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Is an 150 psi air compressor enough for spray staining or painting? I have just tried one and the compressor kept working continuously

Update:

this is the gun http://www.canadiantire.ca/en/pdp/mastercraft-hvlp-air-spray-gun-set-36-pc-0589311p.html#srp

and this is the compressor https://www.lowes.ca/air-compressors-kits/porter-cable-c2002-0-8-hp-6-gal-150-psi-pancake-tank-electric-air-compressor_9676167.html

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    What is the psi needed for the sprayer? If that's not know, what's the make / model of the sprayer? What is hose diameter from the air compressor and how long is the hose? – TWS Oct 1 '17 at 23:15
  • I have added the details you requested – MiniMe Oct 1 '17 at 23:31
  • Your compressor (3.5 cfm @ 40 psi) just matches the sprayer requirements (3.4 cfm @ 40 psi), which means it will pretty much run continuously to keep up, but should handle it. – fixer1234 Oct 1 '17 at 23:34
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    Or you need to take more breaks between spraying sections to let the compressor catch up. You need more volume not higher pressure. – ArchonOSX Oct 2 '17 at 0:07
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    Taking more breaks, as ArchonOSX suggested, is the inexpensive solution. If you want a "bigger" compressor, what is important for spraying is higher cfm. A bigger tank will also buy you more run time between breaks. – fixer1234 Oct 2 '17 at 0:12
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It isn't the maximum air pressure that one should consider when using a compressor for painting. You will want to match the specifications of the device being used to paint with the compressor selected.

If you have a paint gun that requires 10 cubic feet per minute (CFM) at 80 psi, and your compressor provides 2 CFM at 150 psi, look for the ratings at lower pressures. A properly documented product will list more than one figure, not only the high end of things.

Typically, the high pressure figure will have a low CFM to match, but it does not mean that you'll get the higher CFM at lower pressures either.

As part of this research, I located a spray gun that lists to require 6.4 scfm @ 50 psi. If you locate a compressor that provides 7 scfm @ 50 psi, you'd be good to go, but if it lists that 7 scfm figure at 40 psi, you would be risking a mis-match.

Airless sprayers use pumps to force paint through the nozzle, turning it into an aerosol for application. Similar systems use air pressure to apply force to a liquid, driving it through a nozzle in a similar manner but not using the air to convert the liquid to an aerosol, in the manner of ordinary spray painting.

  • according with the specs: -the spray requires 3.5 at 40PSI -the compressor delivers 3.4 at 40PSI Not sure what went wrong and how I should have adjusted the pressure on both compressor and gun (they both have pressure meters) but if I kept the spray open the compressor will run out of air in like 1 minute or so – MiniMe Oct 1 '17 at 23:35
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    I'd bet in this case that the specifications for the compressor are optimistic or based heavily on marketing rather than on engineering! – fred_dot_u Oct 1 '17 at 23:44
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    The tool and compressor specs are likely at ideal conditions. A short hose, no leaks, perfect paint viscosity, no voltage drop supplying the compressor, etc. I would like to have a 10% fudge factor. If 5.5cfm is required by the tool, plan on needing at least 6 cfm. If the compressor spec at 5.5 figure it is likely closer to 5 cfm. – mikes Oct 1 '17 at 23:52
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Probably not, because 150 psi air compressor labels are generally found on smaller pancake and hot-dog type models. The important number is the volume of air supplied which is labelled in cubic feet per minute. (CFM or SCFM on the compressor label) Think of it this way, a bicycle pump provides a very high pressure but you wouldn't want to try spraying paint with one!

Typically spray guns require 6-10 CFM while small portables put out 3-4ish. Some of them are embarrassingly close to the low end too. I vaguely recall seeing one model that was rated below 2 CFM @ 40psi. It's hard to make suggestions without knowing your use case, but here are a couple of options:

Small Compressor, Small Gun

Detail guns need less air. The current HVLP touchup gun at Harbor Freight requires 3.2 to 5.6 CFM @ 40 PSI. There are portable compressors that can meet that output. Of course you won't want to paint a house or car with it, but it is an option for the occasional small piece.

Small Compressor, Special Tools

It's not my forte, but you can run conversion guns and pressure pots off the next step up in compressors. Price wise it's probably the worst of all worlds unless you already have a serious portable compressor.

HVLP Turbine

If you haven't noticed, the compressor is getting to be pretty expensive. Tool companies have noticed and now offer portable turbines for spray guns. They're a reasonable solution if you don't need pneumatic tools other than paint guns.

Airless Sprayers

These pump paint through a tip to aerosolize it, and can often be rented from paint stores. The big draw is that they'll shoot latex right from the can without complaint. It's really the way to go for paints and large surfaces.

EDIT - Specific to your setup

Your compressor matches your gun requirements exactly. Unfortunately most compressors have a duty cycle which limits them to running part time to prevent overheating. Start by checking the manual to find the duty cycle and see if it is an issue. It may not be an issue if you're limited to 7 out of every 10 minutes if you're not painting a building.

If you're doing a lot of painting then a paint pot may be a reasonable purchase. (Alternatively an additional air tank if you use a lot of pneumatic tools or small amounts of paint.) It wouldn't be the most cost effective new purchase, but it would be cheaper than a new compressor. It would also remain useful should you ever upgrade the compressor.

  • True but how do I adjust that... you have the manuals for both in the links that I provided I don't remember seeing anything for CFM just for PSI adjustments – MiniMe Oct 2 '17 at 17:18
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Both have specs at 40 psi. The compressor can make 3.5 cfm at 40 psi, and the gun takes 3.4 cfm at 40 psi. So you're really running it on the ragged edge, and that's why the compressor never shuts off.

Do you have a regulator at the gun? You could try turning that down. IME an HVLP gun is perfectly happy at lower pressure, I run as low as 15 psi.

  • Well the instructions say 40PSI... – MiniMe Oct 2 '17 at 11:01
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The compressor is running at its maximum for the gun if you're spraying at the maximum rate of 1.2 CFM. Perhaps you can run the 0.6 CFM rate? It wasn't clear if it was selectable. Operating at the maximum for the compressor means it never really catches up, sort of like it never gets to catch its breath. The idea about throttling down the compressor would be an example of letting the compressor "get caught up". Hope this helps.

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