1.
Backup Rings - TEFLON
Function of Teflon Back-Up Rings
Teflon
back-up rings are designed to prevent extrusion in rubber o-ring
sealing systems.
Rubber O-Rings generally serve as effective seals for dynamic
and static applications in hydraulic and pneumatic systems equipment.
One big drawback of such o-rings is their tendency to extrude
into the clearance of mating surfaces when subjected to increasing
pressures.
The degree
of extrusion is a function of o-ring hardness, clearance of mating
parts and fluid pressure.
Another variable that must be considered in determining the need
for back-up rings is the operating temperature. Elevated temperatures
(160 degrees F and higher) impose a severe burden on the physical
and mechanical properties of rubber o-rings which further increases
their tendency to extrude.
The combination
of high pressures and high temperatures is a common occurrence
in present day fluid systems. Moreover, the trend is toward still
higher pressures and longer resident times at elevated temperatures.
This places more emphasis on the role of the back-up ring in preventing
o-ring extrusion.
Standard
Configurations
There are three basic types of Teflon back-up rings in use: single
turn (scarf cut), multi-turn (spiral cut) and solid (uncut) configurations.
Heavy
Duty Back-Up Rings
Heavy duty back-up rings are configured with a greater T (axial
thickness) dimension. The extra thickness provides more extrusion
protection for o-rings. These rings are interchangeable with MS27595,
MS28774, MS28782 and MS28783 backup rings used in MIL-G-5514 packing
glands. Heavy duty back-up rings are available in solid (uncut)
and in the single turn (scarf cut) configurations.
Extended
Sizes
In addition to the military standards, we supply three series
of extended dash-size standards which provide back-up rings for
all o-rings in the Aerospace Standard AS-568A Uniform Numbering
System.
These
configurations have proven very useful to fluid systems designers
because of the added flexibility in size selection.
Because extended sizes usually are available, industrial users
are assured of the same quality and service that applies to the
most sophisticated aerospace applications.
Filled
Back-Up Rings
For applications where sealing systems are subjected to severe
duty cycles, or where pressures exceed 3,000 psi and temperatures
are above 275 degrees F, filled Teflon back-up rings are very
useful.
In addition to the more common fills such as glass fibers, considerable
experience with back-up rings of Nylon, Kel-F, FEP, UHMW and others.
We have produced the very standards using these materials as well
as more specialized compounds of Teflon.
Care should
be taken to be sure that the compound chosen is compatible with
the gland or rod materials of construction. There is no point
in over designing components that may cure extrusions, but produce
abrasion or wear problems.
- Single Turn - MIL
Standard MS28774
- Solid, Extended
Series
- Single Turn, Extended
Series
- Single Turn, Heavy
Duty
- Solid, Heavy Duty
- Solid - MIL Standard
MS27595
- Spiral - MIL Standard
MS28782
- Spiral - MIL Standard
MS28783
- Single Turn, Boss
Connection - MIL Standard MS9058
- Single Turn, Tube
Fitting - MIL Standard MS28773
- Spiral, Extended
Series

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