Compressor is a mechanical device that increases the pressure of a gas by reducing its volume. Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas. Liquids are relatively incompressible; while some can be compressed, the main action of a pump is to pressurize and transport liquids

Air compressors fall into two different groups:

1.   Positive displacement  

2.   Dynamic

 

Positive Displacement:

Positive displacement compressors work by forcing air into a chamber. The volume of this chamber is then decreased, by the displacement of a mechanical linkage reducing the volume which compresses the air. Once maximum pressure is reached within the chamber, a valve opens, and the air is then discharged into the outlet system. Both rotary and reciprocating compressors fall into this category.

Dynamic:

         Dynamic compressors pressurize air through the use of rotating impellers which accelerate and decelerate the air. The deceleration, or restriction, of the air is what creates the increase in pressure. Some of these compressors are completely oil-free for highly sensitive environments. Axial and centrifugal are both dynamic displacement compressors.

Rotary Compressor:       

         Rotary compressors are a subset of positive displacement machines. Rotary compressors have a number of features in common even though there are differences in construction. Unlike reciprocating compressor, rotary compressors do not use valves to move the gas through the machine. When compared to a reciprocating compressors rotary compressors:

Ø Are lighter in weight

Ø Experience less vibration

Ø Do not require heavy foundations

Rotary compressors physical design varies widely. Both single- and multiple-rotor construction are used. The design of the rotor is the main item that distinguishes the different types of rotary compressors.

 

Types of Rotary Compressor:

 

1.   Screw

2.   Vane

3.   Lobe

4.   Scroll

 

Screw Compressor:

         Screw type Rotary Compressor make up a large segment of the compressor market today. Inside the unit, there are two large screws that are rotating against each other. Air comes in through an inlet port at one end of the screws, and then flows between the two rotors. As it moves down the length of the screws, the air gap gets tighter and tighter, compressing the air toward the outlet. These compressors are very popular because they are quiet and they can produce large volumes of air with great consistency. In addition, they come in several varieties, including an oil-free option that reduces the amount of maintenance required to keep the compressor running. Since the two screws do not make contact, there is very little wear other than the motor itself.

Types of Screw Compressor:

A. Oil Free Compressor

B.  Oil Injected Compressor

 

A.   Oil-free compressors:

These are used in applications where entrained oil carry-over is not acceptable, such as medical research and semiconductor manufacturing. However, this does not preclude the need for filtration as hydrocarbons and other contaminants ingested from the ambient air must also be removed prior to the point-of-use. Subsequently, air treatment identical to that used for an oil-flooded screw compressor is frequently still required to ensure a given quality of compressed air.

 

B.    Oil-injected rotary screw compressor:

In Oil Injected rotary compressor oil is injected into the compression cavities to aid sealing and provide a cooling sink for the gas charge. The oil is separated from the discharge stream, then cooled, filtered and recycled. The oil captures non-polar particulates from the incoming air, effectively reducing the particle loading of compressed air particulate filtration. It is usual for some entrained compressor oil to carry over into the compressed gas stream downstream of the compressor. In many applications, this is rectified by coalesce/filter vessels. In other applications, this is rectified by the use of receiver tanks that reduce the local velocity of compressed air, allowing oil to condense and drop out of the air stream to be removed from the compressed air system via condensate management equipment.

 

Components in Rotary Screw Compressor:

 

·       ROTORS /ROLLERS

·       COMPRESSION CYLINDERS

·       AIR FILTERS

·       OIL FILTERS

·       BEARINGS

·       SUCTION VALVE

·       DISCHARGE VALVE

·       MOTOR

·       SYSTEM CONTROL

·       STORAGE TANKS

·       SEPARATORS

·       GASKETS & SEALS

 

Screw Compressor Actual Arrangement

Applications of Rotary Screw Compressor:

Ø  Metallurgy and Mining

Ø  Papermaking and Printing

Ø  Medicine and Health

Ø  Household Appliance

Ø  Electronic and Electrical, Etc.

