Please Check Ducting Design

[Dan Schmidt]

I'm purchasing ductwork, and I just received my first design recommendation from Air Cleaning Specialists (ductingsystems.com). The design recommendation surprised me a little bit, so I am looking for confirmation from any of you who have experience.
Dust Collector: Oneida SmartPro 5HP (1625CFM max) with 7" inlet
All of my machines have 4" ports and have min CFM requirements from 400-550 CFM

Attached are the 2 drawings showing the design recommendation in top and side views.

What surprised me a bit about the recommendation was the significant use of 4" ducting. While the machines are all at 4", I expected a recommendation for 6" ducting throughout (including the drops), and then a reducer to 4" after the blast gate. What would you do/recommend? I would normally not question the "expert" design recommendation, but this is an investment and I don't want to regret it.

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[Marty Tippin]

The only thing I might change would be to run 6"all the way to the table saw and change the port on the table saw to 6". You'll get far better dust collection. But that looks like the longest branch and the change will add to the cost quite a bit.

[Dan Friedrichs]

I would not buy that. This design looks like it was optimized like HVAC ducting, where multiple ports are open at the same time. Based on the equipment you're showing, you're a 1 man shop? So if you only have one port open, the system effectively "reduces" to just that branch. As a thought exercise, consider how you would run ducting if you had one blower per machine. You wouldn't go from 7" to 6" to 4"....you'd run 6" or 7" all the way to the machine. So....why does having more than one machine change that logic (hint: it doesn't. It only makes sense to do this stepped diameter ducting if you're designing for more than one machine in use at a time).

Why have a massive 5HP/1625CFM blower, if you're going to choke it down through a 4" port so it only moves 425CFM?

You should be running 6" ducting ALL THE WAY to the machines, and if the machines only have 4" ports, you should be enlarging them to 6" (or finding a way to add multiple ports - such as adding an overarm dust collector on a table saw to supplement the 4" port in the cabinet).

EDIT: Just want to reiterate one thing: You mentioned that you expected them to run 6" ducting then step to 4" after the blast gate. This is not ideal, either. 6" smooth-wall metal duct has slightly less resistance to airflow than 4" duct (because the air will be moving slower in the larger-diameter pipe), but that's really negligible. At these pressures, air is not compressing, so even reducing to 4" for a short distance absolutely kills the total CFM. A 4" port has 6x the static pressure drop as a 6" port (and, thus, significantly reduces your CFM, which is what you need to move dust).

I really think that if you're not going to bother increasing the ports on the tools to 6", you might as well not even bother with 6" ducting or a large blower.

[Ole Anderson]

I would also vote to run a 6" to your table saw, in anticipation of eventually going with table top collection and increasing your bottom to at least 5" if possible. Continue the 7" to the split to the TS. Also I would run 5" on the longer horizontal runs, sticking to a short 4" for the verticals. That is if you don't open up your ports.

[Dan Schmidt]

Why have a massive 5HP/1625CFM blower, if you're going to choke it down through a 4" port so it only moves 425CFM?
Because I have it, and therefore my question about the 4" recommended by Air Cleaning Specialists.....


should be running 6" ducting ALL THE WAY to the machines, and if the machines only have 4" ports, you should be enlarging them to 6" (or finding a way to add multiple ports - such as adding an overarm dust collector on a table saw to supplement the 4" port in the cabinet).
My thinking exactly. Some machines would benefit more by enlarging the port, others not so much, but I'm investing once in the ductwork hopefully so flexibility is key. Some of my machines cannot easily/practically be modifed with larger ports, so in these cases I'd neck down to 4"

[Dan Schmidt]

I would also vote to run a 6" to your table saw, in anticipation of eventually going with table top collection and increasing your bottom to at least 5" if possible. Continue the 7" to the split to the TS. Also I would run 5" on the longer horizontal runs, sticking to a short 4" for the verticals. That is if you don't open up your ports.
Excellent recommendation. I do intend to have overhead dust collection on the T/S, so your confirming my thoughts and I'll consider this one now a must....

[Dan Friedrichs]

There seems to have been a lot of threads, lately, where people have been advocating for 4" ducting in places. I'm not sure why that keeps coming up, but let me try to enumerate some basic principles for 1-man shop dust collection design:

1) More airflow (CFM) will capture more dust.

