How Do Air Compressors Work?
Air compressors are an
invaluable tool for both industrial work and DIY at home, and there are several different types to choose
from depending on the job you need doing. Air compressors have a number of uses, such as to fill gas
cylinders for industrial purposes and scuba diving, to create the power needed to run pneumatic tools and
spray guns, for pumping up automotive tyres, and within heating and air conditioning systems.
As we’ve touched on here, there are myriad uses for air compressors both in commercial and domestic
environments. Within the category of air guns, there are several types, each of which is suitable for a
different job. We’ve compiled a guide to all the major types of air compressor, how they work and how they
differentiate from one another.
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make the proper decisions for your business and industry.
Get all the information you need to know about air compressors, complete with the infographic below,
with our comprehensive guide. We’ll address the benefits of using premium air compressors in your
industry, as well as the questions of ‘what are compressors?’ and ‘how does a compressor work?’,
covering all the essentials in one convenient place.
Since their invention in the 19th Century, mechanical, automated air compressors have continued to be
one of the most widely used tools in industrial settings. Air compressors provide a continuous stream of
power that is safer and cooler than many other forms of energy. For many industries, such as metal work and
mining environments, air compressors are an absolutely essential tool. After the basic utilities of water,
gas and electric, compressed air is actually considered to be the fourth utility.
Air compressors are also an affordable choice of tool for many manufacturing jobs, as they are durable,
and high quality types require minimal maintenance and repairs.
Between the two main categories of compressor – the scroll (piston) compressor and the rotary screw
(reciprocating) compressor, you have a tool for every type of industrial and commercial setting, as well as
various domestic uses.
Single Phase vs. Dual Phase Compressors
The most common types of air compressors are single and dual phase, both of which operate in the same
fundamental way, only dual phase has one more step involved in the compression process. In a single phase
compressor, there is one chamber and the air is compressed a single time; in a dual phase, there are two
chambers and the air is put through compression twice.
Be careful not to confuse single and dual phase compressors with the number of cylinders a compressor
has. Both types of compressor use two cylinders; one-cylinder compressors are less common, because air
balancing is made easier with two cylinders. The difference between single and dual stage compressors is
that in the former the cylinders are both the same size; in the latter they are different sizes.
How Do Single and Dual Phase Compressors Operate?
Single phase compressors, also referred to as piston <a href="http://www.bqdcompressor.com/air-
compresso/silent-oil-free-air-compressor.html" target="_self">silent oil free air compressor, works in
a relatively simple and straightforward way. First, air is drawn into the cylinder; from here, it is
compressed once by a single piston movement within a vacuum system.
The power of this compression is measured in PSI (pounds per square inch) or Bar – the higher the
PSI/Bar, the more power the compressor has. In a single stage air compressor, the air is typically
compressed at a rate of around 120 PSI (8.2 Bar). After the air has been compressed, it is sent into the
storage tank from where it is dispelled into various tools as a source of energy.
Dual phase compressors operate the same way, except there are two stages of compression, rather than
just one. After the first round of compression, the air is sent into a second chamber, where it is
compressed for the second time, at a rate of around 175 PSI (12.1 Bar). After this, the air is sent to a
storage tank in which it is cooled down and ready for application.
Both types of compressor are typically powered by either an electric or petrol motor, which drives the
piston and causes the compression to happen.
Single Phase and Dual Phase Applications
Both function in fundamentally the same way and can be used for similar tasks, such as operating a
pneumatic drill or other high-powered tools such as those found in a manufacturing plant.
Single phase compressors tend to be used within domestic settings for smaller workshop jobs done with
handheld tools, such as woodwork, metal work and general DIY.
Dual phase compressors, on the other hand, are better for larger scale work in operations such as
operations needed in vehicle repair shops, pressing factories and other plants where parts are
Oil-Free vs. Oil-lubricated Air Compressors
Another way to compare air compressors is to look at whether they use oil or not – there are oil-free
and oil-based / lubricated compressors and both are suited to slightly different jobs. For the air to be
drawn into the chamber safely and effectively, the piston needs to be in top working order. To work
properly, the piston must be lubricated with oil.
With regards to lubrication, there are two main types of compressor to choose from: oil-free and oil-
based. The oil is used on the cylinder to ensure the compression goes smoothly.
The Difference Between Oil-Free and Oil-Based Compressors
Oil-free <a href="http://www.bqdcompressor.com/air-compresso/ac-oil-free-air-compressor.html"
target="_self">ac oil free air compressor already have a lubricated cylinder (often with a non-stick
material such as Teflon) and therefore require no further maintenance to work properly. Oil-based
compressors require oil to be added to the piston area and changed regularly. Just how often you need to
change the oil will be outlined in the manufacturer’s manual that came with your compressor.
On the whole, oil-free compressors tend to weigh a lot less than oil-based compressors, as not only do
they not have the weight of the oil, but they are more compact machines, requiring fewer separate parts to
make them work. Oil-free compressors, being less complex in design, also tend to be more affordable than
However, although they’re more weighty and expensive, oil-based compressors have their benefits. For
one thing, they are strong and durable, and usually have a longer lifespan than their oil-free
counterparts. This is usually because over time the greasing material (usually Teflon) begins to wear down
and lose its lubrication abilities.
Another important factor that should be considered when choosing between an oil-free and oil-based
compressor is that the oil-less version tends to heat up faster and to a higher temperature than those
which use oil. Compressors without oil also make a lot more noise than those with, so if you want a less
noisy workplace, this is a factor to consider too.
Oil-Free and Oil-based Compressor Applications
Oil-free compressors are a great option for those in need of a lightweight, low maintenance tool for
home use. Oil-based compressors are better suited to heavy duty jobs and commercial and industrial use, as
although they’re generally heavier and require more maintenance, they are also more robust and versatile.
