Air compressors

[KNOCKABOUT]

Anyone have any experience with air compressors for painting? Would love to spend less rather than more, and I have never used one, but want to get that glassy sheen...

[Bob Cleek]

One of the handiest powered tools around is a decent air compressor. It can inflate tires, blow off dust, run all sorts of power tools (at much less expense than electric drills, grinders and so on), do light sand blasting and spray paint. I have a Binks continuous pressure compressor I use primarily for painting. I also have an Emglo that I use for just about everything else, although it paints as well as the Binks. I would say that spending money on a decent quality compressor that can put out about 125 pounds of pressure at a pretty good volume is a very worthwhile investment.

That said, if you really want that glassy sheen, it's all about surface preparation more so than about how you put on the paint. No matter how good a painter you may ever be, the finish won't ever be any better than the surface it goes on. It's got to be smooth as a baby's bottom first. You can use your compressor to power all sorts of sanders, too!

[Wild Wassa]

A good triple piston compressor doesn't lose pressure ... well worth the bucks if you are painting often. Nothing ruins a paint job like frustration or waiting for the pressure to build back up.

Warren.

[Jay Greer]

Ditto on the tripple piston compressor. I tried a diaphram unit when my old pump died and it was so noisy that I traded it in after a one day cacophony in the shop.
JG

[pcford]

An air compressor is indeed a great tool to have in a shop. But they are not necessary to get a high quality finish.

[Canoeyawl]

The air compressor should be sized for your air tools.
This will be stated as C.F.M. (cubic feet per minute) at a specific pressure for both the tool and the pump. (Example; 10CFM@ 90psi)
If your pump will not keep up with the air powered tools (sanders) it can be a frustrating experience. If you are actually painting, it will be a disaster.
Good air compressors are expensive! You can cheat a little by having a large storage capacity (tank) but this will only carry you for a few more minutes if you are exceeding the limits of the pump.
Study the requirements of the tools you expect to use, don’t cheat…
Then go shopping for a compressor. Bring a chair!
My experience is a 110-volt unit will not do it. Even if it is rated at 5 hp., it’s a lie - this requires 22 amps, not really available in a 110 circuit.

[gary porter]

Canoeyawl has it right, you can get high pressure from a bicycle pump but you can't run a spray gun with it. Sprayers use a lot of volume.
The most popular sprayers now are HVLP high volume.
If you can get something like a 5hp 220 volt compressor with a good size tank on it. The Emglo and the Binks that Bob mentioned are very good brands. Buy the best you can , not the cheapest. You'll be so happy you did.
Gary

[Nicholas Carey]

I've been looking at compressors. "Portable" compressors range in price from something like $100 and go up from there. With stationary compressors...the sky's the limit pretty much.

WRT to compressors, my research tells me that Emglow compressors used to be well-regarded...until DeWalt bought them and DeQualityized them, shipping manufacture offshore.

Other common brands found at the Bix Boxen stored don't last, so I'm told -- Porter-Cable, Cambell-Hausfield, Makita, Hitachi, etc. And they are all made (probably by the same Chinese factories) offshore. A lot of plastic parts, shoddy workmanship. Many of these are also quite loud.

These days, the good portable compressors (though it's hard to call anything weighing 50+ pounds as "portable" :D) are Thomas (http://www.thomasairpac.com/) and Rol-Air (http://www.rolair.net/) compressors, both made in Wisconsin (Thomas is in Sheboygan and Rol-Air is in Hustisford). As it happens, the actual compressor (air pump) used by Rol-Air's compressors is made for them by Thomas -- tankage, regulators/controllers, motors, etc. as Rol-Air's own. And I believe at least some Senco compressors are re-branded Thomas compressors.

A lot of these compressors, especially the ones capable of driving a spray rig, has power requirements, especially during the startup surge, that approach the limits of a 15amp x 120v circuit. From what I've been told the Thomas and Rol-Air compressors don't. The compressor I'm looking at (see below), for instance, draws only 13.7 amps. This might or might not be an issue for you.

The compressor I'm probably going to buy is the Thomas T-2820ST (street price about $450-$500, depending). 2 nominal 1-hp motors, each driving an air pump.

http://www.thomasairpac.com/products/airpac/airpac_electric/T-2820ST/images/T-2820ST_250px.jpg

Other things to consider with a compressor are: oil or oil-less? An oil-lube compressor must be run in a level position; oil-free compressors don't have that problem. Oil-lube compressors are often quieter than oil-free, but they draw more power during startup, especially when during a cold-start or during cold weather when the oil is thick. Oil-lube compressors last longer than oilless compressors, but on the other hand, the rebuild kit for an oilless compress is usually pretty reasonable (c. $75 or so) and the rebuild only takes an hour or two.

