No big issues assuming both tanks and blow off valves are rated for the max pressure you want to run. It's always possible to lower the cut in/out pressures on the higher pressure tank to match the smaller one. The big thing to watch for is which pump is going to do the most work. In a sophisticated setup you might have a controller that staggers which pump cuts in first and uses both pumps every time. However, with the basic setup consider two cases.
Case 1, low draw. In that case which ever pump cuts in at the higher pressure will do 100% of the work to fill both tanks.
Case 2. high draw. In this case the higher pump turns on but it still can't keep up with flow. Thus, even though it's running both tanks continue to drain until the second pump kicks on. Now both pumps work until the one with the lower cut out pressure trips. Then the one with the higher pressure will finish the job.
So if we assume both compressors are safe to 175 psi here is your setup.
System fills to 175 psi. You run something that doesn't draw much air and the system drains to 150 psi. At this point the main pump turns on and refills 140 gallons to 175 psi.
Now you attach the sand blaster. The system draws down to 150 psi and the main pump kicks in. However you keep things up and draw the system down to 135 psi. Well if you stop, the main pump will again work to fill up the 140 gallons. Not really an issue if it's 100% duty cycle rated. Keep sand blasting and the little pump will kick in at 130. Now both will run until you get to 150 psi but the main pump will still be the only pump for the rest of the job.
My feeling is with this setup you will run on the main pump most of the time. However, if you could adjust the in/out pressures (most switches will allow this) to something like 135/155 for the main and 130/150 for the secondary then you are a lot more likely to operate in "Case 2" where the pumps better share the load. Also, if you are starting the whole system from 0 psi you probably want a way to turn the pumps on with a slight stagger so both don't start at the same time.
Correct. 2nd tank mostly for air storage/cooling and backup if needed.
A few cases where they could start at once I suppose, but that's only equal to an 8hp motor starting.
I have a roll of I think "Ramapo" 2-2-2 AL URD I might use. It's leftover from the meter to shop panel connection.
I'll have to run an additional ground wire but no big deal.
Was told it's good for 165 amps direct buried, 120 amp in conduit.
Probably run a 60 or 80 amp breaker. Just the compressors, 2 boilers drawing maybe 15 amps combined, couple lights, maybe an outlet just in case, that's it.
