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Instrument Tubing Bending & Installation

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Instruments around a plant monitor and control systems ranging from pressure differentials to contents of materials measured in percentages. Installing tubing to and from various instrument locations involves an understanding of the process and the application. Tubing installation is often dictated by the requirements of process. Bending, positioning and bracing tubing means more than just measuring a straight line and getting enough tube to fit. Tubing benders permit maximum tolerances for pressurized lines while reducing waste from cracked, misshapen or misaligned tubes of all sizes.


The math needed to install tubing involves an understanding of radius, angles and tube dimensions. A 3-inch radius for three-eighth inch tube is broader than the same radius for one-inch tube. Always consider the tube’s size when measuring the needed radius for a bend. Also, tubing will always “snap back” about 5 degrees when pulled around a tubing bender. Make sure to add this to your calculations when determining the bend radius. For example, for a 90-degree bend (from a straight tube to a right-angle bend), make a 95-degree maximum bend. When the tubing is released, it will snap back a small amount, about 5 degrees.

Using the Tubing Bender

A tubing bender, whether powered or manual, is a simple machine: place the tube in the hold clamp, affix the saddle to the other end of the shoe’s groove and pull the tube around the shoe. Shoes are half-circle attachments with a groove the width of the tube. You need different shoes for different sized tubing. You also need a shoe for every turn radius. So for 3/8-inch, 1/2-inch and 1-inch tube turn for 2-inch, 4-inch and 6-inch radiuses, you would need a total of nine different shoes. Don’t bend tubing too small for the shoe; this causes tube crimping and inexact bend radiuses.

Installing the Tube

Determine the fitting requirements for the individual instruments. Some instruments require a specific minimum straight line to attach to the inlet or outlet fitting. Others are not as exact, and tubing can be bent directly at the fitting. Always work backwards from the instrument when determining the bend locations and the radius of each bend. This will avoid getting to the instrument fitting and finding out you’re too short or too long to make a tight secure attachment. Also, avoid putting the instrument on the tube and then mounting or installing the instrument. Instruments measure specific processes, and it’s best to get the instrument right and adapt the tubing to the instrument’s location than the other way around. As with any precision instrument installation and operation, always measure twice, write down your measurements and then you will only have to bend once. Once a tube is turned, it’s never a good idea to straighten or add more bend. Bend it in the shoe, and when you take it out, make sure it’s where you want it to go.