oil poured into the compressor

Figure 1: Using compressor oil.

The air compressor manufactured by a well-known international brand is widely used in all walks of life with its characteristics of high efficiency, stability, and durability. But many users also find that the air compressor consumes more oils. So what are the reasons for the high oil consumption? This article will help you understand them from six aspects.

Causes of Oil Leakage

* Oil Leakage

Common oil leakage points are located on the head, aging oil pipe, oil cooler, and the sealing of the oil system. Oil leakages in the process of operation are common and easy to observe. It must be dealt with in time.

* Compressor Oil

The problems include oil selection, oil deterioration, and excessive oil. It’s of vital importance to select the quality oil appropriately under the guidance of professional personnel. Oil deterioration will bring a series of failures, which will affect the oil separation or return, causing high oil consumption. Fresh workers in the industry may add oil higher than the normal level. The excessive part will be taken away with the airflow, resulting in high oil consumption.


You should fill the oil by observing the oil level mirror. Generally, the oil level should be controlled at 1/2-2/3 of the oil level of the mirror when the compressor is stably loaded.

the oil level mirror for the air compressor

Figure 2: The oil mirror.

* Oil Return System

The oil check valve is blocked. The clearance between the oil return pipe and the oil bottom is large, or the oil return pipe breaks the oil bottom during installation, or the connection between the oil return pipe and the compressor head is blocked.

The above problems will cause the oil to be unable to return to the head timely, and the condensed oil will be picked up by the compressed air, which will lead to high oil consumption as the compressed air will be taken away after separation.


You should clean or replace the oil check valve and install the oil return pipe to the center at the bottom of the oil separator groove, and thoroughly clean the oil return system.

Note that the delay in oil return will cause oil to be consumed rapidly, which could lead to high-temperature downtime. The after-sales personnel should carefully clean up and install the oil return valve, and return pipe. To check the oil return effect, we suggest you that observe the center at the bottom of the oil separator to know the remaining oil. The remaining oil should be less.

* Primary Separation of Oil Separator

The baffle plate has defects. After years of use, the air compressor will inevitably have some faults. So the baffle plate does. But the baffle plate failure that is easy to ignore will cause the primary separation of the oil from the gas to be not effective. And then the oil would exceed the oil separator load, resulting in a poor separation effect and high oil consumption.

jual henry oil separator

Figure 3: The oil separator.

For this phenomenon, some personnel will simply think it is due to the oil separator. As a result, the problem could not be solved. What’s worse, replacing oil separators repeatedly wastes compressor oil, oil separator, and time very much.

* Use Conditions

This failure mainly includes significant depressurization of the use and the long-term operation at the temperature below 75 ℃.

Because of using more gases, Some factories use the air compressor with much lower exhaust pressure than that notified on the nameplate. For example, an air compressor whose rated pressure is 10 kg, but the actual gas pressure is only 5 kg (or lower). So the air compressor operates for a long time, which can not reach the rated pressure, the exhaust pressure is greatly reduced, and the mixture of oil and gas flow fast. As a result, this aggravates the oil load and leads to high oil consumption.


The air compressor is a type of professional and technical equipment. It should be used reasonably under the guidance of the manufacturer's engineer. And if it is inevitable to reduce the pressure, customized special oil can be used to appropriately reduce oil consumption.

For another, a few compressors are added with a heat recovery system, or the oil cooler is cleaned, the running temperature drops much, causing compressors to run at a low temperature for a long time. The compressed air can not be evaporated timely and attached to the oil filter. Over time, the oil filter structure will be destroyed, resulting in high oil consumption.


You should keep the compressor operate at a reasonable temperature of 80-95 ℃.

* Other Factors

water-cooled screw compressor

Figure 4: The internal structure of the compressor with water-cooling system.

