SUPPORT AS-OIL FILTER 4597541 - Caterpillar

Head Seal and/or Backup Ring Extrusion
Indications
Ribbons of material that flowed into the clearance between the head and the cylinder tube are present at disassembly.
Large amounts of material are missing on the low-pressure side of the head seal O-ring.Possible Root Causes
Head seal extrusion is caused by oil pressures that are too high.
Head seal extrusion failures can also occur if the tube bore is too large. Head seal extrusion failure can also occur if the diameter of the land behind the seal is too small (extrusion gap is too high).
Some failures have been attributed to the stretch of head bolts on the bolted cylinders. Threaded gland cylinders have had failures because of the expansion of the tube at high pressures.RemedyIf the backup ring is extruding use a ring made of a harder material. Reduce the pressure around the head seal if the ring is extruded. Tighten the threaded gland cylinder heads to the proper torque after resealing.Piston Seal Drift
Dieseling
Illustration 23 g03361786
Piston Seal Ring damaged by Dieseling.
Illustration 24 g01202479
Piston Seal Ring Damaged by Dieseling at the Step Cut.
Indications
The cylinder drifts at a high rate.
Oil temperatures are elevated due to flow of oil through small clearances at high pressure.
The piston seal ring or rubber expander ring is eroded in a finger-like pattern. The area around the erosion is blackened and sometimes smells burnt.Possible Root CausesWhen air or other entrained gases that are saturated with oil vapors form in the hydraulic oil, dieseling occurs. When these bubbles are compressed, at a high rate the gases ignite due to adiabatic heating. The resulting explosion erodes adjacent components, especially nonmetallic parts. Refer to Illustrations 23 and 24.RemedyAll efforts should be made to remove air or other entrained combustible gases from the system after resealing a cylinder before using the machine. Extend and retract the cylinders several times before heavy work is done to force air back to the tank.Explosive Decompression
Illustration 25 g01202522
Piston seal expander ring heavily damaged by explosive decompression.
Indications
The cylinder drifts at a high rate.
The rubber expander ring has large chunks of material missing. Refer to Illustration 25.
There is no smell of burning or damage to the seal ring.Possible Root CausesExplosive decompression (ED) occurs when gases that have penetrated into a rubber expander ring suddenly expand due to a rapid drop in hydraulic oil pressure. Also when voiding occurs in the cylinder. The rapid expansion of the entrained gas bubble pops a chunk of material out of the rubber ring. If the damage accumulates, the ring can no longer properly seal.RemedyAll efforts should be made to remove air or other entrained gases from the system after resealing a cylinder before using the machine. Extend and retract the cylinders several times before heavy work is done to force air back to the tank. Refer to the cylinder removal and install procedure for the specific model for more specific instructions. Use dieseling/ED resistant piston seals. These seals are made of a rubber material designed to be less permeable to gases in the hydraulic oil. Use protection piston seal backup