Compressors and Spraying

[Jon Dees]

Howdy, can't say I post much, but I felt that my experience with conversion gun spraying didn't have many direct ancestors on the internet, so I thought I'd share my experience. TL;DR at the bottom. I am also not an expert in the application of finishes using spray guns. I have finished 3 projects using my sprayer setup and know enough to have messed up some. Every spray gun and every spray session are also different, particularly when I'm spraying in my garage in the fall. I think I know enough not to blow myself up with solvent-based finish though (simply not spraying explosive finish is the best option).

Turbine systems are too "lumpy" for my budget - the most I've spent on any one thing in my small shop was an MFT/1080 for $310. I didn't want to spend more than double that for a nice setup like a Fuji with only one gun. It seems to me that having one spray gun is like having one router.

For an air supply for a conversion gun I needed more air than I could seemingly supply. I do not have the flexibility to modify my current electrical supply to add a 220 volt circuit for a large air compressor pump. I also read much about "duty cycle" on portable compressors - your average Porter Cable or other compressor has a warning about using the compressor for more than 50% of the time - in other words, running continuously for 15 minutes while spraying will kill the compressor faster than you'd like.

I found 2 compressors at 2 different times that were fairly good deals. A man-portable unit from Maxus (Campbell Hausfeld pro duty brand, since discontinued EX8016) that was oiled and 3.7 cfm @ 90 PSI for $150 new from Home Depot. Not enough to spray more than small amounts of finish. It was also quite loud - 96 db(A) SPL @ 1 meter. Trolling Craigslist I obtained a Rol-Air 5715K17 from a homeowner for only $130, an even better deal. This one had about double the output of the Maxus and was much quieter - 84 db(A) SPL @ 1 meter. As far as I can tell, this compressor also has the highest output of any compressor that can be run off a 15A household circuit.

I added a T to the tank output of each compressor, a female quick disconnect, a male-male gender bender, and a hose to combine both compressors. It is important to note that these T's should be before the regulator on each compressor. With an HVLP gravity gun (I have the WoodRiver gun and 2 Husky guns) at a higher pressure than I need to spray shellac (low 40's), the 2 compressors in tandem overwhelm the gun and cut off for a bit - quite nice.

I now have a high output air system for spraying much larger amounts of finish, can now run air tools (like cheap air tools from HF) and have spent about $450 for a system that has 3 guns, longer hose, and a much more versatile set of performance characteristics (IMHO) than a quality turbine system. I also have a resale value somewhere close to my investment, an important criteria for chronic tool swappers like me.

I hope this helps someone who likes Rube Goldberg solutions like me.



TL;DR: You can combine smaller compressors to get more output for high air demand applications; troll craigslist for good deals; spraying is interesting and tricky at the same time. The WoodRiver spray gun sprays finishes fine.

[Daniel Berlin]

Howdy, can't say I post much, but I felt that my experience with conversion gun spraying didn't have many direct ancestors on the internet, so I thought I'd share my experience. TL;DR at the bottom. I am also not an expert in the application of finishes using spray guns. I have finished 3 projects using my sprayer setup and know enough to have messed up some. Every spray gun and every spray session are also different, particularly when I'm spraying in my garage in the fall. I think I know enough not to blow myself up with solvent-based finish though (simply not spraying explosive finish is the best option).

Turbine systems are too "lumpy" for my budget - the most I've spent on any one thing in my small shop was an MFT/1080 for $310. I didn't want to spend more than double that for a nice setup like a Fuji with only one gun. It seems to me that having one spray gun is like having one router.

For an air supply for a conversion gun I needed more air than I could seemingly supply. I do not have the flexibility to modify my current electrical supply to add a 220 volt circuit for a large air compressor pump. I also read much about "duty cycle" on portable compressors - your average Porter Cable or other compressor has a warning about using the compressor for more than 50% of the time - in other words, running continuously for 15 minutes while spraying will kill the compressor faster than you'd like.

I found 2 compressors at 2 different times that were fairly good deals. A man-portable unit from Maxus (Campbell Hausfeld pro duty brand, since discontinued EX8016) that was oiled and 3.7 cfm @ 90 PSI for $150 new from Home Depot. Not enough to spray more than small amounts of finish. It was also quite loud - 96 db(A) SPL @ 1 meter. Trolling Craigslist I obtained a Rol-Air 5715K17 from a homeowner for only $130, an even better deal. This one had about double the output of the Maxus and was much quieter - 84 db(A) SPL @ 1 meter. As far as I can tell, this compressor also has the highest output of any compressor that can be run off a 15A household circuit.

I added a T to the tank output of each compressor, a female quick disconnect, a male-male gender bender, and a hose to combine both compressors. It is important to note that these T's should be before the regulator on each compressor. With an HVLP gravity gun (I have the WoodRiver gun and 2 Husky guns) at a higher pressure than I need to spray shellac (low 40's), the 2 compressors in tandem overwhelm the gun and cut off for a bit - quite nice.

I now have a high output air system for spraying much larger amounts of finish, can now run air tools (like cheap air tools from HF) and have spent about $450 for a system that has 3 guns, longer hose, and a much more versatile set of performance characteristics (IMHO) than a quality turbine system. I also have a resale value somewhere close to my investment, an important criteria for chronic tool swappers like me.

I hope this helps someone who likes Rube Goldberg solutions like me.



TL;DR: You can combine smaller compressors to get more output for high air demand applications; troll craigslist for good deals; spraying is interesting and tricky at the same time. The WoodRiver spray gun sprays finishes fine.

How large of stuff are you spraying?
You are right that the CFM output of that compressor is impressive, which makes me wonder why you are bothering to use two compressors for finish spraying. All but the most expensive HVLP spray guns could easily be used with only that compressor, which claims to be 6.9ACFM@100PSI. Most of these guns operate at 29-40PSI inlet, and use between 11 and 14 CFM. Assuming the rol-air is really 6.9ACFM@100psi this would be ~14ACFM@40psi. Once the compressor kicks on, it should always outrun you. In all likelihood, whatever conditions they used to calculate ACFM are ideal. So let's be conservative and assume it's not really 6.9ACFM@100psi. Let's say it's 5ACFM@100psi. This is still great, it should be ~10CFM@40psi. Your tank is 9 gallons, i'm assuming also @100psi. This is 1.2 cubic feet at 100psi, or 2.4 cubic feet @40psi This would mean you could hold down the spray gun trigger @11CFM for at least a full minute (which is a *long* time) without running out of air @40psi. In your case, your woodriver spray gun tops out at 7CFM, and 50PSI. Basically, again, you should never run out of air with a single compressor for finishing spraying in your case with the one compressor. Air tools i can understand using both, but seems like a waste to do it for finishing.

Note that if you use two compressors, you need to make sure the tanks can handle whatever the higher pressure switch is set to (or you need to set the pressure switches to both top out at the min(max tank psi compressor 1, max tank psi compressor 2). Going over the max PSI rating for an air tank is very bad mojo .

TL;DR what you are doing works, but at least for finishing, overkill given the equipment you seemed to have scored, or the manuf spec sheet is way off

[Jon Dees]

I haven't hit a wall with just the rol-air compressor yet. I am only using inexpensive gravity guns at the moment, so it seems unlikely that I'll hit that wall. The key limitation of the rol-air guns is stated in their manual: starting and stopping the motor quite a bit will burn up the motor (at least faster than a continuous run usage pattern).

In the long run, though, I think a pressure pot-based system may use the whole thing.

I also like the greater output for use with air tools. I have one of the Harbor Freight fein-clones in the air-powered version, and it can run through even the output of the rol-air pretty easily when I was undercutting door jambs for a floor project. And some of those obscure air tools are quite cheap compared to their electric versions.

I'm not too worried about the max pressure because the pressure switches cut off at about the same pressure (130 and 135 psi), and my pop-off valves are functioning (critical to proper safety procedure anyways)

My original plan was simply to have 2 of the smaller compressors. I didn't plan on buying an $800ish compressor like the rol-air for $130 (slight gloat here). I would say this plan is more valid for the true skin-flint (as I was planning to be). He could buy 2 PC Pancakes for $50 each off craigslist and have most of the needed air for medium-size projects and gravity guns.