For industrial purposes and extensive, day-long use, oil-based compressors are by far the best option.
If you’re looking to invest in quality compressors for your business, opting for oil-based machines is
almost certainly the best route to take.
Within an industrial or commercial setting, there are numerous uses for oil-based air compressors,
Vehicle painting and repairs
Sanding and woodwork
Creating snow banks in ski centres
Tools within dentistry and other medical environments
Pneumatic construction tools such as nail guns
Air cleaning tools such as blowguns
Oil-free compressors can be used for domestic use, such as small-scale jobs like blowing up balloons,
home workshop and DIY jobs. They are also largely used in industries where there is a need to avoid the
product or consumer coming into contact with oil: food and beverage, pharmaceutical and dental, for
example. In these sensitive applications, the consequences of having oil contamination in the air are too
high to risk, so having an oil free compressor is a must. There is compressed air quality testing from the
International Organisation for Standardisation (ISO) which oil-free technology can help you achieve.
Fixed vs. Variable Air Compressors
Another factor to consider when choosing the right type of air compressor for your industry is whether
they’re equipped with fixed or variable speed. Let’s take a closer look at what these different types of
compressor can do for you.
The main difference between <a href="http://www.bqdcompressor.com/air-compresso/low-noise-oil-free-
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those that use variable speed is the manner in which the motor gets its power. The compression element is
much the same across all machines, but the way the motor operates has an effect on the usability,
efficiency and lifespan of the machine.
How Do VSD Compressors Work?
Variable speed compressors (often referred to as VSD (Variable Speed Drive) or VFD (Variable Frequency
Drive) – compressors) operates by automatically adjusting the motor speed in accordance with the demand
for air. This happens through a system that converts voltage from the mains power supply into a variable
Power is drawn through a converter, inside which it is converted twice. First, it converts AC power
into DC power using diodes. A capacitor then cleans the AC, and then converts it to DC using a transistor,
which acts as switches. These switches control the frequency of power sent to the motor, which in turn
controls the speed of the motor.
A VSD air compressor contains this technology, allowing the speed of the motor and the amount of air
compression used to be closely controlled. There are pros and cons to both variable speed compressors and
their counterpart, fixed speed compressors – check them out below to decide which one is best for your
Fixed Speed Pros and Cons
Fixed speed air compressors send a consistent, continuous stream of power into the motor, which gives
you a reliable frequency in all your air compression jobs. The initial cost of fixed speed compressors is
lower than that of variable speed compressors, is easier and cheaper to maintain and is a must-have within
industries where the power demand is continuous.
This type of compressor is, however, less efficient than its variable speed counterpart. It is also
less efficient at saving energy, and can therefore be more expensive to run, with fewer incentives
Variable Speed Pros and Cons
Variable speed air compressors allow you to control the voltage and the frequency of the power in the
motor, giving the user more agency over the tool. This type of compressor is more efficient when it comes
to power usage, as you can easily control your output and only use what you need. Many industries will find
that this type of air compressor is ideal, as it can be used in line with the demand of the job. When less
power is needed, you can easily adjust the speed of the compressor, saving money and protecting the
environment at the same time.
The downsides of a variable speed compressor are that there is a higher initial capital cost to pay,
and maintenance and repairs are more expensive too. They are also not well suited to applications that
require a continuous stream of power.
Piston Compressors, Scroll Compressors & Rotary Screw Compressors
So far in this article, all the compressors mentioned are operated using pistons, which is a generic
system for one type of compressor – the scroll compressor, also known as a reciprocating air compressor.
The other type is the rotary screw compressor, which doesn’t have pistons and operates in a slightly
Here’s a quick overview of how scroll compressors and rotary screw / reciprocating compressors work,
and what the unique benefits are of each of them.
Scroll compressors are a type of piston compressor, and are also called reciprocating compressors.
These are the most common type of air compressor, due to affordability and general availability. But how
does a reciprocating air compressor work? The piston system works by having a piston travel downwards,
decreasing the pressure inside its internal cylinder through the creation of a vacuum. The sudden change in
pressure causes the door of the cylinder to be forced open, and draw air in. When the piston travels up
again, the air is forced out of the cylinder at a much higher pressure point. This continues in a
reciprocating, ‘scroll’ pattern, hence its name.
One complaint often heard around air compressors is that some of them are noisy due to friction and a
power source, which can be distracting and inconvenient for both commercial and domestic use. The industry
has risen to deal with these complaints however, and there are several low noise air compressors to choose
from, offering a decibel rating of around 40 dB.
40 dB is considered low noise; 60 dB is considered the safest decibel level for compressors; anything
over 85 dB could cause long-lasting damage to your hearing, and you should avoid being exposed to this
level for extended periods of time.
Low noise and silent air compressors are available in both oil-free and oil-based versions, so just how
is the silencing effect achieved?
As well as choosing compressors with low decibel levels, one aspect of this technology that makes a big
difference is the inclusion of an acoustic chamber for containing the noise. Another tip is to opt for
electric-powered compressors, rather than gas-powered, as the former type of power source makes for a
The Bottom Line
Which type of air compressor you go for depends on a variety of factors. You first need to consider
what application the compressors will be used for? Do you need it for continuous, ongoing use in large
industrial machinery, or will it be used sporadically? Your answers to these questions will help you decide
on whether to go for variable or fixed speed compressors.
Another question that you must factor into your decision is: how much do you want to spend? Remember
that the initial price of a quality compressor is not the only expense associated with a compressor;
consider also the cost of the power needed to run the machine, plus any related ongoing maintenance and
repair costs. How much time and energy will investing in high quality compressors save your company? These
are all important calculations that should be made before making your decision.
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