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Thread: Dust collection design for trunk line and branches

  1. #1

    Dust collection design for trunk line and branches

    Ok guys I need some help on my dust collection setup. I have my 10hp dust collector setup in the back corner and plan to run a 90ft trunk line diagonally with 5 direct (straight down) drops and 6 branches. The branches will range from 10ft long to 20ft long. On the far end of the trunk line will be 4 shapers, a wide belt sander, edge sander, upcut saw and edge bander. Closest to the dust collector will be slider, 3x cabinet saws, planer, Ras, ect.

    I absolutely can not change the layout of the machines and location of the dust collector. I have an odd shaped shop and the positions are all necessary. I know that it’s not good to have a wide belt and edge sander that far away, but this is my only option. I have tried reading up on the science and calculations involved for this type of thing, but I am dyslexic and have a learning disability which has caused me to struggle to figure this out.

    I drew up my layout but I am not sure if it will allow me to post. If not, I will try to sign up for a membership today.

    My questions are otherwise;
    1. I plan to have a 12” trunk line and 12/12/6 drops with 12/12/8 branches. Does this sound reasonable?
    2. Should I reduce the trunk line down to say 8” at the last 20ft of it to increase velocity?
    3. Would it be better to have the branches all be 12” instead of 8”?

  2. #2
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    I would base my sizes based on cfm. Have you measured the cfm on the 12" duct? The performance characteristics should dictate your choice.

    It would help if you became a contributor as you could post pictures? I think the advice you receive here is worth$6.

    You might post your question on the Aussie forum under dust extraction. BobL on that forum might help and he is the best expert I have found. In my opinion even better than Pentz.
    Last edited by Larry Frank; 04-09-2021 at 7:55 AM.

  3. #3
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    I would avoid any straight down drops as offcuts may drop down those on their way to the DC. Come out horizontally and add a 90 to go vertical. Here I only have a 2 hp DC, so I went with a 7" main with 6", 5" and 4" drops. Two drops in the second photo you can't see serving the 6" belt sander, BS, 6" jointer and lunch box planer.
    Attached Images Attached Images
    Last edited by Ole Anderson; 04-09-2021 at 10:34 AM.
    NOW you tell me...

  4. #4
    As to Larry's advice, the CFMs aren't relevant to moving sawdust. You need velocity. This is where the engineering data for the fan is used. You need to know how many CFMs the separator and fan are capable of at a given static pressure. This information isn't used for duct sizing.
    The fan is the last piece of equipment to be picked when designing a system.

    Ole is correct.

    We need a single line sketch that shows linear footage, fittings, hose lengths, and machine pickup sizes. If you know the CFM requirements for the machine, we need that information. If you don't, we need the outlet size. What machines operate at the same time?

    It's likely that 10 HP is much bigger than required. You need enough HP to maintain velocity from your farthest drop to the separator and also from your largest machine to the separator. Simply put, you are going to have to move 3500 CFMS all the time to maintain velocity. It will be loud and expensive.

    Post your sketch, we'll start sizing it.

  5. #5
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    Just as a note, I mentioned the performance characteristics will guide the design. One issue with a large duct is what happens when connected to the smaller ducts of the machines. Depending on the fan characteristics, you may fall below the needed cfm/velocity to keep dust moving.

    In the setup Ole described, his 7" duct is likely to large for appropriate velocity. Wood Magazine, showed that a 5" duct is good for a 2 hp collector.

  6. #6
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    Quote Originally Posted by Larry Frank View Post
    Just as a note, I mentioned the performance characteristics will guide the design. One issue with a large duct is what happens when connected to the smaller ducts of the machines. Depending on the fan characteristics, you may fall below the needed cfm/velocity to keep dust moving.

    In the setup Ole described, his 7" duct is likely to large for appropriate velocity. Wood Magazine, showed that a 5" duct is good for a 2 hp collector.

    I'll take the bait Larry! I would argue that a 5" main for a 2 hp dust collector is a gross and incorrect generalization. 6" might be a better general number, but it is so dependent on the fan curve of the DC in question. In my case I have a 2011 2 hp Oneida super dust gorilla which can pull 1227 cfm at 4.1" of static pressure at the 6" floor drop nearest the cyclone, measured. So I can easily pull 950 cfm through the 7" with all gates open, which is 3550 fpm, easily enough velocity to pull chips and offcuts through a horizontal duct.

