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. 

[knave]

I think that Harbor Freight is a pretty good place to get a compressor. That said, I picked up a craftsman 6hp large upright compressor a few years ago and I love it. It's not really portable though. (other than wheeling it aroud if needed.)

Since that's a factor for you I've used pancake style compressors for painting and they do a good job of flowing enough air for the sprayer. Go with one of those.

[atomikbohm]

Strangely enough, I had a similar conversation with a good friend who did some sand blasting every now and again.  He told me the key factors he looks for is a slow RPM motor that allows you to grease / lubricate more than just the air tank.  He explained that the higher the RPMs the shorter the life of the motor.  (Rule of thumb: When the compressor is running, if you have to shout to your buddy next to you don't get it)

I guess the quieter ones are usually more $$$ though so... If you want to hand this down to your kids in 10 years, get a slow motor what can sustain your required air needs.  If you are looking for something to get you buy for the time being get a less expensive one with some good hearing protection.

Good luck.

[ahofle]

Thanks for all the feedback.  I was looking at this model:
http://www.homedepot.com/h_d1/N-5yc1vZ1xhf/R-100497925/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053
but after the harbor freight recommendation, I found this one for less than a third of the price:
http://www.harborfreight.com/air-tools/oil-compressors/1-3-4-quarter-hp-4-gallon-115-psi-pancake-compressor-38898.html

Could those ratings be right?  It's 4.2 SCFM vs 5.2 for the DeWalt -- do you think the harbor freight model will be able to power a sprayer or impact wrench?
At $99, I can't imagine being really disappointed at any rate.

[ahofle]

  
Thanks for that by the way.

[SavannahLion]

I would like to put my two cents in:

Many years ago, I purchased a pancake style air compressor for my father as a gift. It was cheap and it came with two nail guns. IIRC, it was made by Home Depot's internal brand. He had it for about three or four years unopened in the box until I discovered it after his death and took it back.

The nut is that I don't know if it was due to being stored unused for so long but this type of pancake compressor downright sucks. No matter how long I run the thing, the compressor tank never fills beyond a certain PSI. After a lot of research at the time I learned that there are two significant types of compressors on the market. Oil-less (what this pancake compressor is) and oiled (what professional level compressors are I guess). The key difference between the two is how the compressor fills the tank thus requiring or not requiring a bulb of oil. I found accounts of how repair shops have piles of useless pancake compressors destined for the scrap yard and I believe it.

I don't know if atomikbohm's comment about slower motors is indirectly related to the oil-less/oiled compressors. I think I can recall that one of the indicators (besides the obvious such as the ad presented by PBJ above) is a loud vs quiet motor.

TBH, it runs contrary to my nature to buy a tool knowing that it's a piece of crap and is bound to fail long before I can ever hand it down to my own children. However, on the other hand, I do have many of my dad's older tools. While I do know how to use them, I tend to refrain from doing so and keep them in storage. eg, my father built his table saw from the gutted remains of a discarded table saw, angle iron and three door knobs. Starting the ---smurf--- up actually makes the motor growl and dims the lights.  When the saw reaches full speed, it screams like some freaky sci-fi creature from hell. It has no guard whatsoever and has no problems chewing through wood and fingers with equal vigor. I've witnessed kick backs send wood sailing through windows, impaling lumber into a wall and shatter bone. I wouldn't dare teach any of my kids on such a intimidating machine. I would much rather teach them proper table saw practice on a much smaller (translation: much less intimidating) table saw like my fiance's, which is considerably cheaper and will likely require replacement within a few years.

In short, I'm saying basically the same thing as atomikbohm, but for a different reason. Does it make sense to spend  loads of money for something that either A) may not be considered safe by the time your kids get their hands on it or B) that standards have changed so much that parts are impossible to find or the actual techniques have changed? Your kids are going to end up buying their own tools anyways. I have two compressors rotting in the mountains because it's nearly impossible to get hoses for them and their output is so insane that it's virtually uncontrollable.

[drventure]

If you've got it in your area, put a watch on Craigslist for compressors. There are always shops closing up or moving and putting compressors on sale. I picked up a craftsman vertical tank model (it's tall rather than long, so it takes up less space, about as much as a pancake compressor), but it's the oiled type, and has enough capacity to air up 4 tires without refilling. Something like 80$

You just have to be a little more aware of maintenence and check the oil every now and then.

