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

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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SolarFlower_orglemonie

Reply 9 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.

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lemonieSolarFlower_org

Reply 9 years ago

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
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SolarFlower_orglemonie

Reply 9 years ago

Sounds reasonable. What's the function of the compression sleeve?

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lemonieSolarFlower_org

Reply 9 years ago

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

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PKMSolarFlower_org

Reply 9 years ago

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.

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SolarFlower_orgPKM

Reply 9 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.

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kelseymhSolarFlower_org

Reply 9 years ago

Congratulations! Now, where are the pictures to show us what you did? Hmmmm....?

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PKM

9 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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SolarFlower_orgPKM

Reply 9 years ago

It's still the same ethanol system, there's no significant pressure. I was thinking of magnets, but wanted to keep the whole thing as low tech as possible. However it's starting to look difficult to avoid. I'll track down some old speakers and see what I can do with the magnets from them. I would really like to avoid it tho. Any top airspace would contain ethanol vapour, which is probably harder to seal for than liquid. Just a thought: I could have a two liquid system, ethanol at the bottom, and then something of lower density, like an oil, which sits on top where the bearing is. It would need to not dissolve grease, and have a low surface tension and viscosity...

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KitemanSolarFlower_org

Reply 9 years ago

You're not going to get an oil with a lower density than ethanol.

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SolarFlower_orgKiteman

Reply 9 years ago

Thinking about it, it was never going to work on several levels. Anyway... So, magnets. I ripped two reasonably strong cylindrical magnets out of old speakers, which I now realize are absolutely everywhere, and they seem to have sufficient force, at least when stuck directly together. Just to potentially save me a lot of reinventing wheels, what are some simple and effective setups for magnetic couples? The hassle is that the intervening surface kinda needs to be metal. Unless there's something non magnetic which won't corrode in ethanol...

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kelseymhSolarFlower_org

Reply 9 years ago

314 stainless steel is quite non-magnetic, as is aluminum. You could also use a pair of machined blocks of PTFE (teflon) if you want. I'm not 100% sure it would be low enough friction for your purpose, but the material properties are readily found.

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KitemanSolarFlower_org

Reply 9 years ago

Anything non-ferrous will do. And lubricating the magnet against the surface can be done with glass marbles.