2) Blowers produce the most CFM when they encounter the LEAST resistance to airflow.

3) Smaller ducts have larger resistance than larger ducts. Thus, you should avoid smaller ducts. You should also avoid sharp 90 degree bends in ductwork, T fittings, etc, in favor of gradual bends, Y fittings, etc.

4) Just because a tool has a 4" port doesn't mean that's ideal. Smaller ports add resistance which limits airflow. Enlarge all ports to the same size as the ductwork, adding additional ports if necessary to reach the total equivalent area.

5) With only one gate open at a time, the rest of the duct is "idle", and can be ignored. In that case, there is no benefit to reducing from a main trunk down to smaller branches. In fact, it makes construction/assembly/repair more difficult, because now you have multiple different sizes of duct and adapters to deal with. Having different sized trunks, branches, and drops only makes sense in a multi-user shop with multiple gates open simultaneously.

6) Filter resistance also contributes to reduced CFM, so forget the filters (and cyclone), and vent outside, if possible.

7) The horsepower on the motor only matters if you've designed a system to utilize that power. A "5HP" motor coupled to a blower and a long run of 4" ducting is likely to perform about the same as a 1HP motor on the same blower and duct, because it doesn't take 5HP to move ~300CFM. Moving air is what requires power.




Obviously this is a complicated topic and I've ignored many secondary considerations. A few key caveats to keep in mind, though:

1) It is possible to overload a motor. If you remove the cyclone and filter (to vent outside) and use, say, short runs of 7" ducting, you may be moving so much air that you draw more than 5HP of power (and may trip a over-current protection device). In that case, you need to add more resistance to the system. It's good practice to measure the current draw of your motor once it's in the complete system to see how close to the nameplate current rating you are. This is a great way to quantify how well you've designed the system to maximize airflow.

2) It is possible to have horizontal runs where dust settles on the bottom of the duct due to insufficient velocity to keep it entrained. Be mindful of this if you have very long horizontal runs.

[Dan Schmidt]

Dan, we understand your point about smaller ducting. This was my understanding, and the reason I posted this given the "professional" recommendation shown in my drawing.
Once again, keep in mind that not all machines can be or should be hacked to accommodate larger ports. Some operate at 2.5" just fine.
Some machines have internal ducting and can benefit by increased velocity, not only higher CFM.
That said, I plan to shift this design to 6" ducting down to the machine, and where practical/possible increase machine port sizes. Your feedback confirmed my prior understanding - thank you.

[Dan Friedrichs]

Once again, keep in mind that not all machines can be or should be hacked to accommodate larger ports. Some operate at 2.5" just fine.


Absolutely, and sorry if I came across like I was being critical of you - not my intent at all. Rather, "professional" designs like this (and advice often given on this forum) are often presented that are completely contrary to any logical understanding of dust collection.

My bandsaw has a 2.5" port cast into the lower housing - I certainly am not about to hack that out :) But that, coupled with a 4" flex hose atop the table, works great.

[David Kumm]

I think part of the plan might be due to the Smart collector. They are set to adjust speed and operate better under pressure than a typical curved impeller set speed collector. While I'm not sure I would ever use 4" as a main, the smart will pull more cfm from a restricted size pipe than a typical impeller and doesn't pull as much full out as one. My problem with the design is that any change out of machine and you will be replacing a lot of pipe. My tendency would be to run 7" and 6" mains and always have two 4" gates open or at least partially open. That way you can later modify the machinery without reinventing the wheel other than at the machine. Dave

[Jim Andrew]

Dan Frederichs has really given you the right information. The "professional" who laid out your system, probably doesn't even work with wood. I have changed some of my machines from 4" to 6", and it was very beneficial. Especially my edge sander, and my small widebelt. The widebelt had 5". Found that the Grizzly G0453 planer does not need more than a 4" port, as it works excellent with the original port. When I had a 718 Woodmaster, the change to 6" made a huge difference. Some equipment is designed better for dust collection than others. One thing I have learned is, that a small hose over the blade on your tablesaw, is as good as a 4". My unisaw has a sharkguard with 4", and my Hammer slider has a 2" hose over the blade, and they work equally well.

[Anthony Whitesell]

I would check the design with StaticCalc from Bill Pentz website and correlate it to the fan curve for your dust collector.

