compressor capacity rating question

[Rob Giordano]

I am looking for a compressor to spray various finishes. My understanding is that I should be looking for 4-5hp which can deliver 8-9scfm or better. I see one on CL in my area, a Craftsman 20gal., 5hp, 9.0@40psi. for $100. I notice a number of these across the country for about the same so I'm guessing they weren't real expensive to begin with. I search to find what a comparable compressor would be if I bought it new and can't even find one that is a 5hp even if I go as high as $500 or more.

What am I missing here, kinda seems too good to be true.

Thanks, Rob

[Callan Campbell]

Well, don't know the model of the compressor you're talking about, but here's a few facts about compressors that might help you.
Most 5HP rated compressors will have a larger tank because their pump is capable of producing enough air to store inside that tank. Smaller tanks get matched to smaller compressors, since the output is not as high. You'd be waiting forever on a small pump to fill a 60 or 80 gallon tank, and the pump would suffer from all that running as well.

If the compressor you're looking at gives enough air flow for the spraying you want it to do, and you can let the unit cool down at times and not try to make it run all the time while you're spraying, then buy the compressor. The real worry I have is that the tank size of 20 gallons is really small. With that small of a tank, you have no "bank" or buffer of stored air built-up. For spraying usage often, a larger unit would probably be the way to go, as you'd get a larger tank with it. If you do buy this unit, or any other,just remember to change the oil if it's an oil cooled model, change the intake air filter as needed, and give it enough amperage/correct wiring to run on.

[Robert Reece]

Craftsman likes to use "peak horsepower", not running horsepower. You need to look at the current draw of the motor.

My compressor is a true 4 HP, 80 gal, 2 stage and it cost over $1k. It runs wonderfully quiet and with 80 gal, it just doesn't run much.

You might want to keep looking depending on your needs and desires.

[Marty Paulus]

I would be shocked to find a 20 gal true 5 hp compressor. Like was stated that number is peak not running. If it is running on 110/120 voltage there is no way you will ever see anything close to 5hp in a normal residential environment.

Here is a calculator to figure true hp of an electrical motor:
http://www.onlineconversion.com/motor_horsepower.htm

[Rick Moyer]

You buy a compressor to deliver air so the most important property would be how much air for how long. you should mostly be comparing how many cfm at what psi, which will ultimately be the performance of you compressor, somewhat regardless of stated HP or other factors. You will need to know what the requirements are of the tools you intend to use to see if a certain compressor is adequate for your needs.

[Gary Click]

My 5HP compressor (based on current draw of 24amps at 240 volts) delivers 13+/-CFM@175PSI to an 80Gal thank. I think that you will be disappointed with the small compressor you are considering for almost any continous operation like spraying, sanding, sand blastiong, etc.

The 80Gal Vertical Compressor is also MUCH quieter and cooler than the small twin stacked tank unit that is "portable".

If you decide to use a larger stationary compressor also consider the purchase of a programable automatic moisture drain for the tank. Most of the people that say "I don't need that, I will remember to drain the tank", are the same ones that forget to drain the tank. I got mine, a Flair Corporation Model ADV-1711 of eBay for $50. It opens for 3 sec each hour.

gary

[Matt Day]

Look for cfm & psi as stated above. Look at a $75 shop vac - do you really think that little motor is putting out 5 HP?

[Lee Ludden]

Check out Eaton Compressor. They are very well built and American made. The numbers they give are true-use values, not some marketing gimmick.

[Jeremy Brant]

Check out Eaton Compressor. They are very well built and American made. The numbers they give are true-use values, not some marketing gimmick.

I second the suggestion for Eaton. I have one and it's been great for the past 9 months or so that I've had it. It's a 60 gal 5hp 2 stage model that puts out ~19cfm at 100psi. I do not want for air.

That said, it sounds like you're looking for something much less expensive that will do the job. The 20 gal you're looking at will do it. I'd suggest looking into one of the newer LVLP guns. They use much less air and as long as you planned well and took it easy letting the compressor catch up when it kicked on, you'd be fine. Look into a gun like this: http://www.eastwood.com/ew-concours-paint-gun-w-3-tips-plasticandmetal-cup.html. I have a friend with one and it does quite well with his 30 gal setup. The different cups let you shoot both solvent and water-based, and different materials with the different size tips that are provided.

[Brett Nelson]

That 20 gal Craftsman won't even come close to serving your needs unless you're painting pinewood derby cars. Do yourself a favor and search CL for a Ingersol-Rand T-30 in good shape. Got mine in great shape for $600. 80 gal is plenty of air and it will actually outrun my 13cfm HVLP sprayer. IOW, when it kicks on I can hold the trigger open on my sprayer and my compressor will still hit the shutoff pressure in about 2 minutes. Not to mention 100% duty cycle.

You'll need a 240V outlet and these things aren't portable. I've got mine on casters but it weighs about 400lbs. You won't get a compressor capable of any real spraying that isn't 240V though. Just be careful to get a single phase. Lots of 3-phase out there on CL.

[kenneth kayser]

I am looking for a compressor to spray various finishes. My understanding is that I should be looking for 4-5hp which can deliver 8-9scfm or better. I see one on CL in my area, a Craftsman 20gal., 5hp, 9.0@40psi. for $100. I notice a number of these across the country for about the same so I'm guessing they weren't real expensive to begin with. I search to find what a comparable compressor would be if I bought it new and can't even find one that is a 5hp even if I go as high as $500 or more.

What am I missing here, kinda seems too good to be true.

Thanks, Rob

Forget about HP. Determine the air flow you need at the pressure you need, then buy the next compressor size up. Good quality compressors should run continuously without a problem; cheapos, maybe not. Also, cheapos may exaggerate output.

[Karl Card]

there are alot of expensive compressors out there that are well worth the money. eaton, ingersoll rand, just to name a few... I do not have that kind of money so I found a husky at HD (yeah i know) but the thing got descent reviews, 4 year warranty first year on sight, 220 volt, 3.2 hp 60 gallon tank 10.xx cfm at 90psi.. 399.99... it works good for me thats about all i can say.