Air Compressor's

• 5hp vert spec

That looks like a nice unit. Their statement "incredible 19.1 scfm at 175 psig" is that indeed. This is the first 5 hp (true hp) unit that I have seen that delivers that much at that pressure. I have an IR 5 hp unit that delivers 17 scfm at 175 psig. Two extra cfm is a 12% improvement. I don't know how close my motor is to nominal full load rating just prior to shutting off at 175 however. Most good motors will also have a service factor of 1.15. That means they can be loaded to 115% of nominal stated rating continuously without overheating. That's to allow a margin of application error or for other unkowns. Thus a nominally rated 5 hp motor with a 1.15 service factor can be run at a load of 5.75 hp continuously without overheating, provided the circuit breaker has enough extra margin to accommodate it. That may be the case here for the high cfm for a 5 hp unit. I ran across this once with some large (1000 hp) IR centrifugal compressors. The nominal rating of their compressor package under consideration was based on the motor being loaded to 115% of nominal. That fact was unacceptable because we had to be able to feed the compressor with zero degree F air in the winter w/o any motor overheating or reduction in compressor capacity or pressure. Other things being equal, the colder the air supplied, the higher the required hp becomes because of the increased density of the air. Their original package would have worked fine if it was only fed 60F (or hotter) air, since that was their only rating guarantee point. I am not saying this is true in this case because I don't know. Just saying the 19.1 is higher than usual and liberal use of the motor service factor might possibly be a reason. If it is, there's really nothing wrong with it. Sneaky maybe, but legitimate.

Rod

I.m not suggesting they are anything but true specifications. As I said, if they are taking advantage of the motor service factor to maximize the cfm rating (and I'm not sure that's true), it may be sneaky but it is a legitimate practice. It just encrounches on the reserve margin provided by the service factor for unknown application variations. There are many motors (not the better ones) that do not have a service factor at all. They will have a 1.0 stamped on the nameplate in the "SF" location instead of 1.15. That's if the nameplate even has a "SF" location. If the service factor is, indeed, taken advantage of, it will still work fine on a continuous basis, although it could be more susceptible to thermal overload trips if run continuously at or near the high pressure cut-off point when the inlet temperature is abnormally low. That would not normally be the case with this type of compressor that cycles on and off between a high and low tank pressure. The situation is very different from deceptively (fraudulently?) "rerating" a 2 hp motor into a 5 hp one by misrepresenting it as being capable of operating at that level for more than a few milliseconds during starting. Anytime you see an "S" for special or a blank in the nameplate location for "HP" that's the time to run away from that motor. The Baldor you indicate is not like that. The specs suggest to me that it is probably the same as mine - a heavy duty, 1750 rpm industrial motor with a service factor of 1.15 that can be run continuously at 115% overload without a problem. The motor itself is probably worth over $400. Plus the rpm of the pump is quite low so I would expect it to be reasonably quiet, at least as compressors go. And long lived. Both the specs and the cost suggest a high quality unit that should last a long time.

As far as the 5 vs the 7.5 hp unit goes, it all depends on what your needs are regarding cfm. The pumps appear to be the same for both units - the 7.5 hp one just being increased in speed to utilize the additonal power available. But it's still low (which is good) compared to many other compressors. Don't forget the power source available. The 7.5 hp one is a true hp rating also, judging from the cfm noted. That is a big load on a 230 volt, single phase circuit. You'd probably want a 50 amp circuit to accommodate it where the 5 hp unit could be accommodated on a 30 amp circuit. Normal full load current for a 5 hp 230 volt single phase 1750 rpm motor is 23 amps whereas for the 7.5 hp motor, it's 30 amps. Nuisance trips should be expected if the 7.5 hp unit were to be served by a 30 amp circuit - even more so if that service factor is encrouched upon. While the 7.5 hp unit would be a little better for sandblasting with a suction blaster and the appropriate nozzle, you'd probably not notice any difference for all other normal uses. I don't do a lot of sandblasting so the extra $600 would not be worth it to me. But it might to you. As B--- indicates for his, my 5 hp unit works well enough for the sandblasting I do to not justify spending more for additional capacity. I use a 1/8 nozzle in a pressure pot blaster and the 5 hp can keep up with it, although barely so if I keep the nozzle pressure up. Information I have from IR on pressure sandblasting (not suction) indicates that a 1/8 nozzle for a pressure pot requires 17 cfm minimum but for the next larger size standard nozzle (3/16), the air requirement goes to 38 cfm minimum. Assuming that's true, you will not get faster pressure sandblast performance for any reasonable time over a minute or two from the 7.5 hp unit (rated at 25.8 cfm @100) because it would not be able to keep up with the demand. So the extra $600 would provide very minimal gains as far as I am concerned - as long as you are not talking multiple users at the same time for other work or paralleling it with another unit. And I don't think you are. At least that's my personal opinion.

Rod

Yup, that's the same as mine. That big Baldor makes the "5 hp" motors on the Home Depot units look like old 1/4 hp washing machine motors. The T30 compressor has a great reputation as a proven design over many years. It's why I got the one I did. I think I paid about $1800 for mine although it is not as old as yours. I think most any industrial grade, continuous duty, true 5 hp machine is going to be up in that cost ballpark. The under 10 hp category of compressors is highly competitive and there seems to be a lot of deceptive claims out there regarding hp in the lower cost units. Buyer beware. Another thing that adds to the cost is the magnetic starter. That should be standard equipment on any true 5 hp machine. I have not seen a compressor pressure switch (Square D) rated over 3 hp for 230 v single phase. They may work for a while on 5, but i'd expect the contact life to be less than desired.

Rod