Reciprocating Air Compressor: Components, Types And Working Principle

In this article, I will share with you the components, types, and working principles of a reciprocating air compressor.


What is a compressor? A compressor is a machine that receives air from the atmosphere and compresses it with the help of mechanical energy and delivers it to a vessel for storage or to the point of use.


The compressor compresses the air that it receives from the atmosphere and puts it under pressure so that it can be used for several purposes.


Compressed air has many uses like; the operation of power tools, working medium of pneumatic devices, supercharging internal combustion engines and gas turbines, fuel atomizers and so many more.


This clearly shows you that compressed air is very essential and thus understanding how reciprocating air compressor works will help you to appreciate this machine.


The reciprocating air compressor is a positive displacement type of compressor.


If you want to know the difference between a positive displacement and a dynamic compressor, read the article below.


You might like this: Difference Between Positive Displacement and Dynamic Compressors


In short, in a positive displacement, a quantity of given air is trapped within a compression chamber and the volume is reduced mechanically thus increasing the pressure of the air before the discharge.


This puts the under to be discharged under higher pressure.


And this is what a reciprocating air compressor is all about.


reciprocating air compressors are widely used in industries for both air and refrigerant compression.


You might like this: Vapour Compression Refrigeration System: Components And Working Principle


What I can tell you is that, if you understand how a reciprocating pump works, you will not have a problem understanding the working principle of this air compressor.


The only big difference is that the reciprocating air compressor compresses air while a reciprocating pump compresses liquid.


Without wasting too much time, let me share with you some of the components of the reciprocating air compressor and their functions.


Components of a reciprocating air compressor and their functions.

These are the main components of a reciprocating air compressor;

  1. Crankshaft and Connecting rod.
  2. Piston.
  3. Cylinder.
  4. Suction line and Discharge line.
  5. Spring-loaded discharge valve and spring-loaded suction valve.
  6. Electric motor.


Crankshaft and Connecting rod: The crankshaft is used to supply power to the piston via the connecting rod.


The rotation of the crankshaft facilitates the forward and backward movement of the piston within the cylinder.


Piston: the piston is the device that moves forward and backwards within the cylinder reducing and increasing the volume of air within the cylinder.


Cylinder: This is a strong vessel that accommodates the piston and provides the space needed for air to be expanded and contracted.


Suction line and Discharge line: the suction line is used to draw in air from the atmosphere while the discharge line is used to deliver the air to the point of use or an air receiver.


Spring-loaded discharge valve and spring-loaded suction valve: the spring-loaded discharge valve allows the outlet of air from the reciprocating air compressor and the spring-loaded suction valve allows the intake of atmospheric air into the compressor.


Electric motor: it’s used to provide power to run the compressor.


Types of reciprocating air compressors

These are the types of reciprocating air compressors;

  1. Single-acting reciprocating air compressor.
  2. Double-acting reciprocating air compressor.
  3. Single-stage reciprocating air compressor.
  4. Two-stage reciprocating air compressor.
  5. Multi-stage reciprocating air compressor.


Single-acting reciprocating air compressor: this type of reciprocating air compressor accomplishes compression of the air using only one side of the piston.


Double-acting reciprocating air compressor: this is a reciprocating air compressor that achieves its compression of air using both (two) sides of the piston.


Single-stage reciprocating air compressor: this is a type of reciprocating air compressor that achieves its entire compression using a single cylinder or a given group of cylinders in parallel.


Two-stage reciprocating air compressor: this is a type of reciprocating air compressor that compresses air in two stages and in between the stages the air is cooled.


The two-stage reciprocating air compressor provides higher pressure and is characterised by lower discharge temperature (1400C to 1600C) compared to the single-stage which has an air discharge temperature of (2050C to 2400C).  


Multi-stage reciprocating air compressor: this is a type of reciprocating air compressor that achieves its entire compression using three or more steps of compression grouped in series.


They are used where over 100 horsepower is needed thus preferable in most plants.


The good thing about reciprocating air compressors is that are available either as air-cooled or water-cooled, with lubricated and non-lubricated configurations.


The air-cooled reciprocating air compressor is cooled by air while the water-cooled air is cooled by water.


Lubrication in a reciprocating air compressor is by the means of a gear pump which feeds oil-ways in the crankshaft and the big bearings.


The crankshaft and gudgeon pins are lubricated by a splash lubrication system.


Cooling vanes are provided on the exterior surface of the blocks, cylinder heads and the delivery chamber to maximize the cooling effect within the reciprocating air compressor.


Working principle of reciprocating air compressor.

The piston within the cylinder moves upwards and downward or backwards and forward depending on the cylinder orientation.


This reciprocating movement of the piston is brought about by converting the rotating/circular motion of the crankshaft that is provided by the electric motor to linear motion with the aid of the connecting rod.


The top side of the cylinder is covered by valve plate assembly while the other end is open. The open side of the cylinder is where the connecting rod connects with the piston.


Downward movement of the piston.

When the piston moves downward any residual air left in the cylinder will expand due to the increase of the volume until it will reach a pressure that is slightly below the atmospheric pressure.


Since the air outside the cylinder has a higher atmospheric pressure compared to the residual air within the cylinder the suction valve will open allowing air to enter the cylinder.


After the air enters the cylinder the spring-loaded suction valve will close the inlet pipe by the action of the spring thus preventing any air from leaving the cylinder.


During this stroke, the delivery valve remains closed since the air outside the valve is under higher atmospheric pressure than the air within the cylinder.


Upward movement of the piston.

When the piston moves upwards the volume within the cylinder is reduced mechanically and the pressure of air increases.


The slight increase of pressure within the cylinder will close the inlet valve since the air pressure within the cylinder is higher than the pressure outside the suction valve.


As the pressure of air within the cylinder increases the delivery valve will open since the air pressure within the cylinder is higher than the air pressure outside the delivery valve, and this will allow the air to be discharged out of the cylinder under high pressure.


At the end of the compression stroke, the piston will move down the cylinder to allow the process to be repeated.


And this is how the reciprocating air compressor works.


Thanks for reading, if you have any questions you can leave your comment in the comment section.


Related articles to check.

  1. Hydraulic System: Components, Types & Principles
  2. Underground Water Reservoir Design Recommendations
  3. Nuclear Power Plant: Introduction, Components And Working Principle
  4. Thermodynamic Properties Of Refrigerants
  5. Factors To Consider When Designing An Air Duct System Supply

Leave a Comment