of force, or will I have to limit the pressure?

Any comments on the integrity of this design, or suggestions on how to strengthen it without too much added cost would be greatly appreciated.
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Unread postAuthor: spudgunnerwryyyyy » Tue Oct 23, 2007 6:03 pm

Why doesn't your hardware store sell galvanized flanges? Get some high grade automotive bolts and torque them to like 75psi each. Get at least 3/4" bolts. The mythbusters chicken cannon used 1" bolts to bolt the flange to the valve. But that was with a 10" sealing face. 3/4" high grade automotive bolts will work. But torque them high. The bolts that look brassy on the surface are usually higher grade than others. Ask the people at the store, get a higher grade bolt at places like autozone or kragen.
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Unread postAuthor: DYI » Tue Oct 23, 2007 8:04 pm

If you had read my entire post, you would know that my hardware store does sell galvanised flanges, but they aren't very sturdy looking (only about 3/8" thick).
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 23, 2007 10:56 pm

High pressure flange question


That made me chuckle :D
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Unread postAuthor: EGOed » Wed Oct 24, 2007 6:38 am

You will still need a suitable gasket material to place between the flanges for a seal.....The gaskets we use for high pressure applications at the place that I work are actually made out of steel ....The sealing faces of the flanges are also machined with small grooves to grip and seal the gasket ....If you are just going to clamp 2 flat pieces of steel together with rubber gasket sandwitched between them it will probably leak at the pressure you are using . You would need to machine the sealing faces of the steel plates and many more bolts would be required around the diameter of the flanges or it will leak air.
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Unread postAuthor: ALIHISGREAT » Wed Oct 24, 2007 6:41 am

jackssmirkingrevenge wrote:
High pressure flange question


That made me chuckle :D


hehe you're a flange
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Unread postAuthor: jackssmirkingrevenge » Wed Oct 24, 2007 6:41 am

you're a towel
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Unread postAuthor: spanerman » Wed Oct 24, 2007 7:19 am

this is going to go downhill......any chance you could make one? with a lathe? how big do you need?
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Unread postAuthor: DYI » Wed Oct 24, 2007 3:47 pm

I'm machining the flange on a rather large and expensive lathe at school, so if EGOed could post a pic of exactly what he means, I can make it easily. I can machine the sealing faces to a relatively high tolerance, and with the lack of actual work in my tech class, I have all the time that I want.

Does anyone think that aluminum would make a suitable sealing face? I already have some 1/4" alu. plate, and I doubt that I could clamp it tight enough to make steel work.

EGOed, you seem to be pretty knowledgeable about this kind of stuff, and you have given the only useful answer so far, so kudos for that.

If anyone thinks this is going to be done half-assed because it is homemade, you are completely mistaken. With the equipment I have at my disposal at school, I can make this quite good.

P.S. I'm not familiar with Euro slang, so I didn't even think about the title
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Unread postAuthor: Fnord » Wed Oct 24, 2007 7:59 pm

Here's an out-of-the-blue question; Do you think you could get o-rings on a piston to seal at 500 psi?
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Unread postAuthor: DYI » Wed Oct 24, 2007 8:11 pm

O-rings can seal at well over 1000 psi if they're done properly.
Might I ask what this relates to on this topic, if anything?
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Unread postAuthor: Fnord » Thu Oct 25, 2007 1:00 pm

It's a simple valve idea that could you could try before you make custom flanges. Basically it's just a piston that is held in place with a pin, so when you pull the pin out, you are releasing the pressure and the piston will act as a sabot for whatever projectile you are using.
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 25, 2007 1:57 pm

you mean like this?

A pin would allow lateral movement that would lock it in place and prevent it from sliding up without impractical force, that's why I chose a bolt.
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