Usage:
All Caterpillar Equipment
The Scheduled Oil Sampling (S.O.S.) program is an important tool to find the condition of the oil in the hydraulic system. The amount of wear metals in the oil can give an early indication of when repairs to the hydraulic system components are necessary, so a major failure can be prevented.
The S.O.S. equipment (infrared analysis) can also be used to determine when the hydraulic oil must be changed. The Lubrication and Maintenance Guides recommend that the hydraulic oil be changed every 2000 hours or one year. This change interval gives acceptable performance during normal operation. Some conditions, such as coolant leakage into the hydraulic oil or oil that gets too hot, will make an earlier change necessary. The S.O.S. tests will show if the earlier change is needed.
The oil can also be tested at the 2000 hours or one year interval to determine if the change period can be extended. The tests will give an indication of the level of contamination and other oil properties (characteristics). The results of these tests will show if the oil quality is acceptable for reuse.
For the hydraulic oil to be used beyond the normal change interval, several conditions must be met. First, all test results must be within the acceptable limits of the S.O.S. specifications. There must not be any indication that the oil was too hot during operation. There must be no indication of coolant in the oil.
The tests that follow will give the necessary information to find the condition of the oil.
1. Contamination tests:
... for silicon and wear metals
Use the atomic absorption test to determine the concentration of these wear particles. Remember, a filter change may give a reduction in these particles.
... for water
If this water is caused by the normal "breathing" of the hydraulic tank, there is no practical way to prevent it. The amount of water can be checked by differential infrared spectroscopy or by the sputter test.
... for coolant
Cooler leaks can let coolant enter the hydraulic system. Differential infrared spectroscopy can be used to find coolant in the hydraulic oil. Another test procedure is to use the sputter test to find water in the oil and the chemical test for the anti-freeze.
2. Tests for loss of oil quality:
... oxidation
The rate of oxidation in hydraulic oil is controlled by several factors. One factor is the amount of time that the oil is exposed to (in contact with) the oxygen. Another factor is the oil temperature; higher temperatures cause the oil to oxidize more quickly. Also, oxidation is increased when copper, iron or ethylene glycol are in the oil.
Oxidation is measured by differential infrared spectroscopy. When there is oxidation before the normal change interval the cause is usually high oil temperature.
... additive loss
There are several additives in the hydraulic oil. The most important is zinc dithiophosphate, which controls wear in system components. This additive is especially important for vane pumps.
Differential Infrared Spectroscopy can be used to find a loss of zinc dithiophosphate. The most common reason for loss of this additive is high oil temperature.
When the tests show that the oil has become too hot during operation, it is important to find the source of the heat. It is also important to change the oil and filter when the oil has been too hot.
When hydraulic oil has been tested and used beyond the normal change interval, it will be necessary to test the oil every 500 hours. This must continue until the oil is changed.
Hydraulic oil that has been drained from the machine must be stored in clean containers that have covers, if it is to be reused. The oil must be returned to the hydraulic system through a filtering system with a 10 micron filter. Use of a filter with a smaller micron size can remove additives from the oil. For more information about a pump and filter to service the hydraulic system, see Service Methods and Equipment Bulletins SEBF2201 (dated 11-75) and FEG00019-13 (dated 9-71).