Believe it or not, choosing an air compressor for the garage/shop is not merely looking at the size (and price) and thinking that will do the job.
Many have and many have had buyers remorse soon afterwards.
I think an air compressor is an essential item for any garage and buying one should be a thought out process.
Now that process can be as simple as looking for a compressor that is compact and it’s main use is to inflate tyres (tires).
Or it can be as complex as finding a compressor with the right CFM to run air tools with a tank large enough to give the motor the rest it requires for it’s duty cycle.
Does the compressor need to be portable, mobile or remain stationary?
Mostly this will depend on your primary usage, like the air tools you want to power and the location of use (in the garage or on-site)
Builders, carpenters, mobile mechanics and paint touch ups services are some that use portable air compressors.
While home engineers, wood workers, mechanics and car detailers often require larger stationary compressors.
Some large compressors have wheels giving them the advantage of being able to be moved short distances. These are usually horizontal tank air compressors.
The air tools you predominently use should be your first consideration when considering a compressor.
When it comes to compressors CFM – is King!
Air volume produced is measured in Cubic Feet per Minute CFM for short.
CFM is key to choosing the right compressor for the air tools you use. But don’t over-look duty cycle. More on this in a minute.
Every air tool you use has its own rating in CFM (like compresssors). Although tools like air dusters and tyre inflators can be exceptions.
Your choice of compressor should be based on the air tool you use with the highest CFM.
I will give you an example:
If you have a brad nailer rated at 2cfm, an impact gun at 6 and a sander at 11 cfm. Your required compressor is 11 cfm plus a 30% margin.
Based on that example your compressor should have at least 14.3 CFM.
But, if you have two air outlets in use at the same time, then it would be the combined total of the air tools plus 50% margin.
Something Worth Noting
Many air tools like impact wrenches are rated by average use. The 6 CFM rating of a 1/2″ impact gun is based on average use of about 15 seconds.
Rating an impact gun for a full minute would put it’s usage up at 20 plus.
The capacity of the tank (air receiver) counts especially for extended use tools like spray guns or bead blasters.
Having a large tank gives your air tools longer operating time before the compressor cuts back in to refill the tank.
Using high volume air tools on small tank compressors often makes the compressor run continuously – like spray guns – this is not good for many compressors.
Tank size also affects the severity of pressure drops. Again, especially noticeable on high volume air tools.
Large tanks are good for sanders, spray guns, grinders and air hammers.
Small tanks are more suited for staplers, brad nailers, some nail nail guns, riveters and tyre inflators.
PSI is an acronym for pounds per square inch and when related to compressors it’s used as a measurement of output.
Maximum PSI is not really important when choosing a compressor because most air tools are test rated at 90 psi – it’s an industry standard.
And if you have been looking, almost all new compressors have a maximum psi rating of 120 or more.
But, there is one benefit to higher pressure in an air tank…
…it allows air tanks to hold more air without increasing tank size.
Example – 150 psi in a 2 gallon tank is the same amount of air as 100 psi in a 3 gallon tank.
However, there is a psi number you do want to know and that is – What is the compressors psi out-put under continuous operation.
Think of it like this, if there was no tank to receive air, how much air pressure can the compressor put out to run the air tool.
Many compressors fall short of the 90 psi that air tools are rated at. Anyone who has used a die grinder with anything less than an industrial compressor can relate to this.
Horsepower is probably one of the most noticeable specifications plastered over a compressor.
If you are looking at horsepower numbers, the important one is running or rated hp not peak.
2hp (rated/running, not peak) is the max. most domestic (home) power can handle. That applies to most countries.
3.5 HP (peak) is close to maximum on just about any domestic power supply.
Three phase power is used with bigger horsepower motors because it is more energy efficient than single phase.
I was going to leave duty cycle out because it’s not often mentioned or plain to see what it is.
But for a few of you who are considering buying a compressor, that is possibly going to be put to work hard, you need to know about duty cycle.
To find it, in most cases you will have in to take the step and make some inquiries with the manufacturer or sales entity to discover the duty cycle of the compressor that interests you.
Which I think is wrong because really it ranks right up next to CFM and should be shown like they do the other specs, not hidden or shown in some small code.
Duty cycle refers to the amount of time a compressor can be operated in a given time period at 100 PSI, and a standard ambient temperature of 72° F (22° C).
Example – a compressor with a duty cycle of 60%
Translates to a run time of 6 minutes with 4 minutes cool down time. The 6 minutes is the amount of time it takes the motor to reach its rated maximum temperature.
Six minutes is 60% of the total cycle time of ten minutes.
BTW this mostly related to piston type compressors.
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