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CN, I'll throw in my 2 cents worth. If you parallel another compressor of the same capacity, yes, the output would be essentially doubled. One thing you should note if you add a two stage: most 2-stage machines in the 5 hp category are operated with switch cutoff settings up around 175 psg and are supplied with tanks that are good for more than that, usually 200 psig. Single stage machines are unlikely to have tanks rated for more than about 150 psig. If you parallel a single stage and a two stage, be sure your relief valve on the single stage is working properly and that you install check valves on the outlets of both tanks prior to your tie in point - or at least on the single stage unit. You do not want the higher pressure unit to backfeed into the lower rated tank. You could also consider replacing the pressure switch on the 2-stage but that would defeat the extra storage you get when using the higher pressure. Modern breakers should have enough short time overload capacity to accommodate reasonable motor starting currents without tripping. These starting currents can be several times the full load running current noted on the motor nameplate. I would guess that if you made sure that both motors would not start at the same time, then you likely would be OK. No guarantees though :o). Your single stage pressure switch is probably set for something like a cut-in at 95 psig and a cutout at 125 psig (or it could be 105-135). A two stage would likely be provided with a switch with a cut-in setting at 145 psig and a cut-out at 175psig. A 30 psig differential is common. This would mean that they would not start at the same time and that the 2-stage would carry the load until such time that the pressure dropped to 95 psig upon which the single stage would start up. Your problem would come if you powered up with both tanks below 95 psig - both motors would attempt starting and the breaker would probably trip. My 5 hp 2-stage is 17 cfm at 175 psig and 22 or 23 amps at 230 volts. I run that fine on its' own 30 amp circuit. Furthermore your 2-stage (if you use one) will not be at full rated motor load when the single stage starts. It will be running with a discharge pressure down around 95 psig. I don't really want to guess what the actual current might be but it would certainly be less than the nameplate rating. That would be to your benefit. You won't know for sure until you try it but I think you at least have a chance for success as long as nothing else of consequence is in use on that branch circuit at the same time, such as significant lighting or something. Bob is correct on the motor starter. It has nothing to do with either starting or running current. If you are presently using a suction blaster, you might want to consider a pressurized unit for a significant increase in performance for the same air supply. If you are talking about doing entire tractors however, anything you do in the 17 or even 34 cfm area will not likely satisfy your desire for reasonable speed. For that you need the big stuff. My work speed is such that 17 cfm with a pressurized blaster pot is fine for individual parts, even things like fenders, but I wouldn't attempt a whole tractor with it. Rod
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