air compressor question

[lostpilot28]

Just a quick question for those who know. If I have two 30-gallon air compressors connected together with a single T-fitting, will my CFM be the sum of both tanks put together? Basically, each 30 gallon tank puts out 8.5 CFM at 40 psi. Would I get 17 CFM at 40 psi when they're connected to each other?

[N713R]

Compressors are rated a flow at a given pressure. If they both kick on at the same time, and are running together it will work as you describe. If the pressure switches are set different, you will still only flow the amount one compressor will put out. But at 40 PSI, both should be running, if not you need to adjust the pressure switches. You will have more CFM output than that when running on the tanks storage capacity (which will basically be dependent on what you are operating, the size and length of the air lines, and any restrictions you have in the system. You will only be down to 8.5 (17 with both running, when you are flowing enough air constantly that the compressors can only maintain 40 PSI. Likely they either be very small compressors, or you are flowing a TON of air. Unless you are using like a 1" impact wrench constantly, most things you would use in the shop you are on and off enough that the compressor can recover a bit. A die grinder used for long periods of tiem will flow quite a bit of air, but your hand will likely need a break before you are taxing two compressors.

FWIW

[Mike S]

Originally Posted by lostpilot28

Just a quick question for those who know. If I have two 30-gallon air compressors connected together with a single T-fitting, will my CFM be the sum of both tanks put together? Basically, each 30 gallon tank puts out 8.5 CFM at 40 psi. Would I get 17 CFM at 40 psi when they're connected to each other?

Theoretically yes. Assumes both compressors same make/model.

As stated above, cut in pressure on the switch needs to be synchronized.

I would also suggest running a line from each tank to a "T" fitting that your supply hose hooks to, dont feed one tank to the other, then the hose attaches to the second tank. Your statement sounds like this is what you are planning, so that should be a good setup.

Due to vibration issues, I would connect the "T" to the tanks with hose, at least one of the tanks, if not both.

Good Luck.

[lostpilot28]

Sheesh, this is going over my head...I'm an electronics guy, not a fluid dynamics guy.

OK, so the reason I'm asking is because I'm planning on painting my airplane with an HVLP system (Devilbiss Finishline 3), as per Stewart Systems. Dan at Stewart told me that as long as I'm getting at least 13 CFM at 40 psi, then I should be good to go.

So back to the compressors: Ben, what you're telling me is that the CFM rating on a compressor is how much the pump will flow at a given psi. Is that right? And as long as I have above 40 psi then I'll be able to send as much to the gun as it needs, whether that's 8 CFM or 20 CFM...basically the volume gets used at a certain rate, therefore when pressure gets down to 40, then it's up to the pump to supply the air, not the tank. I hope I got this right.

Mike, you're correct...I was going to put a T on one tank and run a short 3-foot line from one tank directly to the T. Then out the other side to the water trap, then onto the gun. I have no idea how to make both compressors kick on at the same time. Any advice?

Thanks, guys!