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Connections of Tygon tubing to the flight instruments and in between the carburetor and the mixture control valve need to be reliable and light weight. I like to use 1/8 inch ID Tygon tubing. I have been sliding the Tygon over straight nipples made from 1/8 inch OD tubing. To ensure a good seal, I use a double wrap of small diameter copper wire with the ends twisted together to provide the clamping force. It works well, except in confined places where it is difficult to wrap and twist the wires.
A simple clamping system that is amenable to confined space is shown on the left. The Tygon tubing is 1/8 inch ID and 3/16 inch OD. The aluminum tube clamping ring is 0.015 inch wall with a 7/32 inch OD. |
To assemble, one slides the clamping ring onto the Tygon so that will be clear of the nipple after the Tygon has been slid over the nipple. Then ring is advanced forward into the clamping position.
Clamping rings are made from aluminum tubing made by K&S Engineering, Chicago, IL. It can be found at most hobby shops. In the past I have tried this scheme without success. I had purchased my tubing from local hardware stores, and I found that the wall thickness was greater than 1/32 of an inch. Then I tried "Tygon R-3603 Laboratory Tubing, 1/8" ID x 3/16" OD x 1/32" Wall, Color: Clear" from SmallParts.com. Dimensionally it is correct and the material is a little softer than what I had previously used. |
Also this system works well with barbed fittings. These can be purchased at most hobby shops.
Once the clamping ring is in position, it is difficult to separate the connection by pulling on the tubing. To disconnect the tube, one must first force the ring away from the cut end of the tube. This relieves the compression clamping force, so that, the tubing can be removed from the nipple or barb. One nice thing is the ring will not fall off the tube. This lets one connect tubes on the back side of the instrument panel by feel. |