MadModder
Gallery, Projects and General => How do I?? => Topic started by: ant... on May 15, 2010, 02:30:47 PM
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This is a 24L Pressure Vessel which I have bought and connected it to my compressor. Its to be used as a poor mans autoclave.
Originally it came with a internal rubber bag which started to leak pressure at 80psi, the bolts created its best seal at a certain torque, if you tightened them more, more air would leak out.
I got rid of the bag and replaced it with these neoprene rubber seals, they are perfectly glued down with PU bond, but they leak at 50psi :bang:
Ive got two ideas to get a better seal, but im unsure about them:
1 fit a metal wire ring to increase pressure at a certain point.
2- Drill & tap another 6 bolts to increase the points of pressure?
Can you suggest any way of improving the seals pressure?
(http://i714.photobucket.com/albums/ww146/anthonyhague/IMG_1128.jpg)
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What you have seen there is a perfect demonstration of the result of 'Elastic Foundation Theory', you can Google it, it's not BS. The bolts bend the flange and induce a wave in it which is why there is a 'best' tension for the bolts. It is a serious issue for large bolted or rivetted stuctures, but with welding far more common these days it is less commonly experienced than a century ago.
You have number of options, but the central issue is to get a stiffer flange, the rolled edge seeks to do this - poorly. Adding bolts halfway between the existing ones effectively does this since the centre distance between the bolts is halved. The bending of a beam is proportional to the square of its length so you would expect a significantly smaller deformation with twice as many bolts (I won't say a quarter because there are other issues to be considered). However, if you were to add a backing ring to thicken the flange, beam bending is inversely propotional to the cube of its thickness so you would get a lot more extra stiffness that way.
It depends on what the mating flange is like, it may not be practical to fit a backing ring to that, 'though two semi-circles may be a possibility. If you try to go too thick with the seal to accommodate the undulations of the flange(s), there is an increasing risk that it will just blow as a result of the internal pressure
Richard
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Ant,
How thick is the gasket neoprene? If its too thick it will make the warping explained by Richard worse, try a thinner gasket, also, try some rubber insertion material, its a gasket material that has a fibre insert woven within the rubber for more stability.
Some jointing compound like silicon sealer might also do the trick, assuming you are using air or water in the vessel?
More bolts will certainly help.
Ian
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Hi guys
Well my first theory has worked. Using some thick wire i made a complete circle and used hot glue to fix it to the rubber.
The wire has increased pressure and taken up some of the slack of the 'Elastic Foundation theory'.
'Elastic Foundation theory' - I love it LOL but the next time i come across this scenario my memory is bound to fail me and i will miss my opportunity to look cleaver.
I had considered making a flange from 5mm stainless steel, but that would be allot of work, as would drilling & tapping another 6 bolts. Just hope my wire idea holds out.
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Ant, Before drilling and tapping more holes you might try a half dozen small "C" clamps to see if additional bolts would solve your leakage problem. From the picture it appears that 1 inch/25 mm clamps would work.
Joe
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75Plus - Thats a good idea, I did actually try it with those silver welding clamps too.
But i fixed it with a wire circle :thumbup: