Two Different Types of Compressors, Oil Free vs Oil Flooded, Which Is Better?
Among various kinds of air compressors, they can be classified in two different types of oil free and oil flooded compressor. Which of this two technologies is better? Let Kotech show you the differences between oil free and oil flooded air compressors from multiple perspectives.
Applications of industrial oil lubricants in air compressors
Working principle of oil free air compressor
The working principle of oil free air compressor mainly involves increasing the density and temperature of air by compressing air, so as to achieve the effect of increasing air pressure. This type of air compressor usually adopts technologies such as screw air compressor or centrifugal air compressor. Its structure is relatively simple and does not have components such as cylinders and pistons in traditional air compressors. The main components of oil free air compressors include air compressor body, motor, control system and treatment equipment.
Specific to different types of oil free air compressors, the working principles are different:
Oil free screw air compressors compress air through two-stage screw rotors and remove water from the compressed air through water-air separator. The rotors of this air compressor is finely processed to ensure the coaxiality and precise fit, so as to achieve long-term, efficient and reliable operation. While working, the oil free air compressor draws air into the machine through the rotating screw or centrifugal wheel, then compresses it, and finally discharges the high-pressure air.
During this process, the gears and bearings of the air compressor are lubricated by special lubricating oil. The oil seal in the main engine prevents the lubricating oil in the bearing cavity from entering the compression cavity, ensuring that the output air is absolutely oil free, while the air seal prevents the air in the compression cavity from leaking outward, so the discharged compressed air is very clean and oil free, which is very suitable for some occasions with high requirements for air purity, such as food processing, pharmaceuticals and semiconductor industries.
Silent oil free air compressor belongs to micro piston air compressor. When the motor drives the air compressor crankshaft to rotate, the piston with self-lubrication and no lubricant is reciprocated through the transmission of the connecting rod. The working volume composed of the inner wall of the cylinder, the cylinder head and the top surface of the piston will change periodically to realize the process of air intake, compression and exhaust.
Water-lubricated oil free air compressor inhales water while inhaling air, water and air are mixed together in compressing possess. This type of air compressor generally adopts a single screw design, uses water as a seal.
In general, oil free air compressor is an kind of environmentally friendly air compressor that produces high-quality compressed air. It has a wide range of applications and has become an indispensable equipment in many industrial fields.
The principle of oil flooded air compressor
The working principle of oil flooded air compressor is to suck air into the air compressor and then compress it into a high-pressure state through the reciprocating motion of the compression piston. Lubricating oil is used here to ensure that the piston has sufficient lubrication effect and air-tightness.
There are also oil flooded screw air compressors, which compress the air through the mutual meshing of the rotors. It is also necessary to spray oil on the screw to lubricate and cool the screws at this process.
After the air compression is completed, the high-pressure air-oil mixture is discharged from the air end and enters the oil-gas separation system, the oil-gas separator is used to separate the oil in the air to purify compressed air. This process can basically remove all the lubricating oil in the compressed air and the separated oil will be returned to the lubrication system.
At the same time, the compressed air flows into the after cooler. The cooler is used to cool the compressed high-temperature air to prevent the moisture in the air from condensing into water droplets, the after cooler system consists of a heat exchanger (air-cooled and water-cooled), a condensate separator and an exhaust device. In this process most of the water vapor contained in the air is condensed and precipitated.
screw compressor line diagram
Finally, the purified compressed air can be discharged for industrial use or may be stored in an air storage tank for later use to meet the air demand in production process.
The advantages of oil flooded air compressors include high compression efficiency, stable air supply, low noise, and long service life.
During air compressing, the air compressor will generate large high temperatures, oil can take away the heat to help dissipate heat and lubricate the running parts in the main engine. The compressed oil-gas mixture will be separated in the oil-gas separation barrel, and the separated compressed air will have an oil content of free than 5PPM after being recovered through the secondary oil return pipe.
Applications: Oil flooded air compressors are widely used in industry, aviation and other fields. In the industrial field, oil flooded air compressors can be used in the production process of factory automation, ceramics, plastics, steel, textiles and other industries; in the aviation field, oil flooded air compressors can be used in aircraft starting, engine operation and other processes.
