What is a Screw Compressor? | What are types of Screw Compressors?

What is a Screw Compressor?

A rotary screw air compressor is a type of rotary compressor. A rotary screw compressor is an air compressor that uses two or more helical screws to compress the fluid. This compressor is also known as a twin-screw compressor. As the screws turn, air compression occurs.

The screws of these compressors mesh with each other. These screws are designed in such a way that they move in the opposite direction to each other.

The screw compressors are most commonly used in applications that need continuous flow and high CFM (Cubic Feet of air per Minute). These compressors are very common in heavy industrial services, such as gas delivery to the pneumatic production lines and conveyor systems.

Working of Screw Compressor

A rotary screw compressor works on the displacement principle. It uses two screws (i.e., male and female screws) to compress the air or gas. As the screws spin, they mesh with each other and create a series of chambers. The movement of these screws generates a vacuum and sucks air from the environment. As the air moves through the compression cylinder, it loses volume and becomes compressed.

A comprehensive working of the rotary screw compressor is given below:

  1. First of all, an electric motor drives the male screw (or rotor). As this screw gets power, it rotates and further rotates the female screw.
  2. The rotation of the screws generates vacuum into the compression cylinder and sucks air from the environment into the cylinder.
  3. The sucked air traps in between the male and female screws and moves along with the motion of the screw.
  4. As the screws move, they reduce the compression cylinder volume, which results in air compression.
  5. As the air is compressed according to requirements, the compressed air is discharged and stored for use. 

Types of Screw Compressors

1) Oil Injected Compressor

These types of rotary screw compressors use oil to lubricate the screws and make sure a smooth working. In this compressor, the oil injects into the compression chamber to offer a sealed cooling sump for working air. After compressing the air, an oil separator uses to remove the oil from the discharged air. This separated air is cooled, filtered, and recycled.

The oil has the capability to catch non-polar particles from the entrance fluid and efficiently reduces the particle load from the pressurized air particle filtration.

This oil also assists to ensure proper cooling of the compressed air and prevents the system from overheating. These compressors are the most commonly used type of screw compressor and are best suitable for most applications.

2) Oil-Free Compressor

The oil-free rotary compressors are most commonly employed in applications that don’t accept dragged oil, like in semiconductor production and medical research. However, this compressor needs proper filtration of air because hydrocarbons and other pollutants from the ambient air must also be removed before use.

These compressors use a two-stage compression process. During the compression phase, air flows by the intercooler to cool and avoid overheating. The oil-free screw compressor removes oil residue and produces very clean air compression. However, these compressors have high costs, complex design, are difficult to maintain, and generate high noise than oil-lubricated compressors.

Parts of Rotary Screw Air Compressor

The rotary screw compressor has the following major parts:

1) Rotary Screw

The rotary crew air compressor has two screws. These screws play a big role in the suction and compression of the air. These screws mesh with each other. They move in the opposite direction to each other.

The screws are installed in a closed cylinder and rotate in a complementary and intermittent manner. When the electric motor turns the screws, a cavity produces, and air enters into the compression cylinder. The rotation of the screws compresses the air.

2) Inlet Air Filter

This is one of the most important parts of the screw compressor. The air filter uses to remove the contamination from the air.

The inlet air filter installs at the inlet valve of the compressor. As the air enters the inlet valve, the air filters remove solid contamination particles from the air and then send filtered air into the compression cylinder for use. 

The proper maintenance and inspection of the air filter are very important for the proper working of the compressor. If you have a damaged filter, replace it immediately; otherwise, it may damage the parts of your compressor.

3) Oil Filters

These filters are most commonly used in oil-lubricated screw compressors. The main function of the oil filter is to remove the oil contamination before oil injection into the cylinder. The oil filter plays an important role in maintaining the cleaning of the compressed air and ensures proper lubrication and cooling of the system.

Mostly the oil filters are equipped with a bypass valve that will alert you if the oil filter is clogged or the internal operating temperature is too high. These bypass valves permit the crude oil to enter the compression chamber but not the oil filter.

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