> I'm looking at two Ingersole-Rand air compressors -- both are 80 gallon.
>
> One is single stage 18 CFM at 90 PSI with 135 PSI max and rated for
> 5,000 hrs (whatever that means).
I think what they're gently hinting at is that this one will wear out faster
than the other one.
> The other is dual stage 24 CFM at 90
> PSI with 175 PSI max and rated for 10,000 hrs.
> I think the single stage is adequate to overkill,
Not really, when you consider that compressors are rated in scfm, and even a
small sand blaster uses 4 cfm @ 90 psi which is about 28 scfm.
> and the dual stage is
> beyond my needs, The dual stage is over twice the price. The only
> advantage is higher PSI as far as I can see. But everyone says buy a big
> one, so I'm asking.
One advantage of the higher pressure is that it effectively packs more air
into the tank.
80 gallons is about 10 cf, so at 175 psi (roughly 13 atm) the tank holds 130
scf. At 135 psi (roughly 10 atm), it only holds 100 scf. Then the residual
when the pressure drops to 90 psi is about 70 scf; so the 2-stage unit will
actually deliver twice as much useful air from the tank.
>
> One other thought. If I bought the single stage at 18 CFM, and I later
> decided I need more volume, what would be wrong with connecting a second
> single stage compressor into common output line with the first
> compressor.
Not a thing, as long as they are rated for similar pressures. One of them
will likely come on first, with the second one kicking in if the pressure
drops further, but that's actually a good thing as it reduces the peak power
requirements. Both will chug along until the pressure rises, then one will
likely shut off first while the second will continue to run for a bit until
it's set point is reached. Should be no problem, as long as the lower
pressure unit can handle the pressure (which of course it can if they are
identical units).
> Seems I could hook them together into a common line at a
> point beyond their pressure regulator valves. The common line could have
> a pressure relief set to a little lower than the two pressure regulators
> on each compressor. Something I'm overlooking?
I'm not sure why you want a pressure relief valve that will blow off all the
time ... maybe I'm misunderstanding something.
> Is there a problem if the
> pressure on the common line was accidentally set higher than the
> regulators on each compressor, or maybe one compressor had a lower
> regulator setting than the other? I guess the question is, is there a
> problem if the pressure beyond a pressure regulator valve is higher than
> it is on the side towards the air compressor? Maybe it's a question no
> one is sure of????
At some point, most regulators will start venting the excess pressure on the
outlet side. But the pressure has to be a fair amount above the set point,
so I wouldn't think this would usually be a problem.
Again as long as the tanks and compressors have similar ratings, I see no
problem with teeing them together before any regulators. Each tank will
retain it's blow-off valve, which is presumably adequate for it's
compressor.
Of course, you'll need twice as much electrical power, twice as much space,
and have twice as much noise to listen to, but perhaps those are not
problems.
Randall
/// unsubscribe/change address requests to majordomo@autox.team.net or try
/// http://www.team.net/mailman/listinfo
/// Archives at http://www.team.net/archive/shop-talk
|