How to seal a system containing ethanol, but low friction?

Still working on my solar device (in Copenhagen now), and it's coming along fairly nicely. Should hopefully have a full instructable in a couple of weeks. However, I'm having problems at the moment trying to keep the thing water tight, where the axle leaves the system, taking out the rotational motion. I'm using the bearing housing from an old bike wheel (photos to come) and I've got it sealed well where it's attached to wall of the container, but the ethanol is flowing pretty freely through the bearings themselves. I need it not to. I could use something like an O ring to seal the axle, but friction is a big issue. I wanted to pack the whole axle and bearing housing with grease, but grease dissolves in ethanol. Solutions? Is there anything grease like which isn't soluble in alcohol? Salt, maybe? Cheers all. (Nearly there...)

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lemonie7 years ago
See this doccument:
http://www.buchi.co.uk/rotary-evaporator_rotavapor.8982.0.html?&no_cache=1&file=381&uid=32888
Page 11 - vaccum seal.
The machine has a Teflon-faced rubber seal on a rotating glass shaft, resistant to solvents and holding a pressure differential of ~1.0mm Hg in good condition. You might not get hold of them very easily, but something like this might be what you're after?

L
SolarFlower_org (author)  lemonie7 years ago
Yeah, that'd be awesome. Depends what the friction / leakage tradeoff is, but it would probably do the trick. It's just a matter of rigging up something similar in concept easily and cheaply. After a few hours research on basic things that don't dissolve in alcohol; salt, sugar, petroleum jelly. If I pack the axle housing with one of these (petroleum jelly / Vaseline sounds best), that should do the trick, no? Maybe a loose-ish O ring to keep it from leaking out of the housing.
I had an idea, You might be able to use the existing bearing and add this on - it forms a Teflon seal (use plumber's tape) ?
solarthin.bmp
SolarFlower_org (author)  lemonie7 years ago
Sounds reasonable. What's the function of the compression sleeve?
It screws the Teflon seal tight, the green-ish bit squashes the Teflon packing as you screw-up the end cap. I see increased friction, but I am thinking Teflon here. Industrial valve packing is done in a similar way, it's the potential pressure & seepage I'm thinking of. For a fluid barrier you might achieve something like this with PVC? L
I'm surprised petroleum jelly doesn't dissolve if grease does, but having looked into it more, petroleum jelly is actually what I thought bearing grease was made of- lubricant grease also contains soap. Who knew? Anyway, that's a much simpler solution than magnetic coupling.
SolarFlower_org (author)  PKM7 years ago
It works! Vaseline aka petroleum jelly works perfectly as a grease substitute, and there's no leakage (well, a tiny amount if it's hung vertically, but I'm sure I can fix that.) Nice. That's a very large chunk of this thing solved. The turbine / water wheel thing is now finished; on to the boilers and stand, which are the same as the prototype, so hopefully won't take much time or effort. Touch wood.
Congratulations! Now, where are the pictures to show us what you did? Hmmmm....?
SolarFlower_org (author)  kelseymh7 years ago
Oh there'll be pictures...
PKM7 years ago
I don't know of any way to make a usual greasebox style liquid-tight bearing for containing ethanol, especially if the ethanol will be under pressure (as I assume it will be, given your last ethanol invention).

There might be some sort of (ahem) water-based lubricant that you could use instead of grease to pack the bearing with, but again I have no idea how soluble they are in ethanol.

Alternatively, there are methods of transmitting force through a liquid-tight wall- Kiteman's manta drive is one example, or the magnetic coupler from the Tesla Turbine pumpkin cutter. Fit the shaft inside the ethanol system with magnets and couple them to magnets on an external rotating shaft to transmit force through a solid wall. The only problem is it doesn't transmit much torque.

My only other thought is to use angle gearing to transmit the torque through an axle leaving the top of the ethanol container rather than the side, where there might be some airspace (not sure how your system works) and the ethanol is under lower pressure. I can draw a diagram if you need one but hopefully that conveys what I mean.
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