carbon deposits
By Published On: July 5, 2024Views: 79

How to remove oil sludge and carbon deposits from the air compressor? In dealing with oil sludge and carbon deposits in air compressors, we must first understand what causes carbon deposits. Then we can accurately solve the problem with the right medicine.

In fact, we all know that oil sludge and carbon deposition are very harmful to all kinds of mechanical equipment which surely includes air compressors, but many of us don’t know how to deal with or avoid it. Let Kotech help you learn about it!

How to remove oil sludge and carbon deposits from the air compressor?

Causes of air compressor oil sludge and carbon deposits

During the long-term continuous operation of the air compressor, many impurities, moisture and other components in the air enter the air compressor inevitably, which is an external pollution source of sediment.

Air compressors often operate under high temperature and high pressure conditions. With the catalytic effects of oxygen, moisture and metal, the air compressor oil will undergo oxidation reactions, resulting in aging of the lubricating oil.

There are also various additives in the oil, which will undergo different oxidation reactions to generate different oxides. The longer the air compressor oil is exposed to high temperature and oxygen, the higher the degree of oxidation reaction. The various oxides generated may aggregate to form precipitation. These precipitations are usually very viscous and are very easy to form deposits on the head, oil circuit and shell. Common deposits include paint film, oil sludge, coking and carbon deposits.

The paint film is a sticky film formed by resin separation and dehydration and/or polymerization on the hot surface. This deposit is not very serious, just a thin film. The paint film is a derivative of the lubricant. When the temperature of the air compressor parts is low, the deposit produced is sludge.

Sludge can be soft or slightly hard in consistency. If the working conditions are mild, the sludge produced may be soft. This type of sludge is called low-temperature sludge, which appears when the ambient temperature is below 95°C. High-temperature sludge appears when the ambient temperature is above 120°C and has a higher viscosity.

Causes of air compressor oil sludge and carbon deposits

When the oxidation of oil products intensifies to a certain extent, a large number of polymers and colloids gather together to form the so-called coking. At this time, the air compressor causes metal wear debris to enter the oil due to wear. These metal ions are natural catalysts for oxidation reactions, which accelerate coking. Coking is also a kind of sediment, which may contain oil, water, resin (similar to paint film) and solid pollutants.

Different types of air compressor oils have different tendencies to produce coking. After eliminating the cause of mechanical failure of the compressor, the quality of the air compressor oil directly determines the coking tendency of the air compressor.

Carbon deposits are a more stubborn type of substance that is harmful to air compressors than sludge. Under the repeated effects of high temperature and high pressure, the colloid produced by oxidation interacts with oxygen, dust, impurities, etc. in the compressed air, turning into asphalt and further carbonizing to form carbon deposits.

Under the following conditions, carbon deposits will accelerate their formation inside the air compressor:

  1. High temperature: High temperature is the decisive factor that causes lubricating oil to oxidize and deteriorate. The higher the temperature, the faster the oxidation rate and the greater the possibility of carbon deposits;
  2. High pressure: After the air is compressed by the air compressor, the pressure increases, the oxygen concentration increases, and the oxidation rate of the oil and the possibility of carbon deposits are increased;
  3. Metal catalysis: Metals play a positive catalytic role in oxidation reactions and will accelerate the reaction;
  4. Inferiorair compressor oil: The quality and amount of air compressor oil will have different degrees of influence on the formation of carbon deposits. If mineral air compressor oil is used, the unsaturated components in the base oil are more likely to form carbon deposits.

Know more about incorrect usage of air compressor lubricating oil: (5 Misunderstandings About Industrial Oil Lubricants Used in Air Compressors)

How oil sludge and carbon deposits damage your air compressor

These harmful hard oil sludge, carbon deposits, grease, and coking may cause the operating temperature of the air compressor to rise, energy consumption to increase, gas production efficiency to decrease, oil circuit to block, parts to wear and other faults.

It will also affect the air pressure, the operating efficiency, decrease the compressor air supply and quality, cause the machine shutdown and increase maintenance costs; in severe cases, they may cause serious safety accidents such as compressor overload tripping, shutdown, even compressor explosion.(overload tripping)

Statistical data show that most air compressor explosion accidents are caused by the accumulation of carbon deposits. Carbon deposits are high-temperature products but they will also spontaneously combust at high temperatures. Usually, the spontaneous combustion temperature of carbon deposits is around 180°C, and the outlet temperature of the air compressor is generally not higher than 160°C, so under normal operation, carbon deposits will not be ignited.

However, when the air compressor has a momentary high temperature or high pressure due to some faults, the temperature inside the air compressor rises sharply, causing the carbon deposits to spontaneously combust, causing the oil in the carbon deposits to vaporize rapidly. When the vaporized oil and gas coexist with the high concentration of oxygen and high temperature in the compressed air, it will cause the compressor to explode and cause an accident.

Air compressor rotor cleaning to remove sludge

How to remove the oil sludge and carbon deposits

There are two main ways to remove carbon deposits and oil sludge from air compressors: online cleaning and disassembly cleaning.

