Air Compressor | Working and Types | Uses of Compressed Air

What is an Air compressor?

An air compressor is a device that converts power (generally electric) into pressure energy of compressed air. An air compressor is generally coupled with a storage tank, which is used to store compressed air.

Here might be a question arising in your mind. What will happen if a compressed air storage tank gets overfilled? Would it burst?

The answer is no, it wouldn’t burst, if all the safety interlocks are working. Now a question could arise in your mind, what are the safety interlocks associated with the air compressors.

Don’t worry we are here with an answer.

The safety interlocks used in modern compressors are the sophisticated sensors, which monitor the pressure of air in the compressor. If the pressure exceeds a specified limit the compressor stops working immediately.

Here could be a question in your mind. What if for any reason the pressure sensor stopped working?

In case of pressure sensor failure, the pressure relief valve works.

What is a pressure relief valve?

A Pressure relief valve is a mechanical device that is used as a safety device in air compressors. Pressure relief valve are manually preset on a particular threshold pressure. If this pressure reaches anyhow in the compressed air storage vessel, the pressure relief valve operates and releases the excess air from the vessel. After achieving a safe pressure, it again closes and stops air outflow.

Compressed air is not only used to inflate our car tyres. There are several other uses of compressed air.

Uses of Compressed air

Compressed air is used in following applications

• Pneumatics, the use of pressurized gases to do work
• Pneumatic post, using capsules to move paper and small goods through tubes.
• Air tools
• HVAC control systems
• Vehicle propulsion
• Energy storage
• Air brakes, including:
• Railway braking systems
• Road vehicle braking systems
• Underwater diving, for breathing and to inflate buoyancy devices
• Refrigeration using a vortex tube
• Air-start systems in engines
• Ammunition propulsion
• Air guns
• Airsoft equipment
• Paintball equipment
• Cleaning dust and small debris in tiny spaces
• Sandblasting in machine shops
• Injection molding
• Food and beverage capping and fermentation

Types of air compressors

1. Reciprocating Compressor

A reciprocating compressor or piston compressor is a positive-displacement compressor that uses pistons driven by a crankshaft to deliver gases at high pressure.

Reciprocating Compressor types

• Single-Stage Reciprocating Compressor
• Two-Stage Reciprocating Compressor

2. Rotary-screw compressor

A rotary-screw compressor is a type of gas compressor that uses a rotary-type positive-displacement mechanism. They are commonly used to replace piston compressors where large volumes of high-pressure air are needed, either for large industrial applications or to operate high-power air tools such as jackhammers.

3. Rotary Vane Compressor

A rotary vane compressor is a positive-displacement compressor that consists of vanes mounted to a rotor that rotates inside of a cavity. In some cases these vanes can have variable length and/or be tensioned to maintain contact with the walls as the pump rotates.

4. Scroll Compressor

A scroll compressor (also called spiral compressor, scroll pump and scroll vacuum pump) is a device for compressing air or refrigerant. It is used in air conditioning equipment, as an automobile supercharger (where it is known as a scroll-type supercharger) and as a vacuum pump.

5. Root Type compressor

The Roots type blower is a positive displacement lobe pump which operates by pumping a fluid with a pair of meshing lobes not unlike a set of stretched gears. Fluid is trapped in pockets surrounding the lobes and carried from the intake side to the exhaust.

Comparison between Rotary and Screw compressor

Rotary Compressor	Screw compressor
For low and medium pressure	For medium and high pressure
Lubrication system is simple	Lubrication system is complex
Maintenance cost is low	Maintenance cost is high
Output is continuous	Output is intermittent
Compressor size is small	Compressor size is relatively big
Less vibration	More vibration

Comparison between Centrifugal and Reciprocating compressor

Centrifugal Compressor	Reciprocating compressor
Suitable for high discharge	Suitable for less discharge
Suitable for low pressure	Suitable for high pressure
Compressor size is small	Compressor size is relatively big
Maintenance cost is low	Maintenance cost is high
Output is continuous	Output is intermittent
Less noisy	Relatively more noisy
Better mechanical efficiency	Relatively less mechanical efficiency
Less vibration	More vibration

Comparison between Centrifugal and Axial compressor

Centrifugal Compressor	Axial Compressor
Good part load efficiency	Poor part load efficiency
It requires more frontal area for a given mass flow rate	It requires less frontal area for a given mass flow rate
Suitable for low pressure	Suitable for relatively high pressure
Not suitable for multi-staging	Suitable for multi-staging
Low starting torque	High starting torque
Low maintenance cost	High maintenance cost
Low running cost	High running cost
Air flow radially	Air flow axially

Image sources:

Pressure relief valve: Attribution: By Mbeychok – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=18559003

Reciprocating air compressor: Attribution: By No machine-readable author provided. Yyy assumed (based on copyright claims). – No machine-readable source provided. Own work assumed (based on copyright claims)., CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=920341

Screw compressor: Attribution: By Airpol PPS – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=71251373

Vane compressor: Attribution: Jonasz at Polish Wikipedia [CC BY-SA 1.0 (https://creativecommons.org/licenses/by-sa/1.0)], via Wikimedia Commons

Roots air compressor: Attribution: By Graphic: Inductiveload Animation MichaelFrey [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], from Wikimedia Commons