There are some critical dimensions missing in the drawing in terms of duct runs and building size. It appears there is 30+ feet of duct between the table saw and the dust collector. Between the losses in 30 feet of duct, 2 bends, the wye, and the cyclone body, the loss is over 8"w.c.

Once you have the fan curve, if you are not in the working range, I would not spend a penny on that design.

[Alan Schaffter]

Another comment- why an orthogonal layout? To many 90° turns, longer runs (diagonal distance is shorter), too much SP (restriction.) You want the straightest runs from each machine to the DC. Though it might take more ducting, it would be better to have a layout that looked like a XMAS tree with DC at the bottom of the trunk with branch mains/branches coming off at 45°. Run 6" to all machines. The main should run straight from the DC to the TS with a single drop (split with blast gates at the bottom) for the sander, planer, sander. A secondary (branch) main should branch off at 45° and run straight to the bandsaw, while a 3rd branch main should run to the spindle sander and router table. (Blue) If possible, it would be better to locate the DC in the upper right corner. (Red)

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[Michael W. Clark]

Where did the design flows come from? I would suspect this is driving the duct size recommendation. The sander is the only machine that could have a larger duct specified based on a minimum of 4000 FPM for wood dust. When we design industrial systems, we look primarily at a minimum duct velocity based on the required flow at the hood/machine.

I don't understand the larger main either.
Mike

[Dan Schmidt]

Where did the design flows come from? I would suspect this is driving the duct size recommendation. The sander is the only machine that could have a larger duct specified based on a minimum of 4000 FPM for wood dust. When we design industrial systems, we look primarily at a minimum duct velocity based on the required flow at the hood/machine.

I don't understand the larger main either.
Mike

From the technical manuals of each machine.

[Michael W. Clark]

From the technical manuals of each machine.
If you go 6" ducting, you need to pull about 800 CFM. This will keep your velocity high enough so dust doesn't settle out in the ductwork. Probably a better operating point for your fan too.
Mike

[Anthony Whitesell]

Where did the design flows come from? I would suspect this is driving the duct size recommendation. The sander is the only machine that could have a larger duct specified based on a minimum of 4000 FPM for wood dust. When we design industrial systems, we look primarily at a minimum duct velocity based on the required flow at the hood/machine.

I don't understand the larger main either.
Mike

The larger main would allow multiple (two) machines to be used at once. As I mentioned earlier, I'm worried the SP loss of 4" duct over those long runs is going to put the SP/Flow off the fan curve. I have a DC that can provide the 400CFM in 4" duct...barely. It works OK for chip collection, but stinks for dust collection. I firmly believe that 4" fittings and dist are popularly sold and included on machine as it represents the price point were people will purchase the equipment and items. Having little to nothing to do with what will/would actually work. Expect for the smallest machines, such as an OSS, 4" ducting is useless. As for the 400-550CFM minimum requirement, it is also the maximum. At the static pressures and CFM ducts collectors run at, air is not compressed (or compressible). Therefore the most CFM you can pull through the a 4" ductwork is 350-450CFM. It is unlikely the will be able to achieve 400CFM at the machine.

[Michael W. Clark]

The larger main would allow multiple (two) machines to be used at once. As I mentioned earlier, I'm worried the SP loss of 4" duct over those long runs is going to put the SP/Flow off the fan curve. I have a DC that can provide the 400CFM in 4" duct...barely. It works OK for chip collection, but stinks for dust collection. I firmly believe that 4" fittings and dist are popularly sold and included on machine as it represents the price point were people will purchase the equipment and items. Having little to nothing to do with what will/would actually work. Expect for the smallest machines, such as an OSS, 4" ducting is useless. As for the 400-550CFM minimum requirement, it is also the maximum. At the static pressures and CFM ducts collectors run at, air is not compressed (or compressible). Therefore the most CFM you can pull through the a 4" ductwork is 350-450CFM. It is unlikely the will be able to achieve 400CFM at the machine.

