The air oil separator is a fluid separator device that designed to separate lubricating oil and water in the gas. It consists of a separator barrel, a filter element, and an oil return system.

It follows the principle of different densities and masses of liquid and gas to separate liquid from air through a special ultra-fine fiber filter, ensures the purity of air and no pollution to the machine and product.

What is air oil separator?

Air oil separator is an important filter device installed after the air outlet of the compressor air end, it is collectively called the three filters of the air compressor along with the air filter and the oil filter. Air oil separator is a key component that determines the quality of compressed air.

Its main purposes are to separate the oil and air from the oil-gas mixture exhausted by compressor, allowing the compressor to discharge almost pure compressed air for users, extend the air compressor life expectancy, also make the lubricating oil to return to the circulation of the lubrication system.

After passing through the air oil separator, the mist-like lubricating oil can be almost completely filtered out from the compressed air, the residual oil particle size can be controlled below 0.1um, and the oil content can be less than 3ppm (parts per million).

Air oil separator mainly consists of three parts, namely air oil separator tank, air oil separator element and the oil return system. The air oil separator tank is a cylindrical metal barrel that can withstand pressure far higher than the exhaust pressure of the air compressor, so that it can ensure the safety of the separation processes of oil and compressed air, and it is the key of how to regulate pressure on air compressor.

The element of air oil separator is composed of multiple tightly fitted ultra-fine fiber layers, a metal support layer, and a gravity sedimentation layer.

The ultra-fine fiber layers are made of multi-layers of fine glass fibers, which intercept and aggregate the fine oil particles and oil mist in the compressed air, so that they are concentrated at the bottom of the element and returned to the compressor lubrication system through the oil return pipe.

The oil return system of air oil separator is composed of multiple metal pipes. There is a larger pipe near the bottom of the air oil separator, which is called oil drain pipe. Most of the separated lubricating oil will flow through this pipe and pass through the after-cooler.

After cooling, it will return back to the air compressor lubrication system. There is also a smaller pipe on the top of the air oil separator barrel, which is called the oil return pipe. It connects the air oil separator element and the air compressor air end. The oil separated by the air oil separator element will pass through it and return to the air end to continue to participate in lubrication.

In addition, the air oil separator also includes a minimum pressure valve and a vent pipe installed on the top. The function of the minimum pressure valve is to help the air compressor system to establish a certain internal pressure at startup, so that the lubricating oil can obtain initial circulation power. Before the pressure value set by the minimum pressure valve is reached, the compressed air in the air oil separator cannot be discharged, thus make the air oil separator capable on how to regulate pressure on air compressor.

The function of the vent pipe is to work with the solenoid valve to make the air compressor enter the shutdown venting or unloading venting state after the air compressor is shut down or reaches the maximum set pressure, so as to ensure that the pressure in the air oil separator is maintained at a reasonable level.

The air oil separator has two separation processes. The oil and gas mixture after the first separation in the air oil separator barrel will enter the air oil separator element for the second separation. The air quality after filtering by the air oil separator element has reached the exhaust standard. Then it will flow through the after-cooler through the minimum pressure valve and then discharged for use or enters the post-treatment equipment for precision treatment.

What does air oil separator do?

Air oil separators are used to remove oil from oily air, and play a vital role in ensuring the efficient and safe operation of air compressors and the equipment and systems using compressed air. High-quality air oil separators not only ensure the high-efficiency operation of the compressor, but also extend the air compressor life expectancy and reduce equipment maintenance costs and failure rates.

Are air oil separators necessary for air compressors? Yes, as we all know that lubricants are needed during the operation of air compressors to lubricate the high-speed rotors and bearings, reduce friction and mechanical wear; and lubricants are also used to absorb the heat generated during the operation of air compressors. The lubricants can be oil or water, but whether it is oil or water, they will inevitably mix evenly with the compressed air while fully lubricating the machinery and absorbing heat.

If there is no air oil separator, various air compressor problems and solutions will happen, such as the lubricants will be discharged along with the compressed air, causing pollution and damage to the equipment and products using compressed air. Meanwhile, the air compressor will be quickly ran out of lubricant.

If the air compressor can not be adequately lubricated and cooled, it will fail, shut down or get damaged, causing economic losses and safety hazards.

How does air oil separator work?

