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Old 06-07-2006, 12:12 PM
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Connecting two 30 gal compressors

I have two craftsman 30 gal compressors...Has anyone had success painting a car with an HVLP and TWO 30 gal compressors (8.5cfm each) connected to one another? I dont want to go and buy a 60 gal to use it one time.

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Old 06-07-2006, 12:37 PM
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It would work OK but definitely not an efficient thing to do.

One compressor will kick on before the other. This will cause that compressor to work harder than the other. Certain situations could cause the compressor that kicks on first to run for a long periods of time while the other one wouldn't be running at all.

If you could run both compressors off the same pressure switch, it would work fine. However, it would use more electricity than one bigger compressor.
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Old 06-07-2006, 05:53 PM
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If you do it you would want to hook them on two different circuits. If they both kicked on at the same time it might throw a breaker if they were both on the same circuit. That could be disasterous in the middle of a paint job.

Danny
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Old 06-07-2006, 08:50 PM
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I don't think it is altogether safe to run them off the same pressure switch. Most pressure switches can be adjusted, so you can tune them in to fire up pretty close to one another. That is the way my two 5HP 80gal compressors work. The new one fires up first, then if the demand warrants it, the older one kicks in about 5 psi below the first.
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Old 06-07-2006, 09:13 PM
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Keep in mind that the tank size of the compressors has absolutely no bearing on their production capacity. The 8 or so CFM rating each may not be accurate, and the 2 compressors may not be able to supply enough air to complete the job without running low on air.

If you are going to connect them together, make sure that the tube is large enough to carry the air that is needed. Simply using a 3/8" hose will probably not do it. You also need to make sure that you have a good water filter, as the compressors will likely be running hot. A fan to blow on them will also help keep the moisture down, by helping them cool.

Aaron
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Old 06-07-2006, 11:20 PM
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Pretty good advice so far.
Yes it definitely can work and work well if the two compressors have adequate capacity. Get an efficient HVLP gun. I used an inexpensive Astro.

I had the two compressors connected to a T fitting on a galvanized pipe. The other end went into a good filter/water separator.

Definitely run them off of different circuits so you don't trip a breaker.

They are gonna run a bit (but so will any 60-80 gallon single stage compressor). I used an extra fan on one compressor to avoid overheating, but in reality, it wasn't necessary.

You can definitely dial them in easily so that they both run a similar amount. (If one runs and the other doesn't -you have them set WAY off). One of mine ran a bit more than the other, but nothing crazy.

Mix your paint so that it doesn't dry too fast, so you can take your time a bit.


No it isn't ideal. But if you have got a couple of 30 gallon compressors with decent CFM and you don't have money for a new 80 gallon, you can do it.
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Old 06-08-2006, 06:23 AM
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If I connect the two -
two compressors and each has 8 cfm... Does that mean I now have 16 cfm so that I can run my HVLP knock-off that requires 11 cfm? Or is this not the way it works.

I do appreciate the replies. If it gets to complicated Ill just buy a big one.
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Old 06-08-2006, 07:26 AM
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Yes, you can add the numbers together if both compressors are running.
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Old 06-08-2006, 07:49 AM
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What are these compressors? What voltage? Direct drive or belt driven? Just trying to make sure you really do have 8 CFM per unit, most small compressor manufacturers get extremely reckless with the truth so don't put a lot of faith in those numbers. In all probability this will work just fine however but the possible problems that have already been pointed out must be considered, especially what Adtkart said about the moisture. Those small units will work hard so they will get hot and a lot of moisture could pass into the air line if you don't use a water separator (mounted AWAY from the tank, the farther the better). Also as has already been pointed out you can not count on the tank size when trying to determine if this will work or not, CFM is what you need to be concerned about because if it is too low then NOTHING else will make this set-up work. It is a huge mistake to refer to a compressor as 30 gallon, 60 gallon or any GALLON because that tells you nothing about a compressors performance and a big tank or multiple tanks does NOT make a big compressor, the tank has nothing to do with compressor output past the first on/off cycle so don't count on that extra tank to help. As an example of what I am talking about when I still had my shop one of the most popular units I sold, a mobile unit for service trucks, was over 24 SCFM and had only a 20 gallon tank due to space limitations. Even with this small tank this thing, with 24+ CFM, put out about TWICE the volume of 95% of the so called 5+ HP 60-80 gallon compressors out there.
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Old 06-08-2006, 08:13 AM
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oldred,

point well taken. i have addressed the issues mentioned and just wanted to make sure that the CFM is okay.

they are craftsman 30 gal / 2hp / 6.4 scfm @ 90 psi (though they were 8.5 cfm)

If other items are addressed... 6.4 + 6.4 = 12.8. If the theory is correct, the cfm will work?
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Old 06-08-2006, 08:41 AM
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You didn't say but from the description I suspect these are oil-less direct drive? Even if they are belt driven they probably will put out a bit less than claimed and if they are oil-less you can bet they will not produce as much as they claim. At this point it is starting to get a bit "iffy" because "if" you have the full CFM claimed (12.8 for combined units) you will have enough but not a lot to spare and if they only put out about 5 CFM@90 PSI, which is in all probability closer to real and maybe even less, then you now are looking at only about 10 CFM total which is going to cut it very close. Even at 10 CFM the numbers are low but with a bit of planing ahead and keeping a close eye on tank pressure you could still make this work but it may be tricky. You will want to make sure the tank is at full pressure before starting any large area to help avoid running out of air at the wrong time. Because these things are going to be working so hard I would strongly recommend trying to get access to a larger compressor if at all possible. Rent one maybe?
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Old 06-08-2006, 01:48 PM
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...much appreciated oldred!
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