Combining Air Compressors for HPLV

[Frankenfoot]

I am in the process of studying the available HPLV spray systems. While researching I saw some information related to combining air compressors to achieve a higher SCFM. I figured that someone here must have tried it and might be willing to share their experience.

I currently have a smallish Craftsman compressor that cannot handle the SCFM required to run a decent HPLV system. However, I can easily see adding a second compressor to generate the capacity needed, plus have the flexibility of a second compressor.

Thoughts?

[dbhost]

How small is your compressor? I have a Harbor Freight 8 gallon compressor, that I use with a Husky siphon feed HVLP gun. Periodic use is about right. Just set the pressure down, and be patient with the compressor. Works fine.

Mind you, I am new to spraying, and am still piddling around with it... But so far so good.

[Frankenfoot]

It's a 1 HP, 7 gallon model. I believe the specs are 2.4 SCFM @ 90 PSI, and 3.7 @40 PSI (??). Most of the guns I've seen need 5.0 SCFM or more. I had never thought of ganging compressors, but it seems like a good idea.

[dbhost]

Okay, now that is a small compressor...

The compressor I have is the older version of THIS one. Specs are similar though.

3.7 @ 40 PSI seems like maybe a little pancake compressor, but with a 7 gallon tank?

If I had to do it over again, I actually kind of like my HF compressor, but would opt for the 10 gallon model with slightly higher CFM ratings. It just wasn't offered when I bought mine...

IF you go with a Harbor Freight compressor, buy the extended warranty, and perform the break in procedure to the letter of the manual and you should be fine...

Mind you, there aren't many smaller compressors I have seen on the market that are actually rated for much over 5 SCFM @ 40 PSI... Generally speaking, that is in the 30 gallon and up models... Which at least in my shop, is too big... I seriously doubt I would be happy with that low rating. You could run the gun for a couple of seconds, then have to wait for the tank to charge up, then spray, wait, etc... Not much fun...

[Frankenfoot]

Mine is an older version of http://www.craftsman.com/shc/s/p_101...1&blockType=L1.

[LCHIEN]

Here is a web Q&A on combining or paralleling two compressors, the information to me seems correct and believable.

http://mgaguru.com/mgtech/tools/ar103.htm

problems you'll get into:
1. as the article says, you must place the compressors on separate breaker circuits unless the breaker can handle the sum of the currents - probably around 30 amps for typical 120V compressors - not your usual 120V breaker. Otherwise you'll be popping the breaker all the time.
2. You can't T two regulated compressors together without at least a check valve as the lower set regulator will bleed the higher set regulator off, and don't tell me you can set them to the same pressure, exactly.
3. The best way is to T the two tanks together and have a single regulator which is what the article linked above suggests. The compressor with the higher set point will do most of the work. you might also have to worry about the lower tank pressure unit having its pressure ratings (tanks, fittings etc) exceeded. and possibly exploding. I don't recommend this unless you know what you are doing.

[Frankenfoot]

1. The electrical shouldn't be a problem, I've got lots of options.
2. That's good advice on the check valve and makes sense.
3. It seems like the check valve should be installed so as to isolate the unit with the smallest tank pressure specifications.

[eezlock]

combining air compressors ?..........

I read and reread your post a couple of times and I'm trying to get it straight in my mind as to what you really need . You said you wanted / needed a HPLV set up...ok, what I think you are really needing is a HVLP ( High Volume Low Pressure) system instead of the other way around. High volume would come from a larger tank capacity or a bigger overall compressor/tank setup.
You would not need two compressors running at the same time.

I ran into the same situation a few years back when doing some sand blasting.I needed more air volume, so I coupled two air tanks together, one compressor to fill them both, worked a lot better than one small tank and the compressor running constantly to try and keep one filled with air. I now have one large 60 or 80 gallon tank and one compressor it does all I need...think about that before you get into all this extra expense and headache of coupling two compressors together and the wiring involved.
Hope this helps.......eezlock

[Frankenfoot]

eezlock,

Thanks for the reply.

About a nanosecond after I hit send, I noticed that I reversed the V and the V. I meant High Volume Low Pressure (HVLP), but didn't know how to edit the post once it was sent.

If I was going to use a HVLP system, my current compressor would a) not keep up with the SCFM demands, and b) not have enough volume. If done correctly, the ganging of compressors could potentially solve a and b. Just adding volume would only solve b. No?

I was just wondering if anyone had done this successfully.

[dbhost]

Your SCFM is determined by the storage capacity (tank size) as well as the compressor head capacity. Think of it this way...

A compressor takes air in, and shoves it into place right?
If there is more "place" to shove it in, or the pressure you can shove in is higher, then more comes out right?
Thus more SCFM...

At least that's kind of the way I understand it...

[cabinetman]

Your SCFM is determined by the storage capacity (tank size) as well as the compressor head capacity. Think of it this way...

A compressor takes air in, and shoves it into place right?
If there is more "place" to shove it in, or the pressure you can shove in is higher, then more comes out right?
Thus more SCFM...

At least that's kind of the way I understand it...

The size of the tank or tanks is inconsequential to the CFM of the compressor. I recommend an oil lubed compressor. Air from a compressor can be compared to water in a hose. The CFM of a compressor is like how much water can flow through the hose. The PSI of a compressor is how fast the water comes out of the hose.

In understanding CFM's, a tank need not be part of the discussion. The CFM's are what air volume the compressor can put out. Lets assume for a moment you got a compressor with no tank. Then you hooked up an airline and operated an air tool of some sorts. And along with this scenario, lets say that the air tool to run at max requires 5CFM, and the compressor output is 5CFM. Well, what would happen is that the tool will be supported, and the compressor will run continuously.

Adding a tank permits a storage of air to run the tool when the compressor has built up the pressure beyond the demand (CFM's of the tool). The regulator deals out the air (PSI's). When the supply of air in the tank gets to the "kick on" (pressure switch), the compressor will then again start and this little story begins again.

While the tank is being refilled, the compressor has to fill the tank, and support the tool at the same time. So, if the CFM requirement is higher than the output of the compressor, the tank will deplete, and the compressor will run continuously because it can't catch up.

What happens then? Well, you will get hot air being pumped out because the compressor is constantly running and doesn't get a coffee break. The air tool will lack in performance due to lower air pressure, and in the end you have a bad day.

What can save your day is to stop periodically if the compressor remains running, and let it catch up. At least it will have a short break, and have a chance to cool off. Of course, as it always happens, you find yourself having to stop right in the middle of a beautiful finish.

As for joining two compressors, I wouldn't do it. You would likely run into the overlap of the smaller on reaching peak and shutting off, and the larger one not starting. It's likely that two supporting compressors can supply a greater SCFM than each of the two. I would suggest a single compressor and tank with sufficient output for the tool(s). Tank size and compressor are pretty well matched for the output.

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