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Air compressor buying guide

Air compressor buying guide

Jeremy, Construction site supervisor, Cardiff

Guide written by:

Jeremy, Construction site supervisor, Cardiff

153 guides

Air compressors can handle a range of tasks from inflating tyres to blasting a car body or powering a blow gun. Whether you go for a portable or semi-pro model, you'll need to choose the right pressure, air flow and tank capacity to match your air tools.

Important features

  • Power
  • Air flow
  • Pressure
  • Tank volume
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Air compressors for occasional use

Looking to blow up a pool, football, car tyres or a bike wheel? Need to use an air blow gun or paint gun to tackle a relatively small surface? A small air compressor will work just fine for occasional tasks that don't require a lot of pressure or air flow. In this case, a portable air compressor will be ideal.

These oil-free, lightweight air compressors usually come with a set of inflating guns. Great for small jobs on the move, these machines are often chosen for their low price point. Around 1.5 horsepower (hp) and maximum pressure of 8 bar (B) or 116 PSI operating pressure should cover your needs. If you are looking to carry out longer jobs, be sure to take breaks as these air compressors only have a small tank (around 6 to 8 litres) meaning the motor needs to run more often. Mini tankless air compressors are designed to work continuously but can only be used for even lighter tasks.

Air compressors for domestic use

For prolonged DIY applications – such as inflating, stapling, nailing, using an air blow gun or glue gun, painting a small surface or checking tyre pressure – you will have to look for a larger single cylinder compressor.

A tank volume of 50 litres will mean you can go for longer without running the motor. If you want to be able to move the air compressor around easily, you'll need a pair of wheels. A CFM rating of about 8.5 and 1.5 motor horsepower should suffice. Air compressor kits offer pneumatic tools with the right pressure for domestic air compressors (usually 8 bar).

Air compressors for regular use

Any DIYers expecting to use an air compressor on a regular basis must have a substantial tank capacity and enough air flow to handle longer tasks like inflating, stapling, paint spraying, gluing, drilling or using an air blow gun for cleaning tasks. A tank capacity of 100 to 150 litres and an air flow of 8.5 to 14.5 CFM will be perfect.

The power of this type of semi-pro machine should sit around 2 to 3 hp. If you mainly work in the workshop or if you need to feed a compressed air system, go for a stationary compressor. If you plan to use the air compressor in multiple locations or outdoors, go for a portable air compressor. Inflatable wheels will make the machine easier to handle.

Professional air compressors

A professional air compressor should cover all basic tasks and the use of pneumatic tools like impact wrenches, sanders, drills and grinders. For heavy-duty tasks that require a lot of air flow, a minimum tank volume of 200 litres and at least 23 CFM of air will be ideal.

A 400v three-phase air compressor is a good choice for a professional workshop. If you need to move around, it's best to go for a tow-behind air compressor with a petrol engine. 

4 key factors for choosing an air compressor 

  1. Any tools that run continuously require a larger air tank so that the motor of the air compressor doesn't need to run non-stop. Underestimating the size of your air tank will make your tasks much noisier and your machine won't last as long. The main types of air tools that need to run continuously include pneumatic drills, paint sprayers (for large surfaces), abrasive blasters and rotary hammers.
  2. The air flow (in cubic feet per minute) and pressure (in bar or PSI) of the air compressor should meet the air requirements of the tools you want to use. Remember to add up the operating air flow of each tool if you want to use several at once. Multiply this total by 1.5 and add 2 or 3 bar to your calculations to ensure comfortable use. 
  3. The power of the air compressor is determined by the air flow and tank volume of the machine and is not necessarily a key characteristic in itself.
  4. Oil-free motors are popular as they don't require maintenance and work just fine for intermittent use.

There are three basic types of air compressor:

  • portable air compressors;
  • single-stage or piston compressors;
  • twin-cylinder or multi-stage air compressors.

Portable air compressors

If you only want to inflate tyres, use an air blow gun, staple gun or glue gun, look into portable, oil-free air compressors. Compact and lightweight, portable air compressors work perfectly well for small jobs. Most portable air compressors will feature a tank capacity of less than 20 litres and a maximum of 1.5 horsepower and 4 CFM (for the most efficient machines).

A portable air compressor is ideal for occasional jobs, outdoor tasks and working in tight spots. Lots of brands offer portable air compressors that run on 230v power. Alternatively, a 12v air compressor that can be connected to your car battery via the cigarette lighter can go with you on the road. Some portable air compressors don't have a tank at all and weight less than 4 kg!

Single-stage air compressors

The most common air compressors for domestic use, single-stage air compressors can deal with more heavy-duty or longer tasks than a portable air compressor. The pump unit is made up of a motor that usually drives a single cylinder.

Single-stage air compressors can range from 1.5 to 6.5 hp and most have a tank capacity of 25 to 250 litres. These machines are able to attain pressures of up to 150 PSI. The air tank is either fixed to a wheeled frame to move around easily with minimal effort or mounted to a wall (if you're feeding a compression network).

Two-stage air compressors

Two-stage or multi-stage air compressors are more powerful machines. Often used in professional settings or in workshops, the large tank capacity and motor power of these air compressors can be used to power a compressed air system. The pump unit contains a motor that drives several cylinders.

Able to deliver over 23.5 CFM and 200 PSI, multi-stage air compressors are ideal for body repair shops, large-scape spray painting or mechanics. They will also work for keen DIYers with a lot of air tools and a workshop to accommodate the air compressor.

