J. Phil Thien's Projects

I was planning to do a top hat, but this has me intrigued.  I do not have much spare time and may not have much time to experiment.  I may try a prototype that's a little different than whats proposed.  The question I have is if the air speed is reduced below ~45 mph, the theory says that the dust will not be picked up by the air flow.  So if the dust is on the wall traveling a speeds ~20 mph and the air flow is diverted from the wall to the center at speeds of ~20 mph, will the dust get pulled away from the wall or does it stay close to the wall if the pipes are vertical?  I also have concerns that with internal baffling (the spiral vanes) in the pipes that clogs may occur which means the design must come apart easily.  Any thoughts appreciated.

Hi all,
This is an amazing site full of DC information. Many credits to all the contributors. I have enjoyed wood working most of my life as a hobby.  I am looking to retire in a few years.  Based on the information in here, I am making a top hat prefilter for a HF DC.  My biggest concern is pressure loss when adding the TH.  When I finish, I will post it some where in here.  I am trying to do a spiral wall so that the incoming flow is parallel with the return flow.  It will be easier to show pictures when its done.  I thought that this would reduce turbulence and minimize pressure drop. I'm using a bellmouth exit pipe and intend to use a simple X straightener.  I am toying with the idea of putting in a flow diverter between the bellmouth and the bottom baffle to help guide the air up the pipe rather than allowing it to spin.

Many thanks to all the contributors on this site. I have been planning a top hat and some thoughts have crossed my mind on this idea.  I think the wall friction is why the dust tends to collect there.  The dust has more frictional losses than the air. To enhance this design a spiral vane (propeller of sorts) inside the feed pipe will tend to spin the dust to the outside before it gets to the smaller pipe separator.  Depending on the extreme of the spiral, flow straighteners may be needed in the smaller receiving pipe to minimize pressure loss.  The other thought would be that the collector Y be much larger but retain the narrow clearance where the small end of the pipe is.  The larger volume will take the wind out of the dust and the back pressure may be less.  Also, the Y could be tilted so that the cavity of the Y uses gravity to keep the dust flowing down the Y.