1.Sealing: They can form a dynamic seal between screws and compression chambers, and between male and female screws, to reduce leakage of refrigerants from the high pressure side to the low pressure side in the compression process.
2.Cooling: They serve to cool down the compressed refrigerants. The lubricants are injected into the compressor to absorb the heat generated by the refrigerant gas in the compression process, and reduce the temperature of the exhaust gas.
3.Lubricating: They can form an oil film between the bearing and screws to support the rotor and play the function of lubricating.
4.Adjusting: They can transfer the force of pressure differences, drive the capacity regulating system and adjust the position of the capacity slider through the actions of loading and unloading the solenoid valve of the compressor, to realize the adjustment of compressor capacities.
5.Reducing operating noise.
II. The lubricants inside compressors are the key to maintain the normal operation of compressors. The general problems of lubricants include:
1.Deterioration of lubricants due to high temperature effects, resulting in the loss of lubrication.
2.Contamination lubricants caused by the entering of foreign matters which blocks the filter.
3.Erosion of the motor due to water pollution and acidification of the system.
III. Instructions for Using Lubricants
Lubricants have a decisive impact on the performances of the main machines of oil-injected screw compressors. Any improper uses or errors may cause severe damage to the compressor; therefore, it is important to follow the following regulations:
1.Our company specially recommends screw compressors; the oil branches are as shown in Table 1.
2.Cautions for Using Lubricants
2.1 The oil grade should meet requirements. It is forbidden to mix lubricants of different types made by different manufacturers, and do not use false or recycled oils.
2.2 Requirements for the features of lubricant are as follows: anti-oxidation, anti-foam, anti-corrosion, abrasion resistance, strong water division, appropriate viscosity, high flash point, and low pour point.
2.3 Do not let lubricants exceed the performance life of the oil branch; otherwise, the quality of the oil will be degraded, and the flash point will also be decreased, which is apt to spontaneous combustion, and thus cause the accidents of burned units.
2.4 Respect the drain intervals. In order to determine the drain intervals according to actual situations, it is recommended to regularly collect oil samples for analysis at an interval of 3-6 months within the previous two years. We will provide technical guidance so as to determine the actual required drain intervals without wasting the oils.
[Note] The running-time for the wear-in of units for the first time is about 500 hours, after which it is necessary to change the oil.
2.5 It is advisable to conduct “cleaning for the system” after a compressor has been used for two years by following the method of twice oil changes in a row. The second time of oil change is conducted six hours after the first-time change.
2.6 It is required to change the oil filter while changing the oil.
3.Factors affecting the time of changing oils
3.1. Poor ventilation, over-high ambient temperature.
3.2. High-humidity environment or rainy season.
3.3. Dusty environment.
3.4. Mixing lubricants of different branches;
Usually, it is required to check or change the lubricant once every 10,000 hours of operation, and after the first operation, it is recommended to change the lubricant and clean the oil filter once every 2500 hours of operation. Because the residues left after system assembly will be accumulated in the compressor after operation, it is necessary to change the oil once every 2500 hours (or 3 months); afterwards, the oil can be changed depending on the cleanliness of the system. If the system is fairly clean, change the oil every 10,000 hours (or a year).
If the discharge temperature of the compressor remains at the high-temperature state for a long time, the deterioration progress of the lubricant will get faster; it is necessary to check the chemical properties of the lubricant on a regular basis (every two months), and change it when it does not comply with the standard. If it is not possible to conduct regular check, refer to the recommended values in the following table for operations.
Exhaust temperature during operations (℃)
Replacement time (hours)
Replacement time (operation months)
Note: The operation period is calculated by 16 hours/day
IV. Replace frozen lubricant and make internal cleanup:
The action for releasing the oil is as mentioned earlier. After the refrigeration oil is excluded clean and the internal and external pressures of the compressor have reached a balance, use a hex wrench to loose the flange bolts. After the connector of the oil filter and the flange in the cleaning hole (or the flange on the oil level switch) are removed, remove the contaminants in the sump of the compressor and check whether the meshed screen of the oil filter has any damages, and then blow off the sludge and pollutants on it, or replace it with a new oil filter. Please be noted that when replacing it with a new filter, screw tight the nuts on the port of the filter and seal it well to prevent internal leakage; the inside gasket of the oil filter connector must be replaced with a new one to prevent internal leakage; it is also recommended to change other flange gaskets.
1. Do not mix frozen lubricants of different branches, especially mineral oils and synthetic ester oils, which should never be mixed.
2. When replacing the frozen lubricant with a different branch, make sure to discharge the remnants of the original frozen lubricant in the system.
3. Because some oil branches have the hydroscopic property, do not expose freeze oil to the air for a long time. During the installation, try to shorten the time of exposure as much as possible, and conduct vacuuming properly.
4. If such an accident as burnt compressor motor has occurred before, pay special attention to removing the acidic remnants in the system when replacing the old motor with a new one, and check the acidity of the refrigeration oil 72 hours after the debugging operation. It is recommended to replace the refrigeration oil, dry the filter, and reduce the potential etching. After that, run the system for about a month before re-test it or replace the refrigeration oil once again.
5. If such an accident as water seepage has occurred to the system, pay special attention to removing the water completely; in addition to replacing the refrigeration oil, it is necessary to pay special attention to checking the acidity of the oil, replace it with new oil and dry the filter promptly.