Other factors include the oil leakage in the oil cooler of the water-cooled air compressor, the sealing failure or open of the minimum pressure valve, and the oil separator, etc. The perforation of the air compressor oil cooler leads to leakage into the water cooler. Because of the high oil pressure and the low water pressure (2 - 3kg /cm2), the compressor oil leaks into the cooling water system through the perforation, causing the oil to run. If the minimum pressure valve is not tightly sealed or opened in advance (the general opening pressure of the minimum pressure valve is around 4kg), the establishment of internal pressure in the early operation of the compressor is prolonged.

At this time, the compressed air in the low-pressure state has a higher oil fog concentration and a faster flow rate, which leads to high oil consumption of the compressor. As an important part of the air compressor, the oil separator consumes excessive oil after workers troubleshot it. It is necessary to replace one.

Case Studies

Case 1

The broken sealing ring of the air outlet of the compressor head led to high oil consumption. For instance, a 90 KW varied-frequency air compressor consumes more oil after using less than 1000 hours of 8 years.

sealing ring is damaged

Figure 5: A broken sealing ring.

The worker opened the door of the compressor and found that there was a lot of oil dripping on the ground. According to the oil trace, he looked for the oil circuit system. Finally, he found that there was oil leakage at the outlet of the compressor. After shutting down the compressor, he found that the sealing ring had been broken and replaced it, then the problem was solved.

Case 2

Excessive oil in the compressor resulted in high oil consumption. For example, a cubic air compressor consumed much oil after just a few days of maintenance. The maintenance worker checked the compressor and found that the machine was operating under good conditions. But when it was loaded and running, the oil exceeded the top of the oil mirror. So he suggested the user that releases a small bucket of oil. 2 days later, the oil consumption was significantly reduced.

the oil level exceeds the top of the oil mirror

Figure 6: Observing the oil level.

Case 3

The oil return pipe broke the oil separator at the bottom, resulting in high oil consumption. There was a compressor that needed two barrels of oil each day. After inspecting the compressor, the worker found that the oil return pipe had punctured the bottom of the oil separator. It was due to the wrong installation of the oil return pipe. As a result, the return pipe penetrated the bottom steel plate of the oil separator, causing some oil and gas mixture to flow into the air outlet directly without passing through the oil separator.

the oil separator punctured by the oil return pipe

Figure 7: The oil separator is punctured.

oil separator protruded at the bottom

Figure 8: The oil separator is protruded.

Case 4

There was a foreign object in the oil check valve, which causes poor oil return and high oil consumption. A permanent magnet varied-frequency air compressor consumed much oil. There was an oil of 10cm in height in the oil separator center. In most cases, it’s the poor oil return effect that led to high oil consumption of the machine. However, when the maintenance man opened the oil return pipe and blew the oil check valve with his mouth, there were no failures.

Then the worker took apart the oil check valve and found that there was yellow sticky material inside (see the figure 9), and the check valve core seriously aging. Finally, he removed the valve core and poured out the oil inside the oil separator. After re-installing and testing the compressor, the air quality has been improved obviously.

oil and yellow materials left in the oil separator and oil check valve

Figure 9: Excessive oil and other materials.

Case 5

The compressor has been running at a low temperature for a long time, resulting in high oil consumption. A compressor was running and releasing much oil from the gas storage tank, and the oil level decreased quickly, which reached the bottom of the oil mirror. Seeing from the control panel, the maintenance worker found that the operating temperature of the compressor was only 68 ℃. After inquiring the user, he knew that the compressor had been operated at a low temperature for a long time. The preliminary judgment was that the long-term low-temperature operation caused high oil consumption.

the flange has rusted

Figure 10: A lot of rust on the flange.

Therefore, he stopped the machine and released much water from the outlet of the oil separator. And he took off the flange and noticed that there was a lot of rust on it. It was verified that water could not be evaporated timely due to the low-temperature operation of the compressor for a long time. So the moisture in the compressed air could not be evaporated completely in the form of gas but had been attached to the oil filter over time. As a result, the structure of the oil filter material was damaged, leading to high oil consumption.

Finally, adjusting the opening temperature of the fan made the operating temperature of the compressor raise to and maintain at 80 - 95 ℃. Therefore, the failure was troubleshot.

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