Combining Two Compressors

by John S
(Springfield, PA)

I have two compressors, one 2.5 horsepower 21 gallon and one 2 horsepower 8 gallon. I want to combine the two to increase CFM. I tried doing this with a "T" hose but without check valve and without altering the shutoff timing of the compressors. My questions are: where can I get check valve for the output hoses and how do I alter the shutoff timing of the compressors? Lastly, how much will my CFM increase? Thanks for your help.


Comments for Combining Two Compressors

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May 12, 2016
Same pressure setting on switch
by: Bill

That both air compressors have the same ON/OFF settings on the pressure switches is immaterial.

Air flows the easiest path. As you are drawing air down the one line, air is being pulled from the tank that has the highest pressure in it, not necessarily from both tanks at the same time.

Regardless, as Doug points out, what's the issue of having two compressors come on at the same time, unless you haven't the power supply necessary?

Or, pick the compressor you want to be master, leave that one at 90 PSI and reduce the start pressure on the secondary compressor to 80 PSI. That will allow it to come on after the first if the air demand exceeds capacity of the one compressor.

Still begs the question, even with two compressors, do you have enough air capacity to run the Sander?

May 11, 2016
dual compressors
by: Doug in

What Bill said, since they are both 125psi...

Just a reminder - if you try to run both on the same circuit (even a 20A one) you'll probably have trouble with the breaker tripping. So, try to get them on separate circuits.

If you already have 220 available, you can probably re-configure that to get two 120 circuits.
(you'll want to bring in a contractor and/or at least get a permit, if you want your insurance to stay in effect)

May 11, 2016
Additional information
by: Original Poster

Both compressors come on at about 90psi and turn off at about 115psi.

May 11, 2016
Two compressors
by: Bill

Much information to help you is here:

Why mess with the pressure switches?

If the two compressor tanks feed to one line, and both tanks have a one-way valve in the line towards the Tee, then the two compressors will cycle on and off as the demand is there through you using air.

You still need to know the CFM requirements of your DA Sander though to know if even the two compressors can generate enough flow.

May 11, 2016
Additional Compressor Information
by: Original Poster

Here is the additional information on my compressors:

8 gallon 2hp 125 psi Air delivery: 4.5 CFM @ 90 PSI, 5.5 CFM @ 40 PSI

21 gallon 2.5hp 125 psi Air delivery: 5.8 CFM @ 40 PSI, 4.7 CFM @ 90 PSI

I added the two check valves as suggested. How do I now want the tanks to come on/go off? Have the 8 gallon come on first or have the 21 gallon come on first? (I realize I first have to determine how the compressors are set now before I alter the pressure switch.) My goal is to increase CFM to run a da sander.

Thanks so much for your help.

Nov 26, 2015
dual compressors
by: Doug in

Partial answer:
Google "check valve" for suppliers. I like, but there are other choices.

The rest depends on the specific compressors and their current pressure settings.

CFM will be roughly the sum of the two compressor's "actual capability" (their "ratings" are likely inflated, so take those with a grain of salt).

So, tell us more about your compressors.

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