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What type of mechanism can I use to connect 2 coaxial pipes of unequal diameters, where the outer pipe can slide over the inner pipe? I was thinking about splines, is there any better way...? Also, if I want the connection to be leakproof, what are the options that I have ?

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  • $\begingroup$ can you add a few details: will there be temperature diffs betwen the pipe, what pressure diff. is there? how leakproff do you need? $\endgroup$ – mart Jun 14 '15 at 19:23
  • $\begingroup$ Actually I am doing a project where the exhaust gases from an I.C. Engine flows inside the pipes, and I want to change the overall length of the pipes by sliding the outer pipe over the inner pipe (the inner pipe connects to the exhaust manifold)...and although the outer pipe can slide over the inner pipe...the connection has to be leakproof , otherwise exhaust might escape before it reaches the end of the outer pipe. $\endgroup$ – ankitsahay Jun 16 '15 at 5:21
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    $\begingroup$ 100 years of tinkering by tens of thousands of hot-rodders and moto-crossers has conclusively determined that's not how to go about it. Use valves in a fixed pipe (or pipes). The conditions of vibration and heat and chemistry just aren't conducive to a sealed slider system, and the key here is seals, since it is the reflected suction pulse you need to preserve. Rigidity is the key. $\endgroup$ – Phil Sweet Jun 26 '18 at 23:49
  • $\begingroup$ So, all classic telescopic joint solutions are right out due to soot accumulating in the pipes and jamming any bushings / slip bearings. The classic approach would be just some brass slip rings and good lubricant, but that doesn't account for fine solid contaminants. $\endgroup$ – SF. Nov 23 '18 at 15:08
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Do the pipes need to be "keyed" such that they cant rotate with respect to each other? If not, you can maybe seal the inner pipe like a piston(inner pipe) in a cylinder( outer pipe) shaft/T/U/oring/seal etc. Not sure how those seals work with gases as they do with liquids, but air is a gas and pneumatic cylinders work the same!

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You would need a dual O ring system with sufficient spacing between the O rings. As for a sealant, use a silicon based lubricant. The interference pressure for would need to exceed the pneumatic pressure in the pipes.

As for picking the pipes in varying positions, an helical cam system would suffice with dual spring-loaded bearing balls that keep it either locked or open through a rotation (twisting) motion.

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