Hey guys, I have an air compressor. It's a 110V 33 gallon 2 hp unit. It has a max pressure of 140psi and is rated at 8.6 scfm @ 40 psi and 6.4 scfm @90 psi.

Basically, what does the scfm rating mean?

The compressor works great for all my air tools but I am looking to attempt body work/paint in the near future and am wondering if it will cut it. I have been toying with the idea of adding an extra 30-40 gallon tank to increase the capacity. I know it won't help with the fill rate but will give me increased working time between fills. Will extra capacity increase my cfm??

I have been looking into air guns for primer and then the base/clear application for the unibody. Most of the spray guns need something around 8.5-12 cfm but at a lower psi (approx 15-25 psi). The scfm ratings seem to increase as pressure decreases. What does that mean for an even lower psi?

I know this is loosely related to slicks but I have asked this same question in a few of the auto body forums with little to no responces. You all have always given me great info/advice so I thought I'd try it here.

In a nutshell I just need an explanation of how all this jazz works so I can get a spray gun that will work well

Thanks a million
Jason

 

Some compressors (according to their spec sheets) hold a rather steady CFM (cubic feet per minute of air output at a given PSI). There are two different types of CFM measurments; one takes an instrument to actually measure the air volume throughput, the other is a mathematical (read this as theoritical that assumes no friction losses and is purely a calc based upon piston sizes and such). I doubt your compressor is going to run many of the body and paint tools you will want to use. Don't even think of running a sandblaster, you'll be out of air in seconds.

The CFM is purely a function of the compressor, adding more tank volume will not affect the CFM. You are correct, it will increase time between fills but each fill will take twice as long. This is only really effective if you are using a tool that requires a large amount of air for a short time. If you want to run a sandblaster (this is probably the largest air user) that extra 33gal tank will help enough to sandblast a very small item or area. You will end up wanting a new compressor with a larger tank and larger capacity compressor.

Do you have access to a 220v 30amp circuit or have the ability to install one of these in your garage for a new larger compressor? I purchased a rebuilt compressor from Harbor Freight for half of the new price with a 2 year warranty. It has a 7.5hp Baldor motor and all SquareD controls with an 80gal tank and ~28CFM at either 90 or 120PSI (Sorry can't remember which). Either way this will provide me with enough air to run my Blast cabinet, a siphon feed or pressure feed sandblaster and any other tool I can think of.

The other piece is if you are going to paint you need to have good moisture seperators and NO oil in the lines. Keep dedicated hoses for painting. Good luck.

 

Manufacturers will always point out how much HP they have or how big their tank is. None of that matters when you get down to the nuts and bolts. What you want to know is the cfm as that is what counts especially since most all guns tell you exactly what cfm they need to run. The same smoke and screen is used when describing how good an LCD T.V. is by talking about contrast ratio. In reality it is a totally useless number which they can charge more for.

 

your compressor sounds simmilar to mine. i'm not a body man buy the way. and what i have done is i bought a small hvlp (high volume low pressure) gun that runs at 40 psi. from harbor freight theyre about 20 bucks. it has a fairly small cup on it and the compressor runs almost the hole time. but i'm doing one fender at a time with duplicolor's paint shop. with really decent results. it's not show quality but i've had many compliments on it. btw i don't have a filter or dryer in line but its working

for a decent do it yourself job match up the numbers pretty close unless your looking for a show winner.

 

Your compressor will be just fine. The HVLP is an excellent suggestion as to which gun to go with. The chinese stuff isnt real good on QC so look the gun over real good. Mine didn't have a relief opening in the cap so it choked the first time I tried to use it. Closer inspection showed the hole was never clearly open during manufacturing. Two suggestions. 1. Get a inline water trap and 25ft of hose. Connect the hose to the compressor then the water trap to the hose, then your working (spray) hose opposite the trap. 25' is minimum line distance for a trap location. Otherwise the water will blow right past it.
2. is get a 6 pack of the at gun water trap bulbs, they work great and are a cheap last defense against water getting into your fresh paint.