robert c noguiera wrote:
>
> A friend has a 2 stage ( 21 amp ) 60 gal compressor with a 180 lbs max
> rating . While looking at it I noticed he had it set to cut off at 140
> lbs . When I asked why he said that since it supplies the volume he needs
> and the regulator is set for 90 lbs why put the strain on the pump and
> motor and use the extra power to bring the tank up to a level you never
> will use . His opinion is that the work the motor has to do to push in
> that last 40 lbs is much greater than it did to get to 140.
>
> Does he know what he is talking about ?
Well, he kind of has a point, but I would rather fill the
tank fully so the pump runs less often. I rather like having
a full tank and using the tools for long periods of time
without the compressor even turning on.
If you "short change" the tank, it'll hit cut-on sooner.
> When they talk about cubic feet per minute, is that assuming the tank has
> no air in storage, or to ask it another way, doesn't a 1 hp unit with
> the tank at 125 lbs deliver the same volume as a 10 hp unit with 125 lbs
> in the tank ?
Only for a short time.
The cfm rating is the rate at which the compressor can deliver
air effectively forever. The tank is a temporary buffer, like
a capacitor in electronics.
This is important for things like sandblaster or painting,
where you use a lot of air for a long time. With the small
compressor and large tank, you can blast for a bit but
once the tank is empty you have to stop and wait for
it to charge.
With the large compressor and large tank, the compressor
itself can keep up with the tool, so when the tank is
empty it will turn on but you don't have to stop, just
keep working while it keeps the tank full.
--
Trevor Boicey, Ottawa, Canada.
tboicey@brit.ca, ICQ #17432933
http://www.brit.ca/~tboicey/
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