Old-Timer,
   Good analysis.  Interesting that the machine obviously was suffering from lack of routine maintence.   Did they happen to mention who told them that they did not need to maintain the filter twice a year as dyson states or occasionally clean the brush bar as with any vacuum?  I am guessing some teenager working at a big box store?

Quote from JimB on 04/18/07 at 2:41pm:

 
 
Sorry JimB:
 
I have to disagree with you on the cyclone configuration, although OT called it right on some of the latter model DC07's having the improved cyclone design of the DC14, 15 and 17.  BTW, this is an old topic on the Forum and discussed in great length before.  You're coming in new to it and may want to get up to speed on the facts.
 
Maybe I should have qualified my analysis to clarify the confusion: Looking at the dyson with both feet on the ground and not upside down.  
 
BTW, other than saying it's so, do you have some proof on the dyson percentage numbers?  Please share.  
 
Carmine D.

Quote from old-timer on 04/18/07 at 1:51pm:

 
As I understand the engineering principle, the cyclone works because, by making the air spin, you create centrifugal force on the dirt particles, which causes them to spin to the outside of the cylinder, where they contact the wall, slowing them down, and causing them to drop out of the airstream. A problem comes if the airspeed drops below the designed airspeed. When the speed is reduced, the centrigugal force isn't as high as was intended, which means dirt doesn't spin out like it should. When this happens, larger dirt or lint, that should remain in the primary cyclone, ends up getting first onto the shroud, and then into the smaller cyclones. It is when this dirt that is larger that intended gets into the secondary cylinders that you have a problem.
 
Failure to clean the secondary filter would reduce the airspeed, which in turn should lead to lint accumulation on the shroud, and could also lead to plugging of the secondary cyclones. My guess is that the clogging was a direct result of the partially obstructed secondary filter.  
 

Quote from JimB on 04/18/07 at 5:32pm:

 
 
Hello JimB:
 
So what you are saying to me on the Forum is that I am wrong.  I don't know what I'm talking about.  That in fact dyson had the correct cyclone design ALL THE WHILE on the DC07: Narrow part on the cone on top and the wide part on the bottom.  Thus, when the vacuum was turned off, any dust and dirt still in the cyclones easily fell from the narrow end of the cyclone cones (on top) to the wider openings on the bottom, and into the dirt bin. Due to the law of gravity.  OK, I'm with you.  I thoroughly agree.
 
Here's the rub.  For some unknown reason, dyson and its 500 engineers, decided to change the configuration on the cyclones on the DC14, DC15, DC16, DC17, DC18 and DC21.  The cyclones now are wider on the top and narrower on the bottom.  So, when the vacuum is turned off, the dust and dirt stuck inside the cyclones falls from the wider area to the smaller area of the cones.  (Law of gravity).  And over time, because the user can't clean the cyclones of the dyson vacuums, they clog up with dirt and become ineffective (even if the premotor filter is cleaned and washed as recommended.)
 
Wow, don't I feel stupid!  All along I was giving dyson credit for correcting what I erroneously thought was a flaw in the DC07 cyclones.  And come to find out (thanks to you) just the opposite is true.  Dyson took a perfectly fine design and inverted it to make it functionally inferior.    
 
Based on the above, I agree with Carl.  The reason the cyclones clogged on the DC07 (which as OT explained have the scientifically correct configuration to avoid clogging due to gravity when the vacuum is shut off) is because the premotor filter got clogged due to lack of cleaning.  
 
Thanks for clarifying for me and the Forum.  No wonder this thread is for dyson-haters.  What company would take a perfectly good cyclonic design and functionally alter it to make it worse?  Yep, you got it: Dyson.
 
Quote from JimB on 04/18/07 at 5:32pm:

 
I retired August 4, 2006 (newsflash).  If you want to post the link for the dyson sales numbers, don't do it on my account.  Do it because you want to show your source and proof for the sales numbers that you and dyson banter about.  
 
Carmine D.
 

Quote from HARDSELL on 04/18/07 at 6:43pm:

 
Hello HS:
 
Actually, it makes no difference what vacuum you use and how often, you can never get all the dirt out of a rug by vacuuming.    That's the reason for the daily vacuuming and yearly cleaning.  And the reason that industry experts recommend 7 rug passes for cleaning.  Most not all the dirt is likely to be removed.  
 
I don't own a boat, I live in the desert.    No need for a life vest.
 
Carmine D.