Reciprocating air compressors - working, types and uses with PDF

Hello there! Today at The Mechanical post we will see What are reciprocating air compressors, their classification, construction, working, advantages, disadvantages, and applications.

Also, you can download and print the PDF on Reciprocating air compressors by clicking on the button provided at the end of the article.

Reciprocating air compressors - working, types and uses with PDF

Definition of Reciprocating compressor 

Reciprocating compressors are a type of positive displacement compressors which by virtue of reciprocating motion compress the air/gas. 

We have a detailed article on the classification of various types of compressors, which you can check out here.

What is a positive displacement compressor?

A positive displacement compressor is defined as "The compressor which causes compression of air/gas by displacement of a mechanical  element is known as a positive displacement compressor." 

A reciprocating compressor is an example of a positive displacement compressor as it consists of a piston (mechanical element) which reciprocates causing compression of air/gas.

Types of reciprocating compressor

Reciprocating air compressors

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Reciprocating compressors are mainly classified into 3 types
  • Single-stage reciprocating compressor
  • Multi-stage reciprocating compressor
  • Diaphragm reciprocating compressor
The single and multi-stage reciprocating compressor are further classified into:
  • Single-acting
  • Double acting
Let us check out each of the above reciprocating compressors in detail starting off with Single-stage single acting reciprocating compressor.

What is a stage in a compressor?

A stage refers to the number of pistons and cylinders present in the compressor. A single-stage compressor means that it that a single arrangement of piston and cylinder. 

Single stage single acting reciprocating compressor

A single acting reciprocating compressor is the simplest type of reciprocating compressors. The suction and compression takes place only at one side of the piston hence the name " single-acting " . 

It is also similar to the reciprocating pump in construction and working with some differences. So let's take a look at its construction and working. 

No machine-readable author provided. Yyy assumed (based on copyright claims).CC BY-SA 3.0, via Wikimedia Commons

Construction of Single acting reciprocating compressor 

  • It consists of an air-tight piston and cylinder arrangement.
  • The piston is connected to a connecting rod which is connected to a prime mover. The prime mover can be an engine or an electric motor.
  • The cylinder is provided with inlet and outlet valves as shown in the figure.

Working of Single acting reciprocating compressor 

  • The prime mover provides reciprocatory motion to the piston.
  • This causes the piston to move to and fro in the cylinder.
  • When the piston moves backward it creates a vacuum thus sucking in the air/gas through the inlet valve. 
  • As the piston moves forward it compresses the air by applying force. And as the piston reaches its furthermost point, the compressed air exits through the outlet valve.
  • As the air is compressed its temperature increases considerably.
  • Thus in two strokes of the piston, the air is compressed.
  • However, the output of compressed air is not continuous as only during 1 stroke compression occurs.
So now, we will now discuss single stage double-acting compressor in detail.

What is meant by single acting and double acting?

When suction and compression occur only on one side of the piston it is known as single-acting reciprocating compressor. 

However, when suction and compression occur on both sides of the piston, it is called a double-acting reciprocating compressor.

Single-stage double-acting reciprocating compressor

In this type of reciprocating compressor, as the name suggests the compressor has a single-stage however it is double-acting. 

Construction of Single stage double acting reciprocating compressor

  • It consists of a piston enclosed inside a cylinder.
  • The piston is connected to a prime mover for providing reciprocating motion.
  • The cylinder has an inlet and outlet valve at one end along with another set of inlet and outlet valves at the other end as shown in the figure below.                                                                                                                                                                                                             

Construction of Single stage double acting reciprocating compressor

  • As the piston reciprocates from one end to another two actions take place i.e on one as the piston advances compression occurs, whereas simultaneously on the other side of the piston suction occurs. Hence the name double-acting.
  • As the suction and compression take place simultaneously the total output is continuous as compared to the intermittent output in single-acting.

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Multi-stage single acting reciprocating compressor 

A multi-stage compressor is a type compressor that consists of more than one stage i.e piston and cylinder arrangement. The compressor is single-acting.

Construction of Multi-stage single acting reciprocating compressor

  • A multi-stage reciprocating compressor consists of two or more stages placed separately. 
  • An intercooler is placed between the stages. 
  • The intercooler's input is connected to the output of the first stage and the output of the intercooler is connected to the input of the next stage.
  • Inside the intercooler, cold water is circulated to cool down the compressed air.
  • It can be said that the intercooler is a bridge connecting the different stages.

Working of Multi-stage single acting reciprocating compressor

  • The air/gas at lower pressure enters the first stage and is compressed to a particular pressure. 
  • During this, the temperature of the air rises considerably.
  • The output of the first stage passes through the intercooler where the air/gas temperature is brought down.
  • The high-pressure air/gas enters the next stage and is compressed at an even higher pressure. 
  • This compressed gas is then exited to its destination via the outlet valve.

Multi-stage double-acting reciprocating compressor 

It is the same as the single-stage double acting compressor however it has more than one stage. 

This compressor consists of more than one stage and all of them are double-acting i.e. suction and compression occur on both sides of the piston.

Brian S. ElliottCC BY-SA 4.0, via Wikimedia Commons

An intercooler is placed in between the stages for cooling of the air/gas. Rest all things are mostly similar to the above-mentioned compressor.

Diaphragm reciprocating compressor

This compressor is very similar to the single-stage single-acting reciprocating compressor except that it has a membrane or a diaphragm in between the piston and the valves.

The diaphragm separates the piston with the air/gas which is to be compressed. So as the piston reciprocates inside the cylinder it causes the diaphragm to move back and forth thus producing suction and compression effect. 

This allows the compressor to compress toxic gases as well as gases that could corrode the piston.

Advantages of reciprocating compressors

  • It is used where high compression is required.
  • It is inexpensive as compared to other types of compressors.
  • It is easy to maintain.
  • It has a good working life.
  • It is durable.

Disadvantages of reciprocating compressors

  • It requires a considerable amount of floor area.
  • It produces loud noise during operation.
  • It gives intermittent i.e not continuous output (except double-acting compressors).
  • Due to reciprocating element frictional resistance is more.
  • Since there is more frictional resistance there is considerable wear.
  • During compression, the temperature of air/gas increases considerably. Thus an intercooler is required especially in a multi-stage compressor.

Applications of reciprocating compressors

  • Reciprocating compressors are used in oil refineries.
  • For pumping in gas pipelines.
  • It is also used in chemical industries.
  • It is also used in many refrigeration and air conditioning systems i.e vapour compression cycle.

That's an overview of the Reciprocating air compressors. If you like this post or have any suggestions do let us know in the comments we would love to hear from you.

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We'll be back soon with another interesting article till then Keep learning and read The Mechanical post!


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