Duty cycle is another thing to consider. Most of these compressors are designed for a 50% duty cycle (meaning the motor/pump shouldn't be operating more than 50% of the time whilst the compressor is in use). Thomas compressors are designed for a 100% duty cycle. Using the compressor outside its duty cycle is liable to void the warranty. Consequently, you need to ensure the compressor has capacity over and above your intended use, especially since most manufacturers are, um, less than conservative in their CFM and horsepower ratings.

Bear in mind that no matter how you slice it, 1 horsepower is equal to 746 watts. At 15 amp, 120 volt circuit can deliver, at best, 1800 watts (Watts = Amps * Volts). Anybody claiming to produce more than 2-1/4 HP or so off a current draw of 15 amps or less on a 120 AC circuit is lying.

Also look at the air intake. If you're likely to use the compressor in a less-than-optimal environent, you should consider this. How's the filtering? How well will it tolerate dusty or dirty environments? If the compressor is sucking grit without filtering it, it's going to shorten the life of the air pump.

Note that none of these compressors is likely to drive a conventional spray rig or a jitter bug (air sander) -- both are very air-intensive.

The HVLP conversion gun technology has improved and become more efficient, reducing air requirements over the past few years. To drive an HVLP conversion gun, you'll probably need a compressor capable of producing maybe 7-8 cfm at 20-30psi or so -- actual requirements depend on the particulars of the gun. HVLP conversion guns run anywhere from about $130 or so (Wagner HVLP conversion gun (http://www.gleempaint.com/hvcongunnew.html)) to maybe $500 or so (Accu-Spray or Asturo at Homestead Finishing (http://www.homesteadfinishing.com/htdocs/asturo3.htm)). Depending on what you're spraying and how big it is, you might want to consider a separate pressure pot

http://www.homesteadfinishing.com/images/QS64Aweb.jpg

The pressure pot hangs from your belt. It holds more paint and since there's no cup on the gun, allows you to spray in place and at angles you wouldn't otherwise be able to pull off.

If the only thing you're interested in the compressor for is spraying, you might want to look at using a "true" HVLP (turbine) rig. No compressor. And here, you gets lots o'options as well.

[Nicholas Carey]

The air compressor should be sized for your air tools.
This will be stated as C.F.M. (cubic feet per minute) at a specific pressure for both the tool and the pump. (Example; 10CFM@ 90psi)Also, you'll see things spec'd out in both CFM and SCFM.

CFM is a rather arbitrary measure.

SCFM (Standard Cubic Feet Per Minute) is defined to be cubic feet per minute at 1 atmosphere and a standard temperature -- often 60F, but the nice things about standards is that there are so many to choose from :D Some definitions use other temperatures.

And some definitions incorporate other criteria such as relative humidity, just to complicate things.

Then there's ACFM (Actual Cubic Feet Per Minute), essentially an SCFM number run through a formula incorporating both the reference and the "current" ambient pressure, temperature and relative humidity as factors so it [theoretically] should represent the actual amount of air being delivered under the conditions of use.

Finally, there's ICFM (Inlet Cubic Feet Per Minute)...oh, never mind :D You get the point.

This paper is informative: http://www.ohiomedical.com/pdfs/11-icfm.pdf

[FGsimmons]

Newer guns don't need the volume the old suction type needed. If you get a 5-6hp with atleast 25gal you should be fine running a paint gun. Now if you break out the DA sander it will never keep up. I have a 5hp with a 25gal tank and I have painted 3 cars and a boat. No problems - make sure to get a good water seperator if your painting. Condensation in the lines makes nice spots :(

[George Ray]

As as pointed out in an earlier post, you can expand the reservoir capacity. I have two little 110V compressors and neither or both togeather can really keep up with most industrial/HD/real air tools or paint guns. HOWEVER, I have an octopus hose made up that can parallel several extra tanks togeather and so, when I have to use the little sandblaster or the paint gun I add tank capacity. (1) Old 100 lb propane tank, (2) Two of the portable 9gal emergency air tanks.

Home shop demand tends to be very intermittent and the extra tanks just do manage to allow work to proceed, but as the usage tends to more commercial type work, the rig (two small compressors and three extra tanks) can barely keep up.

[Ted Ford]

Rather than wire my shop for the 220 volts needed to run a decent size compressor, I purchased two 2.5 HP piston pancake compressors from Harbour Freight ($88 each on sale). Each is rated at 4.2 cfpm at 90 lb. I happen to have two 110 15 amp circuits in my shop with outlets close together, so I can plug in the compressors without using an extension.

I put both compressors on a dolly and hooked them in parallel to a 5 gallon tire inflation tank. Looks odd, but appears to work well. Haven't used for spray painting yet, but it keeps up pretty good with a jitterbug sander.

Ted Ford

[PeterSibley]

Ditto on the tripple piston compressor. I tried a diaphram unit when my old pump died and it was so noisy that I traded it in after a one day cacophony in the shop.
JG

The best use for a diaphram unit is supplying clean ,oil free air to your dust helmet/mask while sanding :)