Brief Analysis of Excessive Oil Consumption of Air Compressors and Pre-Fault Warning Signs
Oil carryover is a common problem encountered in daily operation of air compressors. Apart from quality defects of the oil separator itself, there are other potential triggers. Engineers have summarized multiple causes for oil carryover from field practice.
Failures of air compressors seldom occur abruptly; they are usually preceded by certain warning signs, which may manifest as abnormal phenomena or numerical changes on instruments. This article discusses various precursors prior to air compressor failures, providing references for users to predict equipment faults and arrange maintenance in advance.
1. Improper Design of Oil-Gas Separation Tank
Some air compressor manufacturers adopt unreasonable primary separation systems in oil-gas separation tank design, resulting in poor primary separation effect. The oil mist concentration is excessively high before the gas enters the oil separator, which overloads the separator and exceeds its processing capacity, leading to excessive oil consumption. No matter how skilled the operators are, this problem cannot be eliminated once such equipment is purchased.
2. Overfilling of Lubricating Oil
If the lubricating oil level exceeds the normal range, part of the oil will be entrained by airflow and cause high oil consumption. This simple cause is often overlooked due to careless operation.
3. High Air Consumption and Overloaded Low-Pressure Operation
Overloaded low-pressure operation means the actual discharge pressure fails to reach the compressor’s rated working pressure yet still meets the basic air demand of enterprises. For example, enterprises add more pneumatic equipment and increase air consumption, breaking the balance between compressor output and actual air demand. Assume the rated discharge pressure of the air compressor is 8 kg/cm², while the actual operating pressure is only 5 kg/cm² or even lower. The compressor runs under sustained overload and cannot reach rated pressure, hence higher oil consumption.
Under constant displacement, the flow velocity of oil-gas mixture passing through the oil separator rises, and oil mist concentration increases. This overloads the oil separator and eventually causes excessive oil carryover.
4. Clogged Oil Return Line
When foreign matter blocks the oil return pipeline (including the check valve and filter screen on the pipeline), lubricating oil condensed at the bottom of the oil separator cannot flow back to the compressor main unit. The condensed oil droplets are blown up by airflow and discharged together with separated air. Such blockages are generally caused by solid impurities falling off during installation.
5. Damaged Oil Return Check Valve
If the oil return check valve fails and changes from unidirectional flow to bidirectional flow, the internal pressure of the oil-gas tank will push a large amount of lubricating oil back into the oil separator through the oil return pipe after shutdown. During the next startup, the oil accumulated inside the separator cannot be sucked back to the main unit in a timely manner, and part of the oil will escape out of the compressor along with separated air. This fault frequently occurs on units without oil circuit shut-off valves and main unit discharge check valves.
6. Improper Installation of Oil Return Pipe
During replacement, cleaning or maintenance of the air compressor, if the oil return pipe is not inserted close to the bottom of the oil separator (recommended distance: 1~2 mm from the arc center of the separator bottom), separated lubricating oil cannot flow back to the main unit promptly. Accumulated oil will be carried away by compressed air.
7. Malfunction of Minimum Pressure Valve
If the sealing surface of the minimum pressure valve leaks or the valve opens prematurely (the opening pressure varies among manufacturers, normally ranging from 3.5 to 5.5 kg/cm²), it will take longer for the unit to build pressure inside the oil-gas tank during startup. At low pressure, gas carries high-concentration oil mist and flows through the oil separator at high speed. The oil separator is overloaded, separation efficiency drops, and oil consumption rises sharply.
Pre-Fault Warning Signs of Air Compressors
I. Abnormal Noise and Vibration
Unusual noise during operation acts as an "alarm" for equipment faults. Severe vibration may also occur.
Possible causes of abnormal noise:
Worn main bearings, unbalanced rotating shafts, damaged male and female rotors;
Excessive load on the main unit, pressure trapping or unbalanced pipe network pressure;
Loose bolts, nuts, gaskets and fixing supports;
Foreign objects falling into the equipment;
The compressor unit approaching its major overhaul interval. The axial and radial float of screws gradually reaches the maximum allowable design value. This significantly changes the clearances between screws, between screws and the casing, as well as front and rear end covers, triggering friction, vibration and various abnormal noises.
II. Leakage of Oil, Water and Compressed Air
Leakage of lubricating oil, circulating cooling water and other media;
Visible compressed air leakage with audible hissing sound.
