Air compressors are versatile and low-maintenance devices. Understanding the different types and how they work can help you choose the right one for your application.
If you need to inflate a tire or power an air wrench, sprayer, conveyor belt or piece of industrial farm equipment, you need an air compressor. But what is an air compressor exactly? And how do air compressors work?
All air compressors operate on the same basic premise, but they come in several types, designed for maximum efficiency in different settings, as well as many sizes. Read on to learn more.
Air compressor definition
An air compressor is a device that takes in air, pressurizes it, stores it in a tank as potential energy, then releases it to generate power. When the air is released, the potential energy is converted into kinetic energy, or energy derived from being in motion — the same kind of energy that sends a balloon flying when you release air from its neck.
What is an air compressor used for?
Air compressors are used for countless applications. Below are a few examples.
Inflating bike tires, air mattresses and pool equipment
Powering pressure washers
Powering small pneumatic tools such as sanders and nail guns
Powering an air brusher
Powering paint sprayers and sand blasters
Powering auto repair tools
Powering pneumatic tools from drills to air wrenches to jackhammers
Cleaning machinery using forced air
Moving air through large-scale ventilation and HVAC systems
Powering machinery on production lines and industrial farms
Powering food and beverage manufacturing processes
Powering machinery used in oil and gas operations
How does an air compressor work? Dynamic vs. positive displacement compressors
Air compressors use one of two main methods of compressing air: positive displacement or dynamic displacement. There are several types of air compressors within both categories.
Positive displacement air compressors
Positive displacement air compressors are more versatile and more common than dynamic displacement versions. They can be used for small home projects or major industrial operations. They work by forcing air into a smaller and smaller area in order to increase pressure. This is done using one of three main approaches.
Reciprocating air compressors
Reciprocating compressors are often used in homes or by contractors. They rely on a piston inside a cylinder to compress air. Single stage reciprocating compressors have one chamber and can generate enough energy to power hand tools such as sanders or nail guns. Two-stage or multi-stage air compressors have two or more compression chambers. They generate more power than single stage air compressors but are larger and must be cooled with water, so they’re more often found in factories and professional shops.
Rotary screw air compressors
Inside a rotary screw compressor, two screws turn in opposite directions. This creates a vacuum, trapping air and increasing pressure as the air moves away from the screw heads. Rotary screw compressors are a popular type of air compressor on commercial and industrial sites because they are durable and designed to operate continuously.
Rotary vane air compressors
Rotary vane compressors have an internal rotor located off-center in a circular cavity. The rotor has adjustable-length arms. As the rotor spins, the arms shorten, creating smaller spaces and compressing the air. Rotary vane compressors are a fit for hobby shops because of their smaller size, but they can also be used for commercial or industrial applications.
Dynamic displacement air compressors
Dynamic displacement compressors draw in a large amount of air, spin it at a high velocity, then restrict the flow, causing the air pressure to increase. They are large machines typically found in industrial applications. There are two types of dynamic displacement compressors, centrifugal and axial.
Centrifugal air compressors
Centrifugal compressors use a large rotor to pull in air. The air is pushed toward the edge of the compressor by centrifugal force. From there, it enters a diffuser, which slows the air speed and causes the pressure to increase. Centrifugal compressors are used in HVAC systems and in manufacturing plants, refineries and chemical plants.
Axial air compressors
In an axial compressor, air passes through a series of stationary blades placed closer and closer together to increase the pressure. These compressors are most often found in jet engines, but they can also be used to provide power to pumps or to power stations. They’re more expensive to purchase than other types of air compressors, but they’re also more energy-efficient over time.
How does an air compressor lubrication system work?
Some air compressors need oil to minimize friction between moving parts. The lubricant also helps expel heat. An air compressor that requires lubrication is more work to maintain but often provides higher air pressure and volume.
The answer to how these lubrication systems work is complicated and depends on the type of air compressor. Generally speaking, in many cases, oil is forced by a pressure pump into the compression chamber or “splashed” thereby rotating dippers affixed to the bottom of connecting rods. These dippers “dip” oil from an oil reservoir.
With oil-lubricated compressors, it’s possible for oil to find its way into the compressed air, which may pose a problem in certain applications. If oil gets into the air stream of air tools, the tools can malfunction. Oil-lubricated compressors generally aren’t a good choice for industries such as food production or pharmaceutical manufacturing. Oil filters can reduce the oil present in the air stream, but if you need fully uncontaminated air, choose an oil-free air compressor, which uses special coatings on parts to reduce friction.
Making the right choice
Given the number of types of air compressors, it can be hard to choose the right one. For most hobbyists and contractors, a reciprocating compressor will provide plenty of power. Larger compressors have the might to support industrial applications.
Not sure which type of air compressor is best suited to your application? Ask a qualified equipment vendor.