[DeTomaso] Hydraulic Fittings ETC

[Edward A. Nauman]

>I thought the reason you have to decrease the torque you put on a bolt /
nut if you apply antiseize or oil is that by making the threads slippery you
make it easier to apply too much torque, which strips the threads. Not so?

 

 

Thread stripping has more to do with the shear modulus of the thread
material rather than the friction caused the metal to metal contact.
Putting more torque on a threaded fastener will generate more shear force on
the threads.  If a flare fitting leaks with the proper amount of torque
applied, replace it.  The primary reason Teflon tape is used on pipe threads
is to ease the friction caused by the tapered interference fit, which
reduces the chance of galling. A secondary benefit is  to fill tiny voids in
the thread contact surfaces.  If you are looking for a temporary crutch to a
leaking fitting, you could use a high pressure sealant like Permatex.  But
you really should replace a leaking flare fitting.  I prefer to use Swagelok
fittings in place of AN or automotive double flare types.  Swagelok fittings
use double stainless steel ferrules that are precisely "swaged" to the
tubing by the fitting nut.  When the tubing is installed the first time, the
nut is turned a specific number of revolutions past hand tight.  They are so
accurate that there is a feeler gage that you insert between the nut and the
fitting body to determine the proper amount of fit up.  Once the ferrules
are swaged to the tubing, the line can be removed and reinstalled an almost
infinite number of times without leaking.  The swaged tubing, ferrule and
nut can even be transferred to another fitting with confidence it will not
leak.  They come in several material types.  My preference is stainless
steel which have hardened, precision ground, threads and mating surfaces.
The only drawback is they are expensive if purchased new.  But there is an
unlimited supply available on ebay.  All you have to do is buy new ferrules
from Swagelok and you will never have a leaky fitting again.  Guaranteed.

 

Fast Eddie (#2100)

 

Edward A. Nauman\

C.E.O.

Smart Litez Inc

 

Palmdale, CA. 93551

(661) 305-7636