robert c noguiera wrote:
>
> I've got a chance to buy a two stage (5hp) air compressor for the price
> of a single stage unit. What are the advantages of a two stage unit ?
> Any disadvantages ?
>
> Thanks
>
> Bob
Hi Bob,
You don't say what brand, the amperage draw or the CFM, but generally
speaking, the two stage units use the larger frame, heavier current draw
(more powerful) motors. A typical "6 HP" single stage unit uses a 15
amp motor while the two-stage, 5 HP units use a 20-24 amp motor.
The key design difference, though, is that the two stage units use the
first cylinder (it has more displacement from a larger bore) to
pressurize the air to around 100 psi. The air from that cylinder then
is fed to a second cylinder (one with less displacement, accordingly),
which will pressure the air to about 175 psi. It uses an intercooler (a
"radiator" for the air) between the cylinders to draw out a great deal
of the heat before it enters the second cylinder. Single stage pumps
usually have two cylinders, but each one acts in parallel.
Two-stage pumps are more efficient (provide more pressurized air) given
the same horsepower, and will provide a higher base level of air
pressure (two stage pumps usually cycle on at 125-150 psi while single
stage pumps cycle on at 80-100 psi). The two stage design also provide
substantially more air storage in the same size tank due to the higher
pressure (about 40% more air storage in a given tank if you compare 175
psi to 125 psi.
Additionally, the two stage units usually are more ruggedly built, have
more robust cranks, bearings and better cooling. They are designed and
built for heavier-duty cycles (i.e., commercial vs. home).
The only advantage to the single stage units is that they tend to be
lighter (more portable) and less expensive.
I would jump on the two stage in a nanosecond. What brand and model are
you looking at?
doug
|