learned a little about compressors........

[durango dude]

Some time ago, I picked up a Kobalt 8 gallon compressor.

I used it for tires and to blow off my tractor and motorcycle. I was happy.

I picked up a brad nail gun - and I was still happy. Compressed air is great for cleanup and for drying off work.

Now, I need to do some wrenching on my car ----- so I picked up an impact wrench ----- and I'm NOT happy.

Turns out - most inexpensive compressors aren't really designed to handle impact wrench work.

a) There's not a lot of air in the tank
b) When you run the wrench a lot - it keeps the motor running
c) When the motor runs a lot ----- it gets hot ------- VERY hot.
d) The compressor is god-awful loud.
e) The compressor draws a lot of current. It does not play nicely with my halogen work lamp (which should be replaced ----- don't lecture me)

Seems the best strategy for an air compressor is to think long-term, and to plan for the highest likely use --- and to buy something for that.

I'll eventually re-wire my garage to handle 20 amps, and will put in a larger unit, along with piping into my workshop for the cleanup and brad nail work.

At the moment - I'm doing research ---- but I love the specs on the quite California Air Tool 10 gallon 2 HP unit.

[twistsol]

I have a couple of Porter Cable pancake compressors that can keep up with me just fine with all my nailers. I'm too slow to tax them even with the framing nailer. You're right, they work great for tires and blowing dust out of machines

That said, spraying finishes was painfully slow while waiting for the compressor to catch up so I switched to a turbine based HVLP. I had the same experience as you when I tried the impact wrench that came with a larger compressor, that incidentally failed a day after the warranty but I digress. The impact wrench has been in a drawer ever since and will likely never see the light of day. If you drive a car with only one lug nut it would be great, otherwise a tire iron is faster.

[leehljp]

I have needed just a tad more than the pancake compressors but not as much as a 220V compressor. I settled for HF's 29 gallon 2 1/2 HP. I probably spent a good 8 to 10 hours installing a line cut-off and reel hose. The time taken was not in the installing itself but in the leak seeping. I think I changed every fitting out 3 times before I got to where I had NO seepage. I can fill it up now, turn it off, close the cutoff valve and in a month it still is full. IF I leave the valve open, even with the reel, it takes approximately 2 1/2 to 3 days for it to loose enough air for the compressor to kick back on.

I love having plenty of air. I bought this compressor about 3 years ago for $149 I think.

[mpc]

Compressors are like bandsaws... you'll grow into a larger unit faster than you expect to. Something rated at 6 CFM @ 90 PSI will keep up with impact guns unless you have quite a few fasteners to remove at a time. The CFM rating is key... that's more important than the maximum tank air pressure in my opinion. A compressor rated at 6 CFM at 90psi is about what I'd consider a minimum capacity for home air tool use. Air sanders or paint equipment? They typically need a lot more. Lately I've seen a lot of compressors rated at high air pressures but low CFMs which makes absolutely no sense to me. Unless one has to inflate RV or truck tires that want 120+ psi. Oil vs. Oil free compressors? Having heard a few oil-free units I'd never consider one. LOUD is an understatement. An oil filled compressor isn't exactly quiet to begin with; the oil-free ones I heard (admittedly over a decade ago so maybe technology has improved) were several times louder and would certainly bother neighbors. None of my woodworking tools are as loud as a friends oil-free compressor. Even he hated it when he first got it; he sold it pretty quickly if I remember right.

Some compressors struggle to run air tools even if the CFM and pressure ratings exceed the tool's requirements... because many compressors sold for home use have restrictive regulators on them. The compressor itself may be rated at 6 CFM but the stupid little regulator (between the compressor and your air tool hose) can't flow 6 CFM... especially the ones that are quarter-inch fittings. A regulator assembly with half-inch (or larger) airflow fittings is MUCH better! Swapping out the stock regulator on my Craftsman unit was a night-and-day difference in performance/capability. I had rigged up a "T" fitting ahead of the regulator to allow raw tank pressure to feed the air tools, bypassing the regulator, initially since my tank pressure was only 100psi anyway. Right at the upper limits of my air tool's ratings. With the new half-inch regulator though I can drive the air hammer or the impact gun easily at 90 psi.

Ryobi makes a half-inch drive cordless impact gun. It's got a fair bit of torque and will do quite a lot of car stuff including lug nuts on pickups. It's too powerful for tightening most fasteners... using an impact gun for re-assembly is generally a bad idea anyway. I have one of the Ryobi units and it handles the vast majority of stuff I used to drag out the air powered impact gun for. Only really rusted stuff stumps it. It doesn't like being used continuously though against a really tight fastener - it'll overheat when asked to beat on something for several minutes solid. Other than that though it's pretty sweet. Since my cars are in SoCal and don't suffer winter snow + salt I don't have much corrosion/rust issues even when doing heavy suspension work.

mpc

[cwsmith]

A few things to know about compressors, with the most important being that the compressor CFM needs to be better than the tool you are using. Most all compressors will put out enough CFM (cubic feet per minute) to run an air nailer. They require only a quick "whack"... unless you are bump firing. Primarily a nailer needs around 90 psi and very little volume (CFM).

