In article ,
Matt writes:
"david lang" wrote:

Don't fall for the 'bagless, no reduction in suction' cobblers. True,
bagless cyclone vacs don't lose suction as they fill, but they have a
suction level so low that a nearly full bagged Numatic still has better
suction.

To eliminate the possibility of confusion on the merits of the various
cleaners could you quote the minimum pressure achieved at the nozzle
and the corresponding air flow for:

That measure is rather meaningless. The measurement accepted by
the industry is "suction power" as defined in IEC Standard 60312.
There is however a recognised problem with this measurement.
Bagged cleaners are all measured with new empty bags, which is
not at all representitive of their performance other than for
the first few seconds. Actual performance during most use is
much lower (there's an initial rapid drop and then a steady
decline), and a representitve figure is to half the quoted figure.
Another problem is the figure fails to take into account
how effective a bag is. Cloth bags generally don't drop off as
fast as paper bags, because they chuck much more of the dust out
in the air exhaust, so it doesn't block them.

For a cyclone cleaner, the "suction power" doesn't significantly
drop off. Instead, what happens as they get near full is that the
cyclone stops filtering as well. If they get over-full preventing
the cyclone operating, they then fall back to operating as a
filtered vacuum cleaner using the post-cyclone filters.

So the "suction power" figures are quite heavily biased to favour
bagged cleaners.

a) a bagless cyclone

280 airwatts

b) a nearly full bagged Numatic
c) an empty Numatic

Numatic don't quote "suction power" figures (from which you might
wonder if they aren't prowd of theirs). A top end bagged cleaner
is ~400 airwatts with a new bag, 200 airwatts after a few seconds
of use (better for cloth bags, but that's because they're chucking
all the finer dust out in the air exhaust), and probably somewhere
well under 100 airwatts when bag is getting full, or if you have
sucked up any fine dust which has been trapped in the cleaner.

One tip with a bagged cleaner -- If you are going to suck up any
fine dust (like plaster dust), do not empty the bag first. The
household dust already in the bag will act as a much larger area
filter for the finer dust, delaying it blocking the bag pores.
Conversely, a cyclone cleaner will work better if you empty it
first, and empty it again before it gets full.

In theory, cyclone cleaners should be clear winners. The extracted
dust is removed from the air path whereas with a bag/cloth filter,
it is clearly trapped directly in the air path. What has held
cyclones back is that they work best when they are dustbin sized
and upwards. Getting one to work in something the size of a portable
domestic vacuum cleaner is a challenge, although Dyson seem to have
largely mastered it.

--
Andrew Gabriel