Sunday, December 31, 2006

Leaky O-rings...

In my first little tank I used soft rubber o-rings. These will not work for LOX. So I've spent the last two days trying to get PTFE or FEP encapsulated o-rings to not leak. I've been trying to build a 3" tank to test my PET tank ideas. The picture on the left is the top end of the tank after the first winding step to reinforce the area around the o-ring before starting to wind the longitudinal fibers.
The next picture is the tank with the longitudinal windings in place, about to be filled with water before doing the radial winding. I did not get past this point because....

The third picture shows water leaking around the seal.
Having a light high pressure LOX tank would greatly simplify some of the project, but it's not worth spending a whole lot more time on. I'm going to order some more o-rings from McMaster carr and try one more time , but if I can't build light LOX tanks I'll just use aluminum irrigation pipe and work to get something flying. I have to keep reminding myself that perfect is the enemy of good enough.


John Carmack said...

You need quite a bit of crush on PTFE o-rings to get a seal. You might try a thin metal ring on the outside of the PET tube where the o-ring will seat, so it requires a press to push the closure into it before winding.

Alternately, I bet you could get the PET to act as its own seal with the right tolerance on an internal and external thread, or some kind of ferulle arrangement.

I'm still interested in hearing the data points on the stainless spheres...

John Carmack

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