How Does a Car Compression Fitting Work?

Compression fittings came about as a solution to repairing broken lines or lengthening existing lines. They can also be removed and replaced without leakage problems. They come in many sizes to fit any size water line up to 5/8 inch. These compression fittings can be used in many applications including fuel lines for automobiles, oil furnaces, propane appliances and a countless number of other applications. Compression fittings are an extremely tight connection. They can save a lot of money as a replacement of a section of line as opposed to replacing a whole line. All compression fittings have five parts to them:

1. The center section consists of a straight-line sleeve with threads on either end for its caps;

2. A taper inside the sleeve for the section of line to be inserted;

3. Two ferules that have the appearance of a ring made to slide over the line tightly;

4. Caps with a hole in the top the size of the line being repaired.

To use a compression fitting, make a perfectly straight cut the length of the old line to be replaced with a line cutter. Measure the cut line for length as well as diameter. Acquire a length the same length and diameter and two compression fittings the same diameter as the line. The compression fittings will not work if you do not have the proper size for the line.

The compression fitting works by removing one side of the compression fitting by taking off the cap and the ferrule inside. Insert the cap onto the end of the line that was cut by holding it up with the threads facing out and away from the line. Push it on the line about 1 inch. Install the ferrule and push it on the line up to the cap. Push the sleeve onto the line with the ferrule and cap on it and push it as far on as it will go. Bring the cap with the ferrule up to the sleeve and screw the cap onto the sleeve. While pushing the sleeve onto the line use a wrench and tighten the cap. In the process of tightening the cap the taper in the sleeve will crush the ferrule down tight on the line.

Remove the other end of the compression fitting and install the cap and ferrule on the replacement line end. Push the replacement line into the sleeve as the cap is tightened. Do the same for the other end. Once installed go back and use one wrench to hold the sleeve and another wrench to tighten the cap--it will be a secure fitting and the compression fitting will hold the two pieces of piping together.