4. Oil change standard

In the article "Research on the scientific standard of compressor oil change", the author said that the appearance of the standard of compressor oil change is that there is more sludge and sediment, and the color is dark black. Oil change should be considered for emulsification.
The quantitative description shall be:
1) Chromaticity change greater than 3;
2) The change rate of kinematic viscosity (100 ℃) is 20%.
3) It is more appropriate for the increase of acid value of compressor oil change index to be greater than 100%;
4) Oil change standard of light load oil injected rotary air compressor oil SH / T 0538 about n-pentane insoluble matter,% greater than 2.0;
5) The specified value of min for oxidation stability (rotating oxygen bomb) in the oil change standard SH / T 0538 for light load oil injected rotary air compressor oil is 60;
6) Oil change standard iron content/(μG /g) is 200;
7) Standard silicon content of oil change/(μG/g) is 50.
Among these indexes, kinematic viscosity should be the first. Users can test the viscosity change of compressor oil by themselves or by commission. Larger enterprises may have lubricating oil kinematic viscosity tester, which can be tested by themselves; General users may wish to take oil samples and entrust the local technical supervision and Inspection Bureau or the unit with kinematic viscosity tester for testing.

5. Oil selection reference

Generally, oil III can be selected. The antioxidant capacity of oil III measured by rotating oxygen bomb is 6 ~ 7 times that of class II base oil. It can be imagined that its service life is much longer than that of compressor oil dominated by class II base oil.
The ultra-high performance compressor oil based on oil III, combined with Pao and ester oil and equipped with super antioxidant, antifriction agent, anti-wear repair agent and other additives can meet the needs of more than 90% of high-energy air compressors.

6. Timing of oil change

Fixed Time and Simple Floating Time
1) Lubricating oil suppliers will tell users the service life of a compressor oil, and some users are confused to fix the oil change time according to the lubricating oil life recommended by the supplier.
There are many problems here: the compressor oil supplier does not promise the service temperature and corresponding service life of his compressor oil; The service life of different compressor oils varies greatly due to the use of different base oils and additives. The author explained this in the article "current situation and development of domestic ultra long life compressor oil" in the 7th issue of 2015, but due to the length of the article, the discussion on this problem is not enough.
When the working temperature of class I, II, III and IV compressor oil is above 60 ℃, the service life will be halved for every increase of 8 ~ 10 ℃, that is, the service life of compressor oil working at 90 ℃ is 50% of that working at 80℃.

2)When purchasing compressor oil, compressor users should clarify the service temperature and corresponding service life of the purchased compressor oil. In this way, the compressor user can flexibly grasp the actual working temperature of the compressor according to the relationship between the working temperature and service life of the compressor oil, and adopt the floating service life of the compressor oil - this is scientific, economical, reliable and practical.

7. Oil change method

When changing the oil for the compressor, if the dirty oil or spent oil is not cleaned up, the newly added compressor oil will be polluted, which can introduce a large number of free radicals and accelerate oxidation. As a result, the service life of the newly added compressor oil will be reduced by half. This is equivalent to putting a pot of freshly cooked dishes into a container with rancid leftovers. The taste changes and the dishes deteriorate faster.
In order to achieve good oil change effect, the following countermeasures are available:
Countermeasure 1: carefully clean the oil separator, oil pipeline and oil cooler. When changing the oil, drain the spent oil first, and carefully clean the shell of the oil-gas separator when changing the elements of the oil-gas separator; Determine whether it is necessary to purge the oil cooler according to the situation, and then change the oil after cleaning.
Countermeasure 2: add 3 ~ 5% cleaning agent to the old oil of the compressor. After running for 6 ~ 24 hours under normal working conditions, drain all oil products in the system. After replacing the oil filter and oil-gas fine separator elements, add new compressor oil and start up to operate normally. If the system has not been cleaned for a long time due to the use of mineral oil or poor quality oil, the cleaning time can be appropriately extended, generally 2 ~ 3 days, which has no impact on the system; If a large amount of oil sludge, carbon deposit or colloid suspension is washed out during the period and the filter is blocked, the system may trip. At that time, a new filter shall be replaced for cleaning.
Countermeasure 3: drain the spent oil of the compressor, add 5# spindle oil, drain (drain) after 5 ~ 10 minutes of low-pressure operation, and then add new compressor oil. Keep the discharged spindle oil properly (it should be stored in a plastic bucket with 5 gallons of purified water. When it is used next time, the sediment can be removed) for the next oil change. There is no need to worry about low flash point of spindle oil, large flow of spindle oil with low viscosity, low exhaust temperature, high flushing speed and easy to clean;
Countermeasure 4: drain the spent oil of the compressor, add 5# spindle oil, drain (drain) after 5 ~ 10 minutes of low-pressure operation, blow the oil pipeline (including oil cooler) and oil-gas separator with compressed air or bottled nitrogen, and add new compressor oil after blowing.
Countermeasure 5: qualified users can contact a high-level professional lubricant service provider and entrust it to clean the compressor oil circuit and change the oil.  Countermeasure 6: after adding new oil, add SL anti-wear repair agent with 0.5% of the weight of new oil, which can not only prolong the service life of bearing, but also double the service life of air compressor oil because SL anti-wear repair agent contains antioxidant.

8. Conclusion

8.1. There are many strange compressor oils in the market, and it is difficult for users to choose products with high cost performance. The way to make up for it is to learn more and understand more, be careful to be deceived, and there are many problems and hidden dangers of "three no oil products" and "black heart oil";
8.2. The service life of compressor oil mainly depends on base oil and additives. The service life of compressor oil with different formulations varies greatly, which should be carefully selected by manufacturers and compressor users;
8.3. The real life of compressor oil is also related to the model, configuration and working condition parameters of the compressor;
8.4. The real life of compressor oil is closely related to the oil change method. Good oil change methods and measures can double the real life;
8.5. Mastering the comprehensive compressor oil change technology and careful operation can really prolong the service life of compressor oil by about 5 times;
8.6. The real life of oil injection screw air compressor oil needs scientific, reasonable and effective simulation bench test method, which needs to be accurately determined after test and analysis.

Previous:  Great Knowledge of Elang Screw Air Compressor Oil Change (Part One)