In article ,
Mike Clarke writes:
I've just washed the HEPA filter for the second time in 18 months
(should have been every 6 months but there was a delivery problem with
the tuits), although it was well covered with dust there'd only been a
very slight drop in suction. There's no doubt that the HEPA filter is
very effective, the air outlet on the old vac used to rapidly get coated
with fine tenacious black dust, after 18 months the outlet of the Dyson
is still spotless. I'm not sure how the non-HEPA Dysons fare in this
respect, I'd be a bit concerned if they didn't have some form of filter
between the dust canister and the fan.

My Dysons are both non-HEPA and have the washable pre-motor filter
and a non-washable (I think, never needed to wash it) post-motor
filter. I thought the HEPA filter was an extra non-washable one in
addition to these? And no, there's no dust build-up or even slight
discolouration of the post-motor filters after 4 years of sucking
up rubble, brickdust and plasterdust in the case of the older one
(or the newer one come to that).

I don't pretend to understand the theory of cyclone extractors, the air
appears to be sucked up the cones _after_ passing through the dust
canister and presumably dust also falls down out of the cones, but it's
certainly effective. When we were choosing the new vac I got the
impression that many of the bagless competitors just swirled the air
round a bit as it got sucked into the canister and relied on a (usually
small) filter to stop the dust going any further. I imagine these
filters would need much more frequent cleaning (or even replacement)
than the huge Dyson filter.

I believe Dyson has a patent on multiple cyclone filters.
Cyclone filters themselves have been around for years, and
any original patent on them would have long ago expired.
The clever bit is making them work in something as small as
a domestic vacuum cleaner, as they are more effective the
bigger diameter they are. Prior to Dyson, I suspect the
smallest anyone would have envisioned they would be be
effective would be dustbin sized, and they go up to things
the size of a large room (or probably a whole house if you
look hard enough).

--
Andrew Gabriel