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Discussion Starter #1
I have been reading all the confusing discussions on dust collection piping designs. I understand that having the larger 5 or 6" ports would be optimum but most of my tools are 4" and are not easily modified. My 18" drum sander being the main collection problem. I am purchasing a 3hp cyclone to improve my collection and the supplier says for me to try it with existing piping because I will see much improvement over 1.5hp single stage collector.

I have read that it doesn't help to run 6" pipe with a 4" port as the port will limit the flow no matter what. That is my question. Maybe trial and error will tell.

Does a 4" port limit CFM and installing larger collection piping does no good?
 

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I have been reading all the confusing discussions on dust collection piping designs. I understand that having the larger 5 or 6" ports would be optimum but most of my tools are 4" and are not easily modified. My 18" drum sander being the main collection problem. I am purchasing a 3hp cyclone to improve my collection and the supplier says for me to try it with existing piping because I will see much improvement over 1.5hp single stage collector.

I have read that it doesn't help to run 6" pipe with a 4" port as the port will limit the flow no matter what. That is my question. Maybe trial and error will tell.

Does a 4" port limit CFM and installing larger collection piping does no good?
It does benefit you to run 6" duct and then reduce to 4" at the machine. The longer the run of 4" duct the more the air slows and starves the DC. Where as by running larger duct and reducing down it increases the velocity of the air to try and keep up with the larger duct size.

Sure your 4" duct will work better but the larger DC is going to starve and you loose the full potential of the larger DC system.

By increasing the duct to 6" as I suggested to you my system effiency increased by 50% with a 1.5 hp DC.
 

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I believe you will improve air flow with the larger piping(5 or 6") due to less pressure drop in the main header runs. The 4" connection will be a restriction but not the same as having all 4" piping. I agree you should see an improvement with just the addition HP. I plan on upgrading my DC system within the next 6 months. What supplier are you going with.
Tom
 

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+1 for what Richard said.

I have a 16in drum sander with a 4in port. I am presently running a 1.5HP Jet cannister dust collector. I do not observe any issues with my drum sander. Very little dust remains.

Some people use a larger duct size for the main lines. This reduces pressure drop in the main lines, so actually improves performance.

Your 3HP dust collector will really benefit from a 5 or 6in main duct size, as would the present 1.5HP machine.

My system is adequate for my present needs. I know I could reduce losses with a 4in metal system with large radius fittings, or with larger line size. I am not ready to spend the money when I am not experiencing dust issues with my machines.
 

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Try thinking outside the box. The pic below is my drum sander, just because I couldn't modify the factory hood. May not be pretty, but works like a charm. Besides, by doing it this way, I still have the intact factory hood should I ever try to sell it.

 

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Just about all my machine ports are 4". All my drops are 5" and I have a tapered reducer at the machine to adapt it to 4". It's a lot better than a long 4" line but the restriction shows. If you pull the reducer off the 5" flex pipe and then just put it on (while the DC is on) it will get sucked onto and held on the hose very well. Proving that the reducer has a pretty good restriction.
 

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rrbrown said:
It does benefit you to run 6" duct and then reduce to 4" at the machine. The longer the run of 4" duct the more the air slows and starves the DC. Where as by running larger duct and reducing down it increases the velocity of the air to try and keep up with the larger duct size.
Ok this seems a bit confused. From physics and fluid dynamics I know that Q=v*a, where Q is the volume, v is the mean flow velocity, and a is the cross sectional area of the duct. This means the velocity is roughly twice as high in a 4-inch duct as it is in a 6-inch.

Friction loss is given by the duct equation, which I'm not going to try and do on the iPhone, but there are several online calculators.

Assuming an air volume of 2800-cfm, the 4-inch will have almost 8 times as much head loss as a 6-inch, and 33 times as much as an 8-inch inch.

The 4-inch connection to the machines will restrict flow somewhat, but since the run length is relatively short the increased head loss will not be a major loss, and the increased velocity will help lift large particles out of the machine and into the larger main run.

The carrying velocity for chips and large sawdust is about 4000-feet per minute. Which means for a dc pulling 2800-cfm, that a 10-inch duct will give the least head loss, while maintaining sufficient velocity to carry any sawdust or chips you would ever produce, in a horizontal run.

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Originally posted by rrbrown

It does benefit you to run 6" duct and then reduce to 4" at the machine. The longer the run of 4" duct the more the air slows and starves the DC. Where as by running larger duct and reducing down it increases the velocity of the air to try and keep up with the larger duct size.