 

Rotary Vane Compressor:

         The next type of rotary compressor is the vane type. This system uses a set of vanes that are slightly offset within the inner chamber. As air comes in through the inlet, rotating vanes push the air along into a tighter and tighter edge of the circle, effectively compressing it while using minimal effort and travel of the air itself. These are very simple compressors that are easy to maintain as well, but vanes wear down over time and can become less effective at forcing the air into the compressed space. In many cases, replacement vanes are available to restore the compressor to its original operating tolerances every few years.

Components in Rotary Screw Compressor:

 

·       VANE

·       COMPRESSION CYLINDERS

·       AIR FILTERS

·       OIL FILTERS

·       BEARINGS

·       SUCTION VALVE

·       DISCHARGE VALVE

·       MOTOR

·       SYSTEM CONTROL

·       STORAGE TANKS

·       SEPARATORS

·       GASKETS & SEALS

 

Rotary Vane Compressor Actual Arrangement

Applications of Rotary Vane Compressor:

Ø  Agriculture Industry

Ø  Food and Beverage Industry

Ø  Medicine and Health

Ø  Turbine Operations

Ø  Dry Cleaning, Etc.

 

Lobe Compressor:

The Lobe Type Compressor follow the same model as vane compressors, except that the air comes into a chamber with two spinning wheels. The spinning wheels have small pockets cut into them at opposite ends. As air comes in, it fills that pocket and then gets whisked toward the opposite side of the chamber, forcing it to compress within the shrinking space. This is simply a less wearable version of a vane compressor that is affordable and simple to use. However, lobe type compressors do have some limitations when it comes to capacity, so they may not be the right fit for an application that requires high pressures and constant airflow.

Types of Rotary Lobe Compressor:

A. Two Lobe

B.  Three Lobe

 

A.   Two Lobe Rotary Compressor:

A two lobe compressor is the one which have two lobes these are at an angle of 180 Deg. from each other. When the lobe compressor is working it leads to the formation of 3 packets. These are the most basic type of Lobe Compressor

A. Three Lobe Rotary Compressor:

A three lobe compressor is the one in which there are three lobes they are at an angle of 120 Deg. from one another. During working it leads to the formation of 5 packets. Generally these are used at places wherein more flow rate is needed. With increase in need the number of lobes also increases.

Components in Rotary Lobe Compressor:

 

·       LOBE

·       GEAR

·       COMPRESSION CYLINDERS

·       AIR FILTERS

·       OIL FILTERS

·       BEARINGS

·       SUCTION VALVE

·       DISCHARGE VALVE

·       MOTOR

·       SYSTEM CONTROL

·       STORAGE TANKS

·       SEPARATORS

·       GASKETS & SEALS

 

Rotary Lobe Compressor Actual Arrangement

 

Applications of Rotary Lobe Compressor:

 

Ø   Textile and Clothing

Ø   Electric Power

Ø   Construction and Building Material

Ø   Mechanical and Electrical Machinery

Ø   Petrochemical Engineering, Etc.

 

Scroll Compressor:

Scroll type compressors are similar to screw type compressors, except that the internal parts look a little bit different. In this case, there are two spirals or scrolls and one of them remains stationary. Air comes in along the outside edge of the scroll and gets pulled in toward the center of the spiral in tighter and tighter circles before it is forced down through the center outlet. These compressors require little maintenance and they are notably smaller than screw type compressors so they are perfect for limited space applications.

Components in Rotary Scroll Compressor:

 

·       SCROLL

·       COMPRESSION CYLINDERS

·       AIR FILTERS

·       OIL FILTERS

·       BEARINGS

·       SUCTION VALVE

·       DISCHARGE VALVE

·       MOTOR

·       SYSTEM CONTROL

·       STORAGE TANKS

·       SEPARATORS

·       GASKETS & SEALS

 

Rotary Scroll Compressor Actual Arrangement

Applications of Rotary Scroll Compressor:

 

Ø Household Appliance

Ø Electronic and Electrical

Ø Transportation

Ø Light Industry and Food

Ø Dry Cleaning, Etc.

 

These are the four main types of rotary compressors that you will see today. While vane and lobe type compressors are inexpensive, many industrial operations prefer screw and scroll type compressors because they are able to handle much more air and provide better compression overall.