Compression ring

One specialized type of connector is called a "compression coupling", and this is particularly useful for small diameter tubing. A small ring of metal with bevelled edges slips over the pipe. This is the "compression ring" (sometimes called an 'olive'), whose edges are forced inward to grip the tube when the hollow nut and bolt are screwed together. No soldering is needed, and it forms a gas-tight seal. The only drawback is that this is a one-time joint only, and you'll need another compression ring if you want to reposition the joint using the same nut and bolt.

Thermometer clamps

With slight modification, these small compression ring connectors can be used to firmly hold even delicate items such as glass thermometers. All that is required is a compression coupling with holes in the nut and bolt that are the same diameter as the thermometer, or slightly smaller. If smaller, just drill the holes out so they fit on the thermometer snugly. Instead of the metal compression ring, make your ^^m^^^^BPBHH^^H own "gentle" compression ring by winding some

Teflon® tape around the thermometer, between the hollow nut and bolt. This is squeezed together when the nut and bolt are tightened (only finger tight -you're dealing with glass!) and forms a gas-tight joint. The hollow bolt can be soldered into the side of a column before you introduce the thermometer. This is an ideal way to gently hold a delicate thermometer in place.

Thermometer clamps

Fig. 7-8

Joining small tubes to large pipes

Joining small tubes to large pipes

You can't always find the perfect connector for the job, even if you use reducing couplers in combinations not anticipated by the manufacturer. This is often the case when joining small tubes to larger pipes and, in such cases, you'll have to make your own.

There are three simple ways to join small and large tubes together:

The "direct" butt joint is mechanically weak because it has very little area for support. The small tube should always pass right through an exactly matching hole in the wall of the large tube or plate to maximize the strength of the joint, and should be provided with a supplementary collar, or fillet, if possible. You can make a fillet by winding a couple of turns of copper wire around the small tube where it joins the larger one. When you solder them, the wire will hold extra solder and form a visible ramp of support. A compression ring secured to the small tube by tightening the matching nut and bolt, then removing them, makes an extremely neat "supplementary collar".

The "through" joint has the small tube passing completely through the large pipe and is soldered to both walls of the pipe. The small tube has half its side filed away before assembly to create the actual joint. This is a very strong joint, requiring no supplementary collar, and is preferred where the small tubing doesn't interfere with anything in the large pipe.

A "through" joint made with intact tubing makes an excellent "thermowell" for a thermometer if you don't want to use a compression coupling.

The "side-swipe" joint is the most difficult to make, because it requires careful filing of a groove in the larger tube, using a round file with the same diameter as the small tube. One side of the small pipe is filed away to match the opening in the large tube, and the stub end is blocked, usually by soldering in a piece of rod. This joint makes a good liquid collection point for an offset condenser design, because it covers the width of the liquid reflux. Like the through joint, the side-swipe is quite strong.

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