Hey! I hope you guys will excuse me for barging in here with a question.

I found your forum when I was trying to learn about air compressors online. It seems like you all are very knowledgable about these things, so I thought I'd try asking a few questions here.

I make pottery and I am looking for an air compressor to spray glazes onto my pots. I am thinking of getting a spray gun called the Critter Spray Gun because that has been recommended to me by several other pottery people.

I'm trying to understand the terms used on air compressors to figure out what I need. The Spray gun says it needs 3 cfm @ 90 psi. I know what the abbreviations stand for, but I don't really know what they mean. I was hoping that someone here could explain or point me to a website that explains what those things mean.

Also, if the spray gun has those requirements would it run better if I got something bigger, or would it not make a difference?

I was looking at air compressors at Harbor Freight, but I read some really bad things about them, so I went and looked at Lowe's and found another brand called Kobalt that seemed inexpensive compared to the other brands (Porter Cable, deWalt, Campbell Hausfield). Do you all think the Kobalt brand is any good.

Anyway, sorry if this isn't appropriate for this forum. It's probably not, but you guys just really seem to know what you are talking about, so I thought it couldn't hurt to ask. If this is too off topic, please just ignore it or have your admin delete it.

I'm also going to continue to look through your posts because I'm sure a lot of this has been discussed, although maybe not in terms that I'll understand.

Thanks,
Leigh

 

3cfm @ 90 psi

Compressor must be able to hold/move a volume of 3 cubic feet per minute at 90 pounds per square inch. Most 3/4 horsepower to 1-1/2 horsepower compressors can provide the required amount of volume that you need.

I would get a compressor with slightly more than required, this will keep the compressor from having to keep going through too many refill cycles as you work. (Larger tanks help too).

I prefer Hitachi or Thomas Industry brands for my applications.

DeWalt is another compressor I use daily too.

Buy what you can afford, but don't go "cheap" either.

DEWALT D55151 : 1.1 HP Continuous 4 Gallon Electric Hand Carry Compressor

 

Hi Leigh,
CFM is cubic feet of air per minute. What they are saying is that you need a volume of air equal to thee cubic feet of air compressed to a pressure of 90 pounds per square inch/gauge. That really means air compressed to about 104 PSI because air is already compressed to about 14 PSI at sea level. To put this another way, the pressure required is about 7.4 times that of sea level atmosheric pressure, or more commonly stated as 7.4 atmospheres. Therfore, you need a compressor that will take in around 21 cubic feet of air, compress it down to 3 cubic feet at 90 PSI and deliver it constantly at that pressure and rate without loosing rate or pressure if you were to contineously use the gun.

Now, a 3 CFM compressor is not a very big unit, so it shouldn't be too expensive. You will probably want an oilless compressor so your air will be clean and free from oil residue. A note of caution here, they are usually really noisey.. Harbor freight is not really all that bad if youn watch what you are buying. The reason the Kobalt is so much cheaper is probably because it's made in China. That's justb a guess. If you are going Chinese you might as well go to HF and pay Chinese. Here is a compressor at Harbor Freight that will do the job and it has a regulator to set the output pressure. CLICK HERE for info on that compressor. If you want to spend more I suggest you look at stuff like Ingersol Rand.

You will also want to use a water seperator to keep the condensation of water from the air from going to your gun.

I hope this helps.

Later...

 

Thanks for the info!

That DeWalt looks pretty nice. The price isn't too bad, really.

Dave- your explanation of what the terms mean was really helpful. I wasn't understanding why the compressors I looked at had higher cfm at lower psi (like 3 cfm at 90 psi and 6 cfm at 40 psi) and now I think I do.

I don't think oil would be too much of an issue, as it would burn off in the kiln, although I should probably ask some other pottery people just to be sure. Thanks for pointing that out, because I hadn't even thought of that. I didn't realize the oil got into the air.

Now, I don't understand this... Darren said that most 3/4-1 1/2 HP compressors would go to 3 cfm, but the Kobalt ones I was looking at in Lowe's were (I can't remember exactly) but higher than 3/4 HP, but said 2.4 cfm @ 90 psi. Is that lower enough to make a difference with this spray gun that I am going to be getting? How does HP relate to cfm? I guess, basically what I'm asking is is cfm the most important thing to look at or is it HP?

 

Don't get to hung up on Horsepower. I just used this (HP) as a reference to the physical size of the compressor. The 3/4 to 4 HP compressors are usually compact is size. (more suited for your application). 5 HP and above start getting larger (and may have wheels to move around). More HP units recover quicker and hold more CFM at higher PSI.

Stick to the compact units and you will be fine.

 

Okay, thanks! I really appreciate you and Dave's help!

 

Oil or oilless isn't a big deal, an oil lubed compressor will live longer and be quieter. I would use an inline filter/dryer mounted about four feet out from the compressor at a minimum, and a disposable cartridge filter at the gun, something like Astro Pneumatics #6803. These are right around $3 apiece, and get pretty much everything out of the airstream including oil, water, and dirt.
Oil or water in the air will cause blemishes in the finish, thin or thick spots, bird's eye blotches, etc.

 

At the time I bought my compressor, Campbell Hausfield made compressors for both Lowe's and Home Depot. Lowe's used to specifically carry CH, but I think they just started selling the same compressors with the Kobalt name. My Husky (HD brand) compressor has a Campbell Hausfield ID tag glued onto the backside of the tank.

I temporarily have my brother-in-law's oil-less compressor and that 20 gallon compressor is louder than my 60 gallon one. I imagine what you're doing an oil-less model would get the job done, but for running air tools it is just marginally adequate for my air ratchets.

 

Thanks! I will probably go with a oil running compressor, because I would rather it be quieter than noisier. Someone on a pottery list just told me that they are running their Critter spray gun with a 1/10 HP compressor and that although it runs constantly it's getting the job done. I don't think I will go that small, but it's reassuring to know that a smaller compressor will probably be adequate.

Ford-Six- about how much do those in line cleaner things you were talking about cost? I googled it, but I wasn't sure I was pulling up the right thing. There were some that were fairly pricey and there was one that was cheap, but disposable.

Regarding who makes the Kobalt, it's funny. I tried doing some searches on it and it doesn't seem at all clear to me. Some say CH some say Coleman, some say they are the same as Husky. Most people indicate that the makers have changed at at least one point. I guess Lowe's contracts the making out? I guess that's one of the benefits of buying a brand like DeWalt or IR. At least you know where the darn thing was made and how to get parts for it!

Leigh

 

It's this filter:


They usually sell for $3-$4 apiece, or about $12-$13 for a three pack.

 

Ah, great! That's not what I found. The things I were looking at were in the $70-$90 range. Much better!

I think I am set now. Thanks so much for all your help!