View Full Version : compressor specs?
Hey everybody, I'm in the process of setting my shop up to paint, and I am trying to find what size compressor I need. From the research I have done so far, apparently the da sander is what will require the most from a compressor, the spray guns especially hvlp, require much less. I have also been told that although you should get the biggest compressor you can get, the cfm rating is all that matters, if this is true, if so, what cfm at what psi do I need? I'm trying do stay with a portable plug in compressor, but I haven't found one with more than 5 or 6 cfm at 90 psi is this enough?
02-19-2006, 06:33 PM
Heff, Biggest air hog tools in any autobody/paint shop is air grinders, large sanders, air buffers, and especially sand blasters. Some HVLP spray guns are air hogs in the 15 cfm range. You are not going to find a portable air compressor on wheels that will dleiver the air you're going to need. Here are some basic specs of a shop air compressor (including a hobbiest air compressor). A bare bones minimal set up will be 220 v single phase motor with a 11 cfm pump @ 90 psi with a 60 gallon air tank. I have a small shop and my air compressor is a Quincy industrial rated 5 hp, two stage pump in the 19 - 22 cfm range with an 80 gallon tank. I payed $1800 just for the air compressor (not including the magnetic starter box, stationary air lines, water traps, filters, regulators etc), its been in everyday commerical use for 22 years trouble free ( I did change the electric motor about 4 years ago).
As far as DA's go - most good quality DA's use very little air compared to other bodyshop/paintshop air tools. You could run an Air Vantage orbital sander like Len sells on around 4 actual cfm of air. A National Detroit DAQ or EZQ uses around 6 or 7 cfm. 8 or 9 inch grinders, larger sanders, air buffers use 15 - 20 cfm of air based on my personal experience. A die grinder, air drill and cheap DA's will use upwards of 10 cfm. The average HVLP gun will use 11 or 12 cfm
02-19-2006, 06:36 PM
I'm new, but I've read a lot of posts that say no. I myself have a Gas Compressor that has 11.4 cfm which is enough cfm but thats only part of the equation. I get a lot of water, more than what a filter-separator could ever remove. Apparently you need like a 60-gallon tank to keep the compressor from running during your paintjob and also to de-water the air a little before it goes to the line. Thats why I've ordered a 60-gallon compresor. Not to rain on your portable idea, but it must may not work...
This isn't the one I bought, but from what I hear, its about the minimum...http://www.lowes.com/lowes/lkn?action=productDetail&productId=134819-48540-K7060HFV&lpage=none
02-19-2006, 06:48 PM
Bartmonster, you could have made that gas portable compressor work (obviously with compressor unit running outside in the fresh air). Your problem with the water in the lines is common to all aircompressors. The key to getting rid of the water is in having an air line no less that 20 feet from the first (or only) water trap. That minimum of 20 ft of air line allows the hot moist air coming out of the compressor air tank to cool and condense the moisture into water that gravity flows back to the compressor tank where it can be bled off as needed. A 25 ft length of softer copper line wrapped around a 5 gallon can into a coil works pretty good for smaller compressors.
Smaller air compressors produce more water because they turn faster, run hotter, work harder and run longer without shutting off than industrial type compressors.
02-19-2006, 06:51 PM
I think I should clarify what I meant by 20 ft of air line. What I meant was that you need at least 20 ft of air line between the air compressor tank outlet and the first (or only) water trap.
02-19-2006, 08:30 PM
Well thanks Phil... Probably best that I buy a new one and sell the gas one anyway, d/t possible painting in the middle of the night. I'm still not sure how much these paint fumes will disturb the neighbors, so I figure that at about 2 am, I might squeek by...
Can I interest anyone in Nebraska in a 5.5 HP Gas Wheelbarrow Compresor?? Only about $250..
02-20-2006, 11:05 PM
the limitation on the small portable compressors (even up to 30 gal tanks) is mostly to do with the electrical end.
By that I mean your not going to get a motor running on 110/115/120 volts that's going to build up enough true horsepower to generate the CFM's needed for most autobody tools.
It's a hard lesson we hobbist have to face that you need something running of 220/230/240 volts to do the job of sanding and grinding.
Would you happen to have a picture of the copper line trick? If not, would you run it directly out of the tank then hook your water seperator to the end of it?
02-25-2006, 02:19 AM
Jake, yes you can connect the copper tubing coil to the outlet of the air compressor. Make sure that the bottom part of the copper coil is what connects to the air compressor outlet and the upper part of the coil is where you would hook up your water trap/filter/regulator. I did that with a couple smaller air compressors ( 3 - 4 hp, 20 - 25 gallon compressors). It would also help to point a window box fan at the coil to help in the cooling/condensing of the moisture back to water droplets that gravity feed back to the air compressor tank, where the water can be bled off at your convenience. That whole thing is still far from an ideal setup, but it makes a difficult situation at least workable.
