2001/07/30 Correctly Assembling the Buffer Seal Will Prevent Failure of the U-Cup Seals {7562} Caterpillar


Correctly Assembling the Buffer Seal Will Prevent Failure of the U-Cup Seals {7562}
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2001/07/30 [SEPD0589]
HYDRAULIC SYSTEM
2002/04/08 New Assembly Instructions for Rod Seals on Hydraulic Cylinders are Available {7562}
2001/07/30 Correctly Assembling the Buffer Seal Will Prevent Failure of the U-Cup Seals {7562}
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  • Incorrect assembly of the backup rings and buffer seals can lead to extrusion of the U-Cup Seal. Early failure of the U-Cup Seal indicates an incorrect assembly procedure of the buffer seal. This will indicate a problem with the buffer seal. The buffer seal reduces the pressure that is transmitted to the U-Cup Seal and the buffer seal absorbs spikes in pressure.




    Illustration 1g00812656

    Damaged U-Cup Seal

    The U-Cup Seal will be deformed into a thin band of material, as shown. This damaged U-Cup Seal appears to be melted due to excessively high temperatures. Extrusion of the U-Cup Seal can occur at any temperature if the pressure is excessively high.




    Illustration 2g00812166

    Correct assembly of the buffer seal (1) and backup ring (2) will prevent failure of the U-Cup Seal (3). The backup ring (2) should be assembled toward the rod end of the cylinder, as shown.

    Note: In some cases, the axial width of the AVSpare U-Cup Seal may be different from the U-Cup Seal that is being replaced. The AVSpare U-Cup Seal is correctly sized, based on the rod diameter and the seal groove diameter. The difference in size of the AVSpare U-Cup Seal will not cause a sealing problem, even though there may be unused space in the seal groove. The U-Cup Seal will not move from the downstream groove wall when the rod is retracting. Pressure will hold the U-Cup Seal against the back of the seal groove. Also, the friction on the outside diameter of the seal is much greater than the friction on the inside diameter, which will also keep the seal firmly seated in the back of the seal groove. Because of these factors, the U-Cup Seal will not touch the upstream side of the seal groove. Therefore, the difference in the axial width between the U-Cup Seal and the seal groove is not a factor in providing good sealing.

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