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Packaging and Storing
Backup rings are not color-coded or otherwise marked
and must be identified from the packaging labels.
The dash number following the military standard
number found on the package indicates the
size, and usually relates directly to the dash number
of the O-rings for which the backup ring is
dimensionally suited. Backup rings made of TFE
do not deteriorate with age and do not have shelf
life limitations. TFE backup rings are provided
by manufacturer either in individually sealed
packages or on mandrels. If unpackaged rings
are stored for a long time without the use of
mandrels, a condition of overlap may develop. Overlap
occurs when the ID of the backup ring becomes
smaller and its ends overlap each other. To
correct this overlap condition, stack TFE rings on
a mandrel of the correct diameter, and clamp the
rings with their coils flat and parallel. Place the
rings in an oven at a maximum temperature of
1770 C
(350 0F)
for approximately 10 minutes. Do
not overheat them because fumes from decomposing
TFE are toxic. Remove and water-quench
the rings. Store the rings at room temperature
before you use them (preferably for 48
hours).
Installation
Care must be taken in handling and installing backup
rings. Do not insert them with sharp tools.
Backup rings must be inspected prior to
using them for evidence of compression damage,
scratches, cuts, nicks, or frayed con-ditions. If
O-rings are to be replaced where backup
rings are installed in the same groove, never
replace the O-ring without replacing the
backup rings, or vice versa. Many seals use
two backup rings, one on either side of the O-ring
(fig. 7-12). Two backup rings are used primarily
in situations (such as a reciprocating piston
seal) where alternating pressure direction can
cause packing to be extruded on both sides of
the gland.
Figure 7-11.—Types of backup rings.
Figure 7-12.—Backup ring
configuration.
If only one backup ring is used, place the backup
ring on the low-pressure side of the packing
(fig. 7-13, view A). When a backup ring is
placed on the high-pressure side of the packing, the
pressure against the relatively hard surface of the
backup ring forces the softer packing against the
low-pressure side of the gland, resulting in a rapid
failure due to extrusion (fig. 7-13, view B). When
dual backup rings are installed, stagger the
split scarfed ends as shown in figure 7-14. When
installing a spiral cut backup ring (MS28782 or
MS28783), be sure to wind the ring correctly to
ease installation and ensure optimum per-formance. When
TFE spiral rings are being installed in internal
grooves, the ring must have a right-hand
Figure 7-13.–Location of a single
backup ring.
Figure 7-14.—Installation of cut dual backup rings.
Figure 7-15.–Installation of TFE back up rings (internal).
spiral. Figure 7-15, view A, shows how to change the
direction of the spiral. The ring is then stretched
slightly, as shown in view B prior to installation
into the groove. While the TFE ring is
being inserted into the groove, rotate the component
in a clockwise direction. This will tend to
expand the ring diameter and reduce the possibility
of damaging the ring. When TFE
spiral rings are being installed in external
grooves, the ring should have a left-hand spiral.
As the ring is being 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 damaging the
ring.
In applications where a leather backup ring is
called for, place the smooth-grained side of the leather
next to the ring. Do not cut leather backup rings.
Use a leather backup ring as one continuous ring
and lubricate the ring prior to installing it, particularly
the smaller sizes. If stretching is necessary
for proper installation, soak the backup ring
in the system fluid or in an acceptable lubricant
at room temperature for at least 30 minutes.
QUAD-RINGS
The Quad-Ring® seal is a special configuration ring packing, manufactured by
the Minnesota Rubber. As opposed to
an O-ring, a Quad-Ring® seal has a
more square cross-sectional shape
with rounded corners (fig. 7-16). The Quad-Ring® seal
design offers more stability than the O-ring
design and practically eliminates the spiraling
or twisting that is sometimes encountered with
the O-ring. Quad-Rings® seals are
completely inter-changeable with
O-rings in the sizes offered by the
manufacturer. They may be installed with one
Figure 7-16.—Quad-Ring.
or two backup rings, depending upon the specific seal
groove application and width. The Quad-Ring® seal
works well in, both hydraulic and pneumatic
systems.
Many Quad-Ring® seal sizes have been assigned
NSNs and are stocked in the Federal Supply
System. Quad-Ring® seals in manu-facturer’s sizes
designated as Q1 through Q88 are interchangeable
with O-rings conforming to AN6227.
Likewise, Quad-Ring® seals in com-mercial sizes
Q101 through Q152 are inter-changeable with
O-rings conforming to AN6230 in the
respective dash sizes from –1 through–52. Therefore,
the Quad-Ring® seal stock part number
uses the AN standard O-ring designations AN6227
and AN6230 and the commercial Q dash number
designation. For example, NSNs are found
under such reference part numbers as AN6227Q10
and AN6230Q103. If the letter Q does
not follow AN6227 or AN6230, the part number
is an O-ring not a Quad-Ring® seal. If
Quad-Ring® seals are not available for maintenance
actions, appropriate sized O-rings can
be installed and they work satisfactorily.
QUAD-O-DYN® SEALS
The Quad-O-Dyn®, also manufactured by Minnesota
Rubber, is a special form of the Quad-Ring.
The Quad-O-Dyn differs from the Quad-Ring
in configuration (fig. 7-17), is harder, is
subject to greater squeeze, and is made of a different
material. The Quad-O-Dyn® seal also works
well in O-rings glands. The Quad-O-Dyn®
is used in relatively few applications.
However, for difficult dynamic sealing
applications, the Quad-O-Dyn® can perform
better than the Quad-Ring. Quad-O-Dyn® rings
are installed in submarine hydraulic systems
plant accumulators.
Figure 7-17.—Quad-O-Dyn® seal.
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