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.

[Joe O'Leary]

Try this: http://www.woodworkforums.com/f200

Tons of info (and Aussie humor!)

[Peter Christensen]

This PDF (http://www.lorencook.com/PDFs/Catalogs/Cookbook_Catalog.pdf) was brought up and discussed in that Aussie forum that shows the comparison between a pair of 45s and a single 90. If you look at page 54 you will see the values of how much straight duct each type of fitting creates. The three piece 90 is the worst for drag and it does resemble a pair of 45s and a short section of straight pipe. Even if you prefer the numbers from individual 45s added together with straight pipe they are still higher than the 90 with a 1 or 1 1/2 or more radius. Fewer direction changes are better.

I just found the Loren Cook Company have a number of design downloads including apps. It wouldn't let me download the desktop version, probably because I'm north of the border and I'll have to figure out my Apple password to get the apps. :rolleyes: Thought it might interest some of you.

http://www.lorencook.com/downloads.asp

[Chris Parks]

I am no longer commercially involved with Clearvue due to retirement so anything I write is my view and should not reflect on them in any way.


To keep it simple and avoid confusion when I was selling Clearvues the way I explained it was as follows and keep in mind that we do not recirculate air through filters in Oz as it is not necessary. Very few workshops here have either AC or heating.

If you buy a CV1800 you can hook it up to 6" ducting to the machines and it is plug and play, no duct design, no need to get fancy with inlets etc because it has enough performance overhead to take care of the deficiencies that might be there in the installation. If using a Max, 9" main duct, 6" from that to the machines and if only using one machine at a time then leave an overhead blast gate open to scrub the air as the Max can extract from two 6" lines at the same time. In reality if you are using only one machine at a time and are not going to leave a blast gate open it is doubtful that a Max is a huge advantage at all IMO unless you have a very specific reason to use one. The reason the Max came into being was that if the 1800 was used outside the US/Canada?? it runs at 50hz and this results in an impeller speed of 2850 RPM which drops the air flow below the optimum requirement. The Max at 50hz matches the 1800 at 60hz in airflow through a 6" duct. It most probably slightly exceeds it but I have no evidence to prove that.

If using a generic a 14" impeller or less that is when you have to put your thinking cap on and minimise to the n'th degree all losses because to get anywhere near the performance often quoted as a minimum by the experts then you have to optimise everything from the initial inlet to the exhaust and absolutely avoid using less than 6" ducting. This means that every machine we use needs modifying as the ports on them are too small without exception. You need to do this on every installation in reality but on the less capable extractors it must be done.

Explaining DE that way generally made the lights come on for the customer, it was simple, did not add any more confusion and if they bought the machine they never had any performance issues. I have never had to do any duct design for an average workshop though I see people saying it is necessary all the time in this forum, most workshops are simply not big enough to need it and very few if any one has the knowledge or test equipment to do the necessary testing. The one criteria that must be used is the ducting has to be 6" to all the machines and the ports on the machines opened up to flow the maximum into the duct.

All cabinet machines such as table saws & bandsaws must have enough air inlet into the cabinet to allow the maximum flow out of the extraction port, air in must equal or exceed air out, pretty simple really. A lot of thicknessers do not have good air flow and the hood needs a lot of work to fix it.

[Joe O'Leary]

Very well said, Chris and exactly the same advice I got just today from the CV rep today. They have a sale on the 1800 equipped with the 16” impeller.

[Larry Frank]

Chris is correct about duct size with larger dust collectors. You can pull very good CFM and suction through 6" duct. I have a 5 hp Oneida Super Dust Gorilla and no issues with 6" duct. With smaller ones like the HF, you need to be super careful with duct design.

However, it is not always necessary to enlarge the dust ports on the machines. With a larger dust collector, you may be able to achieve adequate flow with a 4" port. For example, I get 670 cfm with the 4" port on my Sawstop. Would it be better with a 6" ? Yes, but is the improvement worth the effort...in my case probably not.

[Chris Parks]

Chris is correct about duct size with larger dust collectors. You can pull very good CFM and suction through 6" duct. I have a 5 hp Oneida Super Dust Gorilla and no issues with 6" duct. With smaller ones like the HF, you need to be super careful with duct design.

