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The reason for the large consumption of lubricating oil in screw air compressor —Shared by Sollant

tank mounted compressor

In an oil-injected screw compressor, a large amount of oil is injected into the interdental volume of the compressor while the gas is being compressed. The oil-air mixture formed by these oils and compressed gas is discharged into the oil-gas separator of the unit after undergoing the same compression process.

The oil-gas separator is one of the main equipment in the oil-injected screw compressor unit system. In order to reduce the oil content in the unit exhaust and recycle the lubricating oil in the unit, the oil-gas separator is used to separate the lubricating oil from the gas. If the oil component fails, the lubricating oil cannot be separated well, and the lubricating oil will be discharged along with the compressed air.

screw driven air compressor

Therefore, the failure of oil separation and its oil separation core is the main factor for the high oil consumption failure of oil-injected screw compressors.

Generally speaking, the oil requirement for oil-injected screw compressors is that the residual oil content of the compressed air outlet after oil treatment is not more than 3ppm. Excessive oil content in the air at the compressor outlet is usually referred to as high fuel consumption, also known as oil run.

The main causes and hazards of compressor oil failure are as follows:

  1. The oil separator core is blocked

When the oil separator core is blocked, the air compressor motor current will be too large. It is also possible that the oil separator core may be deformed due to excessive pressure, or the main engine may be locked when the motor is seriously overloaded. In addition, if the current is too large, the life of the contactor will be shortened or the contact will burn out and cause a major accident.

Generally, the screw air compressor has a pressure gauge in front of the filter element. When the pressure difference between the pressure gauge in front of the filter element and the air supply pressure gauge reaches 0.08MPa, the oil separator needs to be replaced.

  1. The oil separator core is damaged

When the oil separator core is damaged, the oil consumption of the air compressor will be very serious, and there will be a lot of oil in the air storage tank and pipeline. In severe cases, the air compressor oil will be directly discharged when the air storage tank drain valve is discharged.

The main reasons for this failure are:

(1) The oil separator core was not replaced on time;

(2) The poor quality oil separator core is selected;

(3) During the installation process, it was not operated according to the regulations, such as inserting the oil separation core when installing the oil return pipe, etc.

  1. The oil separator core is burned

The burning of the oil separator core is not common but happens occasionally during the operation of the air compressor. The main performance is that the filter screen of the oil separation core is partially or completely carbonized, and even the metal shell of the oil separation core is burned.

Such failures occur mainly because:

(1) The quality of air compressor oil is poor;

(2) The quality of the oil separator core itself is too poor;

(3) When the oil separator is installed, there is no reliable connection between the oil separator shell and the oil separator barrel and cannot be grounded. When there is static electricity, the oil mist will be ignited and the oil separator will be burned.

electric screw air compressor

  1. The separation effect of the oil separation core is poor

The main performance is that the compressed air contains too much oil, which will cause damage to the post-processing equipment and user equipment.

The reason for this failure is mainly because:

(1) The quality of the oil separator core itself is too poor;

(2) Did not operate according to the regulations during installation.

other reasons

In the actual processing process, we found that a large part of the fault complaints were not caused by the quality of the oil. So, besides oil quality problems, what other reasons can cause oil leakage? In fact, these situations can also cause oil leakage:

  1. Minimum pressure valve failure

The minimum pressure valve is a part to maintain the pressure of the screw compressor system.

If there is a leakage point at the seal of the minimum pressure valve or the minimum pressure valve is opened in advance (because the opening pressure of each manufacturer is different, usually the range is 3.5 ~ 5.5kg/cm2 Between), then the time for the machine to establish the pressure of the oil and gas tank at the initial stage of operation will increase.

At this time, the gas oil mist concentration in the low pressure state is high, and the flow rate is fast when passing through the oil component. The load of the oil component is increased, and the separation effect is reduced, resulting in high fuel consumption.

Solution: Overhaul the minimum pressure valve and replace it when necessary.

  1. Unqualified compressor lubricating oil is used

At present, general-purpose screw compressors have high-temperature protection, and their tripping temperature is usually around 110-120°C. However, some compressors use unqualified lubricating oil, and different degrees of oil consumption will occur when the exhaust temperature is high. (Based on this, the higher the temperature, the greater the fuel consumption).

