Before we go on, let me acknowledge that this will NOT take the place of a good 240 volt, 60+ gallon, oil clubbed compressor! That's not the intent here.
I have a PC 2 HP 6 gallon pancake unit that came with my brad / finish nailer kit. It's a handy tool for nailing, blow guns, and other small draw devices, plus it's very portable.
Looking for a cheap alternative to buying a portable mid-sized compressor to power a touch up gun, I had an idea. I added a brass tee fitting between the pressure switch and regulator. To the tee, I connected an extra quick connect, so that I can connect my 11 gallon air tank. For regular nailing, I can leave the extra tank disconnected.
It works GREAT! I use a small regulator set to 40-50 psi at the gun, set the compressor regulator to 75-80 PSI, and I can pretty much spray all I want without waiting for the compressor to catch up! The initial charge does take quite a bit longer than without the extra tank, and I know I'm adding extra wear to the machine, but it's a lot cheaper than a decent 20-25 gallon portable. Inserting the extra capacity between the switch and first regulator makes the system behave quite differently than if the tank were after the first regulator.
Now I can use the big compressor for regular spraying, the PC, in two versions, for portable applications, or even the 11 gallon tank alone for nailing.
Since I already had the spare tank, the total cost of the mod was under $10.
Barry