02-27-2006, 01:57 PM
Newbie here...looks like a great forum. I'm looking to paint an old car on a very tight budget.
Phil, with the copper tubing...what diameter works best? 3/8" OD, 1/2" OD
I have free access to one like a Sears 6hp (~2hp running) 30 gal with 6 SCFM at 90 PSI.....if you had a second 30 gal tank (only) for storage pumped up to ~125 PSI...would that help in being able to shoot the whole car?
30 gal Compressor>>>30 gal storage tank>>>copper tubing>>>water sep/regulator>>>gun
Is this reasonable or just not effective?
Doug, the extra tank will be of minimal help. If you hooked up another compressor to it instead of just a tank, it would help much more. The main problem is that youll be using more than is being produced, so eventually it will run out. You could probably get by just doing a panel or two at a time, but the compressor is going to hafta have time to catch up sooner or later.
02-27-2006, 06:56 PM
Doug, what you describe with the second 30 gallon tank is definately not an ideal situation but in all honesty you could make it work. But like CDjr said - at some point you are going to run out of air because you're using more air than is being replaced.
You should be able to get around an average size car by todays standards before you run out of air using both tanks. It will take quite a while for that little compressor to pump up both tanks for the initial paint shoot. Moisture is going to be an area of concern because that little compressor pump is going to be running steady trying to keep up with air being used during spraying. That copper coil should help in that respect. I honestly don't remember what diameter of soft copper coils I used with small compressors in the past (that was close to 25 years ago). 1/2" should work fine but the bigger the diameter the better. Check to see what diameter that line is going from the air pump outlet to the compressor tank inlet. Thats probably 1/2" soft copper pipe. I'll say it again, its FAR from an ideal situation but its a short term fix to problem.
02-27-2006, 07:34 PM
Thanks, CDJr and Phil
Saw an ad in the paper tonite...Twin Tank Compressor, Contractor type on wheels, 5hp, 220v, $280
Seller was owner's brother and wasn't up to speed on it. Thought it was single stage, didn't know SCFM, thought each tank may be 5 gals. I'll try to see it tomorrow. He did say his brother had painted Model-T's with it. Hmmmm....seems like you'd want a model-T to look good.
One thing from my searches...I just haven't seen a 110v that looks good enough to shoot a whole car. 220v piqued my interest. But wheels AND 220v?
Does the limited data on this compressor allow anyone to ID it?
Phil, did you run that copper coil through a 5 gal can of water to cool it or did you just mean you used a can to form it into a coil?
Ive never seen or heard of a 220v on wheels either, Doug lol. I gotta see this. :D
02-28-2006, 09:36 AM
The only "twin tank" compressors I've seen are those "dinky" ones used by contractors on site. Usually to run nail guns and the like and yes they are around 5 gallon tanks.
Your going from bad to worse here.
02-28-2006, 09:42 AM
The 5 gallon bucket was just a form used to wrap the copper tubing around to from coils. I have heard of using a 5 gallon bucket and immersing the copper coils in cold water in the bucket. The problem with that is logically both ends of the copper coil come out the top part of the bucket. That means that the water that forms inside the copper coils will gravity feed down to the lower coils in the bucket. it wouldn't take too long with a small compresor working overtime to produce enough moisture to start filling up those coils with water. I've also heard of people using an cars AC condenser plumbed inline and placed in front of a window box fan as a poor mans air drier. Couldn't hurt I guess.
Those contractor twin tank compressors are very low cfm machines. that is unless it has like a 10hp gas engine. I would definately stay away from any small contractors type air compressors. They'd be ok for air up tires etc buy not any use for autobody or paint work.
To the best of my knowledge there is no 110V air compressor that will put out enough air to paint a normal sized vehicle in one sitting (without stopping and waiting for the air compressor to build back up enough air pressure to continue painting. A bare bones minimum air compressor specs for doing autobdy and full paints is a 220V, 60 gallon tank and around 12 cfm Anything less is an exercise in frustration for several different reasons.
02-28-2006, 06:49 PM
Well, I looked at that compressor. It was a Frankenstein....looks like it was once a Rigid 6 hp gasoline wheelbarrow type with 2 x 4.5 gallon tanks. A 220v motor was bolted on. Regulator leaked - motor kicked on every 2 minutes just to overcome the regulator leak. Didn't even have a pressure gauge.
This ain't no car painter, LOL.
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