Re: A/C compressor bracket

[jlandry@domain.elided (John A. Landry)]

On Mon, 22 Dec 1997 23:56:48 -0700, "darrel kline"
<darrelk@domain.elided> wrote:

>That isn't bad at all John.  I also have a Sears sandblaster.  I use it
>with my 5hp, 60 gallon tank, 11 SCFM at 90psi air compressor.  I can blast
>for about 10 minutes before I have to let the air compressor catch up. 
>I think the reason I can blast for so much longer is more because of the
>volume of the tank.  No telling what yours would do with a 60 gallon tank. 
>Sandblasting consumes far more air then any of the air
>tools I own.  

All this talk about horsepower verses cfm made me remember some text I saw
in the Grainger catalog about selecting a compressor...

"Cubic Feet Per Minute (CFM):

The next critical factor is CFM output of the pump.  Users commonly size
compressors based on their HP rating.  A COMPRESSOR NEEDS TO BE SIZED BY
CFM, NOT HP.  YOUR TOOLS OR EQUIPMENT RIN OFF THE CFM AND PRESSURE (PSI).
A larger HP motor/engine allows the pump to run at faster speeds or larger
displacement to produce more CFM at a rated pressure.

It is always better to OVERSIZE A RECIPROCATING COMPRESSOR than to
undersize.  As a rule of thumb, to size a compressor, determine the total
CFM being consumed, with additional future expansion in mind, and multiply
by 1.5.  This will provide approximately a 50% duty cycle.

Undersizing an air compressor will cause the pump to exceed its rated duty
cycle and will shorten the life of the pump.  Continuous run compressors,
such as gasoline engine powered compressors, should be also be sized as
above.  Even though they run continuously, they are not always under load."

[Letters in CAPS were bold in the catalog.]

>Would I be able to buy the pressure switch and the unloader at any air tool
>shop?

Possibly yes, but I found Grainger (www.grainger.com) to be a great and
easy to deal with source.  Your local Grainger in Colorado Springs is at
610 Pope's Bluff Trail, telephone 719-598-9500.  If you visit them in
person, see if you can get a copy of their catalog... a great reference and
is the adult mechanic equivalent to the old Sears Christmas toy catalog
called the "Wish Book." <grin> They must have 20 different Square-D
pressure switches for you to choose from for your compressor setup.  About
half of them have adjustable pressure settings... meaning you can control
the exact point when they kick on and off (so Tom M. can have his start at
200 psi and stop at 250 psi).  I went with the fixed settings to save
money.

Happy holidays,

John
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