Two small compressors equal one big???

[Alex Sauvage]

I always wanted to try pneumatic tools, such as HVLP gun or sanders, but I only had small compressor (5
hal, 5 fpm/40psi; 4fpm/90 psi). Good enough for auto tools, but not enough for anything continuously
running. Then during boxing week I have seen similar compressor on sale for 75$. Now the question is: if
you will run 2 compressor in parallel (obviously on 2 different electrical circuits) would it give you double of
the capacity? 10fpm/40psi should bring it up into the range of most pneumatic tools. My high school
physics tell my that it should work, but I never heard about it being done. Does anybody have any
experience with such set-up?

[Thomas Bank]

This is done with some frequency even with the larger units in a situation where you normally only use pneumatic tools but occasionally use a high volume tool like a sandblaster. In these cases, the "secondary" compressor has the lower limit of the pressure switch set lower than the primary compressor. Normal use and only the primary compressor runs. If it cannot keep up and the pressure drops too far, then the secondary compressor kicks in as well.

Not sure if you could change the pressure settings on the smaller compressors like you have. So you may run into an issue of them both running but for shorter periods of time - which could wear them out faster.

[Lloyd James]

Hi, A compressor that is sized to have the capability of the operation that you plan to do will run and stop as the pressure lowers to a set limit.
I am sure you already know this. I think this is an important part of compressor running. One thing it allows the compressor to cool down.
All compressors have cooling fins and I believe the cooling effect makes
the compressor run better in the long run.
One way to increase your air flow capacity is to add an additional tank, around 20-40 gal. Tanks are not cheap, but one solution might be to buy
a used compressor 3-5 hp, that may not even be in working order. You may have to buy a pressure regulator. You would always have that regulator for a future compressor update. I would buy a more expensive regulator.
My used 3hp compressor when I bought it; and new reg. have lasted 15 yr. I did have to replace the moter though.
This is just my opinion. Good luck

[Jason Roehl]

Lloyd, it's actually quite the opposite on run times and heat.

Air compressors are rated for a duty cycle--they are only meant to run so many minutes out of every hour. My P-C 3HP, 4gal, 135psi is rated for 50% every hour. The longer they run, the hotter they get. Smaller compressors tend to run higher RPM, which means they generate more heat per unit of air delivered, so in this case, where the OP wants to up his capacity on the cheap, a second compressor would be a great solution. An extra air tank would increase the initial fill time, prolong use until the compressor kicks in, but then extend the re-fill time, but will not increase the airflow. Larger fittings/lines will do that, but then we're back to the extended run times that overheat the compressor.

[Paul Ryan]

Alex,

I worked as an auto mechanic for a long time. Every shop I worked in had more than one compressor. The compressors supplies air for the whole shop and usually ran in unison, but sometimes not. They way we always did it was with a dedicated line that went from the compressors to the shop. Both of the compressors were tied into that line. As far as I know, your idea will work but you will need a dedicated line that the compressors are tied to. Or some type of tee with the compressors on it, and then run your tools off of the single side. Leave the requlators on the comprssors to do there own thing. The compressors will run when more air is needed and stop when there are full. Sometimes they will run together sometimes just one.

[Alex Sauvage]

Thank you Ryan, this is what I had in mind. I am pretty sure there is a number of ways to achieve high volume delivery, but it's hard to beat 75$ compressor. Having 2 of them tied together should also drop their "duty cycle" down, hopefully to 50% (what most of non-professional compressors are rated for).


Alex,

I worked as an auto mechanic for a long time. Every shop I worked in had more than one compressor. The compressors supplies air for the whole shop and usually ran in unison, but sometimes not. They way we always did it was with a dedicated line that went from the compressors to the shop. Both of the compressors were tied into that line. As far as I know, your idea will work but you will need a dedicated line that the compressors are tied to. Or some type of tee with the compressors on it, and then run your tools off of the single side. Leave the requlators on the comprssors to do there own thing. The compressors will run when more air is needed and stop when there are full. Sometimes they will run together sometimes just one.

[Charlie Plesums]

My HVLP spray gun is rated at 9 cfm, my compressor is half that. Even though it has a small 13 gallon tank, no problem... or if I get too vigorous in spraying, I just take a rest for the compressor to catch up.

Granted, I am putting a high load on the conpressor, using the tank to fill my short-term needs, and running the compressor closer to 100%, but it is limited to short periods... I can't spray at that rate all day.

If your needs are less than 100% of the time, like spraying or using a pneumatic wrench, you may work fine without any supplement. If you are planning to run an air sander all day, look at your electric bill - 5-10 hp for air, vs. 1/2 hp for an electric sander.

[hank dekeyser]

Good points-

heres my 2 cents - air compressors work by putting more air into a smaller space under pressure allowing you to "tap into" that resource. 2 (or 3, or 4, whatever) small compressors DO NOT equal one big compressor. In theory yes, in practice - NO. The amount of air available to run your tools is determined by the volume of the tank -NOT- the CFM or any other rating o fthe compressor. The compressor rating only gives a best case scenario of what it can do. In other words, it tells you how "fast" the compressor will "catch up" and shut off. If you plan on running spray guns, and air sanders you need a BIG (35 gallon minimum) tank. Even then you will find that you may need to wait for the compressor to catch up. If you plan on doing this for a while, spend some money and get a decent used or new compressor w/ as big a tank you can afford. Or plan on replacing it every few years for something "cheap"
I've replaced a few "cheap" small / portable compressors every couple of years (for shooting down trim/etc) and got tired of it. Bought a good quality small compressor and have had it for 7 years now.
For the shop I bought an old used compressor 15 years ago w/ 80 gallon tank and havent had to do anything to it, excxept change the oil.

You need to decide which is better for you.

[Jason Roehl]

Hank, if the CFM rating of your compressor exceeds the needs of the tool, it will run it, regardless of the tank size. The very large compressors that are used for construction tools (jackhammers and the like) don't even have air tanks...

Jason

[Larry Edgerton]

I do this on job sites once in a while and for whatever reason one of them will not shut off at the normal pressure. I run both hoses to a tee, and then one hose out of the tee the tool, and one compressor will not shut down. Have no idea why, and for the short time I need it I just unplug when I am done using air, but you may want to keep this in mind so as not to burn one up.

If this is for shop use, I too vote for a bigger compressor, if for no other reason than the racket that two small compressors make.

[Sonny Edmonds]

I've done that with two lessor compressors in my old shop.
My "main" compressor was a 2 HP oiled type, and I had a 3.3 HP oil less type I tied with it.
I then set the oiless one to a slightly lowerr (10PSI lower) turn on point.
That way when the smaller one couldn't keep up with my ROS, the secondary one came on to help.
It worked OK and got me by for a long time.
But the single big compressor I have now actually rests between cycles, but that is because it has more capacity than even the biggest air tool I have.

[Steve H Graham]

I don't know of any reason why you couldn't use the pressure switch on one compressor to run both compressors. You would just have to do a little extra wiring. That should make them run simultaneously.