[hyiu]

don't mean to hijack this thread...

but I have always wanted to buy a compressor also. just so far, I don't have a project that really needs it... (I need some excuse to justify the spending. lol...)

after reading all these, I have a few questions:

are the oil compressors more quiet in general ?
in terms of maintainence, is it only we need to like watch some oil level, and that's it ??

I mean, I'm most likely less than a "weekend warrior"...
I don't mind if its just checking oil level before using it every time...
that's manageable...

I was thinking of the porter cable pancake style compressor before...
(thats the oil free one...)

anyone can send me a link to a "recommended" quieter compressor then ?
(oil or maintainence free are both ok...)
let's keep the price reasonable ?? (like around 300-500 max ?!?!)

I do believe in brand names... they might look alike, but brand name tools are actually better most times...

I got a $15 hammer... and I also got a $0.99 hammer...

I was thinking... hammer... is not high tech... it cannot go wrong...
but somehow... its just not right... nails are easily bent and doesn't go in straight when I use the cheap one... so, if possible / can afford, I will go for a brand name better quality tool...

[eds1275]

I use my compressor for just about anything that requires glue. Gonna glue it? Blow it off first. Glue it - then tack it in place with some brad nails from the nailer. I figure that my $80 compressor was worth the 80 and has already earned itself a retirement [used it quite extensively the past 2 years or so]. It's still going strong, and when it dies, I will get a better one big enough to spit paint. But this little oilless one is doing just fine.

[ids]

My $0.02

What I did was look at the requirements of the tools I thought I would want to power with the compressor.  A decent paint sprayer, for example, required something like 6CFM at 90PSI (IIRC).  This put most of the small compressors out of the running.

Ended up getting a great deal on a portable unit that fit the bill, but its rated 14A, so it pretty much needs a dedicated circuit.

If you use it to fill tires and things like that - watch the PSI closely, because it goes up fast!

[jennifer]

Oiled compressor reefers to piston type delivery, as opposed to an oiless which is a diaphram. They both have oil in the crankcase. Noise levels are irrelevent. (got a job to do- make some noise). Pancake style compressors will not get you much more then shooting some nails, any airflow that requires painting would start at 2 horse/20 gallons (for small jobs) For larger jobs like painting a cabinet would require twice that amount.

[whammoed]

I recently went shopping for a compressor.  My immediate need is to install 920 square feet of hardwood.  I also thought maybe I should get a big one that can do more than shoot nails....then I found out how heavy those are.  I realized I will need two compressors.   One portable for nailing and other odd jobs and one larger for sanders, HVLP, etc.  So far I have a  6 gallon Bostitch pancake.   Came with a finish nailer and a brad nailer.  These air tools are so sweet and getting them was long overdue.  Every time I get a new tool I wonder how I lived without it.

[TOK]

I recently went shopping for a compressor.  My immediate need is to install 920 square feet of hardwood.  I also thought maybe I should get a big one that can do more than shoot nails....then I found out how heavy those are.  I realized I will need two compressors.   One portable for nailing and other odd jobs and one larger for sanders, HVLP, etc.  So far I have a  6 gallon Bostitch pancake.   Came with a finish nailer and a brad nailer.  These air tools are so sweet and getting them was long overdue.  Every time I get a new tool I wonder how I lived without it.

I bought a couple hoses so I can reach anywhere in or around the house with my garage compressor. That has worked out great so far.

[whammoed]

I bought a couple hoses so I can reach anywhere in or around the house with my garage compressor. That has worked out great so far.

That's a good idea and I thought about doing that too.  Wanted to be able to throw this in the car too though.  Help out my parents, family, etc.

[SavannahLion]

Oiled compressor reefers to piston type delivery, as opposed to an oiless which is a diaphram.

Yeah, that makes sense. My father had a piston type (I guess) and they're rotting in the mountains right now because I can't get the hoses for them (at a reasonable price anyways). Makes me sad to see them rot away, but there isn't much I can do about it. The world wants to use ---smurfy--- cheap compressors nowadays.

