How should compressor oil be properly replaced?
Release date:
2024-04-25
How to properly change compressor oil? Let’s find out together!
Most compressor manufacturers specify oil‑change intervals in their respective manuals. However, basing oil changes solely on operating hours is not entirely reasonable, as compressors of the same type can experience varying degrees of lubricant degradation depending on their operating conditions. Consequently, determining appropriate oil‑service intervals and establishing clear oil‑change criteria is a critically important issue.
1. Oil change criteria for compressor oil:
(1) Oil‑injected compressors: For high‑pressure applications, internal lubrication is provided by the cylinder, with oil‑contaminated lubrication used for primary lubrication; for low‑pressure applications, both the cylinder and bearings are lubricated externally, with oil‑change quality criteria as follows: viscosity change greater than ±15%, acid value greater than 2.0 mg KOH/g, residual carbon greater than 1.0%, and n‑heptane insolubles greater than 0.5%.
(2) Rotary compressors: rotor and bearings—oil‑change quality criteria are: viscosity change exceeding ±15%, acid value greater than 0.5 mg KOH/g, and n‑heptane insolubles exceeding 0.2%. (3) Velocity‑type compressors: seals and bearings—oil‑change quality criteria are: viscosity change exceeding ±15%, acid value greater than 0.5 mg KOH/g, and n‑heptane insolubles exceeding 0.2%.
2. Oil‑change criteria for light‑load rotary air compressors: at 40°C, the kinematic viscosity change exceeds ±10%; the acid value increase is greater than 0.2 mg KOH/g; the n-pentane insolubles exceed 0.2%; and the lubricant’s oxidation stability is less than 50 minutes (SH/T 0193).
3. Oil‑change criteria for ammonia‑resistant compressor oil: the rate of change in kinematic viscosity at 40°C exceeds ±10%; the increase in acid value is greater than 0.2 mg KOH/g; the open‑cup flash point is 8°C lower than the new‑oil standard; water content exceeds 0.1%; demulsibility time is longer than 80 minutes; the liquid‑phase rusting test (using a 15‑steel rod, 24 hours, in distilled water) shows rust formation; oxidation stability is less than 60 minutes; and the ammonia‑resistance test is failed.
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