TUBING

Compression Tube fitting.

The most common type of tube fitting for instrument impulse lines is the compression-style

fitting, which uses a compressible ferrule to perform the task of sealing fluid pressure. The essential components of a compression tube fitting are the body, the ferrule, and the nut.            The ferrule and body parts have matching conical profiles designed to tightly fit together, forming a pressure-tight metal-to-metal seal. Some compression fitting designs use a two-piece ferruleassembly, such as this tube fitting shown here (prior to full assembly):

Just prior to assembly, we see how the nut will cover the ferrule components and push them into

the conical entrance of the fitting body:

After properly tightening the nut, the ferrule(s) will compress onto the outside circumference of

the tube, slightly crimping the tube in the process and thereby locking the ferrules in place:

This happens to be a Swagelok brass instrument tube fitting being installed on a 3/8 inch copper tube.

Cutting the Tube End

To insure a good joint, tube must be cut off square. This can be accomplished with either a tube cutter or hacksaw. Tubing Cutters are more com-monly utilized on softer tubing

Tubing Cutters are more com-monly utilized on softer tubing

      

such as copper, aluminum or

even “soft” steel tubing. If a tube

cutter is utilized with stainless

steel tubing, remember that a special cutting wheel, designed for use with stainless steel

 tubing should be employed. The use of dull or improper cutting wheels can work harden the S.S. tubing near the cut area. This CAN adversely affect the fittings sealing ability.