Are you looking for a reliable and efficient power source for your industry? Kotech dealers are experienced in finding the perfect air compressor for your needs.
Contact your local Kotech dealer today and discover how an air compressor can increase your productivity and safety.
The lubricating oil in air compressors
Definition of oil free and oil flooded
It should be noted that oil flooded and oil free is defined basic on whether the compressed air contains oil, not whether the air compressor uses lubricating oil. Oil flooded air compressors produce compressed air by separating the oil-gas mixture before it entering the after treatment equipment.
Oil free means that there is no lubricating oil in the air compressor cavity. It is possible to lubricate with other lubricating medium like water or completely without lubricating medium.
The International Organization for Standardization(ISO) has developed global standards for compressed air specifically for industrial and commercial purposes. According to the final air purity (determined by the number and size of particles contained per cubic meter of air), compressed air can be ranked from ISO Class 1 to Class 5. The original version of the ISO compressed air purity standard was compiled by filter manufacturers in 2001 and updated in 2010. It defines five levels of oil concentration, with the lowest oil content being ISO Class 1.
ISO Class 1 requires an oil concentration of 0.01 mg/mยณ at 1 bar (14.5psia) and 20ยฐC (68F), which was then known as a “technically oil free solution”. However, the latest standard now specifies limits for total oil content (aerosol, liquid and vapor), introduces a specific standard for oil vapor measurement, and adds a new class (Class 0) to meet more stringent air quality requirements. ISO Class 0 represents the highest level of compressed air quality and only 100% oil free compressed air can be certified.
ISO Class 0 oil free air compressors guarantee 100% oil free air while air compressors rated as “technically oil free” ISO Class 1 are still at risk of oil contamination because they are actually oil-lubricated air compressors that equipped with oil-gas separators.
The role of oil in air compressor
Air compressors require oil mainly because air compressor oil plays vital roles in the operation of the machine, including lubrication, cooling, sealing, rust prevention, anti-corrosion and other multiple functions:
Lubricating effect: Air compressor oil can significantly reduce friction and wear between mechanical components. When the air compressor is working, severe friction will occur on the surface of the compression device. A function of air compressor oil is to form an oil film between moving parts, separate the contact surfaces, replace dry friction with wet friction, and change solid friction into liquid friction. This protects machinery and components and prolongs their service life.
Sealing effect: The air-tight oil film formed by the air compressor oil has a strong sealing effect, which can prevent air leakage, dust removal, air blow-by, and keep the internal environment of the air compressor clean and stable.
Cooling effect: The oil sprayed into the screw air compressor can take away the heat generated when compressing air and the heat generated by mechanical friction, which is crucial to maintaining the normal operation of air compressors.
Anti-rust and anti-corrosion effects: Air compressor oil can adhere to mechanical parts, isolate air, prevent rust and corrosion, and further protect the air compressor from the external environment.
In addition, air compressor oil also has the characteristics of anti-emulsification and anti-foaming properties, allowing oil flooded air compressors to adapt to various complex working environments.
Comparison of two types of air compressors
Characteristics of oil free air compressor
Compared with traditional oil flooded air compressors, oil free air compressors have shown significant advantages in below aspects.
High compressed air quality: First of all, the main advantage of an oil free air compressor is that its compressed air does not contain oil, so the output air is cleaner and is suitable for applications with high air quality requirements such as food, medical, and pharmaceutic industries. Besides, oil free air is more friendly to environment.
Compact structure: Secondly, oil free air compressors usually adopt a small cylinder design, making the overall structure more compact and lightweight. This design not only improves the flexibility and balance of the air compressor, but also reduces the size requirements because it does not require installation of additional devices such as oil-gas separator.
The vibration is slight and the pulsation is small: In addition, the vibration amplitude of the oil free air compressor is small, which further increases its stability and reliability. In terms of performance, due to the small stroke volume of its single cylinder, the pulsation at the intake and exhaust ends is controlled to free than 1%, eliminating the need to install a pulsation elimination device.
