Since most air tools work at 90psi or less the primary advantage to a 2 stage would be storing more air in a given tank size. More energy will be required to take the pressure higher that energy will be wasted as heat. Compressing air creates a lot of heat. You need to dissipate that some how. The little cooling fins on a typical small compressor are not enough to lower the temperature much so you are filling the tank with quite hot air. As the air in the tank cools it contracts leaving you with less useable air & causing the compressor to start again. The warmer the air is the more moisture it can hold. Wet air is hard on almost all air tools and is especially bad for spray guns & paint. So as the air in your system cools it will reach the point where the moisture will condense. Moisture traps will catch some of it but as the tool or spray gun uses the air, the drop in pressure causes rapid cooling resulting in more condensation.
The only real solution is to use a refrigerated or desiccant air drier.
In many ways oil does much the same thing. So you need a filter down stream of the drier to take out the oil. Nothing worse than oil in you painted surface.
Tank size: A big tank doesn't create any compressed air but it does store more. That means it will take longer for a big tank to reach a useable pressure but the pump will have to cycles fewer times but run for longer each time it cycles. Each time a motor starts it draws a spike in power that has to be dissipated as heat. So fewer starts is better. A piston compressor generally isn't able to dissipate heat fast enough and so will get very hot if run continuously. That heat tends to break down the lubricating oil resulting in deposits that will shorten the life of the compressor. Synthetic lubes will hold up better.
Horse power: There are a lot of "cheater" 5HP compressors sold. Motors that don't actually put out 5HP. You can easily tell by the watts or amps the motor is rated for. 745.7 watts = 1 hp but you need to deduct for the efficiency of the motor. To meet NEMA standards the motor must convert at least 84% of its energy into shaft power. So it takes 887 watts to make 1 hp at the shaft. 4434 watts input for 5HP. If you have 115V that means 38 amps. 230V means 19amps. The motor will draw more than twice the running amps at startup. How's your wiring?
Last edited by Larry42; 04-24-2019 at 06:54 PM.
Reason: Bad typing