Ok this seems a bit confused. From physics and fluid dynamics I know that Q=v*a, where Q is the volume, v is the mean flow velocity, and a is the cross sectional area of the duct. This means the velocity is roughly twice as high in a 4-inch duct as it is in a 6-inch.

Friction loss is given by the duct equation, which I'm not going to try and do on the iPhone, but there are several online calculators.

Assuming an air volume of 2800-cfm, the 4-inch will have almost 8 times as much head loss as a 6-inch, and 33 times as much as an 8-inch inch.

The 4-inch connection to the machines will restrict flow somewhat, but since the run length is relatively short the increased head loss will not be a major loss, and the increased velocity will help lift large particles out of the machine and into the larger main run.

The carrying velocity for chips and large sawdust is about 4000-feet per minute. Which means for a dc pulling 2800-cfm, that a 10-inch duct will give the least head loss, while maintaining sufficient velocity to carry any sawdust or chips you would ever produce, in a horizontal run.

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I think you just said the same thing as I did but you confused the hell out of me with all your technical info.:confused1::confused1::confused1:

I'm a simple man and I hate he technical explanations.:laughing:
 

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Discussion Starter #10 (Edited)
port sizing issues

Oneida says the 4" port will limit the cfm to about 350 - 400 and 4000 fpm no matter what the duct is. I had heard this in other postings but can't recall where.
The cfm then will slow the fpm flow in a larger diameter pipe. If that cfm doesn't go back up and I don't know why it would then there isn't and benefit and a potential of going way below 4000 in the 6 inch line.

I think it is not a problem with larger chips but fine sanding dust it maybe another problem.

With all that said what you all are telling me is that from real world experience you don't agree.

I can see the static losses go down on 6" duct but at the lower flow the velocity is taking a hit. I really boils down to does the cfm go back up from the restriction caused by the tool port.
 

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Discussion Starter #11
sander hood mod

Try thinking outside the box. The pic below is my drum sander, just because I couldn't modify the factory hood. May not be pretty, but works like a charm. Besides, by doing it this way, I still have the intact factory hood should I ever try to sell it.

That is the same sander I have. I really like the hood you made.
What hp collector where you using before and after the mod?
 

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The problem with the above calculation is that you assume that the duct can support 2800 CFM which it will not. For static pressures involved in dust collection for the home shop, the air that we are moving is under fairly low pressure. The air acts as in incompressible fluid and therefore your smallest duct will determine your CFM. A 4" duct will move about 400 CFM regardless of the size of the dust collector. If the impeller is larger, the CFM will increase a bit as the air becomes compressed a little. The 4" ducts will starve the dust collector regardless of how long the main header duct is. If your collector has a published fan curve, you will see what static pressure will give you 800-1000CFM. Design your duct system with 6" while trying to keep static pressures within the range that gives you the CFM fan curve. Typically a 6" duct will give you this air flow. You need to take the 6" duct right to the machine. Fine dust is the enemy and is hardest to capture. Once it gets beyond the influence of the negative pressure well created by the dust port, it can escape into the shop, floating around for hours, even days. This is why you need a large volume of air. What you need to do is read Bill Pentz site. He has a static pressure calculator that is quite useful for duct design.
 

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DPJeansonne said:
Oneida says the 4" port will limit the cfm to about 350 - 400 and 4000 fpm no matter what the duct is. I had heard this in other postings but can't recall where.
The cfm then will slow the fpm flow in a larger diameter pipe. If that cfm doesn't go back up and I don't know why it would then there isn't and benefit and a potential of going way below 4000 in the 6 inch line.

I can see the static losses go down on 6" duct but at the lower flow the velocity is taking a hit. I really boils down to does the cfm go back up from the restriction caused by the tool port.
The cfm is only going to be what is coming thru the 4" opening unless you are also pulling on another machine at the same time or if air is some how leaking into the system. Basically air in equals air out.
Tom
 

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If you plan on operating more than 1 machine at a time then anything more than 4" drops will not work. However 4" line at a tool port will draw 400 CFM, not much more regardless the size of the dust collector. if you are going to run 1 machine at a time then running your 6" line directly to the machine will ensure that you capture the stray dust that gets away momentarily from the machine. You need volume for that and a 4" line will not suffice. You shouldn't be worried about the big stuff. It's the small stuff that you can't see that is the problem.

I agree that opening another blast gate in the system will increase the velocity in the main so that chips and dust stay in suspension in the airstream. However, that doesn't benefit the tool port you're working on. When I installed my collector I researched it to death. 7" mains and 6" drops to my machines is the best thing I ever done. If you want to see my setup you can look at my review on lumberjacks:http://lumberjocks.com/reviews/2869

I measured the fan curve for my system ala Bill Pentz methods and designed my duct system around that. 6" is the way to go. Regardless of the length of pipe, a 4" orifice on the end of a 7" pipe gives about 400-500 CFM and static pressures on the order of 10-11 for a 14" impeller. A cyclone itself has a certain amount of static pressure inherent in it's design. These measurements take this into account.

