On Tue, Aug 10, 2021 at 9:58 PM John T. Blair <jblair1948@cox.net> wrote:
>
> 1. What really controls how much a comperssor can generate, ie. SCFM?
Actual power available from the motor, more or less. More power, more air.
>
> 2. What controls how long your compressor can supply air before having to
> start
> the motor to refill the tank? I realize that some air tools use a LOT more
> air, but
> I'm speaking for any given tool, not compairing something like spray painting
> to
> undoing 5 lugnuts on a car.
Size of tank, the pressure of the stored air, and the settings on the
pressure switch.
Bigger tank means longer run time before the compressor kicks in,
higher pressure means longer run time before the compressor starts.
Pressure switch controls when it comes on, so there can be more or
less usuable air in the tank. Most tools are limited to 90 psi, so as
long as the system pressure is above that, the compressor doesn't need
to run. In industrial settings, where there can be strict
requirements about air pressure, the cut in pressure can be different.
I used to work in a shop with three compressors ganged together, and
they were set up with different cut in pressures. First one would
come on, and if pressure kept falling, the second would start; more
pressure drop, the last one cut in. They'd all run until 175 psi was
reached.
Siz>
> 3. Why is a bigger tank better? After the compressor's pressure switch kicks
> on,
> doesn't it take longer for the compressor to reach the shut off pressure with
> a
> larger tank?
It holds more air which lets you have surge capacity that uses more
air than your compressor produces, at least for a little while.
It also gives the air longer to cool down, which lets water condense out of it.
>
> 4. How can a 1.7 hp compressor deliver a peek of 175 psi and a regulated 155
> psi
> when my 5 hp can only charge to 125 psi. I realize part of that is due to the
> pressure switch, mine is 110 on - 125 off, but really. Can I put a pressure
> switch in mine and 175 psi. I don't really think so. Is this more
> advertising hype like
> when they were rating compressors at their starting current vs running
> current for
> hp? They could get 7hp of of a 110V motor - NOT!
>
Pump design, and how its been chosen to be driven. Higher pressure
means more storage in a tank, and more pressure to overcome pressure
drop in lines. the last shop I worked in, I was 75 pipe feet or more
away from the compressors, I had to set the regulator at my drop to
130psi to get a running psi of 90 or so on my impact gun. The lift
closest to the compressor, I could turn it down to 95 or 100. In
tuned industrial applications, pumps are often run at less than
maximum capacity, for less noise, less power use, and longer life.
--
David Scheidt
dmscheidt@gmail.com
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