Leakage problems mainly stem from aging equipment and spare parts or inadequate maintenance, including improper and careless operation by staff. These seemingly minor issues may lead to severe hidden consequences.
Taking compressed air leakage as an example: leakage directly wastes substantial electric power and increases electricity costs. It also causes pressure drop in the system, reduces efficiency of pneumatic equipment and shortens service life. In addition, air leakage leads to more frequent equipment cycling, extending the running time of air compressors, which brings extra maintenance work and potential unplanned shutdowns. In short, compressed air leakage creates unnecessary demand for compressor capacity.
Combined with the common problem of system operating pressure higher than required, leakage will cause so-called false demand, keeping the air compressor loaded continuously without rest.
All these factors negatively affect production efficiency and shorten the service life of nearly all system equipment and pneumatic tools. Extra energy consumption and accelerated equipment aging form a double blow to factory operators, which must be taken seriously.
III. Peculiar Odors
Special odor generated when the motor overheats or lubricating oil enters the cylinder and burns;
Burnt smell from damaged insulating materials caused by short circuit or ground fault of circuits;
Burning odor emitted by rubber and similar materials.
According to media reports, on May 25, 2017, a gas leakage incident took place in the workshop of Kocheng Technology (Suqian) Co., Ltd. in Suqian. More than 80 employees were hospitalized due to physical discomfort after inhaling certain gas.
Subsequent investigation by the Administrative Committee of Suqian Susu Industrial Park confirmed that this accident was a secondary incident triggered by mechanical failure of the air compressor. The screw bearing of the power air compressor was worn, resulting in seizure between the bearing housing and screw shaft. Massive heat generated by friction cracked lubricating oil inside the screw cylinder, producing small-molecule hydrocarbons as well as sulfur, phosphorus compounds decomposed from additives. These irritant gases spread through compressed air pipelines to workstations and the workshop, causing discomfort among operators.
This accident with multiple hospitalized staff caused by peculiar odor from an air compressor tells us: even if faults have already occurred when odors are detected, peculiar smells can help us quickly locate fault causes and positions, serving as a warning for all users.
Conclusion
Air compressor failures rarely happen suddenly; they are always accompanied by warning signs in the form of abnormal phenomena or changing instrument readings.
Therefore, we must stay alert to all kinds of pre-fault signals, helping operators and maintenance personnel detect potential accidents at an early stage and prevent failures before they occur.
Failures of air compressors seldom occur abruptly; they are usually preceded by certain warning signs, which may manifest as abnormal phenomena or numerical changes on instruments. This article discusses various precursors prior to air compressor failures, providing references for users to predict equipment faults and arrange maintenance in advance.
1. Improper Design of Oil-Gas Separation Tank
Some air compressor manufacturers adopt unreasonable primary separation systems in oil-gas separation tank design, resulting in poor primary separation effect. The oil mist concentration is excessively high before the gas enters the oil separator, which overloads the separator and exceeds its processing capacity, leading to excessive oil consumption. No matter how skilled the operators are, this problem cannot be eliminated once such equipment is purchased.
2. Overfilling of Lubricating Oil
If the lubricating oil level exceeds the normal range, part of the oil will be entrained by airflow and cause high oil consumption. This simple cause is often overlooked due to careless operation.
3. High Air Consumption and Overloaded Low-Pressure Operation
Overloaded low-pressure operation means the actual discharge pressure fails to reach the compressor’s rated working pressure yet still meets the basic air demand of enterprises. For example, enterprises add more pneumatic equipment and increase air consumption, breaking the balance between compressor output and actual air demand. Assume the rated discharge pressure of the air compressor is 8 kg/cm², while the actual operating pressure is only 5 kg/cm² or even lower. The compressor runs under sustained overload and cannot reach rated pressure, hence higher oil consumption.
Under constant displacement, the flow velocity of oil-gas mixture passing through the oil separator rises, and oil mist concentration increases. This overloads the oil separator and eventually causes excessive oil carryover.
4. Clogged Oil Return Line
When foreign matter blocks the oil return pipeline (including the check valve and filter screen on the pipeline), lubricating oil condensed at the bottom of the oil separator cannot flow back to the compressor main unit. The condensed oil droplets are blown up by airflow and discharged together with separated air. Such blockages are generally caused by solid impurities falling off during installation.
