I was wondering if anyone could advise me on a question of motor rpm on an air compressor. I have an industrial compresser with a 5 hp 3 phase motor that runs around 1700 odd rpm. I want to put a single phase motor on it to use house current. I found a single phase, 5hp motor, but it's some 3400 rpm. I fear the almost double rpm will harm the compressor. Can anyone confirm or deny from experience? Thanks for reading this over.
Running your head twice as fast would require twice the horsepower, and is likely to ruin your compressor head (unless, for some strange reason, it ran at 2x below its maximum RPM before).
What most people do is try to find a smaller pulley for the motor. Another possibility is to sell this motor on eBay and buy a similar, but slower, 1740 RPM motor.
i
So? Halve the size of the motor pulley.
LLoyd
A smaller motor pulley may cause slippage since it'll have much less contact with the drive belt. At the least it may squeal upon startup. At worst, it may sit there and burn up the belt(s). Depends on how small the pulley is to start with. Better to get the correct motor. While you are at it, make sure that the motor is actually rated for compressor duty. Some compressors take a LOT of starting current. 3 Phase motors have a lot of starting torque, but many single pahse motors don't.
Maybe try to contact the mfr and see what they suggest.
Pete Stanaitis
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Lloyd E. Sp>
As has been said, it's not a good idea to run the pump at 2X speed... so cut the motor pulley diameter in half (if you can).. But more importantly get a motor rated for 'compressor duty'... Compressors are notoriously had on motors, they start against a load (even with a relief valve) and they usually run long duty cycles..
--.- Dave
Double the circumference, (Pi x Dia.), of the compressor pulley and Bobs your uncle. (Using a smaller motor pulley might work, but might also decrease belt life due to the sharper bend, and gives less driving area which might lead to slippage.) More is better here. Lack of adjustment room in the mount might call for a longer belt. MadDog
If a compressor is equipped with unloading valves, it starts with no load aside from the friction of turning the compressor. Better quality compressors are so equipped.
Harold
Not no load, just reduced load. The compressor is still trying to shoot a fire-hose through a pea-shooter. Before my repulsion start motor gets the compressor up to running speed (when cold) the load get's high enough to keep it in "start" mode. That is WITH an unloader. (motor is just on the edge of too small - the small side of the edge) When warm, it manages to start OK. I turn the heater on for about 10 minutes, blowing at the compressor head, before attempting to start it when below about 65 F.
And then the motor is up to speed so the start switch kicks out and then hits an 80 PSI load... and LLLUUUGGGGGSSSS DDDOOOWWNNNN
There is a reason they make compressor duty motors... uh.. to run compressors...
--.- Dave
depending on the compressor, doubling the circumfrence of the compressor pulley could still be a challenge - on my quincy compressor, the compressor pulley is around 24 to 30 inches (never measured it) - if the OP has that kind of arrangement, he would need a really big pulley to do the trick - getting the right motor (or better yet, using a cheap VFD to operate the 3 phase motor so there is not start surge) would be a much better approach
Chuckle!
Well, my 5 horse Quincy, purchased new in '68, doesn't suffer from that problem. Key here is that little part I said about quality. They not only start without a load (which was my point), but are also equipped with an adequate motor (a Century 5 horse in this case). The unloading valves on the Quincy allow for the compressor to *not* produce air until the motor is up to speed. No fire hose in this instance. Further, when it starts producing air, it's pushing against 125 PSI, not 80. On @ 125, off @ 175. There's a world of difference between over rated *5* horse single stage compressors and serious compressors.
I have no problem with the comment about a proper motor. They are not all created equally.
Harold
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