    IMO a 7" main is the sweet spot between velocity and friction losses for many 2-3 hp dust collectors which is why I argue for steel duct as PVC is not available in odd sizes. The minimum recommended flow for a TS with top and bottom dust collection is 800 cfm, the most common high demand tool. Recommended minimum velocity for horizontal runs is 3000 fpm (4000 fpm for vertical runs). 6" pipe at 800 cfm will have 4074 fpm velocity, excessive velocity resulting in higher friction losses. 8” pipe will only have a velocity of 2292 fpm, too low. 7” pipe velocity at 800 cfm will be 2993, right at the recommended velocity. Recommendations are from Bill Pentz. http://www.billpentz.com/woodworking/cyclone/index.php I don’t agree with everything he says, but this link is the definitive encyclopedia on hobby/small shop dust collection. He also states that 7” is the preferred size main duct for most common 2-3 hp systems

    I have been using this system for 10 years now without a dust clog. My lunchbox planer is at the end of the 7" main and has a 5" drop connecting to the planer with a 4" slinky. Certainly not achieving recommended velocity in the 7" main. If a clog starts, the effective pipe size decreases and the velocity will increase creating a cleansing velocity at the plug. Has anybody ever had a main plug? I doubt it. What we need is for someone to construct a whole system with clear duct so we can really see what happens!
    NOW you tell me...

  7. #7
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    Honestly, the big issue here is that the OP has a very large collector and a very large main trunk. The air volume expectations of those two things make for an interesting situation if he is going to operate as a one person shop...IE, can't really use one drop with all the others closed off. That's true for a multi-worker situation, too....the air demands of the DC need the equivalents of most of the area of a 12" main to be "open" at the gate/machine ends.
    --

    The most expensive tool is the one you buy "cheaply" and often...

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    Jim is absolutely correct and what I was trying to mention. You need to keep the velocity in the largest duct high enough to keep things moving. It may require having at least two gates open. One needs to calculate air flow under various conditions at all points along the duct.

    I am surprised that a 2 hp Super Dust Gorilla can actually provide 1227 cfm at 4.1" SP. Are those Oneida Specs or how measured.

    I have a 5 hp Super Dust Gorilla and measured 1550 cfm at 4" SP and similar to the Oneida performance curve. I am running a 8" duct and then 6" PVC for my main line and get very good cfm to all machines. My measurements were taken with a hot wire anemometer across an 8" measurement duct.
    Last edited by Larry Frank; 04-10-2021 at 8:08 PM.

  9. #9
    Quote Originally Posted by Ole Anderson View Post
    I'll take the bait Larry! I would argue that a 5" main for a 2 hp dust collector is a gross and incorrect generalization. 6" might be a better general number, but it is so dependent on the fan curve of the DC in question. In my case I have a 2011 2 hp Oneida super dust gorilla which can pull 1227 cfm at 4.1" of static pressure at the 6" floor drop nearest the cyclone, measured. So I can easily pull 950 cfm through the 7" with all gates open, which is 3550 fpm, easily enough velocity to pull chips and offcuts through a horizontal duct.

    IMO a 7" main is the sweet spot between velocity and friction losses for many 2-3 hp dust collectors which is why I argue for steel duct as PVC is not available in odd sizes. The minimum recommended flow for a TS with top and bottom dust collection is 800 cfm, the most common high demand tool. Recommended minimum velocity for horizontal runs is 3000 fpm (4000 fpm for vertical runs). 6" pipe at 800 cfm will have 4074 fpm velocity, excessive velocity resulting in higher friction losses. 8” pipe will only have a velocity of 2292 fpm, too low. 7” pipe velocity at 800 cfm will be 2993, right at the recommended velocity. Recommendations are from Bill Pentz. http://www.billpentz.com/woodworking/cyclone/index.php I don’t agree with everything he says, but this link is the definitive encyclopedia on hobby/small shop dust collection. He also states that 7” is the preferred size main duct for most common 2-3 hp systems

    I have been using this system for 10 years now without a dust clog. My lunchbox planer is at the end of the 7" main and has a 5" drop connecting to the planer with a 4" slinky. Certainly not achieving recommended velocity in the 7" main. If a clog starts, the effective pipe size decreases and the velocity will increase creating a cleansing velocity at the plug. Has anybody ever had a main plug? I doubt it. What we need is for someone to construct a whole system with clear duct so we can really see what happens!
    Can you explain in laymen’s terms how I do the calculations for sizing my trunk, branch and drops? My dust collector is a 10hp with a 12” inlet and it has (3x) 72” filter bags.

    I will have 5 regular drops that will split to 7 machines out of those 5 drops then it would have a 5ft branch going to my 3 router tables, a 20ft branch going to my RAS and line borer, a 10ft branch going to my upcut saw and Blum machine, another 10ft branch going to my miter saw and shaper, then a 10ft branch going to my wide belt that goes another 15ft to my Whirlwind and edge sander, and another 10ft branch that goes to my edge bander. My trunk line is roughly 90 foot give or take and at the very end of my trunk line are 3 more shapers. I will diagram it and post the diagram today.

  10. #10
    Quote Originally Posted by Larry Frank View Post
    Jim is absolutely correct and what I was trying to mention. You need to keep the velocity in the largest duct high enough to keep things moving. It may require having at least two gates open. One needs to calculate air flow under various conditions at all points along the duct.

