The Basics for Choosing the Right Air Compressor
Posted: Thursday, July 21, 2005
by Cooper
Red Hill Supply - Online Air Tools
There is a lot of confusion out there about selecting the right size air compressor to run your air tools. Basically, there are several factors to look at when choosing the proper air compressor for your shop or garage.
The first criteria is horse power rating. Most people assume the higher the horsepower rating on the box, the better the air compressor. However, all horse power ratings are not created equal and can easily be misrepresented. What I mean is, you go to your local giant hardware retailer to pick out a new air compressor to run your impact wrench. They have a 5 hp unit that is priced really cheap. Why is that 5 hp industrial unit cost so much more? 5 hp is 5 hp, right? Not necessarily. Let me explain. Look at how much power the hardware store unit draws. It probably needs around 15 amps from a normal 110 volt circuit. At this rating, you are really getting only 2 hp. The 5hp rating on the box is inflated. To really produce true 5 hp you need at least 24 amps from 220 volt circuit to get it. If you are looking for 5 hp electric compressor, buy the industrial unit and stay away from the cheaper unit at your local hardware store. I am not saying that every air compressor at your local hardware is junk. A lot of times one of those units is all you need. Just be aware of the true horsepower rating.
The next consideration when purchasing a new air compressor is, "How much PSI will I need?" For the newbies, PSI is short for "pounds per square inch" and this is how most compressors in the
The next rating criteria for air compressors is CFM. CFM stands for "cubic feet per minute". It is a measurement of volume. Basically it is how much air is being moved. Air tools require a certain amount of air volume to run on. PSI is just part of equation. Don't be confused by different CFM ratings at different pressures. Every manufacturer is trying to make their product look better by giving higher CFM ratings at different pressures. The only real concern is how much CFM you will get at 90 PSI. Remember 90 PSI is what most air tools require to operate. To find out what your air tool needs to run, just look on the box for the manufacturer’s specs. Generally, air tools require 4 - 6 CFM. A good rule of thumb on air compressors is you should get 3 -4 CFM per real HP at 90 PSI.
The final factor to consider is tank size. Tank sizes are generally stated in US gallons. For example, 30 gallon is a common tank size. So the question remains, how large a tank do I need? First of all, don't confuse a large tank with more run time for your air tools. If you use your impact intermittently, a large tank is fine. However if you have need for continuous use, you will need a small tank with big enough pump and motor. If the pump and motor are powerful enough, you shouldn't run out of air. You can save some dollars by purchasing an air compressor with a large tank and smaller motor for intermittent use. If you need to run a 1" impact wrench (about 20 CFM) intermittently, and have a small compressor with a large tank, you might have enough air stored in the tank to do the job. However, if you are constantly running your air tool, you will need to invest in a more powerful air compressor to do the job.
You should be able to select the air compressor armed with this information. Basically, you need to decide ultimately what you going to use the unit for and pick the appropriate model.
Okay write up- its very hard to come across any tips on what the specs mean on air compressors. Explanations here could be better tho, like on the hp ratings so ppl know exactly what a certain hp will do- I was reading it and wondering
No. No discussion about the differencs between direct drive vs.belt, oil less vs. oil lubed.
Not especially helpful. It touched of CFM as a third consideration while most other "compressor selection" articles refer to CFM as the most important. I just wanted to know the difference between an oil-less compressor and an oil lubricated. One of the complaints concerning larger oil lubricated models is that they tend to leak oil into the air supply Kahetchapek.
Oil lubed compressors will generally last alot longer then oiless assuming the oil level is checked and changed periodically. CFM is the truest rating for the common person. Hardware stores sell these big 80 gallon compressors that only run about 12-15 CFM with a 6 HP motor. If that were a true 6HP motor with a 6Hp pump it should be around 20 CFM or so. I'm not an expert by any means, but I have done alot of research before buying my latest compressor. I learned alot, and am still learning. The truth is the hardware store compressor will work fine for the majority of your home shop projects. But spraying makes a compressor work alot so a large tank and a larger CFM as well as at least a top quality filter system if not a dryer would be a good investment. Also air sanders take more draw then pretty much any other tool, usually about 12-15 CFM at constant use. Hope I helped someone out there.
Thanks Kevin. I'm just starting down this road and your info was indeed helpful.
Thanks! Good 411 on compressors and answered my ? .
Thanks Kevin - your info was the most helpful. I am looking for a compressor for home/garage, mostly an air sander - you answered my questions.
I think you know your stuff but the article is uneuseful for me. Statements are confusing and do not give information on how "not being confused". Additionaly it doesn't help to decide what you need. The reference to the needs is too general. Thank you anyway. At least it puts a yellow line in one.
i knew a little and now i know a little more. the first sentence says the word "basically" and that's what it is. i think it's a great article for a beginner.
If I want to run 10 air tools, each consuming 10 cfm @ 90 PSI, how can I determine the size of an air compressor ?Thanks - BilluIn theory you would need a compressor capable of coping with 1.5 times your total cfm requirement. This is to allow for higher drain in the firs instant of start-up and any other variables such as your tools are getting older and mean that the compressor is not working flat chat the whole time.
If you need to run 4 x 4cfm tools you would need:
(4 x 4 cfm) x 1.5.
= 16cfm x 1.5
= 24cfm
To use your example you need 10 x 10cfm constant use tools.
= (10 x 10cfm) x 1.5
= (100cm) x1.5
= 150cfm.
If however you need this much air power now you may want to consider future proofing by a further .5 and get a 200cfm system.
By now you really are talking about a significant investment into a commercial compressor. These last for as long as you maintain them so buying a little more that you need becomes better economics.
My requirements are very low so I only have a cheap one. Horses for courses.
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