However, it is not always necessary to enlarge the dust ports on the machines. With a larger dust collector, you may be able to achieve adequate flow with a 4" port. For example, I get 670 cfm with the 4" port on my Sawstop. Would it be better with a 6" ? Yes, but is the improvement worth the effort...in my case probably not.


How did you measure the air flow?

What is adequate air flow and why is it not worth opening the dust port? Why wouldn't you want to maximise the air flow?

Larry, I think this is precisely the stuff that confuses people as it instantly raises questions that haven't been explained in your post. If I say to someone it is simply 6" all the way from machine to dust extractor that is as clear as it can get, enlarge the ports, hook up the dust extractor and press G for go. If the question is how to get a small impeller to pull 1000 CFM through a 6" duct then it gets harder, not in the duct design itself but in the ends, both entry including dust hoods and where the duct enters the DE and it will be a lot of work and usually more expense. I can't expand here on years of work that has been done in Oz, there is simply too much of it so it will require going there and reading what has been done. I am sure Peter C. will back me up on this as he has read it all.

[Joe O'Leary]

Chris, et. al.,
Fascinating reading on the Oz site about bell mouth entries. I need to drastically improve this on my General cabinet saw and SCM band saw. If I cut 6" holes, I assume it would benefit by having the inside of the entry be BM and let it act as inside flange. Does this make sense?

[Chris Parks]

Chris, et. al.,
Fascinating reading on the Oz site about bell mouth entries. I need to drastically improve this on my General cabinet saw and SCM band saw. If I cut 6" holes, I assume it would benefit by having the inside of the entry be BM and let it act as inside flange. Does this make sense?

A bell mouth will always increase entry air flow into a duct. We first started talking about this stuff a few years ago and I used bell mouths on car carburettors so dug out a few old books on it and things moved on from there. As I said in a previous post you must have air entry matching extraction in a cabinet machine.

[Larry Frank]

Chris...I posted how I did this and my results on SMC. However, the post got edited by a moderator for some reason and now is difficult to read. I used a hot wire anemometer and measured multiple positions across the duct. I used a digital meter to measure static pressure. I also checked the meter against a U-tube manometer. The performance curve that I developed was similar to the manufacturer curve but slightly lower. I believe that is as accurate as reasonably possible without going to rigorous testing and more expensive equipment.

Why wouldn't I want to enlarge the port? I do not want to spend the time to chop up my Sawstop and do not want to change the insides. To do a proper job means a lot of work on the inside ducts and such. It would mean changing the inside flex hose to a larger size and completely changing the area around the bottom of the blade. Unless you also do these things, it makes little sense to change the port size. Several of my machines would be extremely difficult to enlarge the port. To me the question is really how effective the current port works. I have a Supermax 16/32 sander with a 4" port and it works very well. I am not satisfied with the idea that one needs to change all the 4" ports on machines to 6". As I said before, the necessity is driven by the dust collector that you are using and how it works with your 4" ports.

Changing the port size is a ROI calculation . Is the cost in time and money going to make a big enough improvement? With my system and tools the answer is no. However, I have the advantage of knowing the real performance of my system. Many people with the HF or 1.5 - 2 HP dust collectors either do not know the true performance or think it is much better than it is.

[Jeff Bartley]

If 7" mains are better for a CV1800, and 7" pvc is not available, has anyone here mixed metal with pvc? Seems like using a 7" metal main with 6" pvc drops might be a good combo?

[Chris Parks]

Chris...I posted how I did this and my results on SMC. However, the post got edited by a moderator for some reason and now is difficult to read. I used a hot wire anemometer and measured multiple positions across the duct. I used a digital meter to measure static pressure. I also checked the meter against a U-tube manometer. The performance curve that I developed was similar to the manufacturer curve but slightly lower. I believe that is as accurate as reasonably possible without going to rigorous testing and more expensive equipment.

Why wouldn't I want to enlarge the port? I do not want to spend the time to chop up my Sawstop and do not want to change the insides. To do a proper job means a lot of work on the inside ducts and such. It would mean changing the inside flex hose to a larger size and completely changing the area around the bottom of the blade. Unless you also do these things, it makes little sense to change the port size. Several of my machines would be extremely difficult to enlarge the port. To me the question is really how effective the current port works. I have a Supermax 16/32 sander with a 4" port and it works very well. I am not satisfied with the idea that one needs to change all the 4" ports on machines to 6". As I said before, the necessity is driven by the dust collector that you are using and how it works with your 4" ports.

