5hp compressor pump w/3hp motor?

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Sep 2, 2003
Metro NY
I have a 220 single phase Baldor electric motor rated at 3hp
I have a 4 cylinder Speedaire compressor pump that wants 5hp that is spec'd at 16.7 CFM at 90psi with a 5hp motor

Can I run this pump with this motor? If so what will I be giving up vs a 5hp motor? (Max pressure?, CFM?)

I'll be running air tools in a home shop environment (not lots of air all the time)

Probably just burn up the motor. PSI is regulated by the switch, so it's gonna run the motor until the PSI hits the cutoff. The motor's gonna be straining hard to run a 4 cylinder pump, eventually it's gonna give up the fight. That's my logical guess, anyway.
most 5hp pumps can be run at 3hp. You just gotta slow them down a bunch.

That makes sense, you slow them down by putting a smaller drive pulley on the motor?
So... given the choice to slow a 4 cylinder pump down vs leaving the 2 cylinder pump alone - all on the 3hp motor... is there any reason to use the "bigger" pump? Is it all just math to figure out what will yield the "better" net result ("better" in this case is higher CFM, not higher pressure)?

I COULD buy a 5hp motor - clearly the best option... but not what I aspire to at this point.

Hey guys, my name is Alex, live in Tucson.

I'm new to the forum, but this is exactly what i want to do, to power a 5HP compressor pump with a 3 HP motor.

the Model of the Motor is from harbor Freight 3600 RPM(i may upgrade later...) is 68302

compressor is a brand new 5HP - 60 Gallon tank # 4ME98 . Nominal CFM is 90PSI-16.0, and 140PSI - 14.2CFM. pump RPM rated at 950.

Please tell me what y'all would do to make it work, and not burn up my motor.... like Sheave Size, belt, etc. obviously i don't want to change the pulley on the pump. the motor on the compressor now is a 3 phase, 3450 RPM.

Thanks Guys. Please go easy on me. I'm a smart guy, just have never done anything like this before..
Just gear down the 3 hp to run the pump at 60% of the speed of the 5 hp. However the hp ratings on motors are not always accurate. If there is a wattage rating it is probably more accurate and 1 kw = 1.34 hp.
Not only are horsepower ratings not accurate, but you also need to consider the type and duty cycle of the motor. An industrial motor rated continuos operation with a high service factor will obviously outlast a general purpose unit. But as @Pin_Head mentioned, you need to slow the pump down if you want to use a smaller motor. Most compressor manufacturers will give the proper size pulley for the motor hp, so you might be able to get that from their website. If not, just slow it down 60% and use a clamp on ammeter to monitor the current draw just before the pressure switch opens. If the current draw is over nameplate, check that the motor temperature rise is not excessive. Typically motors are rated 40 deg C rise above ambient, so if you allow the motor to cool between cycles, or add a cooling fan, you might be able to get away with using it. The other thing is to make sure the motor has a thermal overload built in. This will open when you overheat the motor, hopefully saving it. However, it comes down to what your usage is, i.e. are you just airing up tires, and occasionally using an impact gun, or are you running a die grinder? If you plan on heavy air operation, i.e. die grinder, air sander, etc, buy a quality 5 hp motor rated for compressor operation.

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