Hi I'm Will, new member from the UK here.
I've joined because I've decided to build a Thien top hat for my dust extraction system, after lots of reading here I have gleaned lots of useful knowledge, I still have a couple of questions.
So, my plans are for a 100mm diameter PVC ducted system with a round to rectangular transition feeding into a 438mm diameter separator through a 40mm wide drop slot into a 70l dust bin below.
The (100mm dia) round to (195mm x 40mm) rectangular transition is built from 3mm plywood and I have started on the bottom plate of the separator. I plan to use a 550cfm blower to power the system.
Various calculations show that I should achieve about 6800fpm velocity through my 100mm pipework which is plenty more that the 4000fpm minimum required to entrain air with dust.
The transition's rectangular end is 195mm high and 40mm wide to match the drop slot width. The round end is aligned with the top inner face of the rectangular end to force the are to expand downwards towards the drop slot prior to entering the separator unit. Is this theory correct or should it be aligned with the bottom inner face of the rectangular end?
I have a question regarding the rotation direction through the top hat in relation to the blower unit. Is there any benefit to matching these? I don't really want to have to build an air straightener as well.
Anyway I hope someone can help. Thank you in advance
On the air straightener question - if you read through retired2's build thread you will find they improve performance quite a bit. They are not that hard to build. I used 2 pieces of aluminum flashing crossed in the outlet of the separator and epoxied to the sides.
Thank you for your reply Clydeone, I have read through Retired's thread, that was what inspired me to build my separator and also include the tall narrow inlet.
I've got an idea for how to build an air straightener doing something similar to what you have done. I think I will use some 40mm pvc pipe I have left over from fitting my bathroom, a single length inside the 110mm pipe with several radial fins of 1/8" ply supporting it. How long does it need to be? would 100mm be long enough?
Anyone any ideas on what to do about the height of the inlet? I am at a stage in the build that would allow me to put it either way up.
I completed the bottom plate and drop slot and fabricated the two rings that will support the top and bottom of the side walls last night, it is starting to take shape. I plan to use multiple narrow strips of 1/8" ply for the side walls, I have loads of this stuff nocking about in the workshop so I might as well use it rather than spend any money on clear plastic.
So, I have finished my separator.
In summary it uses 110mm soil pipe and a 1hp blower. The collection receptacle is a 70l plastic bin under the chamber, wedges under the bin maintain the seal to the underside of the chamber to prevent scrubbing. The chamber itself is about 480mm diameter by 200mm tall and constructed from multiple 3mm thick plywood strips. The top and bottom faces are constructed from 15mm thick MFC with a drop slot 40mm wide, the underside of the drop slot has a heavy chamfer to assist in capturing the rotating debris. The round the rectangular transition is similarly constructed from the same material. The whole cart is mounted on locking castors to allow me to move it around the workshop though it will be permanently situated once the rest of the workshop cabinetry has been built.
I didn't bother building an air straightener, I thought I would try it without before going to that effort. However, I did replace the inlet plate on the blower with a sheet of ply and drilled out a larger hole to suit the 110mm pipe I used, the original diameter was about 90mm. This also gave me a suitable surface with which to mount it to the separator chamber.
Initial testing has shown there to be no bypass. Ultimately it will be hard plumbed in with the exhaust venting outside the workshop.
Thanks should be made to Retired for his thread which I used extensively in the design of my separator.