Cómo funcionan los compresores de tornillo rotativo

Working principle of oil lubricated screw compressor

Let’s first understand the working principle of an oil-lubricated screw air compressor. Here, the motor drives the male rotor, which in turn drives the female rotor. Oil acts as a lubricant in this process. In addition to this primary purpose, the oil also acts as a coolant and seals the compression chamber.

In this case, the main engine compresses a mixture of air and oil. The mixture then flows into a so-called knockout tank. To keep the compressed air clean, most of the oil is separated here. This separation process uses centrifugal force, where air swirls around the tank and heavier oil particles fall out. Used in conjunction with an oil separator element, it can remove most oil from the air.

The separated oil will be reintroduced to the main engine or passed through the oil cooler. This usually depends on its temperature, which is why the compressor also includes a thermostatic valve to direct the oil to the correct path.

On the other hand, the air moves to the cooler and from there reaches the application.

Compressors also usually have a minimum pressure valve. This does not allow air to leave the system until a minimum pressure is reached that allows the compressor to self-lubricate. Additionally, it has several filters. Having an oil filter removes contaminants from the oil, such as tiny particles or water. There’s also an air filter to keep the intake air clean. Finally, the compressor also includes a blowdown valve to relieve trapped pressure when the compressor is idling.

Working principle of oil-free screw compressor

In an oil-free screw compressor, the timing between the two rotors is controlled by a set of gears. While the absence of oil ensures cleaner air, it also means the chamber cannot be sealed. Therefore, single-stage oil-free compressors cannot achieve as high pressures as oil lubricated screwcompressors. This is why many oil-free models are two-stage compressors.

Additionally, without oil to act as coolant, these compressors run hotter, reducing efficiency.

Although both types of compressors have similar designs, they are not the same. For example, an oil-free screw air compressor usually has two main engines with an intercooler between them. Additionally, they often include a lubricated gearbox that contains the gears of these main engines. To prevent oil from entering the air, there are usually oil seals.

On the other hand, there is no need for a knockout tank, oil cooler or thermal valve. Other than that, however, the components are the same.
Due to their differences, oil-free and oil-lubricated screw compressors are used in different applications. For example, oil-free rotary screw compressors are used whenever very high air quality is required. In particular, this is suitable for applications in the pharmaceutical or food and beverage sectors.

The role of oil in screw compressors

In oil-lubricated screw compressors, oil plays a vital role. This oil has three main uses:

Refrigeración: The oil absorbs the heat generated during compression, keeping the compressor cool.

Sealing: It provides hydraulic sealing that helps prevent air from leaking from the discharge side back to the suction side.

Lubrication: Oil lubricates the moving parts of the compressor, reducing wear and ensuring smooth operation.

What other types of compressors are there?

There are many types of compressors. In addition to oil-based air compressors and oil-free air compressors, there is another common positive displacement compressor – a reciprocating or piston compressor. Their counterparts are dynamic compressors, such as centrifugal compressors, which expel air through radial blades. Additionally, there are different types of screw compressors, including fixed speed and variable speed drive (VSD) variants.

Fixed-speed compressors operate at a continuously fixed speed, but this high efficiency only comes into play when the facility requires continuous operation at 100 percent capacity. However, in most cases, facilities do not require such high capacities, so fixed-speed compressors may continue to run before shutting down, resulting in wasted energy and money.

Correspondingly, variable speed drive (VSD) technology can rotate the motor at the appropriate speed according to the required air volume, thereby providing more flow. When air demand decreases, the motor automatically slows down to save energy and ensure proper flow. Especially when production is slow, workflow is interrupted, or during second and third shifts, VSD technology can greatly improve efficiency. This type of air compressor saves a lot of electricity and money compared to fixed-speed models.

In addition, there is a modern high-speed oil-free screw compressor with an asymmetric screw profile that significantly improves energy efficiency by reducing internal leakage. At the same time, external gears are often used to synchronize the position of counter-rotating rotors. Since the rotors do not contact each other or the compressor casing, there is no need for lubrication in the compression chamber, ensuring the oil-free characteristics of the compressed air. However, the built-in pressure ratio of such compressors is limited by the extreme temperature difference between inlet and outlet, so multi-stage operation and interstage cooling are often required to achieve higher pressures.

Another variation, known as an oil-lubricated screw compressor, injects oil into the compression chamber. This oil cools and lubricates the compressor elements, helping to dissipate heat while minimizing leaks in the compression chamber. This type of compressor element can be manufactured for high pressure ratios, but often with some compromise in energy efficiency.

Choosing efficient equipment is very important to save energy, which accounts for more than 80% of the cost of an air compressor, so the choice of compressor type and drive method is crucial.

Why Choose Rotary Screw Compressor?

Screw compressors offer several advantages that make them ideal for heavy-duty applications:

Efficiency: These compressors are designed to operate continuously, providing a steady supply of compressed air. This makes them more efficient than reciprocating compressors that require stopping and starting.
Durability: Screw compressors are built to last. They are rugged and can handle tough conditions, making them a reliable choice for heavy-duty applications.
Quiet Operation: Unlike other compressor types, screw compressors operate quietly, which is a significant advantage in noise-sensitive environments.

At BISON, we are committed to providing high-quality machinery that meets our customers’ needs. Our screw compressors are no exception. They embody our principles of efficiency, service, quality and integrity.

To learn more about our products or to discuss your specific needs, please Contacto BISONTE. We are dedicated to providing you with high-quality products and one-to-one high-quality service. Let BISON be your trustworthy partner in the field of machinery.