2010/04/30 Caterpillar

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ReferenceApplied Failure Analysis, REHS2811, "Hydraulic Cylinder Seal Failure Analysis"

The hydraulic cylinders may make noise during cylinder movement. The noise may be due to uneven surface on the outside diameter of the nylon seal ring. The uneven surface must be reworked to maintain proper contact with the inside diameter of the cylinder assembly so that the noise can be reduced. The nylon seal ring is a part of the seal assembly that is used in the piston.

Illustration 1	g02149531
Cross-section of seal assembly (1) Nylon seal ring (2) Seal expander

Use the following rework procedure in order to correct the uneven surface on the outside diameter of the nylon seal ring:

Note: 100 percent clean-up of the nylon seal ring is not required. The nylon seal ring must only be reworked circumferentially. It is not recommended to rework the nylon seal ring in an axial direction. Reworking the nylon seal ring in an axial direction will promote oil bypass. This procedure can be applied to any nylon piston seal ring. This procedure should not be used on piston seals that use the polyurethane or PTFE ring.

1. Use a sheet of 120-grit emery paper attached to a sanding block in order to rework the nylon seal ring.

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Illustration 2	g02149290
Outside view of the nylon seal ring

2. Lightly drag the sanding block over the surface on the outside diameter of the seal in a circumferential pattern as shown in Illustration 2.

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Illustration 3	g02149520
Removal of high spots from sanding

3. The sanding removes the high spots and high corners on the seal ring so that the uniform contact surface is obtained. The sanding of the nylon seal ring also provides a better surface for lubricant to be carried on between the seal ring and the inner stage seal surface.

4. The nylon seal ring should be reworked lightly until the continuous contact can be seen around the circumference.

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Illustration 4	g02149291

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Illustration 5	g02149524

5. After sanding the surface on the outside diameter on the nylon seal ring the surface should be as shown in Illustration 4 and Illustration 5.