[Mgs] Off topic: Stationary Air Compressors

[Barney Gaylord]

At 06:23 PM 7/2/2008 -0700, Ron King wrote:
>In the market for a stationary air compressor, and wondered if 
>anyone had personal experience/thoughts/opinions?  Usage will be 
>mainly automotive but haven't ruled out the occasional spray paint 
>job which I understand takes more CFM as well as PSI.

Find half a dozen air compressor tech articles starting here:
http://mgaguru.com/mgtech/tools/ar101.htm

If you are contemplating auto restoration, sanding, grinding, 
painting, etc, a real 2-HP belt driven compressor is a nice size for 
a home shop.  2-HP is that largest motor that can run on a 120-volt 
20-amp circuit (with a 15-amp plug), drawing about 13-amps under full 
load, slightly higher on startup.  Most of the 2-HP motors can also 
be wired to run on 240 VAC drawing half the current.  Do not be 
fooled by the "peak horsepower" marketing ploy.  If it runs on a 
120-vac 15-amp line cord it cannot be more than 2-HP.

A real 2-HP slow running belt driven compressor can put out about 
9-CFM at 40-PSI, and a bit more than 7-CFM at 90 psi.  Common paint 
sprayers need about 8-CFM at 40 PSI (or less), so a 2-HP compressor 
can give continuous operation of a spray gun.  A small die grinder or 
2-inch angle sander can run near contuinuous at 90-PSI.  A larger die 
grinder or 3-inch cut off grinder can run 50% to 70% duty cycle at 
90-PSI.  A dual-action sander might run continuous at 40-45 PSI in 
orbital mode, or 50% duty cycle at 90-PSI in high speed circular 
mode.  Running an air ratchet or impact wrench or inflating tires are 
intermittent operations that need large flow for short time, no 
problem at all.  I have run my home shop for decades on a 2-HP 
compressor and seldom feel the need for more air.

If you're thinking about running a sand blaster continuously you 
would need at least a 5-HP motor running on 240-VAC with a 2-stage 
compressor, and same for a high speed circular sander.  A real 5-HP 
2-stage compressor can do 15 to 19-CFM at 125-PSI, very efficient at 
higher pressure.  The larger capacity compressors also come with 
larger air tanks, and you can cram a lot of air into a larger tank at 
higher pressure.

Barney Gaylord
1958 MGA with an attitude
http://MGAguru.com