since 1940

Static Electricity and Teflon Aircraft Hose

Stratoflex Teflon Hose inner tube Aircraft Teflon hose has carbon black added to the inner wall to dissipate static electricity and dielectric breakdown of the PTFE (hose failure). Teflon hose without a black inner liner will not dissipate static electricity Note the thickness of the inner liner. Most automotive Teflon is considerably thinner.  .

"Garden Sprinkler hose" (Referring to soaker hoses that are designed to leak)  is how some of the older aircraft mechanics described Teflon hose back in the early 1970's. Teflon hose worked great on trucks, industrial equipment, and race cars but on airplanes, Teflon hose developed pinhole leaks.

The problem was quickly found, fixed and forgotten  for 30 years. So successful was the fix that few now have ever heard of the problem. Then, a few years ago, a Kit airplane manufacturer starts supplying cheap Teflon hose without a conductive inner liner for their kitplanes; thereby duplicating the problem that the aircraft industry fixed 40 years ago!

Static charge generation occurs as liquids flow through hoses and is dependent upon the potential of the hose surface to accept or donate electrons, the speed at which the liquid is moving and the conductivity of the hose liner. Electrostatic discharge in the form of an electric spark occurs from the hose inner tube to the steel braid thereby creating a pin hole leak.

The aircraft industry realized that static electricity in an  airplane is quite different than a truck or automobile (I've never seen static wicks on cars) and could, albeit infrequently, cause a hose failure.  The fix  was to increase the conductivity of the hose inner liner. All aircraft Teflon hose meets a minimum inner tube conductivity requirement.

 Military Specification MIL-H-25579E Hose Assembly, Tetrafluoroethylene, High Temperature, Medium Pressure  requires that hoses (through -8)  be capable of conducting a direct current equal to or greater than 6 microamperes with a test potential of 1,000 volts dc between the hose inner liner and one end fitting. The Teflon hoses we build at Sky Ranch meet this requirement.

To quote Resistoflex Static Electricity Considerations for Fluoropolymer Lined Hoses "The conductive properties of the liner will not prevent charge generation, but will allow the charge generated to be relaxed to ground quickly, thereby preventing the risk of electrostatic discharge. This electric spark is capable of creating pinholes in the liner."

To quote Otto Von Bismarck, founder of the German Empire: "Fools say that they learn by experience. I prefer to profit by others' experience" 

Copyright 2003 by Sacramento Sky Ranch Inc. All rights reserved.  Prices subject to change without notice. Not responsible for typographical or misprint.
Disclaimer: sacskyranch.com contains abundant information relating to aircraft maintenance. The information provided  is not intended to supercede or supplement the F.A.A. approved  maintenance and/or operator’s manuals. Those F.A.A. approved manuals must be utilized when performing maintenance and/or operating aircraft.