Before looking at any designs for systems or parts, we need to discuss sealing. Ethanol is a very volatile substance, and its hot vapor will escape through the tiniest gap. Every time you join one part to another, and those parts will be carrying vapor, you should ask yourself, "is it really 100% gas tight?" A slight water leak in a condenser is annoying, but not dangerous. However, if hot ethanol vapor can escape, it will spread everywhere. This is not only unpleasant and wasteful, it is potentially dangerous, because in a confined space it can form an explosive mixture with air! Since safety comes first, always bear in mind that ethanol and gasoline are very similar when it comes to flammability and explosive characteristics. Treat it with respect and keep it where it should be with good seals and gaskets.

Never rely on screw joints alone to provide a vapor-tight fit, even if they're the tapered kind supposed to seal themselves. Professionals always use some sort of sealing compound with threaded joints, and so should you. Get some thread seal tape, string, or jointing compound and always use it on every screwed vapor joint. These are all readily available. The best all-around choice is PTFE (Teflon ® is a well-known trade name for this) plumber's tape. It is cheap, solid, durable, and will not contribute any flavors to the vapor.

For all other joints and sealing points, using ordinary rubber for seals and gaskets is out! Hot ethanol has the ability to leach out flavors and smells from almost everything, and most types of rubber are right at the top of the list. Even the kind used in glass preserving jars is no good in a still. This type of seal works well for jams and preserves, but will ruin any batch of ethanol you produce. The best material for a seal or an O-ring gasket is Nitrile®, which is inert to ethanol. Teflon® is also suitable, although more expensive. Take care though, because Teflon® absorbs hot ethanol and can become spongy, requiring mechanical support of some kind. (This is not an issue in threaded or clamped joints, which are intrinsically self-supporting.)

A very useful alternative is silicone RTV (Room Temperature Vulcanizing) sealant. This comes in a variety of forms and is made by many manufacturers. Many of these sealants are intended for outdoor use and contain mold inhibitors. The type you want to is marked food grade or suitable for aquariums, contains no toxic substances and is clear - many of the other types are colored. Apply a very thin layer of petroleum jelly to one of the surfaces you want to be sealed (so the cured seal will release) and apply the RTV sealant to the other. Hold or clamp the surfaces together until the sealant has cured and you will have a perfect ethanol resistant seal that is permanently attached to the surface that was not coated with petroleum jelly. If you want the seal to be released by both surfaces, then smear the petroleum jelly on both of them.

If you can't find of any of these materials, there's nothing wrong with using the old plumber's trick of winding a bit of frayed string around threads to ensure a good seal, or of making simple gaskets for flat-faced flanges out of a few sheets of ordinary paper. It is a nuisance to have to replace these simple gaskets whenever you take the joints apart, but they are effective. The only time you will encounter difficulties using these simple methods is if you try to make large gaskets to seal, for example, a lid on a big pot. Here, the old moonshiners's technique was to use a flour-water paste to make seals, and this worked very well, though they could be difficult to clean up after baking in place.

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