If you are going to run an air tool, well that takes a bit more volume, as the air flows continuously to turn the air motor... like running and electric drill, it takes power as long as you hold the trigger down.

An air-operated spray gun takes even more and for that you'll need considerable volume, albeit at a much lower pressure (PSI) ... usually in the neighborhood of 40 to 50 psi at 10 to 12 cfm. I have a 150psi, 33-gal oil-less that puts out about 8 cfm at 40 psi and it will not keep up with a typical paint gun.

The other thing is that your air compressor has a rating, usually given in PSI/CFM. For example the label might say "8.6 scfm @ 40 psi and 6.4 scfm @ 90 psi" most always the ratings are stated at both 40 and 90 psi, so as to give you some idea of your tools' use on that compressor. Likewise your tool with have a single pressure rating, stating it's PSI requirements and possibly it's volume at that particular pressure.

The other thing to be aware of is the "duty cycle" of that particular compressor. While many compressors are rated for 100% duty cycle, most cheap compressors are not... usually 50 or 75%. That means that if you're using it for something like a paint sprayer or air tool, that compressor cannot run more than a short time every period. So you need to run and rest, or you risk damaging the compressor.

Lastly, lubricated units (oil in the crandcase) generally will outlast an oil-less and they will run considerably quieter. But lube vs oil-less doesn't necessarily effect duty-cycle, so be aware of your compressors ratings.

Hope this helps,

CWS

[capncarl]

Reinforcing something CWS said..... concerning duty cycle. Without checking the spec sheets on each compressor I would venture to say that few to none of the large compressors sold at the big box stores, Tractor Supply and retail homeowner type stores are 100% duty cycle. Maybe the higher end, larger than most hobbyists would purchase for our shops might, just might be 100% duty cycle. I doubt that my 5hp Ingersol Ran compressor is truely 100% duty cycle as I’ve had it overheat and blow head gaskets several times. I think a 2hp/35 gallon tank unit is adequate fo most woodworking shops that occasionally have to operate air impact tools. When my compressor dies I will probably replace it with larger capacity compressor.

[cwsmith]

As CapnCarl stated about duty cycle, and to add to that. From my experience "100% duty cycle" doesn't necessarily mean that a compressor can be run for hours at a time. Even the big industrial air compressors I don't think are meant to run 'full-out' for days at a time. Basically that is what the tank (at Ingersoll-Rand we referred to them as "receivers") is for... to provide air storage. However, from my experience when I-R built air compressors at the Painted Post plant prior to 1987, every single compressor had a long-term run test. Of course those were the Type 30 and 40 and the larger industrial ESH-ESV, PHE, LLE and XLE class units (all much bigger than what we might have in our home work shops). But even than, most applications didn't have compressors running 24/7.

Both my compressors are Craftsman units, with one being a little 2-gallon, 1 hp (hot-dog) lubricated, 125 psi, rated at 2.4 scfm @ 90 psi. It is a 50% duty cycle compressor and is ideal for running a nailer. The manual states that it should not be run more than 30 minutes per hour, but that doesn't mean it should run for a full 30 minutes at one time either; as it will definitely overheat. I use this compressor for running my nailer (even a framing nailer) and it will inflate my tires just fine, though it may recycle a time or two. I like this little compressor because even with a short 25-ft hose, you can stand to work near it.

My bigger compressor is an oil-less 33-gal, 150 psi vertical tank unit with a running 2 HP. It is rated at 8.6 scfm @ 40 psi and 6.4 scfm @ 90 psi. About the only time I use this compressor is when I'm spraying finish. It is so noisy that I have to wear both foam ear plugs, but also ear muffs. Located in the basement, you can hear it out in the garage... that level of noise should never have been allowed on a consumer grade compressor in my opinion! The manual states, "This air compressor pump is capable of running continuously. However, to prolong the life of your air compressor, it is recommended that a 50%--75% average duty cycle be maintained; that is, the air compressor pump should not run more than 30=45 minutes in any given hour. (Again, that is accumulative and not continuous running.)

While I really like the smaller, oil-lubricated unit, the larger oil-less is just absolutely painful to be anywhere near and I will be dumping it once I have my new shop completed.

[capncarl]

One drawback I find in residential compressors is the speed (rpm) they operate at. My 5hp compressor operarates at 3600 rpm, and will scare you to death if it cycles on if you are not expecting it. It is also terribly loud. One of my friends has a compressor from an old service station with a probably 250 gallon tank, larger compressor pump than mine and a 1-2 hp motor running a small to large pulley setup. It makes very little noise, though it does run a long time to fill the tank. Like I said in a previous reply, when I have to replace my compressor I will probably try to install a larger pump and slow the motor speed down with different pulleys and/or a lower speed motor.