Air oil separator mainly uses the difference in specific gravity and density between gas and liquid to separate oil and compressed air from the oil-gas mixture through gravity, centrifugal force and barrier. In this process, there are many factors need to be considered, such as the flow rate, viscosity, density of oil and air, temperature of gas, as well as what type of oil to use for air compressor. How does air oil separator work can be summarized in the following steps.

Centrifugal separation:

• The compressed air from the air compressor mixed with a large amount of oil mist enters the air oil separator barrel. Since the air inlet on the air oil separator is installed on the cylindrical barrel wall, the compressed airand oil mixture gushing in with high pressure begins to rotate around in the cylindrical barrel.
• Because the density and mass of oil is greater than that of air, the oil in the air will be inertiallyseparated and thrown onto the wall of barrel, slowly gather and flow down the barrel wall due to gravity, and sediment at the bottom of the air oil separator

The lubricating oil that just separated from the air still has a high-temperature, it will be extruded to the after-cooler through the oil pipe system under the action of separator barrel internal pressure, after cooling it will enter the lubrication system again to provide lubrication and cooling for the air compressor.

Collision separation:

• After the centrifugal separation, the remaining small amount of oil particles will enter the second separation process together with the compressed air—the air oil separator element for secondary separation. The multi-layer fine glass fiber filtersin the air oil separator element can almost intercept all the remaining oil particles in the air.
• These intercepted oil particles gather together to form larger oil droplets and flow into the sedimentation plate at the bottom of the air oil separator element along the metal mesh support wall. Then, under the action of the internal pressure in the air oil separator barrel, they enter the air compressor air endagain through the oil return pipe that connect the air oil separator element and the air end to participate lubrication

The compressed air after secondary separation and filtration by the air oil separator element has reached the exhaust standard of the air compressor. These de-oiled compressed air will enter the after-cooler through the minimum pressure valve and exhaust pipe at the top of the air oil separator and be cooled and discharged for use or enter the post-treatment equipment.

Principles of how does air oil separator work

How does air oil separator work depends on following simple principles:

1. Centrifugal separation. Principle: When the oil-gas mixture rotates around inthe barrel, the oil particles with higher density will be subjected to greater centrifugal force due to their larger mass and inertia, gradually separating from the oil-gas mixture and continuously gathering on the barrel wall, forming larger oil droplets that slide down the barrel wall. This can separate most of the oil mist and larger oil particles in the oil-gas mixture.

2. Collision separation. Principle: When the airflow encounters an obstacle, it changes its direction and speed, causing the tiny oil particles in it to continuously aggregate in the obstacle circle. In the meantime, an oil film is formed under the action of the surface tension of liquid. When it contacts the oil-gas mixture, more tiny oil particles will be retained and aggregated into large oil droplets, which will then settle down due to gravity.

3. Gravity sedimentation separation. Principle: Relying on the different relative densities and masses of oil and air to achieve air-liquid separation. Usually needs to be used together with the other two working principles to achieve the best effect.

4. Oil return circulation. Principle: The lubricating oil separated from the compressed air will gather at the bottom of the air oil separator barrel and the bottom of the air oil separator element, and will be discharged from the air oil separator under the action of internal pressure in the air oil separator barrel, and will re-enter the circulation of lubricating oil in the air compressor through the oil pipe system.

Principles of how does air oil separator work

How does air oil separator work depends on following simple principles:

1. Centrifugal separation. Principle: When the oil-gas mixture rotates around inthe barrel, the oil particles with higher density will be subjected to greater centrifugal force due to their larger mass and inertia, gradually separating from the oil-gas mixture and continuously gathering on the barrel wall, forming larger oil droplets that slide down the barrel wall. This can separate most of the oil mist and larger oil particles in the oil-gas mixture.

2. Collision separation. Principle: When the airflow encounters an obstacle, it changes its direction and speed, causing the tiny oil particles in it to continuously aggregate in the obstacle circle. In the meantime, an oil film is formed under the action of the surface tension of liquid. When it contacts the oil-gas mixture, more tiny oil particles will be retained and aggregated into large oil droplets, which will then settle down due to gravity.

3. Gravity sedimentation separation. Principle: Relying on the different relative densities and masses of oil and air to achieve air-liquid separation. Usually needs to be used together with the other two working principles to achieve the best effect.

