CUP 8J6314 - Caterpillar

Carryover of oil occurs as a normal part of air compressor operation. A high percentage of complaints that are related to air systems are due to a concern of excessive carryover of oil. This document will outline the procedures that must be used in order to accurately troubleshoot the root causes of excessive carryover of oil.Air compressors rely on carryover of oil in order to provide lubrication to the compressor's pistons, valves, and piston rings. The discovery of lubricating oil at the inlet port, or the discharge port, of the air compressor could be an indication of normal operation of the compressed air system.The presence of lubricating oil at these other components within the air system may also be an indication of proper system operation:Air dryers - Most desiccant air dryers incorporate a separator, or a filter, that is used to remove liquid oil from the compressed air. The proper operation of the air dryer minimizes the amount of oil that passes through the system to the supply reservoir. The oil, and moisture, that is allowed to collect in the air dryer is periodically purged from the dryer. Ensure that the drain for the dryer is in a location that will not allow the system to be purged onto other components. If the air dryer is purged onto the fuel tank or onto the fender, the concern over excessive carryover of oil is sure to be amplified.Aftercooler - Aftercoolers are occasionally used in order to cool the air that is used by the compressed air system. Aftercoolers that utilize condenser assemblies to cool the air may replace the air dryer completely. Many aftercoolers utilize designs that promote the collection of oil and moisture. Collection of a small amount of carryover of oil in this type of aftercooler will indicate the proper operation of the aftercooler. The location of drain cocks, or valves, that are used for expelling the contaminants from the aftercooler should be considered during the investigation of a complaint that involves excessive carryover of oil. Ensure that the drain for the aftercooler is not in a location that may amplify the concern of excessive carryover of oil.Supply reservoir - The supply reservoir is also a system component that has been designed to collect oil and moisture. Again, ensure that the drain for the supply reservoir is not in a location that may amplify the concern of excessive carryover of oil.Use the drain intervals that are specified in order to verify that your compressor may be producing an excessive carryover of oil. Information that is specific to your application can be found in the manufacturer's service manual.Identifying Excessive Carryover of Oil
As a preliminary check, you are instructed to perform a walk-around inspection. A visual inspection of the air system will allow you to identify system problems such as fluid leakage or air restrictions.Excessive carryover of oil will be identified by evaluating the quantity of oil that is produced by the system during a specific interval of time.Use