It's around this time of the year that weekend warriors and DIY stalwarts emerge, who have spent years converting their garages into spacious workshops that sometimes resemble laboratories more than they do work stations.
There are a range of bits, bobs, tools, machines, cutters, lathes and power equipment inside - but in most of them these days you might find an air compressor.
Air tools are a popular choice for many of the discerning Do-It-Yourself-ers, and sales of home use compressors have rocketed in the last decade as prices for the smaller and more portable units have tumbled.
Whether you already have air tools or you are thinking of moving towards kitting yourself out with an air compressor and some tools to use with it, there are always some basic things to keep at the forefront of your decision.
The last thing you want it some new shiny air tools and a compressor that has no hope of powering them.
Here are some basic things to look out for...
Cubic Feet per Minute (cfm):
CFM is probably the most important factor in selecting a compressor.
CFM is the volume of air a compressor is able to move or push.
All air tools have a cfm rating, and your compressor’s maximum output has to exceed the cfm rating of your tools to function properly, or sometimes even at all.
The best thing do to is group your tools together and make a note of all of their cfm ratings.
When you have found the tool with the highest requirement, base your compressor selection on this air tool. Or, if you have a compressor already, make sure you know what it's limitations are and make your tool purchases on the back of your compressor's rating.
Tip: Most compressors will have two cfm ratings given to them. The ratings however, denote different factors. A compressor's pump displacement is also measured in cfm. However, the pump displacement does not convert into actual delivered air, but this cfm rating is usually the higher of the two ratings. As such, a lot of compressor manufacturers use the higher cfm rating to sell their products, when the FAD (Free Air Delivery) in cfm is usually lower. So, when looking for a compressor, make sure you look at the cfm rating for the Free Air Delivery (FAD) and not the pump displacement; otherwise, you could come up short.
Pounds per Square Inch (psi):
PSI is the pressure at which the air is delivered from the compressor and is different from the volume of air measured in cubic feet per minute.
However, just like air volume, the air tools you have or that you will buy do require a minimum pressure to operate properly, so psi is quite literally the next most important factor that you are looking for.
The majority of tools require around 90psi at least, but this can change depending on the tool, so you always have to check.
Typically, most air compressors, even the smaller ones, will produce more maximum pressure than that but you will want to check the compressor’s cfm output. This is a better indicator of whether a compressor can handle the air tools you want to use or intend to buy.
Tip: No surprises here but there are no prizes then for guessing that the greater pressure your air compressor puts out, the wider range of potential tools you’ll have at your disposal and will be able to run.
Massively underrated as a requirement and often overlooked or misunderstood when selecting a unit for you, the tank volume relates to the size of the tank your compressor has and obviously to the amount of air your compressor can hold in reserve.
In the UK, we measure the tank capacity in litres but some imported compressors from Italy or America are usually measured in gallons.
A larger capacity tank will lessen the load on the motor of your compressor, since it won’t have to cycle as often to replace the dispensed air, which is a big plus point if you’re keeping the compressor in your workspace or garage at home as even electric units can be a bit 'shouty'.
Tip: With a motor not having a larger load on it, it will run quieter; however, tank reservoir size does have an impact in terms of cost and the larger the unit, the more expensive it can become, so accurately sizing the unit you need is the best advice here. Definitely don't go too small, but don't go overboard.
In our opinion one of the key factors in any compressors operation, we find the majority of new users to air compressors are not aware of the duty cycle.
Simply put, the duty cycle of a compressor is the amount of time a compressor motor can safely operate before it shuts down to cool off.
For example, a compressor with a 50% duty cycle will only run for half of any given time period before shutting down for a required amount of time.
Compressors with short duty cycles can pose a problem for continuous use in your workshop, and air tools like grinders and sanders that require a greater and more prolonged flow of air to work properly can struggle on units where the duty cycle restricts the operation of the compressor itself.
Tip: If you want to use these types of tools, be sure to get a compressor with a larger tank, bigger motor, and a duty cycle rating of more than 50% or more.
Horsepower is used to measure the output of your compressor’s motor, but cfm and psi are much more accurate measures of your compressor’s effectiveness.
Generally, cfm and psi increase as horsepower increases.
Tip: You can gauge the power of any air compressor in relation to the size of the motor. Therefore, if you need more power for your tools, go for a compressor with a larger motor in terms of its horsepower output.
Powering Your Compressor:
Considering a home use or DIY compressor will be used mostly in an environment where there will be mains power, there isn't a huge problem with being able to power your compressor and, hence, use your air tools.
However, a lot of people find that they want to keep a separate means of power, such as a generator.
It's important to remember the start up current on something that starts under great resistance. A motor on an air compressor is one such item with this type of resistive motor.
If you consider that 1hp is equal to around 0.75kW of power, a 3hp motor on a standard home use compressor is rated to 2.25kW.
However, because it starts under greater resistance, the start-up current of the motor can be 2-3 times higher, meaning that the inrush current from the power supply can be anything up to 6.75kW.
When connected to mains, the National Grid will supply whatever is needed during the starting of the motor.
In terms of duration, this inrush can last only a matter of seconds, but it there is no getting around it.
When on generator power, a generator has a ceiling; a limit to the amount of power it can produce.
Tip: It's important to remember that even if a generator's power can cover the amount of power required to run an item, it has to cover the start-up also, so even the smallest of air compressors can require a larger generator in terms of weight, size and overall output just to start. Make sure, if you are going to buy a generator for your compressor, that you get one that is sized correctly and is adequate for running your compressor motor when switched on. If you've got a large compressor, be prepared for a large generator, but make sure you know what you need and know also your limitations.
For our pick of the best air compressors out there, click here.