Really you need the fan curve for your system and a method to estimate static pressure for you duct design (Bill Pentz spread sheet). This will give you a better idea of how much air you will be moving at the tool port for you real world situation.

Keep in mind that without a manufacturers fan curve, the reported values of CFM and static pressure are useless. They typically measure CFM at an unconstrained open inlet with maximum air flow and measure the static pressure by closing off the inlet to measure the "vacuum" pressure of the system. This basically gives you 2 points on teh fan curve: the beginning (where static pressure is so low that it doesn't correspond to any real world DC application for moving air) and the end (where there is no air moving at all).

hope this helps

DJG
 

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That is the same sander I have. I really like the hood you made.
What hp collector where you using before and after the mod?
The only DC I've had hooked to this sander is the one I now have: an Oneida SDG. It started life as a 2 HP units, and has since had the motor upsized to a 5 HP (very long story, don't ask). But with the setup I now have I estimate I'm getting very close to the 800-900 CFM at the hood, that's likely reduced if the table is very close to the drums (sanding 1/4" thick pieces, for example).
 

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Discussion Starter #17 (Edited)
piping losses

The problem with the above calculation is that you assume that the duct can support 2800 CFM which it will not. For static pressures involved in dust collection for the home shop, the air that we are moving is under fairly low pressure. The air acts as in incompressible fluid and therefore your smallest duct will determine your CFM. A 4" duct will move about 400 CFM regardless of the size of the dust collector. If the impeller is larger, the CFM will increase a bit as the air becomes compressed a little. The 4" ducts will starve the dust collector regardless of how long the main header duct is. If your collector has a published fan curve, you will see what static pressure will give you 800-1000CFM. Design your duct system with 6" while trying to keep static pressures within the range that gives you the CFM fan curve. Typically a 6" duct will give you this air flow. You need to take the 6" duct right to the machine. Fine dust is the enemy and is hardest to capture. Once it gets beyond the influence of the negative pressure well created by the dust port, it can escape into the shop, floating around for hours, even days. This is why you need a large volume of air. What you need to do is read Bill Pentz site. He has a static pressure calculator that is quite useful for duct design.
I looked on Bill Pentz's site at FAQs and found this response---- ( only a portion of response included)

Does a 4" connection at the machine negate the benefit of the 6" duct going right to that machine? Yes, it kills the dust collection performance. At typical airspeeds and pressures for dust collection, air is virtually incompressible. Air can speedup some to get around a short obstruction, but just like a water valve, closing down the opening greatly restricts flow. The standard 4" connections on our larger hobbyist machines kill the CFM below what we need to collect the fine dust. We pretty much have to replace all the 4" ports on our larger machines if we are going to collect the fine dust at the source.

The other part of your question is what is the impact on airflow when using a 4" drop attached to a 6" line? My engineer friends at Dwyer Instruments that build most of the air measurement meters say roughly 10 diameters of pipe will both stabilize the airflow and set that airflow to about the same duct speed as your main. Most air engineers that are just interested in getting sawdust build systems targeted to get an airspeed of 4000 FPM in the main. That 4000 FPM when pulled through more than about 40” of 4” diameter duct will end up with a total air volume of 350 CFM. That is plenty for good chip collection at most small shop stationary machines, but far short of the 1000 CFM I recommend for good fine dust collection. The bad news is that roughly 350 CFM ends up with our main only having an total airflow of about 1782 FPM. That is way short of the minimum 2800 FPM needed to keep a horizontal main clear. The result is the main ends up building up first the larger chips then finer dust. It will continue to build up this dust until the duct is sufficiently restricted that the airflow is again fast enough to keep the remaining area clear.
************ check his site FAQ for entire response **************

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Bill says that you should only have a 1 inch difference in main to drop size. I don't know if the 6 to 4 will kill it since it seems alot of people do that.
I have done a little with his calc sheet trying to understand how it works. I think it is setup for a single size duct at a time since it has one cfm input cell. I would like to see if I can have the two different sized ducts input together to see the overall impact.

I guess I need to see what ports I can modify realistically. I didn't say but I only operate one machine at a time.
 

