TFE-O-SIL silicone, Viton® or EPDM O-Rings encapsulated with FEP or PFA are designed to address the growing problem of sealing in the most hostile chemical and temperature environments. TFE-O-SIL combines the best qualities of two materials, FEP or PFA on the outside with its chemical inertness and an elastomer on the inside for resilience. This unique combination forms a highly effective, long lasting seal for the most demanding applications.
TFE-O-SIL O-Rings are available in over 60 standard cross section sizes from .063″ (1.60mm) to 1-1/4″ (31.75mm). Standard TFE-O-SIL O-Rings are comprised of FEP over silicone, Viton®, or EPDM, and can be used in temperatures from -75° to +400°F (-60° to +205°C) depending upon the choice of elastomer core.
For high temperature applications to 500°F (260°C), TFE-O-SIL is made with PFA over silicone. PFA has higher mechanical strength than FEP or TFE at elevated temperatures and has excellent crack and stress resistance.
Encapsulated O-Rings are primarily used as a static seal (axial or radial).
Standard TFE-O-SIL O-Rings in round or square cross-sections are manufactured in sizes to AS 568A industry standards. Non-standard sizes are also available for custom designs, along with a full range of metric (ISO) sizes.
TFE-O-SIL Gaskets provide a superior seal for any bulk liquid transfer in manufacturing, distribution or storage.
The straight lengths can be supplied with “open ends” or “closed ends” providing total encapsulation of the elastomer.
Introducing a foreign material, cyanoacrylate, may cause contamination thru permeation of the FEP or PFA jacket.
Certain chemicals, thru permeation, will attack and break down the glue, causing premature seal failure.
The quick glue bond is dramatically weakened during a rise in temperature and breaks down completely nearing 400°F; whereby the elastomer shrinks and the joint separates leaving a gap between the ends of the Viton cord.
When heating and stretching a glued O-Ring to fit over a shaft, the bond may break.
Insist on ROW, Inc. TFE-O-SIL® vulcanized encapsulated O-Rings! Ask your supplier what method they use to join the ends of their Viton encapsulated O-Rings…or simply run your own test by placing the O-Ring in an oven at 350°F for only 15 minutes. It will be clearly visible that the splice has completely separated, creating a gap or potential leak path.
The air gap allows considerably more compression set and reduces the resilience of the encapsulated O-Ring, resulting in premature leakage.
Run compression tests to compare TFE-O-SIL encapsulated O-Rings with other supplier O-Rings…or specify ROW TFE-O-SIL O-Rings which have no air gap.
Note: All decimal equivalents are rounded to the fourth.
Available Cross Sections for Encapsulated O-Rings and Groove Design Data
|CROSS SECTIONS (A)
|CROSS SECTIONS (A)
*PFA / Silicone Only
Cross Section Tolerances
|.063″ – .125″||±.004″||±.006″|
|.126″ – .139″||±.005″||±.008″|
|.140″ – .210″||±.006″||±.010″|
|.211″ – .275″||±.007″||±.012″|
|.276″ – .312″||±.012″||±.015″|
|.313″ – .350″||±.015″||±.020″|
|.351″ – .500″||±.020″||±.030″|
|.501″ – .787″||±.025″||±.035″|
|.788″ – .1.000″||±.035″||±.050″|
|1.001″ – 1.250″||±.050″||±N/A|
Instructions for Installing TFE-O-SIL O-Rings
Any surface in direct contact with the O-Ring should be smooth and free from sharp edges, burrs and deep scratches. A 20 micro-inch finish is recommended.
If it is difficult to install the O-Ring over a shaft, it may be “stretched” by first immersing the O-Ring in boiling water for a few minutes. This softens and enlarges the O-Ring. After installation, it may be necessary to apply heat to the O-Ring once again so it will shrink back to a tight fit when cooled.
Do not bend the O-Ring too sharply as the Teflon will tend to kink under the strain, however, if it does become kinked, it will not affect the operation in most applications.
Sealing with Teflon encapsulated O-Rings is sometimes a little different than sealing with rubber O-Rings. A rubber O-Ring will readily flow into imperfections of sealing surfaces. Teflon, being harder, takes time to flow into imperfections. The O-Ring may leak on initial start-up. To correct this situation if it occurs after installing the O-Ring, allow it to rest in place under load for a few hours or overnight. This allows the Teflon to coldflow and fill voids for proper sealing on start-up. Another method is to install a pre-heated O-Ring, and allow to cool under load. The heated O-Ring is softer and flows quicker into imperfections.
Within normal use temperatures, Teflon is attacked by so few chemicals that it is easier to describe the exceptions rather than list the chemicals with which Teflon is compatible. Teflon should not be used with the following:
1. Alkali metals such as elemental sodium, potassium, lithium, etc. These alkali metals remove fluorine from the polymer molecule.
2. Extremely potent oxidizers, fluorine (F2) and related compounds (e.g., chlorine trifluoride, CIF3). These can be handled by Teflon, but only with great care, as fluorine is absorbed into the resins, and the mixture becomes sensitive to a source of ignition such as impact.
3. 80% NaOH or KOH, metal hydrides such as borances (e.g., B2H6), aluminum chloride, ammonia (NH3), certain amines (R-NH2) and imines (R-NH) and 70% nitric acid at temperatures near the suggested service limit.
Design and engineering assistance is available from TFE-O-SIL at no charge. However, any selection or application suggestions offered by TFE-O-SIL, are only to assist the customer…and in ALL CASES, determination of fitness for purpose or use is solely the customer’s responsibility.
Hints for Inserting Coupling Gasket
Teflon encapsulated coupling gaskets are more rigid than plain elastromeric gaskets due to the Teflon encapsulation and are therefore a little more difficult to insert. After installing just a few, you will be an expert.
Insert gasket perpendicular to opening with OD of gasket 90° from the locking arm holes to prevent damage to Teflon. Tip gasket and insert lower part of gasket into groove directly under 1 locking arm hole. Cover the other locking arm hole with a thin flat object such as a 6″ stainless steel pocket rule and work balance of gasket, starting from the part already in the groove, past the covered locking arm hole and into the groove.
Teflon encapsulated coupling gaskets are far superior to other gasket materials when used in corrosive applications.
When you take a straight length of elastomer cord and FEP or PFA tubing, and form it into the shape of an o-ring, the mechanical stresses placed upon the elastomer dictates that the cross section will not remain ROUND, but become OVAL.
This is particularly relevant on encapsulated o-rings with small inside diameters on all cross sections; but especially on large cross sections. (Standard elastomeric o-rings are molded; therefore this condition is not present).
The o-ring cross section will become oval with an enlargement of the axial cross section; and a reduction in the cross section to the radial axis. (see diagram A) Without knowing the intended application (axial or radial seal), the only method that can be used to determine the correct dimension, is to apply the average cross section measurement from the axial AND the radial axis. The average of these 2 figures is used to determine if the o-ring is within manufacturing standards.