I received a technical assistance call about performance of one of our air knives. The customer complained that the air coming out was “wimpy” and there were dead spots in the air flow. I asked him to take a picture of the air knife and indicate where the dead spots were.
He did not have to mark them as it was apparent what his problem was, Teflon tape used as pipe dope. He insisted that he did not use any in the installation of the air knife. Since there is no teflon used in the manufacture of the air knife, it had to come from somewhere in his compressed air system.
Upon further investigation, he discovered a new line had been added to their system. The plumber got carried away with wrapping pipe threads with the teflon tape. Not only did it find its way into our air knife, it also found its way into their air tools and cylinders.
Contrary to popular myth, PTFE tape does not seal, it only acts as a lubricant for better pipe thread engagement. Never try to repair a poorly fitting joint by applying more than the recommended amount of tape. Applying an excessive amount of tape can cause loose fragments.
The proper application of PTFE tape should start with two wraps taken about two or three threads from the end of the pipe. This will avoid tape fragments breaking loose and entering the plumbing system. Wrapping should be done in the direction of the threads. Each wrap should cover half the width of the previous wrap. This would give consistent two-layer coverage. Two layers are all you want. Wrapping should continue the entire length of the threads.