Improper diagnosis and maintenance will cause continuous high-temperature alarms, oil filter clogging, and bearing wear on your screw air compressor. In serious cases, it will lead to rotor jamming and unexpected shutdowns. In contrast, the oil free compressor requires no lubricating oil during operation, fundamentally eliminating all oil failure risks.
1. What is the Fundamental Difference Between the Two Types of Faults?
For traditional screw air compressor equipment, oil coking is caused by long-term high-temperature oxidation, while oil emulsification is triggered by moisture ingress. Coking occurs in high-load and overheating working conditions, whereas emulsification often happens during long-term low-temperature and light-load operation. These two typical lubrication failures do not exist in oil free compressor systems.
2. Lubricating Oil Coking: The Final Product of High-Temperature Oxidation
Coking in screw air compressor units is a complex chemical degradation process including oxidation, polymerization, and cracking under long-term high-temperature conditions. As the lubricant ages, it first forms a varnish film, then sticky gum deposits, and finally hard carbon sediment, which is defined as coking.
Main Causes of Coking
First, continuously high discharge temperature is the primary cause. When a screw air compressor runs steadily above 100°C, light oil components evaporate rapidly, and antioxidant additives fail quickly, shortening oil service life drastically. The optimal temperature range is 85–98°C, and the warning limit should not exceed 105°C.
Second, using lubricant beyond its service cycle accelerates aging. Many factories replace oil only by operating hours, ignoring harsh working environments such as high temperature, heavy dust, and full-load operation, which cause screw air compressor oil to fail in advance.
Third, mixing different oil brands leads to chemical reactions, precipitation, and gelation, speeding up carbon accumulation inside the screw air compressor oil circuit.
Common Symptoms
Rising discharge temperature, increased oil filter pressure difference, shorter oil separator lifespan, black carbon sludge inside the main unit, and poor bearing lubrication. These problems form a vicious cycle and greatly reduce the stability of screw air compressor operation.
3. Lubricating Oil Emulsification: Moisture Is the Real Culprit
Oil emulsification is another typical hidden fault of screw air compressor equipment. When external moisture enters the lubricating oil and undergoes high-speed shearing by bearings and gears, the oil turns into an unstable milky emulsion. Normal compressor oil is transparent and yellowish, while emulsified oil appears milky white or cloudy brown and completely loses its lubricating performance.
Main Sources of Moisture Ingress
Long-term low-temperature and light-load operation is the most overlooked cause. When a screw air compressor runs under light load for a long time, the oil temperature remains 60–70°C, which cannot evaporate water vapor. Condensed water accumulates continuously and mixes into the oil circuit. Low-frequency operation, night low-load production, and low winter temperatures all increase emulsification risks.
In addition, blocked or failed automatic drain valves cause condensed water in coolers and oil-air separators to fail to drain, resulting in circulating water pollution throughout the screw air compressor system.
Severe Hazards of Emulsification
Emulsified oil breaks the protective lubricating film, causing boundary friction, viscosity decline, bearing corrosion, and frequent filter clogging. Most premature air-end bearing failures on screw air compressor units are caused by oil emulsification rather than simple oil shortage. As a zero-lubrication device, the oil free compressor completely avoids all these hidden dangers.
4. How to Prevents Coking and Emulsification Precisely
Temperature control is the core of screw air compressor maintenance.
Below 75°C: Prone to emulsification; properly increase operating load
85–95°C: Optimal operating temperature for screw air compressors
Above 100°C: Obvious oxidation acceleration
Above 105°C: High coking risk zone
Many operators misunderstand that lower temperature equals better performance. In fact, only stable and reasonable temperature can keep the screw air compressor lubrication system healthy.
Standard oil replacement procedures are also essential. Simply draining old oil and adding new oil is incorrect. The correct maintenance steps for screw air compressor units include fully draining old oil, replacing filters and separators, flushing residual sludge if needed, draining leftover dirty oil, and finally adding new lubricant. This prevents old oxidation contaminants from polluting new oil.
Conclusion
Lubricating oil is the blood of a screw air compressor. Coking is a high-temperature oxidation problem, while emulsification is a moisture-induced failure. Scientific temperature control, standardized heat dissipation, and strict oil change cycles can effectively reduce lubrication faults. For factories that want to completely eliminate oil coking, emulsification, and oil maintenance costs, upgrading to a high-quality oil free compressor is the most reliable long-term solution.
Excellent equipment operation and maintenance focuses on prevention rather than repair. Regular inspection and fluid analysis keep your screw air compressor running stably, while oil free compressor technology leads the new trend of low-failure industrial air supply.
