Figure 2-48.—Teflon® backup ring damages caused by
improper handling.
maximum temperature of 350°F for a period of
approximately 10 minutes. The rings are then
removed and water quenched.
NOTE: After this treatment, rings should be
stored at room temperature for a period of 48
hours prior to use.
IDENTIFICATION.—Backup rings are not
color coded or otherwise marked and must be
identified from package labels. Backup rings made
from Teflon® do not deteriorate with age, and are
unaffected by any other system fluid or vapor. They
tolerate temperature extremes in excess of those
encountered in high-pressure hydraulic systems. The
specification number of a backup ring can be found
on the package label. This specification number is
followed by a dash (-) and a number. The number
following the dash indicates the size. In some cases,
this number is directly related to the dash number of
the O-ring for which the backup ring is intended to be
used. For example, the single spiral Teflon® ring,
MS28774-6, is used with MS28775-006 O-ring; and
the double spiral Teflon® ring, MS28782-1, is used
with the AN6227B-1 O-ring.
INSTALLATION.— Care must be taken during
the handling and installation of backup rings. If
possible, backup rings should be inserted by hand and
without the use of sharp tools. The Teflon® backup
rings must be inspected prior to reuse for evidence of
compression damage, scratches, cuts, nicks, and
fraying conditions, as shown in figure 2-48.
To install the Teflon® backup ring (fig. 2-49), the
following steps should be used.
1.
2.
3.
4.
5.
6.
7.
8.
9.
Examine the fitting groove for roughness that
might damage the seal.
Position the jam nut well above the fitting
groove, and coat the male threads of the fitting
sparingly with hydraulic fluid.
Install the backup ring in the fitting groove,
and work the backup ring into the counterbore
of the jam nut.
Install the gasket in the fitting groove against
the backup ring.
The jam nut is then turned down until the
packing is pushed firmly against the threaded
portion of the fitting.
Install the fitting into the boss, and turn until
the packing has contacted the boss. (The jam
nut must turn with the fitting.)
Hold the jam nut and turn the fitting an
additional one-half turn.
The fitting is then positioned by turning it not
more than one turn.
Hold the fitting in the desired position, and
turn the nut down tight against the boss.
When Teflon® spiral rings are being installed in
internal grooves, the ring must have a right-hand
spiral. View A of figure 2-50 shows the method used
to change directions of the spiral. The Teflon® ring is
then stretched slightly prior to installation into its
groove. While the Teflon® ring is being inserted in
the groove, rotate the component in a clockwise
direction. This action will tend to expand the ring
diameter and reduce the possibility of damage to the
ring.
When Teflon® spiral rings are being installed in
external grooves, the ring should have a left-hand
spiral. As the ring is inserted into the groove, rotate
the component in a clockwise direction. This action
will tend to contract the ring diameter and reduce the
possibility of damage to the ring.
2-37