5. Damaged Oil Return Check Valve
If the oil return check valve fails and changes from unidirectional flow to bidirectional flow, the internal pressure of the oil-gas tank will push a large amount of lubricating oil back into the oil separator through the oil return pipe after shutdown. During the next startup, the oil accumulated inside the separator cannot be sucked back to the main unit in a timely manner, and part of the oil will escape out of the compressor along with separated air. This fault frequently occurs on units without oil circuit shut-off valves and main unit discharge check valves.
6. Improper Installation of Oil Return Pipe
During replacement, cleaning or maintenance of the air compressor, if the oil return pipe is not inserted close to the bottom of the oil separator (recommended distance: 1~2 mm from the arc center of the separator bottom), separated lubricating oil cannot flow back to the main unit promptly. Accumulated oil will be carried away by compressed air.
7. Malfunction of Minimum Pressure Valve
If the sealing surface of the minimum pressure valve leaks or the valve opens prematurely (the opening pressure varies among manufacturers, normally ranging from 3.5 to 5.5 kg/cm²), it will take longer for the unit to build pressure inside the oil-gas tank during startup. At low pressure, gas carries high-concentration oil mist and flows through the oil separator at high speed. The oil separator is overloaded, separation efficiency drops, and oil consumption rises sharply.
Pre-Fault Warning Signs of Air Compressors
I. Abnormal Noise and Vibration
Unusual noise during operation acts as an "alarm" for equipment faults. Severe vibration may also occur.
Possible causes of abnormal noise:
Worn main bearings, unbalanced rotating shafts, damaged male and female rotors;
Excessive load on the main unit, pressure trapping or unbalanced pipe network pressure;
Loose bolts, nuts, gaskets and fixing supports;
Foreign objects falling into the equipment;
The compressor unit approaching its major overhaul interval. The axial and radial float of screws gradually reaches the maximum allowable design value. This significantly changes the clearances between screws, between screws and the casing, as well as front and rear end covers, triggering friction, vibration and various abnormal noises.
II. Leakage of Oil, Water and Compressed Air
Leakage of lubricating oil, circulating cooling water and other media;
Visible compressed air leakage with audible hissing sound.
Leakage problems mainly stem from aging equipment and spare parts or inadequate maintenance, including improper and careless operation by staff. These seemingly minor issues may lead to severe hidden consequences.
Taking compressed air leakage as an example: leakage directly wastes substantial electric power and increases electricity costs. It also causes pressure drop in the system, reduces efficiency of pneumatic equipment and shortens service life. In addition, air leakage leads to more frequent equipment cycling, extending the running time of air compressors, which brings extra maintenance work and potential unplanned shutdowns. In short, compressed air leakage creates unnecessary demand for compressor capacity.
Combined with the common problem of system operating pressure higher than required, leakage will cause so-called false demand, keeping the air compressor loaded continuously without rest.
All these factors negatively affect production efficiency and shorten the service life of nearly all system equipment and pneumatic tools. Extra energy consumption and accelerated equipment aging form a double blow to factory operators, which must be taken seriously.
III. Peculiar Odors
Special odor generated when the motor overheats or lubricating oil enters the cylinder and burns;
Burnt smell from damaged insulating materials caused by short circuit or ground fault of circuits;
Burning odor emitted by rubber and similar materials.
According to media reports, on May 25, 2017, a gas leakage incident took place in the workshop of Kocheng Technology (Suqian) Co., Ltd. in Suqian. More than 80 employees were hospitalized due to physical discomfort after inhaling certain gas.
Subsequent investigation by the Administrative Committee of Suqian Susu Industrial Park confirmed that this accident was a secondary incident triggered by mechanical failure of the air compressor. The screw bearing of the power air compressor was worn, resulting in seizure between the bearing housing and screw shaft. Massive heat generated by friction cracked lubricating oil inside the screw cylinder, producing small-molecule hydrocarbons as well as sulfur, phosphorus compounds decomposed from additives. These irritant gases spread through compressed air pipelines to workstations and the workshop, causing discomfort among operators.
This accident with multiple hospitalized staff caused by peculiar odor from an air compressor tells us: even if faults have already occurred when odors are detected, peculiar smells can help us quickly locate fault causes and positions, serving as a warning for all users.
Conclusion
Air compressor failures rarely happen suddenly; they are always accompanied by warning signs in the form of abnormal phenomena or changing instrument readings.
Therefore, we must stay alert to all kinds of pre-fault signals, helping operators and maintenance personnel detect potential accidents at an early stage and prevent failures before they occur.
