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deathbypontiac 03-03-2007 02:25 AM

air compressor motor RPM
i am looking to buy a 2 stage air compressor for body work at home. the two finalists are Eaton and Castair. both are comparable in price and quality, the Castair is build in my home state of MN and i will save $200 in shipping over the Eaton. the one thing i am nervous about is the castair motor spins at 3450 rpm and pump spins at 710 RPM, where the eaton motor spins at 1750 RPM and pump spins at aprox 800 RPM. the compressor will be in an unheated garage next to my shop. Eaton says that "MOST" the 3450 RPM motors need to be in a heated compressor room. i would like to hear some opinions before i call castair because i am sure they will say it will be fine. also how many true CFM does it take to run a DA in the real world.

oldred 03-03-2007 08:34 AM

The thinking is that the colder pump will require higher starting torque at least until it warms up but on a quality compressor it really should be no problem either way.

FWIW, My vote would be for the Eaton.

DA really needs about 16 or more CFM and even at 16 you may find the compressor working pretty hard but a lot of people get by on quite a bit less than that with good air management.

SteveU 03-03-2007 03:14 PM

One thing that helps out is to use synthetic compressor oil in it after you break it in. It doesn't get as thick in the cold and gives the motor less resistance for this reason. The amsoil PCK I have in mine has a pour point of around -50* F and will start up in my compressor at 17* F no problem. The Mobile Rarus 427 that originally came in it has a pour point of 45* F which means at 17* F it would be like set up jello making the compressor unusable in the winter as it is in an unheated (except when I am in there working) shop. I've never seen the castair but have the 5hp single stage Eaton, the motor on this compared to the HD compressors is like comparing a big block to a 4 cyl. I like mine & it's a good feeling not to have to look at how much air a tool uses, with these if you hook it up it will run, mine will pump up & shut off while running a 6" DA sander. I too would vote for the Eaton, probably because I have one & like it so much :D

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