I was especially hoping you would respond, Randall. Thank you.
Terry
>> Two stage compressor, minimum 6 to 7 horsepower,
>
> Although the situation has improved somewhat recently, it's still
> imprudent to
> use "horsepower" as an indicator of compressor size. Look at the CFM
> rating
> instead (but see below).
>
>> I wrote in my notes from the list, but can't find in archives anywhere,
>> recommendations for an Eagle brand blaster that (I can't read my notes)
>> gives
>> 10.5 cfm @ 90PSI? Sound anywhere close to right?
>
> Don't know the brand, but that cfm rating seems a tad on the small size.
>
> Ideally, you'd like to have a compressor that will produce as much air as
> your
> blast rig consumes. But that usually winds up being impractical, because
> sandblasters use a *lot* of air. It doesn't help that an air compressor
> "cfm"
> isn't the same as a tool "cfm". Both are rated by cubic feet per minute
> going
> in; but because air gets much smaller when it is compressed, the output of
> an
> air compressor is much smaller than the intake. You can get a pretty good
> guess
> as to how much smaller by taking the ratio of the absolute pressures :
> roughly
> 15 psia at the compressor inlet to 105 psia (90 psi gauge plus atmospheric
> pressure), or about 7:1. That means you need a compressor rated at 28 cfm
> (at
> 90 psi) to keep up with a tool rated 4 cfm @ 90 psi !
>
> Which is where the big tank comes in. A larger tank lets you run an
> oversize
> tool longer, even though the compressor can't keep up.
>
> Two-stage compressors are preferable because they are more efficient at
> higher
> pressures. Most single stage compressors still work fairly well at 90
> psi, but
> their output drops to almost nothing by 150 psi or so. Two-stage
> compressors
> are generally still quite efficient at 175 psi. (And here again, the
> higher you
> can pump up the tank before starting work, the longer you can work.)
>
> Randall
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