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Troubleshooting Article Archive:  July 2006          
Avoid the "Invisible Hand" of Hose Twist



Right way

   Wrong way
Last month I saw a hydraulic hose unscrew itself.  The wrecker bed it was installed on was brand new, and the customer's complaint was that the hose leaked oil no matter how often he tightened it.  To see the leak with my own eyes, I tightened the hose and operated the equipment.  When oil pressure filled the hose, the hose end immediately unscrewed itself from the fitting it was attached to, as if by an invisible hand.

The hose unscrewed itself because the builder's final tightening of the hose ends left the hose twisted instead of straight.  When oil pressure filled the hose, the hose tried to straighten itself out, thus unscrewing the end.  Because hydraulics operate at high pressure, the force trying to straighten the hose is substantial enough to unscrew even a hose end that was put on very tightly.

Most hydraulic hose comes with a colored stripe, colored lettering, or an embossed linear marking of some kind repeated periodically along the length of the hose.  Hose specialists call that the "lay line."  When installing hydraulic hose, watch the lay line to make sure the hose is not twisted.

On hoses that have a flare-nut end, hose installers commonly twist the hose in the last few moments of tightening.  When the flare nut's almost done up, and you twist the flare nut another quarter-turn to make it tight, the whole hose tends to twist that last quarter-turn along with the flare nut, leaving the hose tight and twisted.  Avoid this hose twist by using two wrenches:  one on the main body of the hose end, and one on the flare nut.  Use the wrench on the main body of the hose end to hold the hose still while using the wrench to tighten the flare nut.