Suppose you are driving your car on a hot summer day and it break downs. Now one of the many probable reasons that come into your mind is that your car needs an oil change. The car uses oil to keep its engine lubricated for smooth functioning. Similar is the case with oil-injected air compressors that use oil as a lubricant because of its viscosity.
The oil injected in the air compressors also acts as a cooling agent to help cool down the compressed air. This enables oil-injected air compressors to work as a reliable workhorse, delivering you the desired amount of compressed air without any disruptions.
Oil-injected air compressors - Also known as an oil-lubricated or oil-flooded compressor, an oil-injected air compressor uses oil to lubricate its compression chamber and compressor bearings. Oil is used in sealing the air chamber because of its exceptional sealing properties and viscosity making it a good lubricant. This helps in reducing leakages within an industrial air compressor as the oil covers various inlets of the compression chamber. When the oil heats up during the process of cooling compressed air, it is circulated in a cooler within the compressor where it cools down and then is re-used within the industrial air compressor. This saves you the hassle of changing oil whenever it gets too heated up.
ISO air quality standards - To ensure the compressed air quality of oil-injected air compressors, the International Organization for Standardization (ISO) has put forward the ISO 8573-1:2010 standard that needs to be followed by every company. The reason being that the compressed air might be contaminated with oil vapors or particles that would not be suitable for your industrial processes. The ISO has formulated six different classes for air purity according to the number of particles per cubic meter as a function of particle size. The compressed air quality ranges from ISO Class 0-5 where Class 0 being 100% oil-free air and ISO Class 1 being technically oil-free air. The oil-free compressors need to comply with the ISO Class 0 standard whereas the ISO Class 1 is the best possible standard that can be achieved by an oil-injected air compressor. The ISO Class 1 specifies an oil concentration of 0.01 mg/m3 at 1 bar 14.5psia and 20°C.
Types and working principle - The working principle in all industrial air compressors is essentially the same; air gets compressed, its volume decreases, and its pressure increases. Industrial air compressors come in different types, makes, and models. Two of the most commonly used oil-injected air compressor types and their working principles are explained as following for your understanding:
a. Oil-injected rotary screw compressor - An oil-injected rotary screw compressor is generally used in those facilities, which require a constant supply of highly pressurized compressed air. In an oil-injected rotary screw compressor, oil is inserted in the compression chamber to lubricate and cool down the compressed air. It also helps in reducing any leakages of compressed air from the valves of the chamber. The cooled air then passes through several oil filters to minimize the oil carryover in both liquid and vapor form in the compressed air and to make it ISO Class 1 compliant. The oil is then cooled within the compressor before it is again circulated back in the compressor chamber.
b. Oil-injected piston compressor - Also known as a reciprocating compressor, a piston compressor is a positive-displacement compressor that uses its piston to compress air. When the piston moves downwards, air enters the compression chamber because of the vacuum created. As the piston moves upwards, the compressed air is pushed outside of the compression chamber with the help of outlet valves. The compression chamber of an oil-injected piston compressor is lubricated with oil using pressure lubrication or splash lubrication. This oil helps in cooling down the compressed air along with a reduction in friction generated due to the movement of the piston.
Applications - The use of an oil-injected air compressor or an oil-free air compressor depends on the application of the compressor and the specific industry sector involved. Oil-injected air compressors are generally used in manufacturing industries such as plastics, furniture, rubber, silicone, and in the automotive industry. There is a misconception that oil-injected air compressors cannot be used at all in the food and beverage industries or in the healthcare industry. However, you can use oil-injected air compressors too in such industries as well.
The only precaution is that compressed air generated through oil-injected compressors should not be used where there is a probability of it getting in direct contact with the final product and contaminating it. In such cases, you should be using an oil-injected air compressor that uses food-grade oil as a lubricant and cooling agent.
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