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? $\endgroup$– martCommented Jun 14, 2015 at 19:23
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$\begingroup$ 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. $\endgroup$– ankitsahayCommented Jun 16, 2015 at 5:21
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2$\begingroup$ 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 SweetCommented Jun 26, 2018 at 23:49
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$\begingroup$ 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.Commented Nov 23, 2018 at 15:08
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3 Answers
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Based on your comment it sounds like this is a prototype and the following might apply.
- The solution is temporary and doesn't need to last.
- It's not required to be gas proof, just tight enough that leaks are negligible to the performance of the system.
- You can replace the seal if it fails.
If my assumptions are correct you could probably get away with wrapping fiberglass weave or exhaust wrap around the inner pipe to create two rings of equal thickness and then slide the other pipe over them, slightly compressing them. Weld some small pieces or add some spacers to prevent the rings from moving around.
Considerations:
- If the outer pipe is smooth on the inside it's probably easiest to fix the rings to the inner pipe.
- If the outer pipe is rough on the inside you can add a flange on the end of the inner pipe to stop the seal from falling in, then you add a spacer of some sort to keep the seals apart.
- Over time sooth will accumulate and roughen the inside of the outer pipe, so if you plan to use this system for longer periods and not clean/replace the outer pipe then the second option might be preferable.
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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.
