Cyclone to the first fitting, distance?

[Jim Andrew]

I need to lower my cyclone so it will clear my ceiling, my piping is on top of the ceiling joists in my shop, and the cyclone sits high up, and now I'm finishing the area where the cyclone is located, and would like to install 2 45 degree elbows and lower the unit about 2'. Read on a thread sometime back about there being a distance from the cyclone to the first fitting for the cyclone to operate correctly, could someone please advise?

[fred klotz]

I've just finished a new (to me) cyclone install, and had done plenty of research on just that question. General consensus was minimum 3 pipe diameters.

[Dan Hintz]

As with electricity, water flow, etc., any issues disappear into the noise floor at roughly 10x the constrictor (in this case, pipe size). So, ideally you want that figure, but you'll see increasing restrictions as you go shorter... I would also consider 3x a bare minimum, but the law of logarithms plays here, so don't try to shortchange if at all possible.

[Mike Cruz]

When I got my ClearVue, the instructions said something like at least 4 or 5 feet (IIRC) of straight pipe feeding into the opening of the cyclone (6" pipe). Because of my setup, I simply CANNOT do that . I've got a fitting within about a 1 1/2 feet of the intake. Still works fine. Maybe not absolutely per specs, but works fine...

[Wade Lippman]

I didn't know that and have a 90 immediately. I have plenty of power even when I forget to close all the blastgates and good separation. What more would I have if I had done it properly?

Three previous posters all ended their names in "Z"! You don't see that every day.

[Mike Cruz]

Wade, I'm not so sure that the straight line to the intake is about power...I "think" it is more about having the air that is going into the cyclone going in in a straight line, as opposed to going in with some sort of curve or bend. I know I didn't describe that correctly, but I hope it makes enough sense. I don't know enough about air flow to tell you exactly why it might make a difference, but apparently it does for maximum efficiency. I'm pretty sure it has to do with the design of the cyclone body and how the air is "supposed" to travel through it...wanting/needing air to enter in a straight line with no bends creating directional flows that will altar the path of the air as it spirals down the cyclone body...but that is just a guess.

[Wade Lippman]

I understand and don't doubt that straight flow is better all things being equal; but all things aren't likely to be equal unless you have very high ceilings.
It can't very well be about separation; once it hits the impeller it doesn't much matter what went before.
So if it isn't about power (ie. suction), then what else is it?

Its been a while since I was an engineer :), but it is hard to see how adding 5' of pipe to my system (instead of having the 90 directly off the cyclone, moving the cyclone over 5' and adding a 5' pipe; which I could actually do by cutting some shelves down and swapping the shelves and cyclone positions...) would help anything. I suppose it would give turbulence from the 90 a chance to die down, but does the impeller care all that much about whether the air is turbulent?
I hope I am not coming across as argumentative, but I just don't see it. I would think the extra 5' of pipe would add drag to the system.

[Mike Cruz]

Wade, my impellor is after the air has gone through the cyclone, not before. So, the air is going straight into the cyclone with whatever turbulence that is created by the bends before the cyclone body.

[Robert Payne]

The primary reason for an extended straight duct entry into the cyclone is to reduce turbulence inherent with airflow through elbows and to promote a more laminar flow as the dust laden air enters the intake ramp of the cyclone. Separation will be better with "laminar" flow (I put the word in quotes since there is always some turbulence). The air getting to the blower is well past the separation section in most cyclones (unless they are "push-through" designs like Alan Shaffter's), so turbulence in the center of the cyclone below the impeller is of little issue here. In the push-through design, turbulence can be reduced by a longer straight entry as well. I suspect the percentage improvement will be in single digits at best, so it certainly is not a make or break decision (testing might reveal some actual improvement levels).

[Ole Anderson]

In my case, I couldn't get a straight piece prior to the cyclone, I had to use 7" aluminum flex and an adjustable bend to make up the final connection. I don't think it affects the amount of flow or suction you get other than friction losses from the bends. It has more to due with wanting laminar (non turbulent) air flow as you start the spiral in the cone of the cyclone. And I presume that is so that the dust and chips swirl in the best fashion possible so as to maximize cyclone dust removal efficiency and reduce loading on your filter. My poor entrance setup probably explains why I get more into my filter than I was hoping for.

[Wade Lippman]

You are absolutely right about where the impeller is! I suppose turbulent air would affect separation in the cyclone.

But... I have emptied my 35 gallon dust bin three times since I bought the cyclone 6 months ago and there is maybe 2 cups of dust in the bag below the filters; so my separation is still pretty good.


Sorry about the foolishness about where the impeller was. I got to sleep about 1 last night, woke up at 3 and realized I forgot to put my son's bike tire in my wife's car like she asked. So I went out and did that; leaving a note that she shouldn't buy new ones unless the bike store guy said it was necessary. I got back to sleep about 6, and at 7 my wife woke me up to ask why I left her a note about tires; what was wrong with her tires? So I am a bit under the weather.

