Inputs and larger top hat build

[corydoras]

Hi,
I have had great success with several baffle builds for 5 gallon buckets and shop vacs. I also built a top hat for a 40 gallon trash can to use with my 3/4hp dust collector.
I have now outgrown the small DC, and  at a demolition of a production line at work I found a dust collector that I ripped the fan out of to use for my new build.
Its a fairly large fan with a 14" steel diameter fanblade, and 6" tall, so it move a huge amount of air with the 3 hp motor.
I put a VFD on it so that I have full control on speed, ramping and current.
BUT, my major issue in my setup is that my basement shop has very low ceilings and the largest piping I can install are 4"
I would have preferred 6", but sadly there is not enough headroom. The longest stretch of pipe is aprox 21 feet, containing four 90 degree turns.
I run pvc pipes, and unfortunately no long sweep bends.
With the small dc and the thien top hat I managed to get 2300FPM at center of pipe inlet.

The new large fan has a 10" inlet, and I have built 3 filterbags on the exhaust with a diameter of 8" and 68" tall.
I will get some photos of my setup tomorrow.

I am going to build a new top hat, and was thinking about making it 23" in diamter and 11" tall.
I have two 4" pipes coming in from different parts of the shop, And was wondering if I should make an inlet with the 2 pipes stacked,
Normally Only 1 pipe will be used at a time, but I might reconfigure the lines, so that I get for example one 4" line for the bottom of the table saw, and one 4" for the overhead arm dust collector.

I am planning on ending these pipes in a smooth transition to a square inlet.

My major question is What size pipe would be best for the output?

Would it be wisely to make a 10" output, as long as I only have a 4 inch line on the input? ( maybe two in the future, or more),
So if I add more pipes later on, I will not have to rebuild., But are there any negative sides of using 10" in my setup?

How will this affect the FPM in my lines?

Any info is greatly appreciated

Best regards
Roy
Norway

[nucww]

Some thoughts to ponder:
- Larger pipe is so much better for high flow that you may look at other alternatives like:
--Figure out where the ceiling joists run.  Situate your DC so that you can remove the ceiling surface until you see the joists and run the pipe between the joists.  If you care, you can redo the ceiling and only have the pipe entrances and exits showing.  I only had to remove insulation for mine.
--Any PVC bigger than 4" gets really expensive for the connectors.  I used 5" HVAC ducts, used two 90 deg elbows to make more gradual turns. Tape all joints; it makes a huge difference in air flow.
--Y connectors are expensive and/or not available but you can make them out of straight metal duct.  Online calculators can give you the patterns to cut. It doesn't have to be exact, there is tape and putty to use to make it air tight. 
-The only negative of a 10" outlet that I can think of is that with these high flows it may be too close to the inlet flow near the perimeter (only 6.5" away) and dust may bypass the collector.  This may be one of those things that you try it and if it doesn't work well enough, try something else like a tapered pipe that's 10" at the top and maybe 6-8" at the bottom.
-You have so much flow that maybe a cyclone may be better.
-A large trunk line to the collector with 4" feed lines off it would solve the dual 4" inlet pipe issue.
-It sounds like you will have enough flow to have more than one 4" line active at once which can be effective for tools other than a table saw like a sanding table which needs very high flow.
-If you are scientifically inclined, there is information to estimate the effect of using different size pipe runs.  In the end, its a comparative calculation and you will have to guess the effect unless you know the CFM characteristics of your DC versus pressure drop.
Everyone's situation is different with space, layout, tools, $, time, DC, etc.  I hope some of these ideas may be useful for your situation.

[corydoras]

Thank you very much nucww for taking the time to reply to my questions.
You have a lot of interesting thoughts.

As I live in the metric part of the world the drain pipes are actually 110mm, and have rubber sealing in the joints, so they have absolutely no leaks.
Unfortunately my shop configuration makes it "impossible" to use any larger pipes, as I have to do most of the lines across the joists, and therefor have to stay below.
Crossing close to a wall is an option, but most walls are occupied with cabinets and such.

I think I will try to see how it works.

I temporarily tested the new fan with the old separator and got a pretty decent airspeed at the intake point of the longest pipe run.
The longest one has a round to square adapter, as it is connected to my cnc, but managed to get 4500 fpm

I will do some testing with a larger 8" pipe between the fan and the top hat, but I am unsure if this will make any difference, as the bottleneck are the 110mm piping with its restricted air volume capacity.

I also added the 3 filter bags temp. and they did not affect the airflow.
They will have a dropbox for any fine dust passing through the separator to fall into when I shake the filter bags.

I attached a couple of construction images for fun.

Thanks again for taking the time to write down your thought, but as you say, maybe the main issue here is the 110mm pipes, and I have reached the limit of what they are capable of moving

[EPMiller]

In the HVAC industry we use oval duct to fit in restricted spaces.  I don't have my ductulator here, but my guess is an ovalized 7" or 8" pipe would do the job to fit in your max 4" headroom, depends on how much you have to flatten it.

[kayak]

I have no idea if this is viable or not.  Would a rectangular duct with a cross section area equal to that of and 8 or 10 inch round duct be usable in a dust collector system?