Usage:
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Reference: Service Magazine; December 9, 1985, Page 2; "New Ratchet Wrenches Available For Tube Fittings".
Reference: Caterpillar Service Technology Group promotional ad, "Ratchet Wrenches for Tube Fittings", NEDG5005. Torque Specifications, SENR3130, for all Service Manuals.
Face-type seals and connectors for tubes and hoses that carry fluids are being phased into many existing systems, and are already used in most new products. Several million of these seals and connectors will be used each year in Caterpillar products, and most servicemen, if not already, will be servicing these seals and their fittings.
Some face-type seals have leaked because of incorrect assembly. Also, difficulties in assembling of these joints have been reported. This article provides brief features of the seal and joint design, new recommendations for assembly, and tools available from Caterpillar to use on these fittings. The correct use and assembly of these fittings provides a reliable leak-free joint and will be more economical than other fittings in the long run.
Seal And Joint Design
The face-type seal and joint combination provide a reliable, leak-free seal at higher operating pressures than the metal-to-metal JIC (Joint Industry Council) 37° flare-type fittings. When a JIC fitting is retightened to stop a leak or seepage, the metal-to-metal surface is slightly deformed because of overtightening, and the leak probably will resume later. In some cases, the leak may be cause by an irregularity (scratch, nick, etc.) in the sealing surface. Retightening in this case will not cure the problem. Illustration 1 compares the flare-type joint to the face-type seal joint.
Illustration 1. Comparison of the face-type seal joint with the former flare-type joint commonly used by Caterpillar.
The face seal joints can endure higher pressure spikes and vibration forces. Service problems, downtime, and oil and fuel leaks are minimized.
Some other advantages of the face-type seal are:
... Sealing up to 41 250 kPa (6000 psi). JIC fittings are not recommended for pressures above 20 625 kPa (3000 psi).
... Connections can be made and broken without disturbing nearby plumbing.
... Reduces problems of misalignment during reassembly.
... Retightening to stop leaks is not required.
... Less sensitive to overtightening.
... If not damaged when the joint is disconnected and reconnected, the metal parts have unlimited reuse.
As shown in Illustrations 1 and 2, the O-ring seal fits in an annular groove in one end face of the connector (or fitting). When the nut on the mating part is tightened on the connector (or fitting), the two mating faces come together and the O-ring seal is retained tightly in its groove.
Illustration 2. Face-type seal joint for a hose or tube.
Face-type seals on machines in the field can be either an O-ring or a square section type. See Illustration 3. (Only the O-ring seals are now used in production.) Either seal will work, provided the seal is the right size for the groove. Be sure you use the seal identified by the part number in the Parts Book. Do not be confused by the descriptions of the seals, because in some cases a square seal installed as the original part at the factory will be identified as a "Seal, O-ring" in the Parts Books.
Illustration 3. Cross-section view of face-type seals.
Assembly Recommendations
These joints can be assembled dry when the joint is in the horizontal position. When the joints are vertical or overhead, use either the 1U6396 or 1U6395 O-ring Compound now available. This is a tacky, gel compound which keeps the seal in the annular groove during assembly. The 1U6396 Compound is a 226 g (8 oz) tube, and the 1U6395 Compound is a 3.8 liter (1 gal) container with a pump.
Apply this tacky compound sparingly, preferably with your fingers. Or, smear the compound on a flat surface, and lightly press the seal into the compound. Do NOT brush on this compound. Always install the seal with its coated side toward the groove.
NOTE: Too much compound on the seal can cause the seal to be displaced during assembly of the joint. Both the seal and compound should be only in the groove. Keep this compound off all threads. Do not use grease or petroleum jelly because either one can later melt due to normal operating temperatures, seep out of the joint, collect dirt, and give a false indication of a leak.
1. Place the tacky seal in the groove. When installed, the seal should be slightly above the joint surface. If not, either an incorrect seal is being used, or the groove is not machined correctly.
2. Align the mating parts of the joint and assemble from a straight position.
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Do not slide the hose or tube coupling face across the seal during assembly. If necessary, temporarily remove any hose clips that might prevent moving the coupling face to get good alignment. This helps to prevent cutting or pulling the seal out of the groove. Reinstall the clips.
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3. When a nut for a hose connection is tightened, hold the hose on the hose assembly flats. See Illustrations 2 and 4. This prevents the face of the hose coupling from turning and cutting the seal. This will also prevent the hose from twisting during assembly. It is not necessary to hold tubes during reassembly because they are strong enough to resist turning or twisting when normal tightening torques are used.
Illustration 4. This shows holding the hose to prevent it from turning when the face seal is tightened. Note the new tube-type ratchet wrench with its square drive hole for a torque wrench.
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Twisting a hose assembly when the fitting is tightened can cause the hose to loosen when the hydraulic system is cycled during operation. Twisting also shortens hose life. When installing hoses with angle couplings, hold the hose in position with your hands as the joint nut is tightened.
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Special Ratchet Wrenches For Tube Fittings
The right tool for any job is critical to get the machine back to work with minimum downtime and cost. Ratchet wrenches, made specifically for tube fittings, are available from Caterpillar. Simply snap open the large jaw, engage it on the fitting or nut, snap it closed, and turn the wrench. See Illustrations 5 and 6.
Illustration 5. The ratchet wrench groups for tube fittings available from Caterpillar.
Illustration 6. Typical use of one of the special fitting wrenches.
These wrenches are available in a wide range of sizes, either in groups or individually. One group of wrenches has handles for use with a torque wrench. (See Illustration 3.) For more details, read the Referenced Publications.
Face-type seals require a certain torque to prevent leaks, and when retightened, the torque need not exceed this amount. Service Manual Module SENR3130 contains the torque specifications for the seal nut and the connector (fitting end) for face-type seals, as well as most other standard torques. The form has been in all recent Service Manuals and additional copies can be ordered.