Changing the port size is a ROI calculation . Is the cost in time and money going to make a big enough improvement? With my system and tools the answer is no. However, I have the advantage of knowing the real performance of my system. Many people with the HF or 1.5 - 2 HP dust collectors either do not know the true performance or think it is much better than it is.

If the machine port is not enlarged why use 6" ducting, wouldn't that be a waste of money?

[Larry Frank]

No not a waste.... it allows me to deliver the best flow and static pressure to the machine cheaply and easily. If I ran 4" duct from the dust collector to the machine the static pressure loss would be significant.

[Peter Christensen]

What I plan on doing to the SawStop is cut out the 4" port and let the 4 inch hose sit in the opening of a 6" (or 7" tapering to 6", perhaps using a slightly longer 4" hose so it stays in place when tilting the blade. That will still clear the 4" and scavenge the rest of the cabinet of the dust getting by the blade shroud. The hose in the bigger port will also straighten out the excess hose that has the sharp bend in the existing design that allows tilting and adjusting blade height.

[Larry Frank]

That is an interesting concept of how to increase the size of the port on the SawStop. I took a look at my SawStop PCS and noted that there are a number of holes in the cabinet both ust up under the cast iron top and in the sides. This would allow a lot of air into the cabinet and reduce the sawdust in the cabinet. However, my thought has been that I want the dust collection as close to the source as possible. The current as purchased configuration directs all of the flow up around the saw blade. It works pretty well. I am wondering what will happen if you do as Peter suggested. I think a lot of the flow will come from other openings on the cabinet and not directly from around the blade. If you have a large dust collector, it probably will be fine but with a smaller one you may not have sufficient from around the blade. After looking at my Sawstop, it is not something that I would try. But, maybe you try it and it works great.

[Joe O'Leary]

Larry, Peter,
Do you guys have some pics. Hard to visualize what your referencing.
Thanks

[Peter Christensen]

I took some pictures for you but excuse the dust. I'm using a 2" vacuum on it until I get the CV-Max setup, but it was no better when I had the 4" hose to a 3hp DC. There are two shots are from the top showing the chute around the blade with the blade raised and lowered. Two more from the underside of the extension table also blade raised and lowered. You can see that the top of the chute is not touching the top and dust gets out from around it into the cabinet. You can also see how much the hose is made into a very tight radius but it can't be shortened to straighten it because the hose won't be long enough when the blade is tilted. If one still didn't want to cut a bigger hole in the base the belt access door on the left side of the saw could be replaced with a panel and hole for another port in it. That would help scavenge the dust in the cabinet but it's half way up so there would probably be some larger dust settling on the bottom.

[Joe O'Leary]

Thanks, Peter.

I have an "open" shroud around the blade on my General 650. The first pic is the 4" port below the access door, which is open. That port is a 6" run from a 6" main run from a Jet 1100 C. Does virtually nothing. Second shot is from same direction, but closer and higher. You can see the cast iron shroud around the blade. The bottom of the shroud is a 3" X 12" opening. ofThe other side of the shroud has a similar open profile, which you can see, looking down from the table top.
I'm thinking of hooking an HVAC transition fitting to a 4" round and enlarging the machine port to 6" when I get my CV 1800 (16").
390926 390928 390929

[Peter Christensen]

Makes you wonder if the designers at General weren't talking to each other. The guy doing the trunnion wanting a 6" hose to the shroud (36 sq ") since the area is close to the 28 sq " area of the hose but the guy doing the cabinet did 4" because they had the parts and tooling for 4". Was there ever another piece below the shroud on those saws?

Are you going to have a pipe going to a blade guard too? Or just doing an under cabinet pipe? With my CV-Max I can run a 6" under and another 6" over the saw.

[Joe O'Leary]

There was never another piece. I think when I bought it, any 4" port anywhere was considered big.
Yeah, I need to build a blade guard, too. I'll run 4" to that. The Shark Guard stuff is very nicely made, but a little steep in price.
I think it's a fair price for the quality, but a lot to spend on a blade guard.