Air Compressor Capacity = Run Time

[Brian]

Hi All,

 

I'm trying to determine how air compressor capacity relates to run time or if it even matters.  I see many compressors available at Sears, HD, etc. but I'm not sure what capacity size fits my needs.  I'd use a compressor for some hand tools (nail gun, drill, etc.) and maybe a sand blaster.  Also, what's the difference between oil less and oil lube.  Is one less/better performing than the other.

 

Thanks

-Brian

[John Schaben]

Hi Brian the two specs on a compressor I'm most interested in are the hi and low pressure volume. Usually will see XXXCFM @ XXPSI. The psi ratings usually run around 40 or so for the low pressure and 90 or so for the high pressure. You need to match the compressor capacity to the tools. Tank size and max pressure play into it but the important ones when shopping are the volume specs to determine whether the thing can keep up with you without burning itself up. Of the tools you listed, nailers are reasonably low volume and a small compressor can handle those easily. Sanders, drills, die grinders, etc are air hogs and require a medium to large compressor. Sand blasters are air gorillas and require high volume at high pressure.

[Bob S]

The bigger your air tank, the longer you can go between having the motor kick on to refill the tank.  As noted in the other reply, some tools, like nailers, don't use air very fast, but some, like grinders or impact wrenches, use a lot of air in a hurry, so the CFM @ PSI rating is very important.  I've got a 33 gallon compressor and it has always kept up with what I do, but I don't use it professionally or anything.  My son has a small one with only about a 4 gallon tank, and he can nail floors down, but it's not worthwhile to use his impact wrench.  My next door neighbor has an 80 gallon compressor, but it cost about five times what mine did.

Mine runs until it's got 150 psi in the tank, then kicks back on when the pressure drops to about 120 psi.  Since most tools don't need more than 90 psi, it's very rare that you drop too low.  It's a function of which tools you want to use along with how long you expect continuous use of the air hog tools.

[James P. Cottingham]

Oil less compressor are motors that are sealed and self lubricating. Many smaller compressor are oil less compressors. The disadvantage to these are they are usually smaller motors. They cannot be run for long lengths of time. My "pancake" compressor says only run once every 15 minutes. This means that you cannot run tools that require a lot of air like an air wrench or paint sprayer. You also have to provide lubrication to the tools you do use. I have to put a few drops of oil in my nail guns whenever I use them. The main advantage is cost. They are also smaller so they can be moved easier. I can carry my pancake compressor to the roof of my house when I work on it.

 

Oil lube compressors need some oil in the motor. They are usually found on bigger compressors. They automatically lube the tools, too. The big disadvantage is they will have oil in the lines so you will have to trap the oil if you plan on using tools like a spray painter. (Oil and paint, esp. water-based paint, don't mix and the oil for motors isn't the same as the oil in oil-based paint.)

 

As mentioned above, if you plan on using a sand blaster, get a bigger capacity tank and an oil lube motor. A good compressor will last a long time.

[John Schaben]

"They automatically lube the tools, too."

 

Sorry, I don't believe this is true. The oil remains in the compressor and does require periodic change as with an internal combustion engine. Tool oilers and water traps are add-on devices which depend on the application a compressor is intended for. ie, a paint shop will not only have water traps but probably driers installed but never an oiler. A mechanic shop will have water traps, seldom driers, but invariably oilers. Both types of shops are high volume air users and would never be able to keep an oilless compressor.

James P. Cottingham said:

Oil less compressor are motors that are sealed and self lubricating. Many smaller compressor are oil less compressors. The disadvantage to these are they are usually smaller motors. They cannot be run for long lengths of time. My "pancake" compressor says only run once every 15 minutes. This means that you cannot run tools that require a lot of air like an air wrench or paint sprayer. You also have to provide lubrication to the tools you do use. I have to put a few drops of oil in my nail guns whenever I use them. The main advantage is cost. They are also smaller so they can be moved easier. I can carry my pancake compressor to the roof of my house when I work on it.

 

Oil lube compressors need some oil in the motor. They are usually found on bigger compressors. They automatically lube the tools, too. The big disadvantage is they will have oil in the lines so you will have to trap the oil if you plan on using tools like a spray painter. (Oil and paint, esp. water-based paint, don't mix and the oil for motors isn't the same as the oil in oil-based paint.)

 

As mentioned above, if you plan on using a sand blaster, get a bigger capacity tank and an oil lube motor. A good compressor will last a long time.

[James P. Cottingham]

Yep, you're probably right.

 

[Uncle Bob]

And by the way, once you start using air, you will probably add more pneumatic hand tools than you do electric.

 

I probably have a dozen or so now.  Use at leas one almost every day.  I've been using a 33 gal/150 max psi/6 hp oil less for the last several years and it keeps up with me.  I had a 20 gal oil lube for may years (120 psi?/?hp).  When I was sanding, I got to take a lot of short breaks waiting for it to catch up. 

 

Most sanders also take a lot of air.   All pneumatic hand tools I know of recommend a drop or two of oil daily.  Be careful about the oil that may come out of the air discharge getting on (wooden) work pieces.