Project Cases

The True Service Life of Compressor Oil

　　The service life of screw compressor oil should be the minimum duration under normal operating conditions. Accurately determining the lubricant’s service interval is challenging, and manufacturers’ specifications vary. Typically: Group I mineral oils are rated for 2,000 hours; Group II mineral oils can last up to 4,000 hours (later reduced to 2,000); Group III mineral oils can reach 6,000 hours (later reduced to 4,000); PAO-based oils may last up to 8,000 hours (though some sources cite 6,000); and polyol ester oils can endure as long as 12,000 hours (with some suggesting 8,000).
　　The service life of compressor oil is specified by the lubricant manufacturer. If the oxidation stability, as determined by the rotary oxygen bomb test, falls below 50 minutes—beyond which the rate of oxidation begins to accelerate (with an oil‑change interval typically set at 60 minutes)—the compressor oil is considered to have reached the end of its service life. The service life of different types of compressor oil varies considerably, and their oxidation stability depends on the nature of the base oil and the formulation.
　　For Class III oils blended with a portion of PAO and ester-based lubricants, the service life of compressor oil can reach 5,000 to 6,000 hours (under air‑compressor discharge pressures of 0.7 to 0.8 MPa). The acid value remains below 2.0 mg KOH/g for at least 10,000 hours, and the rotary oxygen bomb oxidation stability can exceed 1,500 to 2,000 minutes. Note that the two figures—“a service life of 5,000 to 6,000 hours” and “≥10,000 hours”—appear somewhat contradictory; this will be further discussed later.

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The Necessity of Changing the Compressor Oil