[MonMotha]

The hoses should be relatively standard.  At worst, you'll just need some weird adapter to get it hooked up at the compressor end, but most are just 1/4" NPT, at least in the USA (European destined units may use metric threads).  You'll probably want quick connectors, of course, but those just screw on to the ends of the hoses or whatever.  If there's some oddball quick connector on the compressor, you can probably replace it with something more modern/standard.

Oh, and Harbor Freight sells cheap crap.  It's crap, but it is cheap, so if you don't plan to use it much, it's a good deal.  However, if you plan to use it a lot, well, it's crap.

[gazz292]

i'm in the uk, so things may be a bit different (we're on 230 volts for a start)

but i got a compressor about 10 years ago,

i looked at the cfm requirments of all the tools i wanted to use, wanted to use a spot blast gun, so needed over 7cfm for that, and the compressor i chose has i think 9.5 cfm rating... but beware, that the cfm rating on compressors is like the peak watt rating on speakers and amps, it's the absolute max recorded during destructive testing in lab conditions.

there is another rating that shows the real world air volume delivery, cant recall what it is tho, but my compressor is just over the 7 cfm in real terms that i needed.

i got a 50 litre tank, direct drive single piston unit, think it has a 2.5 or 3 hp motor, not sure of it's power consumption, we can pull 13 amps from a normal socket over here (that's at 230 volts remember, and thus is just under 3 KW

it as set to 120 psi, but i was able to adjust it to run at 150 psi on the cut out switch, the tank is certified to something like 250psi, and it's a common thing to bump the pressure up a bit on these compressors, the instruction manual showed how to adjust the pressure switch and what the safe settings were,

i needed the higher pressure to run my air greas gun, which i use to grease the UJ's on my motorhomes propshaft, at 120 psi it didnt have enough pressure to get grease in them all the time, at 150 it always gets the grease in em,

my biggest regret.... going for direct drive, noisey, due to the motor having to run so fast, i really wish i'd spent the extra and got a belt drive compressor, but then i'd have wanted a twin piston compressor head, an after cooler, 100 litre tank and so on, i'd prolly talk my self into getting a 3 phase model so i could get 50 cfm and 200 psi up in 10 seconds if i didnt keep my self in the reality zone

But honnestly, if you plan to use the compressor a lot, try to get a belt drive one, much quieter, less stressfull on the motor, lower power draw etc,

and as others have said, avoid the oil less ones, the oiless ones over here at least are piston compressor heads (the diaphram ones are more for air brushes, nowt serious can be run from a diaphram compressor)

just the oiless compressors have teflon coated cylinder walls and teflon block bearings, ok for occasional light diy use, but run them too long and they wear out very fast, and they are then a throw away item,
oiled compressor heads, you just need to check the oil lever every so often, think i check mine every year, change the oil every 3 or 4 years, and if you wear a bearing out, you can get replacements easily from any beariung supplier.

My compressor has a built in regulator, but also has an unregulated take off point in the form of a large allen screw in the centre of on end of the tank, i've not used that yet, but plan to get an external high volume regulator one day, and feed it from the centre take off like they do in pro instlations.

other maintinance... drain the water from the tank often, all compressors buil up water in the tanks, moist air is drawn in, and gets trapped in the tank, some better compressors have auto drain valves that open for a second every time the compressor shuts off.

i believe you can also buy an auto drain valve kit from your big diy stores in the us to etro fit, i'd highly recomend one, and wish i could get one cheaply and easily over here.

i have my compressor located in a store room at the end of my garage, i then ran some nylon air pipe from it, and down the length of the garage, i have a tee halfway along with a drop to a standard airline quick disconnect, and the rest of the lines run terminates at the front of the garage in a 25 meter long self retracting hose.

tools i run... spray gun, touch up gun, grease gun, caulking gun (with an adjustable regulator on the gun, otherwise you empty a cartridge in 2 seconds spot blasting gun, blow gun, drill, die grinder, cut off wheel, air chisel, sheet metal nibbler, shultz gun (under seal sprayer thingy) parafin/gunk sprayer gun, 1/2" impact gun, 1/2" ratchet driver, (could do with a 3/4" impact gun for half the nuts on the motorhome) and of course a tyre inflator gun (one for commercial vehicles, with the long stem dual ended tyre valve fitting to inflate dual rear wheels, and able to inflate to around 80 psi and still be accurate)