Drawbacks of oil free compressors
However, oil free compressors also have their limitations.
Higher investment cost: The initial purchase cost can be very high, sometimes may even be twice as expensive as oil flooded compressors.
High operating temperature: The working principle of oil free compressors causes them to generate a lot of heat and are not easy to cool. They are free efficient or have higher temperature rise when running under high load or continuously. The higher their working pressure or the higher the pressure of compressed air required by the factory, the greater the possibility of wear of the compressor or the generation of heat sufficient to burn and/or distort parts.
Low gas production and compressed air pressure: Generally only suitable for places with high gas requirements, such as hospitals. Since oil free compressors require the use of higher-grade air compressor oil or special coatings as pre-lubrication, the maintenance requirements are more stringent.
Higher noise level: Generally, the noise level of oil free compressors is higher than that of oil flooded compressors because it cannot use lubricating oil in the compression chamber to reduce mechanical friction.
Shorter service life: Generally, oil free compressors donโt last as long as oil-lubricated compressors. The Teflon coating that lubricates the internal cylinders can wear out over time, and this wear is exacerbated when the oil free compressor is exposed to extreme temperatures or used for long periods of time.
Maintenance and care: Generally, to extend the service life of an oil free compressor will take more time, effort, and money than oil-lubricated compressors, as oil free compressors require a higher grade of air compressor oil and require more stringent maintenance operations from technicians.
Characteristics of oil flooded air compressor
Relatively low initial purchase cost: oil free air compressors are much more expensive than oil flooded air compressors, sometimes even twice as expensive. If you have limited funds and don’t have to worry about oil residue or contamination, lubricated air compressors may be the most affordable choice.
More compressed air output: Oil flooded air compressors have higher efficiency and higher output pressure because they use oil to lubricate the air compressor head and bearings, allowing them to operate more efficiently.
High compressed air pressure: In addition, oil flooded air compressors are able to produce higher compressed air pressures and are suitable for applications that require higher pressures, such as the automotive industry, steel industry, etc.
Continuous working ability: Under high loads and continuous operation, they usually still possess high efficiency and stability.
Long service life: The use of lubricating oil helps to cool the machine and greatly extend the service life of the machine.
Maintenance and care: The maintenance of oil flooded air compressors is relatively simple, and most of the time you only need to replace the lubricating oil and oil filter regularly.
free noise: Because the use of oil lubrication greatly reduces various mechanical frictions in compressing process, so it is quieter than oil free air compressors.
Drawbacks of oil free compressors
Compressed air contains oil: The compressed air generated contains a certain amount of oil, which needs to be processed through an oil-gas separator.
Risk of oil contamination: Since the oil-containing air compressor mixes compressed air and oil together, there is a certain risk of oil contamination even after passing through the oil-gas separator, so it is not suitable for occasions with high air quality requirements.
Additional maintenance: If the machine’s working intensity is high, the oil and filter need to be replaced frequently, which increases the maintenance burden.
Choose oil free or oil flooded air compressor?
When choosing between oil free and oil free compressors, you first need to evaluate the compressed air needs of your equipment. There are situations where the consequences of oil contamination are so severe that an oil free air compressor is necessary. Most machine manufacturers and small workshops use oil flooded compressors because the consequences of oil contamination are not as severe as in food production.
If oil free compressed air is not a must, an oil flooded compressor is a more economical choice. oil flooded screw compressors cost much free than oil free compressors. Want to know which specific kind of compressor among oil flooded or oil free compressors is better suitable? Take a look at our previous page-How to Select Air Compressor Rotary Compressor vs Reciprocating Compressor๏ผ
When choosing an oil free compressor, always choose an ISO Class 0 oil free compressor rather than a “technically oil free” compressor. oil free compressors are usually much more expensive, but they are safer to use in sensitive applications. With a Class 0 oil free compressor, you can be sure that the compressed air will not contaminate your end equipment and products.
If you are unsure whether to choose an oil flooded or oil free air compressor, or if you don’t know how to choose an air compressor, you can seek advice from a compressed air professional. Kotech is happy to assist you at any time!
