My Calibration Tube Failed

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“I got my liner in and shot the calibration tube right after. It only took me 15 minutes from the time I mixed resin until I had pressure on the calibration tube and life was good. Then, after 5 minutes of curing, I lost all pressure in my calibration tube. I figured I better get the calibration tube out before everything sets up, but all my efforts to pull it back failed and my liner and calibration tube were laying in the bottom of the pipe. It cured that way and when I dug up the line, found my calibration tube all bunched up with liner very close to the main line. Why wouldn’t my calibration tube come back? I still had the pull strap in my hand . I tried connecting it to the bumper of my truck but it wouldn’t budge and then broke. Shouldn’t it have come back the way it went in?”

To understand why it wouldn’t pull back, let’s explore the physics of the liner and calibration tube as it was installed. The liner was short of the main line and the calibration tube shot beyond the end of the liner to keep the end rounded out and where you wanted the liner to end. Under pressure everything is round. Then you lost pressure. The calibration tube and the liner you could see at the installation end laid down in the pipe – flat with the pull strap or rope in the middle of the assembly. Now you begin pulling and the flat calibration tube tries to pull back toward you but as it is pulled it encounters the end of the liner. If you were fortunate enough to have the liner rounded out to the wall of the pipe, your calibration tube may slip past the end and you would retrieve it. If it was laying in the bottom of the pipe flat, and the end of the calibration tube came up to it, there is little chance that the liner would open up enough to pull the liner back toward you. At this point the panic increases and you twist the calibration tube and pull. Still no luck, so you hook a rope to the bumper and tie off the pull strap. After a couple of attempts at this method and the pull strap breaks somewhere down the line so that option is gone. Then you try tying the calibration tube to the rope on the bumper of the truck and try pulling it again. This time the calibration tube rips and you have nothing to hold on to. Now you are in full panic mode and have run the course of options available to you. The next call is for the excavator to rescue your job and it could have all been avoided.

We all know that things go wrong. Doesn’t matter what system or method you are using, if something is mechanical, it can fail. The trick here is to be prepared for it. To prepare for a job, I always recommend that  a contractor take double everything he needs for the job. When something breaks or fails you have a back-up. In this case having double the calibration tube would have let you abandon the original calibration tube in place and let it lay on the bottom of the host pipe with the liner. You would then prepare a second calibration tube using the same dimensions as the first and invert the new calibration between the liner and the failed calibration tube. NOT INSIDE THE OLD CALIBRATION TUBE, BUT BETWEEN THE HOST PIPE AND THE LINER. We don’t know at this point why the original calibration tube failed, but if the end of the calibration tube is still in tact, you would be trying to “dead head” a new calibration tube to the end of the failed calibration tube and physics that this wouldn’t happen because as soon at the inversion pressure fell below the internal pressure you build when installing the second calibration tube, your second calibration tube would stop short. Once you have the new calibration tube in place, pressure it up and hold it until your liner is cured. The exit process would then be, pull the new calibration tube, then pull the failed calibration tube and find your liner cured as was intended. No excavator needed.

For more tips, read past blogs at At the bottom of the page are page numbers of past blogs that pertain to our industry. If there is a topic you like to see covered, contact me at


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