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Help buying an air compressor
ahofle:
I recently borrowed a compressor from a friend to nail in some base boards and now I am hooked and want one for myself. Being new to this arena, I am trying to determine what I need. I would like to keep price under $500, preferably in the $300-$400 range. My friend's compressor was rather large (I believe one of those $300 30+ gallon Craftsman models) and difficult to move -- ideally I'd like one that can fit in the back of an SUV/wagon. But I understand that those smaller models have a lower CFM. In fact I am getting a bit confused on these CFM ratings because some models claiming 5-7CFM @ 90 PSI have people reviewing them saying they can only unscrew one lug at a time with an impact wrench and then have to wait for the motor to kick on and the tank to refill.
The tools I'd most likely use are nailers (pretty easy to drive if I understand correctly), sprayers, and possibly wrenches/drills. I don't really see myself doing any grinding or sand blasting, or most of the tasks with higher air requirements.
Any pointers to help an air tools newbie would be appreciated.
MonMotha:
When looking at air compressors, you have to consider a couple things. One is how fast the compressor can actually compress air, and the other is how much air storage capacity it has. The two are fairly independent of each other. You then have to think a little about how you'll commonly be using it to determine how the two will interact.
Air storage is like a battery. You've got a bunch of power (compressed air) stored up. You can draw it down fairly fast, but once you draw it down, you have to wait for it to "charge up" again. This is controlled strictly by how big the air tank is and the maximum pressure the compressor can build up to.
The other major factor is how fast the compressor can replenish the tank to keep it topped off and up to pressure. This is the "power" of the compressor, and it's often given in HP in the USA (or probably Watts in the rest of the world). It actually requires a fair amount of power to make compressed air. Some quick math says that to increase the pressure of 4 cu ft of air by 90 psi in a minute requires about 1.5 horsepower, and that's not accounting for efficiency losses in the motor or compressor or heating of the air: that's just the increase in potential energy of the gas! Most small compressors don't have that kind of power, and even the bigger portable units that do aren't designed for continuous operation (they'll overheat). The idea is that the compressor tops off the tank periodically and you work off that.
There is also a device called a "regulator" that lets you "dial in" a certain air pressure. The regulator can only pass a certain amount of air in a given time, and there will be a pressure drop across it. Some of this drop is necessary since you want the pressure at your tool to be less than that in the tank, and you gain some control over it in the process. The rest of the drop is due to the inability of the regulator to pass more than a certain volume of air in a given time. Larger air compressors don't have an integrated regulator, so you can choose one that meets your air delivery needs, but most portable ones have one built in.
The stats given on cheap compressors in terms of CFM (a measure of air volume - cubic feet per minute) at a pressure usually seem to be that which the regulator can handle coming off a fully topped off tank. The higher end ones seem to give the stats on what the compressor can actually provide while running, which will be the limiting factor in the system if you were to try to use it continuously. I'm not sure that there's any real standard for conditions on those specs.
In general, for intermittent use e.g. nailing, a larger tank and smaller compressor works. For continuous use e.g. spraying paint, a larger compressor and smaller tank works. Obviously you can have both if you want, but the unit is larger/heavier/costlier.
FWIW, I've got a ~1.5HP Bostitch 6gal pancake style unit. It's a little heavy to casually carry around, but it's easily moved when justified, and it has plenty of power for finish nailers (it can easily keep up with me) as well as larger nailers and air cleanup tasks e.g. blow gun, and I only have to top it off once to air up even fairly low car tires, but the regulator can't deliver enough air to run a cut-off wheel, and the tank would get depleted too quickly to be of much use for that purpose, anyway. You can add an outboard storage tank for increased reserve capacity, if you want, or just get a larger, non-portable model for those sorts of tasks.
eds1275:
I have a 2 gallon CH that came with a finish nail gun. The nailgun works just fine, as does the tire inflator and some of the other tools I bought for it. You can clean off a small table with the blower before it needs to recharge - there is definitely not enough air to spray paint. I can lift it with one hand and it's pretty small. It was $80 on sale with the nail gun, worth every penny. I too want one that can paint :)
jennifer:
You may want to look @ amp draw too, a compressor with a five horse can generally be hooked to 110 or 220, Its draw for big jobs [IE painting]
can make your supply wire on a 110 get pretty hot.
I have [2] twenty gal. comps. running off 2 supplys [110] tied together into a regulated 30 gal tank. This works out nice because you can buy
1 comp. at a time and get a feel of how much air you really need.
TOK:
I have a 30 gallon 120v Craftsman that has worked fine for the same type of stuff you're describing. Its beltless and I think the power numbers on a lot of this type compressor are exaggerated. Its portable in the sense that it has wheels, but not really convenient for moving in and out of a car. They are also absurdly loud compared to the better belted compressors.
If portability is a big issue for you, I'd say look at one of the smaller twin tank versions and read reviews to get the best one you can find because the smaller the capacity is, the more the power and efficiency are going to matter.
My budget was tight when I bought mine, so I settled. The next one I get is going to be a 240v belted so I can run it in the garage and still hear myself think. :lol
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