4. Oil return circulation. Principle: The lubricating oil separated from the compressed air will gather at the bottom of the air oil separator barrel and the bottom of the air oil separator element, and will be discharged from the air oil separator under the action of internal pressure in the air oil separator barrel, and will re-enter the circulation of lubricating oil in the air compressor through the oil pipe system.

How to replace air oil separator element?

As one of the three major filters of the air compressor, the air oil separator element is also a wearing part. The solid particles in the compressed air are retained in the filter layer when passing through the air oil separator element, which leads to the increasing pressure difference (resistance) of the air oil separator element.

As the air oil separator is used for a longer time, there might not only be obstacles gather in filter element to block air flow, but also carbon deposits and oil sludge may sediment in the air oil separator tank.

When the pressure difference of the air oil separator element reaches 0.08 to 0.1Mpa, the element must be replaced, otherwise it will reduce the working efficiency and increase the operating cost (power consumption) of the air compressor. The general replacement circle that OEM recommended is to replace it every 2000 hours. If the working environment of the air compressor is harsh, the replacement cycle needs to be shortened. The following are the steps and methods of how to replace air oil separator element:

KSFU Series Compressor air oil/water separator

When the pressure difference of the air oil separator element reaches 0.08 to 0.1Mpa, the element must be replaced, otherwise it will reduce the working efficiency and increase the operating cost (power consumption) of the air compressor. The general replacement circle that OEM recommended is to replace it every 2000 hours. If the working environment of the air compressor is harsh, the replacement cycle needs to be shortened.

The following are the steps and methods of how to replace air oil separator element:

1. Shut down the air compressor and disconnect the power, open the vent valve, make sure that all pressure in the system is released.
2. Disconnect the pipelines that connected to the air oil separator barrel cover.
3. Remove the exhaust pipe from the minimum pressure valve outlet to the after-cooler.
4. Remove the fastening bolts of the air oil separator barrel cover.
5. Remove the air oil separator barrel cover.
6. Now the air oil separator element can be seen, take it out and replace it with a new one.
7. Install the air oil separator barrel cover and pipes in the reverse order of disassembly.
8. Turn on and run the air compressor for a while to check whether the air oil separator is completely sealed, if there is any air or oil leakage.

Special precautions:

• During install the barrel cover back, make sure that the distance from the oil return pipe that penetrates into the air oil separator element to its bottom is about 2~3mm.
• During the replacement of the air oil separator element, prevent any foreign matter from falling into the air oil separator barrel and affecting the operation of the air compressor.
• The air oil separator element generally has a paper pad to help seal. When installing a new element, ensure that there is no paper pad left on the air oil separator by the the old element affecting good sealing of the new one to prevent air or oil leakage.

The method of how to install air oil separator is similar to replacing an element, except that no need to open the air oil separator barrel. Instead, just need to unscrew the upper and lower fastening screws, remove the connected pipes, take down the air oil separator, and replace it with a new one. Note that the lubricating oil in the air compressor must be drained before replacing the new air oil separator, and then add new lubricating oil after installation.

How to use air oil separator?

There is a safety valve on the side of air oil separator, when the air pressure in the air oil separator reaches 1.1 times the set value, the safety valve automatically opens to release some compressed air to reduce the pressure in the air oil separator. The method to check the safety valve is to gently pull the air release lever on the safety valve when the compressor is fully loaded. If the safety valve can exhaust air to the outside, it is considered normal.

A pressure gauge is installed on the air oil separator to monitor the internal pressure of the air oil separator. A drain valve is installed at the bottom of the air oil separator. The drain valve should be opened regularly to drain the sedimented water and dirt deposited at the bottom of the air oil separator.

There is a oil level indicator next to the bottom of air oil separator which indicates the oil level in the air oil separator. The reasonable oil amount is when the oil level is in the middle of the upper and lower degrees.

If it is too high, it means that there is too much lubricating oil, which will increase the resistance of the main engine during operation and increase the workload of the air compressor and the air oil separator. If the oil level is too low, it means that the lubricating oil is insufficient, which will affect the safety of the whole machine and needs to be added in time.

The air oil separator is a high-pressure container and must be produced by a professional manufacturer with manufacturing qualifications. Each air oil separator will have a nameplate indicating the safe use pressure range, volume and certificate number. Do not use unqualified air oil separator.

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