Then why even bother having any filters at all?
 
And as you stated in your post below and I quote:
 
(cprohm)
 If you clean the washable filter on a regular schedule, the Dyson should never lose airflow.  
 
It would appear from your quote listed above, that washing the Dysons air filter (and isn't it called an air filter, because it is filtering the dirt from the air)
is part of maintaining air flow, so if a dirty air filter reduces air flow, at what time does this reduction take place?  
After 5 minutes of vacuuming or 25?
 
And if washing the filter is all that is necessary to restore maximum air flow, how is it any different than just replacing a bag , couldn't any  
manufacture with a bag system make the same claim that Dyson does?
 
And I wont even mention all the different areas around the rubber seals that the Dyson leaks, well not in detail any way.

vac repair guy, I understand your point, and some time ago I would have agreed with you. Certainly it is true that the airflow through the washable filter starts declining as soon as dirt begins to reach it, and would ultimately reduce to nothing if it were never washed. I was curious about this, so I read about the lawsuit in England where the claim of no loss of airflow was challenged in court. It was in reading that case that I realized that the resistance to airflow in the cyclones was actually decreasing as it collected dirt, more than offsetting the loss of airflow in the pre-motor filter, so that as the vacuum was used, the overall airflow actually inceased initially before beginning to slowly fall, and that during the test period it always remained above the initial airflow level. How long was the test period? How long does the airflow remain above the initial level? I don't know. How does the airflow after 6 months compare to the airflow out of the box? I can't give you a number, but if it is down, it isn't down much.  As a practical matter, most consumers wouldn't notice any difference unless they didn't clean the pre-motor filter.  In advertising you can make all sorts of claims, but the fact is that if consumers can clearly see that the claim is false, there will be a significant negative backlash in time. That hasn't happened with Dyson because consumers have found the claim to be true.
 
As a pratical matter, if you have tested the vacuum, and I'm sure you have, you realize that the airflow is remarkably constant. You also realize that the cleaning schedule given for the pre-motor filter, every 6 months, is realistic, and that if the filter is cleaned on that schedule, a user will always have excellent airflow, but whether that number is 92% of new or 101% of new I can't say.  Some other filtration methods, such as Filtrette bags, also do fairly well at maintaining airflow better than conventional bags, and some methods, such as pleated filters, do worse than conventional bags. Water filtration also maintains airflow, but as everyone knows, has other drawbacks (dirty water, trouble dealing with non-wettable dust, etc.)
 
I'm not here to tell you that the Dyson, or any other vacuum, is perfect. I don't work on vacuums as a profession, but I do own a lot of them, only a few of which are Dysons. The Dyson has its strength - the filtration, and the ability to maintain airflow. It also has its weaknesses - the beater bar and the soleplate rollers, to name two. If you want to criticize the Dyson for its weaknesses, fine, but don't be like some other posters and forget to give it credit for the things it does well.

Hello Kenneth J:
 
You fought the good fight.  Be at peace with yourself.  BTW, the DC15 Ball is doing a Claude Rains at all major retailers: They are disappearing off the shelves due to lack of sales and interest and after dyson lowered the prices more than $100.  So perhaps you won in street justice rather than court justice.  
 
Carmine D.
 

THe DC15 Ball was only dyson vacuum in the top 10 AND the only vacuum in the top 10 that scored only a "GOOD" rating for carpet cleaning.  All the others scored very good and/or excellent.  It is also the most expensive in the top 10.  
 
That's probably the reason it is doing a Claud Rains: Disappearing like the invisible man.  
 
Carmine D.

I have the patent!   Kenneth J. Weger  Patent# 5,794,305  
 
I really didn't have a "trial" as I understood a trial to be and it was appealed federally. Live and Learn.  I contacted Dyson too introduce my patent.  He said he would get back to me in fifteen days….and 5 days later I was sued by 14 New York attorneys. He sued me.
 
Oh Hello there.
 
My case was decided on summery judgment…Before a "trial" as I understood a trial to be, not like on TV….On the ordinary meaning of the word "pair" as used in my patent. Yes that’s right.  My dictionary said a pair was corresponding things…. and the person who sued me' dictionary said a pair has to be separate things.  So my case was decided on one word before a jury trial.  "Pair"  
 
Ok….fine
 
I still believe that the patent shows the world the best way, A pair of wheels for left and right turns...then and now…..I also believe that I will one day get a license arrangement and the full potential of this wonderful idea will be realized…
 
I had the "Eureka" moment when I discovered, recognized and patented this incredibly innovative solution that added the mobility that those with arthritis lacked into the upright vacuum…The idea received a design award from the Arthritis foundation...No one can take that or that moment away from me…
 
I invented it…. Kenneth J.