Online cleaning agents mainly use the strong polarity characteristics of certain types of synthetic oils and the principle of similar compatibility. They have a certain compatibility with sludge and carbon deposits. When used, they are added to the compressor oil to be replaced in a certain proportion to achieve a certain cleaning effect. Its advantages are that it is relatively safe to use, has good compatibility with compressor oil, and has less adverse effects on equipment; it is easy to use and does not require disassembly.

The disadvantages are that the cleaning effect is general, and it can clean light pollutants, but it is not effective for heavy pollutants or stubborn deposits such as paint film, coking, and carbon deposits; the cleaning time is long, generally ranging from 40 to 80 hours.

Disassembly cleaning agents are mainly organic solvents, alkaline water-based cleaning agents, and acidic water-based cleaning agents. There are many kinds of products on the market, some of which have good cleaning effects, but disassembly cleaning products all have obvious defects: organic solvents have low flash points, and the safety of use has always been criticized by users.

The flash point of some organic solvents is even below 40°C, which belongs to the regulatory scope of hazardous chemicals; and water-based cleaning agents, whether alkaline or acidic, will cause varying degrees of corrosion to the equipment, especially in the case of improper handling and residual cleaning agents, the damage to the equipment is long-term and fatal.

Disassembly cleaning requires the screw compressor head and even the oil circuit components to be completely disassembled, and they need to be reassembled after cleaning, which greatly increases the maintenance workload and requires longer maintenance time. It cannot meet the requirements of continuous and stable operation and pursuit of high efficiency of the air compressor station.

How to remove the oil sludge and carbon deposits

Prevention of oil sludge and carbon deposition in air compressor

In order to prevent the above problems and even the combustion and explosion of the air compressor, oil sludge and carbon deposits must be reduced. In view of the generation mechanism of oil sludge and carbon deposition, the following effective measures can be taken to maintain the good working condition of the air compressor:

According to the operating conditions and your own conditions, choose clean, high-quality air compressor oil that meets the regulations. The key is to improve the thermal oxidation stability and antioxidant capacity of the lubricant used (flash point ≥ 215℃).

Choosing high-quality maintenance accessories and materials, and replace them regularly according to maintenance requirements. High-quality and efficient oil separators, oil filters, and air filters can effectively filter external and endogenous pollution sources to ensure the normal operation of the air compressor.

Maintaining normal working temperature and working pressure and ensuring effective ventilation of the air compressor station is a means to achieve twice the result with half the effort.

Adopting auxiliary cleaning methods to keep the compressor clean, choose mature online cleaning fluids, and clean the air compressor regularly to keep the head rotor and oil circuit clean and prevent problems before they happen.

KWI Series 100% Oil Free Water Lubricated Screw Air Compressor

KWI Series 100% Oil Free Water Lubricated Screw Air Compressor

Common problems in dealing with oil sludge and carbon deposits

In the cylinder, gas tank and pipeline, due to too much lubricant supply, there is a lot of dust in the inhaled air, forming scale in the cylinder, gas tank and pipeline. Solution: The lubricant supplied to the cylinder should be appropriate, and the oil supply of the oil injector should be ≤2 drops/turn, which meets the requirements of the equipment grease supply standard and inspection standard; the air compressor should be overhauled as planned (usually 4000h routine overhaul), and the gas tank should be cleaned regularly.

Due to the abnormal operation of the air compressor (such as poor heat dissipation effect of the cooler), the compressed air temperature is too high. Solution: Clear the scale on the water side of the cooler surface and the carbon deposit on the gas side, keep the guide cover intact and sealed, ensure good heat dissipation of the cylinder water jacket and cooler, and do not exceed the specified temperature at all levels (generally the exhaust temperature does not exceed 160℃).

There is a large amount of local scale or sparks in the cross section of the air compressor pipeline or air compressor passage. Solution: The pipe gate valve and check valve leading to the gas storage tank should be inspected and cleaned on schedule to prevent excessive resistance and carbon deposits.

The air compressor pressure suddenly increases, the safety valve does not work, and the load regulator fails, resulting in exceeding the strength limit of the gas storage tank or pipeline. Solution: Regularly inspect and patrol the load regulator, safety valve, pressure gauge, etc. to see if they are sensitive and accurate, and promptly eliminate equipment failures with abnormal pressure.

The secondary exhaust valve is not tight, and the high-temperature and high-pressure air in the exhaust pipe leaks back to the cylinder, causing high temperature near the secondary exhaust valve, and then encountering oil sludge and carbon deposits, thereby inducing combustion and explosion. Solution: The secondary exhaust valve is leaking. If high temperature occurs, it should be repaired in time, and the carbon deposits on the valve and piston should be removed to prevent high temperature near the exhaust valve.

The oil and water condensed in the cooler and gas tank are not discharged in time. Solution: Implement the point inspection system and discharge the sewage on time.

The intake air is too dirty. Solution: Clean the air filter regularly to prevent the inhalation of dirty air.

