[TheForge] air compressors, CFM, and psig

[terry l. ridder]

hello mike;

On Thu, 7 May 2009, CGRAF wrote:

> Bruce Freeman wrote:
>> Terry,
>> One of us is befuddled.
>> What I described to you was how ideal gases behave.
>> If you now want to redefine CFM at atmospheric pressure, then that
>> changes the description, but not the facts.  I cannot see how your
>> concern about the time factor makes sense in the first (simplest)
>> analysis, and I have no intention of taking this beyond the first
>> analysis.
>> In my limited experience, CFM is defined at the operating pressure of
>> the compressor.  If so, then if you run a "10 CFM @ 120 psi"
>> compressor into a tank then bleed that tank through a regulator, you
>> can get 10 CFM at 120 psi, or 20 CFM at 60 psi, or 40 CFM at 30 psi,
>> etc.  These are not exact figures. They don't allow for non-ideal
>> behavior of air.  They don't allow for condensation of moisture.  They
>> don't allow for pressure drops through orifices (equivalent to
>> friction in a mechanical system).
>>
>
> All of which is important if you are trying to run the equipment 100%
> and directly off of the compressor. Once you factor in that 90% of the
> time the compressor will only be supplying makeup to a tank and that
> there will be slower bleed off from the tank than the compressor is able
> to supply the whole exercise becomes academic.
>
> For about six months I ran my bull power hammer from the tank of a large
> compressor that I hadn't yet wired. The air was supplied by a little
> compressor designed for nail guns. Most of the time, working by myself,
> the little compressor was able to keep the big tank up to working
> pressure. On paper the poor little thing was drastically undersized and
> I am certain that I worked it to death, but the air was there when needed.
>

so one of the deciding factors for an air compressor would be the size
of the air receiver. my amish friends use 500 gal bulk tank normally
used for lpg for air receivers. their air compressor is a 3-pt hitch air
compressor  pto-driven by the tractor. my friend kenneth drives the air
motors in his home for nearly a month before having to run the air
compressor again. there are several bulk tanks available locally. would
need to have them inspected before i would trust them with 175 psig of
air.



>
> Mike Graf
>

-- 
terry l. ridder ><>