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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