Clean the motor: The motor operating environment should always be kept dry, the surface should be kept clean, and the air inlet should not be accumulated with dust, fiber and other debris. When the thermal protection and short-circuit protection of the motor are continuously activated, it should be checked whether the fault comes from the motor or the overload, or because the protection device is set too low. The motor can be put into operation only after the fault is cleared. The motor bearing should be re-lubricated with grease after running for 1500~2000h.

The maximum bearing temperature should not exceed 120℃. When the temperature is below 70℃, the interval time for re-lubricating grease can be appropriately extended. When filling oil, use a grease gun, first remove the grease plug on the oil drain pipe, add new grease until the original grease is discharged from the oil drain hole, wipe it clean with a rag, and after filling oil, tighten the oil plug.

KOE Series screw compressor

KOE Series Oil-lubricated Screw Air Compressor

Actual case analysis

The following is an actual case operation method of Kotech to deal with an air compressor with serious carbon deposits:

During the maintenance of the air compressor, we conducted a comprehensive inspection and treatment of the oil circuit, gas circuit, and water circuit, and no abnormalities were found. However, the serious carbon deposits made us focus on the air intake filter of the air compressor.

The filter is divided into three parts: the outer cylinder, the inner cylinder, and the outlet pipe. The upper part of the interior is a swirl plate and a filter screen, and the lower part is connected to the outer cylinder. The bottom of the cylinder is filled with compressor oil.

The air enters the outer cylinder from the tangential direction, and the dust particles in the air flow are separated after the cyclone dust removal. Then the air flow passes over the oil surface and turns sharply upward. The air is bathed in oil when passing through, and the dust particles in the air flow are captured by the oil film.

The oil film flows back along the wall and becomes a drooping oil curtain. The airflow rotates and rises in the inner cylinder, and after passing through the swirl plate, the rotation intensifies, and part of the oil droplets entrained in the airflow are thrown into the oil return groove and flow into the bottom of the cylinder through the oil return pipe, and part of it flows back along the inner cylinder wall, washing the dust captured by the oil film on the cylinder wall to the bottom of the cylinder, and forming a new oil film.

Finally, the airflow returns and passes through the filter screen again, filtering out smaller dust particles and oil droplets, achieving the purpose of filtering air and eliminating noise.

Actual case analysis

We observed the oil level from the inspection window, and no oil was visible from the lower scale; opened the muffler cap and checked the filter screen, and found that the filter screen was seriously blocked and the amount of oil in the oil pool was seriously insufficient, reducing by about 4 or 5 kilograms. After analysis, it was found that the air compressor had an overly dense air intake filter (using a 50-mesh filter with a square hole size of 0.3mm, 6 layers stacked), and the pressure difference increased after long-term use.

When the air compressor inhaled air, the inner cylinder formed a negative pressure, and the airflow brought a large amount of oil mist into the cylinder, which was continuously deposited in the air path. Under the action of high temperature, the carbon deposits accumulated more and more, especially in the secondary cylinder outlet pipe.

Finally, a large piece of carbon deposits with a length × width × thickness = 70 × 40 × 30mm was cleaned out. The cause of the serious carbon deposits in the air compressor was finally found! The next step is to organize maintenance personnel to clean the filter, replace the filter with a suitable density (use a 20-mesh steel wire mesh with a steel wire diameter of Φ0.3mm and a square hole size of 1.0mm), and add new oil to the center line of the observation window. Finally, after a thorough analysis and comprehensive and detailed treatment, the exhaust temperature of each level of this air compressor dropped from 160℃ to 140℃, and the temperature of the inter cooler dropped from 80℃ to 40℃.

Not only were all the operating parameters normal, but the factors that easily caused carbon deposits were also effectively prevented and controlled. After being promoted to other air compressors, good results were achieved. Combined with the continuous and in-depth implementation of the full-staff equipment charter management system, equipment defects and hidden dangers can be eliminated more promptly, and the safe operation of the equipment is further reliably guaranteed.


Since air compressors are used frequently, the internal parts will inevitably wear out and form oil sludge and carbon deposits due to various reasons during use, such as oxidation of lubricating oil caused by high temperature, excessive working pressure of equipment, oxidation reaction of metal, and mineral oil used in air compressor oil, etc., which will cause oil stains and carbon deposits inside the air compressor.

Instead of being in a hurry after the air compressor has problems or handing the air compressor to the air compressor repair manufacturer, but they just take a look at the problem and then replace new parts, which will not only cause great harm to the production process, but also the cost of maintenance is frighteningly high. T

herefore, the best way to solve the oil stains and carbon deposits inside the air compressor is to operate the air compressor correctly, use qualified lubricating oil, and regularly clean, maintain, and replace the various parts of the air compressor as necessary. At any time, avoiding problems happen is the best solution.

Wanting to get services of air compressor nearby? Kotech may be able to help! Professionally manufacturing air compressors for over 10 years, we have everything you want! Contact us for free~