Running Two Compressors Together

      Further advice on tag-teaming compressors (it does get a little tricky). March 9, 2008

Question
I have two 80 gallon, 5 hp, two stage air compressors I'd like to hook together to run air sanders. Someone told me to pipe the tanks together, then pipe one compressor to the main pipe that runs into the shop. Another guy said just T them both onto the main pipe that runs to the shop. What's the best way to go?

Forum Responses
(Cabinetmaking Forum)
From contributor K:
Either way should work for the piping. The issue will be the kick in pressure of each. Unless you take the time to adjust them the same, one of them will do most of the work.



From contributor A:
I believe in an ideal world you would want to put them in line. Use only one of the pressure switches to turn on both compressors at the same time. Otherwise, as mentioned, one will be dominant.


From contributor V:
Sanders tend to drain tanks faster than most tools, so it may be possible that the kick-in won't be much of an issue. I am assuming that you need two compressors because they are small. If the pressure drops quick enough and one of the compressors can't restore pressure quick enough, then the other should come on as well.


From contributor J:
Years ago we fought the same problem as we grew and added one pneumatic tool after another. First, have you done a thorough evaluation of your total CFM demands? That done, the setup of your system is extremely important.

#1, run your piping in a closed loop layout. If you only have a straight run, you will starve the tools at the end of the line.
#2, draw your air off the top of your pipe to eliminate moisture.
#3, make sure you have large enough supply piping. We run a 25hp rotary screw compressor with 45cfm capacity and found that we had to send 1 1/2" supply lines to both ends of our shop to feed into our 3/4" loop system.

We also added an 80 gallon tank 3hp compressor (with our loop dumping into a side port on the tank to use it as a backup reservoir) on opposite end of shop that kicks in when pressure drops to 90lbs (this rarely happens). If you tie both your tanks together and set the threshold on one of your compressors 10lbs lower than the other, you will use both to fill your system upon startup, but rely primarily on one compressor to top off 160 gallons of capacity and you should be okay. If this does not do the trick, you really need to consider more capacity.



From contributor D:
I used to run an automotive shop and we had two large compressors hooked together. You can adjust and fine tune all you want and one will always come on first and work itself to death while the other is not coming on enough. The one compressor is trying to fill its tank and then back feed through the line and fill the other tank. We had to get an alternator installed that would alternate each compressor every time they cycled.


From contributor A:
Why won't using one pressure switch on two compressors work?


From contributor R:
You'd be starting two motors at the same time. What I'd do is hook the two together and put a run unloader on one. That way it unloads when it reaches pressure but keeps running with no load and kicks back in when more air is needed.


From contributor I:
"I believe in an ideal world you would want to put them in line. Use only one of the pressure switches to turn on both compressors at the same time. Otherwise, as mentioned, one will be dominant."

I have been running two 5 hp 80 gallon compressors just as contributor A said since 1997. For me, it is the only way to go. When I replaced the unloader on one - I still had shop air while locating a new unloader.

Don't forget to check motor rotation after you rewire them up if they are three phase!



From contributor I:
I just hooked the two tanks together. That was much easier than messing with the major plumbing.

While you're at it, you might want to think about tossing the worthless petcocks on the bottom of your tanks, and replacing them with 10 or 20 feet of good air hoses with ball valves on the ends, so you can drain the water from the tanks without having to crawl around underneath them. You can then drain them right into a mud bucket or something. Your tanks will get drained much more often when it is that easy.

The compressors come on simultaneously and go off simultaneously, which is exactly what I wanted - the most air in the least amount of time having to listen to them chugging.



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