    I am surprised that a 2 hp Super Dust Gorilla can actually provide 1227 cfm at 4.1" SP. Are those Oneida Specs or how measured.

    I have a 5 hp Super Dust Gorilla and measured 1550 cfm at 4" SP and similar to the Oneida performance curve. I am running a 8" duct and then 6" PVC for my main line and get very good cfm to all machines. My measurements were taken with a hot wire anemometer across an 8" measurement duct.

    Let me see if I have this right. I need to maintain 4500fpm velocity for wood dust. My highest demand machines that are the furthest from my dust collector are my wide belt sander and my edge bander. I do not know the CFM requirements for my Cantec C251 25” wide belt sander. I couldn’t find it in a quick google search but I will check my manual when I get back to my shop. My Biessee ERGHO 3 edge bander claims to need 2,300cfm. Ouch! This is where I am stuck.

    So from here I have no idea what to calculate next? I know that the ideal velocity is 4500fpm and my largest demand machines that are the furthest are the bander and wide belt and require approx 2,300cfm and around 400cfm for a total of 2,700cfm but I don’t know what to calculate from here. How does the fan curve factor in? How do I calculate what my actual dust collector is capable of? By the way my dust collector does not have a brand or label on it and I have no clue who the manufacturer is. It is a large red 3 bag (72” filter bags that are 24” in diameter) with a 10hp 3ph Balder motor.

  11. #11
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    Bobby, it's not just velocity...there has to actually be air available to move and it takes a lot of air to fill up that 12" main so you can have the air flow you need to move the dust and chips. Measurement aside, what Larry and I (and others, I believe) are saying is that "if" you are only going to be using one machine at a time, you're still going to need several drops open simultaneously in order to have enough air to fill the duct work to an acceptable level. I don't think that there is much concern that your system cannot handle your individual machines...that's a huge DC...it's more about how to make it work functionally if you don't have a production shop. I could be wrong, but I believe this thread is about your personal shop, not the other one.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  12. #12
    Bobby, take a look at this design guide https://airhand.com/designing/. It is relatively simple to use to figure the duct sizes and static pressure losses in the system that will allow you to size the blower correctly. There are some links within that page that detail what the drop sizes would typically be for various machines and the resistance for various size ducts and fittings. You also have to consider the loss due to filters.

    I have used this guide for my own small shop and also for a shop with dozens of drops and a 15 hp blower, and both systems work well. You are starting at the wrong end of the process by settling on your blower first. Given that your edgebander requires 2300 cfm you will probably need a 10" duct for that machine and the main. As others have said, using a 12" main you will have to keep several gates open on various branches to supply enough air to keep the dust in suspension all the way to the blower. and that would also be true using a 10" main when your edgebander is not in use.

    It may well be that your 10 hp blower is a good choice but you need to do the arithmetic. I don't know what it would take to establish a fan curve for your unit. Maybe if you post a picture someone could id the manufacturer.

    If you can't make the numbers work using this guide, it would pay to hire an engineer experienced in wood dust collection systems to advise you, given the potential cost of the parts for a system this size. Another alternative would be to buy a system from Oneida- I believe they will include ductwork design if you buy a system from them.

    By the way, the filters on your blower seem way too small. You appear to have only about 115 sq ft of filter area for a blower that should be in the 3000 cfm range. I believe a commonly accepted target is 1 sq ft of filtration per 10 cfm of airflow. More filter area will increase the system efficiency as well as making the air cleaner.
    Last edited by Kevin Jenness; 04-11-2021 at 3:14 PM.

  13. #13
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    Are we discussing a single stage DC , w/ 3 bag filters ? Not a cyclone .

  14. #14
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    Quote Originally Posted by james manutes View Post
    Are we discussing a single stage DC , w/ 3 bag filters ? Not a cyclone .
    With a 12" inlet and 10h, .I seriously doubt it's a single stage, at least in the sense that we generally envision within the SMC community.
    --

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  15. #15
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    Duct design has to compromise the contradictions between wanting as much flow at the single outlet in use vs wanting to maintain a minimum velocity in the main duct. To achieve the latter folks want to open another blast gate to artificially increase that flow. By doing that they are reducing the static pressure, therefore the flow at the tool, in order to satisfy the notion that you must maintain a minimum velocity in the main at all costs. But isn't the ultimate goal of dust collection to collect dust at the tool? I would argue that that is more important than always maintaining velocity in the main duct. As I asked in my first post, has anyone ever had their main clog due to insufficient velocity? Other than knowing there might be a bit of a buildup in the bottom of the main, what is the problem? I don't really care if there is a buildup in the bottom of my TS as long as the bell mouth 5" outlet remains clear to flow as much as possible. Once in a while I will open both gates on the end of my 7" main run to clean it out. Done.
    NOW you tell me...

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