Duct size for Clear Vue 1800

[Matthew Curtis]

I am planning on getting the Clear vue 1800 cyclone that has a 6" intake.

Does it make sense to use a main run that is larger than 6"? My thought is that this will slow the flow down in the main duct too much, and not increase overall volume of air moved due to the restriction at the cyclone inlet.

What is the best thing to do? Keep the 6" main, or go bigger?

[Jim Becker]

No, your main duct will be optimized at the inlet size they provide. Running larger may hamper performance.

[David Kumm]

It is not true that you must or even want to run the same size main as the cyclone inlet. The longer the run at 6" vs 7", the higher the static pressure and the lower the cfm. The 15" blower will benefit from a main run of 7" eventually dropping to 6". If I were buying, I'd go with the max or at least find out if the cyclone with the 8" inlet cost much more. Then I would reduce down to 7" but have the ability to swap at a later date. A 15" impeller can handle an 8" main for some distance but I'd not run that with a 6" inlet. The CV was originally designed to use with 6" pvc as it is cheap but the system will perform much better with a larger main. Dave

[Matthew Curtis]

Doesn't the inlet size essentially determine/ limit the volume of gas regardless of duct size, and decreases velocity in the larger duct. looking at the fan curves the 8" duct performs with less cfm as compared to the 6".

[Chris Parks]

Yes and no. The duct being longer and thus having a large surface area will benefit by being larger in area up to a point and seat of the pants past experimentation has shown a 7" duct is beneficial in that regard. Some people have been putting the 16" fan in a 15" housing which seems to work well. Another advantage that can be gained is to use a three phase motor and vfd and run it faster that 60hz, I run mine at 65hz and it hasn't exploded yet and I wish I could by 7" ducting but it is mission impossible in Australia.

[Larry Frank]

I have the similar Oneida SDG unit with mainly 6" PVC. It has plenty of capacity and any improvements will be minor going to larger ducts and more expensive.

Is there a worthwhile return on investment?

[Chris Parks]

I have the similar Oneida SDG unit with mainly 6" PVC. It has plenty of capacity and any improvements will be minor going to larger ducts and more expensive.

Is there a worthwhile return on investment?

By minor what do you mean? Unless you have optimised absolutely everything from modifying the dust pick ups, dust hoods, machine ports, running 6" to everything, bell mouth pick ups, minimised flexy hose etc where applicable then it can always be improved. Is it worth going to all those measures? that is a discussion between you and your lungs.

[Larry Frank]

I thought that this was a discussion on duct size. I measured 1360 cfm at 4.85" SP with a 6" duct. Based on the Pentz info this is sufficient.

I made no reference to pickups, flex hose and the OP did not mention them. Of course these are all important but not in the original question.

I certainly support all efforts to do a better job of getting dust at the source. Getting good collection at the source is the most difficult thing to do. It seems the majority of people remove the guards on the table saws because they are not convenient and a lot of dust goes in the air. Maybe we need more threads on dust pickup ideas.

[David Kumm]

The problem is that the fittings, flex, and machine design all add SP so the working pressure might be in the 8-10" range. Reducing the pressure by even an inch is huge when you get to the high end of the curve. If you are using steel, the larger diameter is a no brainer. If you are set on PVC, you are limited and can never really do much to upgrade but you still have a pretty good system for newer machines. Dave

[Chris Parks]

Larry, I was picking up on your point of "minor possible improvements" As David points out the system has to be treated as a whole and if that hasn't happened then there are always improvements to be had. There has been some changes in the thinking since BP did his original work and things have been found out that explode some of the thinking that was thought to be good.

[Joe O'Leary]

“There has been some changes in the thinking since BP did his original work and things have been found out that explode some of the thinking that was thought to be good.”

Chris, can you give some examples of these changes you mention?

[Chris Parks]

The main one is that bends that are shorter flow better which is exactly opposite to what we all assumed and yes there are flow tests to prove it in the Oz dust extraction forum. As for the CV1800 a lot of guys in the US have found that 7" pipe will flow more air that the usual recommended 6" pipe. There has been a lot of work done on pipe inlets in Oz using bell mouth entries and that also picks up the flow rate a fair bit. All the bag/filer style generic dust extractors leak air and consequently dust without exception unless a great deal of care is taken to fix them and this has become apparent in the last few years with a lot of testing on different machines.

[glenn bradley]

And therein lies the hazard of being too black and white in dust collection threads. Air has mass. Moving a larger mass will be different than moving a smaller mass. Air speed, volume, so many things factor in; figures and truths supplied for one instance may not apply in yours. Facts and figures are base line input information to help you make an informed decision. Sifting through the threads for the info that is applicable to you is your task.

It is pretty certain that folks that know how, and have experience and test equipment to confirm, could come into any one of our shops and tweak our systems to improve performance. It is also pretty certain that there are some pretty terrible DC builds that have been cobble together over time. My oversized bagger comes to mind. Lots of good info here and elsewhere. Enjoy the journey.

[Joe O'Leary]

"bends that are shorter flow better"

Chris, does this mean we're better off with a standard 90º el than two 45's , for example?

[Roy Petersen]

there are flow tests to prove it in the Oz dust extraction forum.

Have a link to that thread or forum you can share? I'd like to read some of that.