The reason is that after the primary separation of the oil and gas barrel at high temperature, some oil droplets can have the same order of magnitude as the gas phase molecules, and the molecular diameter is ≤0.01μm. It is difficult for the oil to capture and separate them, resulting in excessive fuel consumption.

Solution: Find the cause of the high temperature, solve the problem and reduce the temperature, and use good quality screw compressor lubricating oil as much as possible.

all in one air compressor

  1. The design of the oil-gas separation tank is not standardized

Some compressor manufacturers, when designing the oil-gas separation tank, the design of the primary separation system is unreasonable, and the primary separation effect is not ideal, so that the concentration of oil mist before entering the oil component is high, the oil component is overloaded, and the processing capacity is insufficient, resulting in excessive oil consumption. high.

Solution: The manufacturer improves the design to improve the primary separation effect.

  1. Too much gas

The amount of refueling exceeds the normal oil level, and part of the oil is taken away with the airflow, resulting in excessive fuel consumption. the

Solution: After stopping the machine, after the air pressure in the oil and gas barrel is released to zero, open the oil drain valve and drain the oil to the normal oil level.

  1. The oil return check valve is damaged

If the oil return check valve is damaged (from one-way to two-way), the internal pressure of the oil separator tank will pour a large amount of oil back into the oil separator through the oil return pipe after the shutdown.

The next time the machine is running, the oil in the oil separator will not Suck back the machine head in time, causing part of the oil to run out of the compressor with the separated air (this situation is common in machines that are not equipped with an oil circuit stop valve and a one-way valve for the exhaust outlet of the machine head).

Solution: Check the one-way valve after dismantling it. If there is debris stuck to it, just clean up the debris. If the one-way valve is damaged, replace it with a new one.

  1. Improper installation of oil return pipe

When replacing, cleaning, and maintaining the compressor, the oil return pipe is not inserted into the bottom of the oil separator (reference: 1-2 mm from the arc center of the bottom of the oil separator is better), so that the separated oil cannot return to the machine head in time, and the accumulated oil will flow with the Compressed air runs out together.

Solution: stop the machine, and after the pressure release returns to zero, adjust the oil return pipe to a reasonable height (the oil return pipe is 1~2mm away from the bottom of the oil separator, and the oil return pipe with an oblique opening can be inserted into the bottom of the oil separator).

 large consumption of lubricating oil in screw air compressor

  1. The air consumption is large.

The overload and low pressure are used (or the oil treatment capacity selected before the machine leaves the factory is too tightly matched with the exhaust volume of the machine)

Load low-pressure use means that when the user uses the compressor, the exhaust pressure does not reach the rated working pressure of the compressor itself, but it can basically meet the gas consumption requirements of some enterprise users.

For example: the enterprise user has increased the gas consumption equipment, and the gas consumption has increased, so that the displacement of the compressor cannot be balanced with the gas consumption of the user.

Assume that the rated discharge pressure of the compressor is 8kg/cm2, but the actual pressure is only 5kg/cm2 Even lower, so that the compressor is in a load operation state for a long time and cannot reach the rated pressure value of the machine, resulting in increased fuel consumption.

The reason is that under the condition of constant displacement, the flow velocity of the oil-air mixture increases when passing through the oil, and the concentration of oil mist is too high, which increases the load on the oil and results in high fuel consumption.

Solution: It is recommended to contact the manufacturer to replace an oil product that can match the low pressure.

  1. The oil return line is blocked

When the oil return line (including the one-way valve on the oil return line and the oil return filter) is blocked by foreign matter, the oil that has condensed at the bottom of the oil component after separation cannot return to the machine head, and the condensed oil droplets are blown up by the air flow. It is taken away with the separated air. These foreign objects are usually caused by solid impurities dropped during installation.

Solution: Stop the machine, remove all the pipe fittings of the oil return pipe after the pressure of the oil barrel is released to zero, and blow out the blocked foreign matter. When installing the built-in oil separator, pay attention to clean the oil and gas barrel cover, and at the same time, pay attention to whether there are solid particles remaining at the bottom of the oil separator core.


The brand “Sollant” specializes in the R&D, manufacturing, sales and after-sales of compressors, oil-free compressors and hosts, special gas compressors, various air compressors and post-processing equipment. Provide customers with high-quality, environmentally friendly and efficient air system solutions and fast and stable technical services. Sollant Corporation is customer-centric. Customer satisfaction is the purpose of our Sollant people.



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