Discussion on criteria for selecting the correct air compressor for home or industrial use. Covers tank size, pressure, pumps, motors and duty-cycles of compressors and reviews air consumption of typical mechanic's air tools.
Alright, today on Repairs101 Iím going to address a request from a viewer that I got back in January, and well, itís June right now so I got to say Iím really sorry it took me this long to get to it.
Alright , well today on Repairs101 weíre at the shipyard, and weíre going to talk about air compressors and pneumatic tools. There is a serious compressor. So hereís a beautiful air compressor set up. That oneís just permanently mounted in the back of this service truck. You can see that it says thirty gallons. So thereís an engine mounted air compressor, direct-driven on the side of this fairly new Cummins diesel. Hereís a good sized tank on the back of this service truck.      Truck mounted Air Compressor with 30 gallon tank
Alright now, speaking of air compressors, hereís a couple of ďtow behindĒ air compressors made by the SULLAIR company. SULLAIR tow behind compressors - tankless, 100% Duty cycle This bigger one over here delivers a hundred and twenty-five pounds of pressure and four hundred and twenty-five cubic feet per minute Ė which is quite an impressive amount of air. Youíd use that for sandblasting equipment or jackhammers Ė that kind of air operated equipment.
When you go to choose an air compressor, whatís funny is that the first thing that youíll see listed about it is the tank size Ė which in reality is about the least important thing to do with the air compressor. Whatís really important is the pump size and the motor size. And the pump will be rated in cubic feet per minute. If you canít find the rating for how many cubic feet per minute the air pump is going to make then itís safe to say that youíre going to get three or four cubic feet per minute for every horsepower. A lot of hobbyist machines, the horsepower has been exaggerated by marketing departments in order to sell more. If itís a one-ten plug in then itís not going to be more than two horsepower, otherwise it will have a two-hundred and twenty volt hook-up.
You know the pressure rating on it again is not that important, they should all make at least ninety to a hundred and ten PSI. Now if you need higher pressure than ninety to a hundred and ten youíre going to have to look at a two stage air compressor. When you have a two stage compressor you might have as high as a hundred and seventy-five PSI.
So the duty cycle of your air compressor is one of the more important things that you can try and find out. The duty cycle is how long itís rated to keep running during use. So if you have a hobbyist air compressor thatís duty cycle is fifty percent that means that fifty percent of the time youíre using it that motor can be running safely and without overheating. If you exceed fifty percent of the time then youíre in danger of wearing out your pump a lot faster than you had bargained for. Commercial duty air compressors, on the other hand, have duty cycles of seventy five percent and even a hundred percent. You donít even need a tank if youíve got an air compressor with a hundred percent duty cycle. Home made tankless compressor - 100% Duty Cycle  So if youíre a hobbyist you know fifty percent duty cycle is probably all you need, but if youíre running a shop and youíve got a lot of guys perhaps youíre going to want to look at something industrial with a seventy-five or even a hundred percent duty cycle. A five horsepower compressor with a hundred percent duty cycle is going to make more air than a seven and a half horsepower compressor that only has a seventy-five percent duty cycle. If it is for commercial use you really should get as big a compressor as you can afford because you wonít be sorry. 
So to choose the right compressor youíre going to have to ask yourself what kind of demands youíre going to be making. What are the air tools that youíre going to be using, what applications are you going to be using them for? Are they going to be more than one user at a time? Is it going to be intermittent use or is it going to be continuous duty?
Letís go open my file folder of ownerís manuals and technical data. OK this is forÖ three cubic feet per minute then just to operate this little right angle grinder. And a right angle drill this time, again, six cubic feet per minute. This little cut-off saw here four cubic feet per minute. This is an air body-saw itís basically a pneumatic hacksaw, great for doing bodywork. Six cubic feet per minute for this one. Alright so this is an air hammer. Itís rated at ninety PSI of course and four point four cubic feet per minute. This pistol grip drill consumes four cubic feet per minute again rated at ninety PSI. Three eights impact gun thatís rated at four cubic feet per minute. Another style three eights pneumatic wrench again rated at four cubic feet per minute. And four cubic feet per minute for this one as well. As far as my personal impact tools go, this is my heavy hitter and again it only uses four cubic feet per minute. One inch impact gun, you need a real good air supply to drive something like that.
OK so now just a couple of drops of motor oil in the end of your tools. Might be ten w thirty or fifteen forty or five thirty. You know, whateverís around Ė straight thirty weight oil.
Now I picked this little beauty up for twenty bucks. One gallon tank with a little tiny compressor on the back. Perfect for Ė you know, inflating bicycle tires or doing cleaning around the shop, that kind of work. You canít really power any tools with something like this but for the money I paid for it, I donít expect very much out of it. You can see I put a quick connect fitting on the end. Quick connect like that so you connect it, there now itís already part of the system. Just pull back like that, snap it on, pull back and it comes off. So hereís examples of three different fitting ends. Anyway, there are all kinds of different fitting ends that you might pick to go with your quick connector and I would recommend that you just look at the place where you work or what fittings came with the equipment you bought and just go with that.
So donít forget to wear your safety glasses and please remember what I always say about power tools Ė which is ďuse both hands and both eyesĒ.

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