Air compressors are relatively simple machines: a motor or engine is used to drive a cylinder (or cylinders) which compresses the air into an airtight tank. The tank is kept within a pre-set pressure range and can vary in terms of capacity. Once the tank reaches its pressure limit, the motor switches off. The pump unit is formed by the motor and cylinder(s). The compressed air generated can be used to operate one or several air tools at a time, such as: 

  • an air blow gun;
  • a paint sprayer;
  • an air nail gun, and so on.

The most important feature of an air compressor is the amount of air it can supply. Air flow is measured in cubic feet per minute (CFM). This is provided in the product specs as a CFM rating. The CFM rating depends on the volume of the air tank as well as the speed at which the air compressor is able to fill it.

It's important to note that some compressors don't have a tank at all, though this only applies to low-end portable air compressors. In this case, the motor has to run constantly to produce compressed air. In order to choose the right air compressor, you need to calculate the amount of air you need as accurately as possible.

How to calculate a CFM rating

A simple but effective formula can be used to estimate the amount of air you need and therefore choose the right air compressor for your needs. Basically, you need to add up the CFM rating of the air tools you want to use and multiply this number by 1.5.

The CFM rating of your pneumatic tools can be found in the technical specifications of each product. This information is easy to find if you are investing in new air tools and can be used to determine the amount of air flow you need from your air compressor. 

The motor power of an air compressor and its tank capacity will generally increase as the air flow increases.

Safety devices

An air compressor is fitted with several safety devices without which the machine would not function correctly:

  • The pressure switch works like an automatic switch. As soon as the pressure drops below a certain level, the pressure switch relaunches the motor. Featured on all modern air compressors, pressure switches are usually factory set to a minimum of 4 bar.
  • A pressure regulator is a type of valve that allows you to set the operating pressure and/or the downstream pressure that powers your air tools. Please note that pressure regulators are used to protect any tools connected to the air compressor and not the user, and should not be confused with the pressure switch.
  • Pressure gauges can be manual or digital. They are used to provide a visual indicator of the tank pressure and/or the outgoing air and are used to control pressure adjustments.
  • A pressure relief valve is used if there is a fault with your pressure switch or regulator to limit pressure build-up and prevent accidents. The relief valve is designed to let out air and ultimately prevent an explosion.
  • A direct outlet can be used to connect your tools directly to the tank and bypass the regulator. This outlet provides the maximum pressure from the air compressor.

Air compressor pumps 

Oil-free air compressors 

Oil-free air compressors can only be used occasionally or for short tasks.

These models don't require as much maintenance but they won't last as long as other models! They are also usually noisy to operate.

Cast iron pumps 

At the other end of the scale are cast iron pumps which are used to equip the largest heavy-duty air compressors.

Cast iron offers optimal heat exchange meaning the pump cools down more readily. These pumps therefore offer a longer service life.

Aluminium pumps 

Aluminium pumps are more common and featured on most air compressors used for DIY applications.

However, they are not recommended for heavy-duty or professional use as they do not cool down as quickly as cast iron pumps which will reduce the service life of the air compressor.

Air filters 

Air compressors are fitted with an air filter to prevent damage to the pump unit.

Professional models may also be fitted with air filters on the tank outlets to ensure the outgoing air is clean and dry.

Maintenance

To ensure your air compressor lasts, it's important to carry out regular maintenance.

  • Clean the air filter on a regular basis: the air surrounding your air compressor that is sucked in and compressed. If this air is filled with dust, you can end up damaging your air tools. It's important to ensure that the air filter is clean to ensure it works as effectively as possible!
  • Drain the air tank: compressed air that contains moisture will create condensation on the inside of your air tank. To prevent this moisture from freezing or damaging the metal, air compressors are fitted with a drain valve located beneath the tank. Drain the air compressor regularly, especially if you don't plan on using the machine for a while. Of course this advice doesn't apply to tankless portable air compressors!
  • Check oil level and change oil: be sure to check the level of the oil regularly and change the oil in your air compressor at least once a year.

Air compressors are relatively noisy and can be dangerous if used incorrectly. As long as the motor is running, protect your ears with ear plugs or ear defenders.

To reduce the risk of accidents, it is highly recommended to study the operating pressure of your tools carefully. Air compressors should be serviced on a regular basis (around every 12 months or so) and should be subject to a thorough inspection every 4 years. A range of accidents can be traced back to rusty tanks or faulty pressure regulators. Remember: safety comes first! 

Air compressor tools and accessories

For small tools like air blow guns, inflating guns or air brushes, go for a smaller air hose of around 6 to 8 mm. For larger tools, choose a larger air hose of 10 to 12 mm. To ensure your air tools can work as expected, be sure to maintain the same hose diameter from the pressure gauge (where the air is released) to the tool connector.

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Guide written by:

Jeremy, Construction site supervisor, Cardiff, 153 guides

Jeremy, Construction site supervisor, Cardiff

Electrician by trade, I first worked in industrial estates where I installed, wired and fixed a large number of electrical installations. After this, I managed a team of electricians for this type of work. 10 years or so ago, I turned to building and construction. From the modest family home, to gyms and theatres, I have been able to coordinate, audit and organise all sorts of construction sites. For 4 years now, I am restoring and building an extension to a bungalow in the heart of the Welsh countryside. My experience in manual work and my knowledge means I am proud to be of service. Terraces, interior design, roofing, plumbing, electrics, anything goes! My wife, daughter and I, built almost everything we have from scratch! So to answer all of your questions and advise you on choosing your tools? Easy!

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