This type of connector eliminates all tube
flaring, yet provides a safe, strong, and depend-
able tube connection. This connector consists
of a fitting, a sleeve or ferrule, and a nut.
(See fig. 5-18.)
Although the use of flareless tube
connectors is widespread, NAVSEA policy
is to reduce or eliminate use of flareless
fittings in newly designed ships; the extent
to which flareless fittings are approved for
use in a particular ship is reflected in
applicable ship drawings.
Flareless-tube fittings are available in many
of the same shapes and thread combinations as
flared-tube fittings. (See fig. 5-16.) The fitting has
a counterbore shoulder for the end of the tubing
to rest against. The angle of the counterbore
causes the cutting edge of the sleeve or ferrule to
cut into the outside surface of the tube when the
two are assembled.
The nut presses on the bevel of the sleeve and
causes it to clamp tightly to the tube. Resistance
to vibration is concentrated at this point rather
than at the sleeve cut. When fully tightened, the
sleeve or ferrule is bowed slightly at the midsection
and acts as a spring. This spring action of the
sleeve or ferrule maintains a constant tension
between the body and the nut and thus prevents
the nut from loosening.
Prior to the installation of a new flareless-tube
connector, the end of the tubing must be square,
Figure 5-18.Flareless-tube connector.
concentric, and free of burrs. For the connection
to be effective, the cutting edge of the sleeve or
ferrule must bite into the periphery of the tube
(fig. 5-19). This is ensured by presetting the sleeve
or ferrule on the tube.
Presetting consists of deforming the ferrule to
bite into the tube OD and deforming the end of
the tube to form a shallow conical ring seating
surface. The tube and ferrule assembly should be
preset in a presetting tool that has an end section
identical to a fitting body but which is made of
specially hardened steel. This tool hardness is
needed to ensure that all deformation at the tube
end seat goes into the tube.
Presetting is done with a hydraulic presetting
tool or a manual presetting tool, either in the shop
or aboard ship. The tool vendors instructions
must be followed for the hydraulic presetting tool.
If a presetting tool is not available, the fitting
body intended for installation is used in the same
manner as the manual presetting tool. (If an
aluminum fitting is used, it should not be reused
in the system.) The manual tool is used as follows:
Failure to follow these instructions may
result in improperly preset ferrules with
insufficient bite into the tube. Improperly
preset ferrules have resulted in joints that
passed hydrostatic testing and operated for
weeks or years, then failed catastrophically
under shock, vibration, or normal operat-
ing loads. Flareless fitting failures have
Figure 5-19.Unused ferrules.