Tandem Air Compressor Theory

[trpearcy]

So, my old thread got some really good info, and I have my shop air set set up how it’s gonna be until I retire (30ish years from now lol.
Here’s the question I have now. Running two compressors in tandem, the newer one as the master, older one as the slave, what’s the best theory for setting the pressure regulators? Right now my new Jenny is set as On-120psi, off-150psi.
Then I have an older IR set to come on at 115psi, off at 145.
Is this the most efficient use of two compressors? Or would it make more sense to set both to come on at 120, off at 150, so that they fill in half the time? Uses double the electric, but if it fills in half the time, it works out, right?
Or is it better like I have it set now? Slave only comes on for big drops to help out the master.
Thanks, and I appreciate any info


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[American Locomotive]

The way you have it set up now is correct. One compressor will run most of the time, the second will only come on when needed. Trying to set them up to both come on at the same pressure and turn off together won't really work well with mechanical pressure switches.

 

[MattT]

Main thing is to set it up so that both compressors aren't starting at the same time. Beyond that it'd be better if you could set it up to alternate master and slave, so both compressors get regular use, but that's easier said than done with standalone pressure switches.

 

[trpearcy]

Ok. Hmm. Alternating them is interesting. What if I ran the pressure switches to a switchable relay, or some other device so that I could switch outputs, and then I could switch which compressor was the master? Wait. Nah. That might be too much money and effort... id have to have 2 relays, one for each pressure switch.


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[trpearcy]

My other thinking was that it would be interesting to have a timer, so that the slave compressor automatically came on after the master ran for over 6 minutes or so. That was if I was continuously using air, the other could come on and help it catch up


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[American Locomotive]

Not necessary. If you were using more air than the main one could supply, it would eventually drop in pressure enough for the second compressor to come on.

You're over thinking this. The way you have it configured is how it would be in the real world.

 

[karoc]

At work we have single tanks but duel pumps and thats how they are setup.One will come on when psi is needed to maintain tank pressure but if it can't keep up it will bring on the other pump.Which they also alternate which one is lead,so I say you have a good setup.

 

[trpearcy]

Ok, thanks for the input. I realize I’m overthinking it. But I wanted to see what other people do, and see if my setup was correct


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[larry_g]

I've done as your doing when using air everyday. If your in the hobby realm then probably more air than you need. If part time use Consider mechanical valves that allow you to select either one or the other compressor online or both. If not needing a lot of air all the time then it might be a waste filling and emptying both tanks.


lg
no neat sig line

 

[The Cobbler]

a side note, if you are hooking up the tanks after the regulators, most regulators bleed air from the regulated side if the pressure is higher than it's set point , for example a reg set to 120 psi is joined to a reg that is set to 140 psi , the 120 psi reg will bleed air because it sees 140 psi & is set for 120. make sense?
so it's best to join the tanks before the regulator

 

[md21722]

The alternating theory works best on a true duplex setup with one tank. In fact, this is how almost all duplex compressors are sold.

What the alternating relay concept does is separate the pump/motor from the pressure switch. So if you have pressure switches on each tank and wiring them into the alternating relay and some valves closed you are going to relying on your blowoff valve to keep things from exploding because one tank won't ever see the pressure, and the other is going to be blowing off.

Alternating relays are not especially expensive, I have done this before as an experiment and removed it for lack of need and added complexity. They will work fine with all shutoff valves open.

The way you have it is fine.

 

[trpearcy]

I've done as your doing when using air everyday. If your in the hobby realm then probably more air than you need. If part time use Consider mechanical valves that allow you to select either one or the other compressor online or both. If not needing a lot of air all the time then it might be a waste filling and emptying both tanks.


lg
no neat sig line

I’m a full time auto shop. And the tanks are never emptied. They’re full and on 24/7. No leaks at all, so they don’t run during the night at all.





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[trpearcy]

a side note, if you are hooking up the tanks after the regulators, most regulators bleed air from the regulated side if the pressure is higher than it's set point , for example a reg set to 120 psi is joined to a reg that is set to 140 psi , the 120 psi reg will bleed air because it sees 140 psi & is set for 120. make sense?
so it's best to join the tanks before the regulator

I don’t have any regulators in the system.


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[sberry]

With the tanks plumbed together I don't even have the breaker to my slave on.