[Jeff Duncan]

Just out of curiosity....if your duct work is on top of your joists.....why not raise the cyclone up to the duct instead of lowering it?

JeffD

[Jim Andrew]

The duct is straight into the cyclone now, but I'm doing a shop improvement and putting a ceiling where the cyclone is. Want to bring it down under the ceiling. I'll have a nice room with storage for my plywood and lumber when I'm finished.

[Michael W. Clark]

Generally 6 duct diameters or more of straight is preferred. However, the main concern is that you do not install a horizontal elbow that puts the air spinning opposite to the cyclone rotation. May be confusing without a sketch.

The straight duct is a marginal improvement, not a deal breaker.
Mike

[fred klotz]

I don't think the issue of straight pipe is power, but turbulence, form what I've read. And the impeller/fan is after the cyclone in the flow of debris, so nothing but dust should be hitting it. Cyclone manufacturers make a pretty big deal about the slope and shape of the intake, so i would think that turbulence at the intake would have at least some effect on the dynamics in the cyclone.

The cyclone I just installed was removed from a friends shop, and it had a tight 90 degree ell right at the intake, and the ducting in general seemed to not be optimal. The larger portion of his debris was sanding dust, as opposed to chips and shavings. When I dismantled the four large bag filters and emptied the cyclone canister, there wasn't anything but fine dust in the bins at the bottom of each bag. No larger debris. So the cyclonic separation seemed to work just fine with no straight pipe on the intake.

[Jim Neeley]

FWIW, I called Bill Pentz and asked this very question on my Clearvue.

His recommendation is to try to allow 6' of straight pipe on the inlet to the cyclone to get the best fine dust separation. His tests showed little gain past that point.

He said that pushed more of the fines to the outer perimeter of the cyclone, where more of them will settle and drop into the collection bin.

I then told him my two options were 3' of straight pipe and using 2 90's (with straight pipe in between) or come off the cyclone with a 45, 4' of straight pipe and another 45, knowing he recommends avoiding using 90's where possible. He told me I'd get the best separation if I use as much straight as possible and then use the 90's.

Just one man's opinion, FWIW..

Jim in Alaska

[Alan Lightstone]

Wow. This is all news to me. My 5HP Oneida cyclone goes directly into a long sweep 90 degree turn, and after emptying at least 15 bins from the dust collector I finally emptied the fines box at the bottom of the filters and there was very little in them.

So while this may make perfect sense theoretically, and perhaps be more important with a smaller cyclone, I can't say that my system is lacking for performance or air quality safety by plumbing it the way I did.

275150

[Wade Lippman]

FWIW, I called Bill Pentz and asked this very question on my Clearvue.

His recommendation is to try to allow 6' of straight pipe on the inlet to the cyclone to get the best fine dust separation. His tests showed little gain past that point.

He said that pushed more of the fines to the outer perimeter of the cyclone, where more of them will settle and drop into the collection bin.

I then told him my two options were 3' of straight pipe and using 2 90's (with straight pipe in between) or come off the cyclone with a 45, 4' of straight pipe and another 45, knowing he recommends avoiding using 90's where possible. He told me I'd get the best separation if I use as much straight as possible and then use the 90's.

Just one man's opinion, FWIW..

Jim in Alaska

I don't doubt he is right. If I had 6' of straight pipe, instead of 0', I might have reduced the blow through on 100 gallons of dust from 2 cups to 1/2 cup; but I don't think I would care. The difference between 99.88% separation and 99.97% separation is having to spend a minute each week cleaning the filter instead of each month.

[Alan Schaffter]

I don't doubt he is right. If I had 6' of straight pipe, instead of 0', I might have reduced the blow through on 100 gallons of dust from 2 cups to 1/2 cup; but I don't think I would care. The difference between 99.88% separation and 99.97% separation is having to spend a minute each week cleaning the filter instead of each month.

If you are getting two cups in the filter bag, how much dust is impacted in the filter pleats? Is that two cups after carefully cleaning the filters or is it just collecting there?

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http://www.ncwoodworker.net/pp/data/1329/medium/P10100401.JPG

[Wade Lippman]

If you are getting two cups in the filter bag, how much dust is impacted in the filter pleats? Is that two cups after carefully cleaning the filters or is it just collecting there?





It is 2 cups after cleaning the filters half a dozen times over 6 months. I expect a certain amount is seasoning the filters, but that would be true regardless of the efficiency of the cyclone. X cups is stuck on the filters, and 2 cups, or 1/2 cup has fallen to the bottom depending on the amount of straight before the machine.
The grizzly has a cord that runs a brush up and down. It doesn't seem to do much, but the suction is very strong, so I guess it is adequate.