As you stated earlier, depends on the fan curve and the system SP requirements. With a 5hp blower, I think he would be at a better point on the fan curve running 6" assuming you have enough fan to deliver 800 CFM through the system. You will get better separation at the cyclone too at the higher flow.
Mike

[David Kumm]

While I disagree with the 4" mains, the Smart collector is designed to pull more cfm through small diameter ports than a traditional BC impeller. My radial blade will pull 850 cfm through a 4" port but it is a slightly bigger system than the Smart. The mains should be 6" and the ports used to maximize the flow and velocity ( keeping the 4 and 2.5" both open, and adding an overhead port to the table saw ) but the Smart collector is designed for smaller pipe and will under perform a regular 5 hp 16" impeller system with large pipe and ports. The Smart will adjust speed to keep the amp draw and cfm fairly uniform whether running 5,6,or 7" pipe so it will exceed the regular collector under pressure but under perform at low pressure. Dave

[Ray Newman]

See what Alan Shaffter posted in post #13. His design makes sense.

Does Oneida still offer a duct design service? Might be worthwhile to contact them for a design and then compare the two.

[Frank Pratt]

These are my thoughts. In a 1 man shop, where only 1 machine will be run at a given time, it's best to run a large duct the entire distance to each machine. As long as enough velocity can be maintained to keep the duct clear, the larger diameter results in less static pressure loss.

I have a 5 HP Oneida cyclone system with 8" duct run to every machine, reducing to 4" or 6" for the drop as required. I've had not problem with the ducts filling with debris.

Of course, if more machines are running at once, it gets a lot more complicated maintaining balanced flow to all machines.

[glenn bradley]

Lets be careful that this thread doesn't become argumentative and therefor unhelpful. As you have noticed from the responses here, the duct design is wrong in a lot of ways. I would just forget you ever saw that. If you want a "professional" recommendation I would approach someone who displays some awareness of wood spoil collection and transport; a list of previous clients, references and so forth.

A more direct route may be to follow something like what Alan S shows that better follows known best practices for this sort of thing. I should say that the designer may have been hobbled by any number of restrictions you provided like "keep the duct near the walls" or whatever. I would like to think that anyone who had any experience with this sort of thing would try very hard to talk you out of a design that involved a bunch of undersized pipe and right angle turns. Good luck and please let us know how things develop.

[Dan Schmidt]

Thanks all for the very constructive feedback --- exactly what I was looking for. This is my first ducted system, and as I contemplated my shop over the past few years I always knew I would rely on the "professional" design services that these ducting companies offer because I didn't have time to research and become a semi-expert. I certainly didn't over constrain them with anything -- just locations of machines, machine port sizes & CFM needs. I now lost confidence in the free service, so now I need spend the additional time to research and become more informed.

Given your input I will go back to them with detailed questions and challenge the concepts until I'm satisfied. Also, in parallel I'm starting my own detailed design in Sketchup based on a non-orthogonal layout as Alan Schaffter suggested, larger mains, and enlarged ports for certain machines. Will also research the available tools and calculations..... Stay tuned, I'll update you with a round #2 design asap.

Thanks again all!

Dan

[Chris Padilla]

Generally speaking and grossly simplifying things, run as large pipe as possible for as long as possible as straight as possible. If reductions are needed for the tool, do it as close to the tool as possible but seriously consider modifying said tool's port to accommodate a larger pipe.

If your DC inlet is 7", try to use that all the way to the tool.

For my system, I ran 6" PVC everywhere and modified ports where I could. If I couldn't modify the port, I gently stepped/tapered it down from 6" to the port size.

For the table saw, I ran 6" as the main port and tapped off a 2.5" for above the table saw/blade guard/riving knife dust collection.

My system was a home built cyclone with 14" impeller and a 5 hp Leeson motor turning it. I believe it had a 6" inlet. Here is my build thread (http://www.sawmillcreek.org/showthread.php?9933) from way back when. :)

Anyway, near as I can tell and I haven't measured anything, it sucks up everything very well: jointer/planer, drum sander, tables saw, bandsaw.

[Jim Becker]

It's also important to consider that a step-down design like this isn't new...in fact, it's just the opposite. This type of design (in general) was how things have been done for many years and the designer may very well just have been using the same tools and techniques that they also have been using for years. There's almost no "wrong" answer here, although there are more efficient ways to design duct work with today's collection systems and our general willingness to modify machines to support larger diameter collection ports. 5" and 6" duct is a relatively "recent" demand in the home shop arena.

My system is stepped and that's how Oneida designed it many years ago. Over time, I refined things to insure larger diameter collection paths were available to the machines that had the greatest flow demands for efficient collection (jointer/planer and my slider with their 120mm ports) as well as for my floor sweeps. Performance is good.