I'm considering scrapping my 120mm dust collection system and replacing it with larger diameter ducting. After a few airflow tests using the Dwyer 477AV-2 and 166-6 pitot tube, I'm confident the ducting is limiting the performance of my system.

I have a 3HP blower assembly connected directly to an Oneida steel Super Dust Deputy and a pair of Wynn 35BA222NANO filters. The ducting is 120mm (4.7 inches) Schuko steel tubing with lots of bends starting at the SDD. Now that I've had time to use the system I installed, I'm ready to sacrifice style over performance where needed and make the ducting from the SDD to the first 45-degree branch connection as straight as possible, even if it means tearing up some of the gypsum wall board to ensure there is enough unobstructed room for the duct. I can patch the walls later. There will still be some bends along the wall and ceiling, but not as many as I have now. I can also eliminate at least one of the branch connections, as it's not needed now.

For now, I'm keeping the blower, SDD (with the 5-inch inlet), and filters. I'm looking for a European source for the SDD XL that has the 6-inch inlet, or equivalent, that will fit in my DC closet. For the ducting, I have a choice of 150mm (5.9 inches) and 160mm (6.3 inches) in steel, or 160mm PVC S&D pipe with a 152mm (6 inch) inner diameter. All are readily available locally, and the source for the steel duct is where I bought my saw and existing ducting. They will likely take the 120mm duct in partial trade towards the new duct.

The pro for the 150mm and 160mm options is all of the fittings, angles, branches, couplings, reducers, and blast gates are available from one source in Mannheim, which is a 20-minute drive from me. The con is the cost, but I'll suck it up. The pro for the 160mm S&D pipe is the price and availability of angles and 45-degree branches. The selection of reducers is limited and the only source of blast gates that should fit (assuming I don't make my own) is Clear Vue. The Clear Vue gate is the only one I found that appears to fit over the S&D pipe.

I will buy a two sections of 2-meter 160mm S&D pipe, along with a rubber coupling to fit the SDD inlet. I'll reposition the SDD in the closet so the pipe can connect directly to the inlet without any bends so I'm eliminating as many variables as possible. I'll also pull down enough pieces of the existing duct to make a 4-meter section of the 120mm duct and test it the same way. It comes apart easily in 1-meter sections.

Here are my questions, but understand there are physical limitations in my shop that prevent me from making LASER straight duct runs to the equipment. Also, the measurement for the steel ducting is the inner diameter.

1. Am I chasing unicorns trying to improve the performance of my system?

2. Given the options of the 150mm steel, 160mm steel, and 160mm (152mm ID) PVC S&D, which is the preferred size for my blower assembly, SDD, and filter pack? I don't want to install ducting that is too large and wind up with a lower air velocity that can't pull the dust and chips to the cyclone.

3. Is there any return on investment (mostly time) on replacing the steel SDD with the SDD XL? I bought the steel SDD during one of my trips back to the States. The shop had it in stock and I was able to repackage it for mailing through the USPS. I think the SDD XL might be too big to mail, so it might not be available to me unless I can find a stocking distributor or pay to have it shipped as freight.

Time and money are two resources I have, but I only have one set of lungs and want to keep them in the same healthy condition. My shop is completely contained in a finished basement with a low ceiling and no external access, so any dust created has to be dealt with by the DC system.

Thank you in advance for any advice!

For reference, here is the thread describing my shop DC build and showing the duct routing:

Dust Extraction Routing - High or Low?