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As Bill said, 4" drops kills the airflow. There are two downsides to this: First plugging in the larger mains and second, killing the airflow necessary to collect the stray fine dust that gets beyond the influence of the dust ports. I put alot of time and effort into designing my own system. I use a 7" main throughout and step down to 6" at each tool. The pipe crossection is about 36% larger in teh 7" duct but my dust collector gives me about 1000 CFM (measured using a pitot and dwyer digital manometer) so that equates to about 3800 fpm which should be OK to prevent the ducts from plugging. I also only operate 1 tool at a time so I ran the 6 inch duct to the machine knowing I really wanted to get excellent dust collection including the fine rogue dust that attempts to make its way out of the machine during cutting. I think I have achieved my goal but I really won't be able to tell until I get my Dylos particle counter.

As for the static calculator. It assumes a single duct size. What I did is use the calculator to try to minimize my static pressure in the main and minimize the length of 6 inch duct and 6" flex to connect to the machine. I then measured the static pressure/CFM in my duct system using the tools I mentioned above in order to give me a better idea of my real world scenario.

I can say as cost was rising I felt that I was getting in too deep. However, I am now happy. My dust collection is the best it's ever been thanks to Bills work.

DJG
 

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I looked on Bill Pentz's site at FAQs and found this response---- ( only a portion of response included)

Does a 4" connection at the machine negate the benefit of the 6" duct going right to that machine? Yes, it kills the dust collection performance. At typical airspeeds and pressures for dust collection, air is virtually incompressible. Air can speedup some to get around a short obstruction, but just like a water valve, closing down the opening greatly restricts flow. The standard 4" connections on our larger hobbyist machines kill the CFM below what we need to collect the fine dust. We pretty much have to replace all the 4" ports on our larger machines if we are going to collect the fine dust at the source.

The other part of your question is what is the impact on airflow when using a 4" drop attached to a 6" line? My engineer friends at Dwyer Instruments that build most of the air measurement meters say roughly 10 diameters of pipe will both stabilize the airflow and set that airflow to about the same duct speed as your main. Most air engineers that are just interested in getting sawdust build systems targeted to get an airspeed of 4000 FPM in the main. That 4000 FPM when pulled through more than about 40” of 4” diameter duct will end up with a total air volume of 350 CFM. That is plenty for good chip collection at most small shop stationary machines, but far short of the 1000 CFM I recommend for good fine dust collection. The bad news is that roughly 350 CFM ends up with our main only having an total airflow of about 1782 FPM. That is way short of the minimum 2800 FPM needed to keep a horizontal main clear. The result is the main ends up building up first the larger chips then finer dust. It will continue to build up this dust until the duct is sufficiently restricted that the airflow is again fast enough to keep the remaining area clear.
************ check his site FAQ for entire response **************

_________________________________


Bill says that you should only have a 1 inch difference in main to drop size. I don't know if the 6 to 4 will kill it since it seems alot of people do that.
I have done a little with his calc sheet trying to understand how it works. I think it is setup for a single size duct at a time since it has one cfm input cell. I would like to see if I can have the two different sized ducts input together to see the overall impact.

I guess I need to see what ports I can modify realistically. I didn't say but I only operate one machine at a time.
As Bill said, 4" drops kills the airflow. There are two downsides to this: First plugging in the larger mains and second, killing the airflow necessary to collect the stray fine dust that gets beyond the influence of the dust ports. I put alot of time and effort into designing my own system. I use a 7" main throughout and step down to 6" at each tool. The pipe crossection is about 36% larger in teh 7" duct but my dust collector gives me about 1000 CFM (measured using a pitot and dwyer digital manometer) so that equates to about 3800 fpm which should be OK to prevent the ducts from plugging. I also only operate 1 tool at a time so I ran the 6 inch duct to the machine knowing I really wanted to get excellent dust collection including the fine rogue dust that attempts to make its way out of the machine during cutting. I think I have achieved my goal but I really won't be able to tell until I get my Dylos particle counter.

As for the static calculator. It assumes a single duct size. What I did is use the calculator to try to minimize my static pressure in the main and minimize the length of 6 inch duct and 6" flex to connect to the machine. I then measured the static pressure/CFM in my duct system using the tools I mentioned above in order to give me a better idea of my real world scenario.

I can say as cost was rising I felt that I was getting in too deep. However, I am now happy. My dust collection is the best it's ever been thanks to Bills work.

DJG
I understand where you gettting your ino but I tested my system made changes one at a time and tested again. Using just 4" duct and ports first.with a 1.5 hp DC and a standard crappy 30 micron bag filter.

I then changed to the Wynn canister filter leaving everything else the same. I recorded a 50% increase in velocity and the suction pulled 50 % harder.

I then changed out the duct to 6" all the way to each machine reducing down to 4" immediately at the machine or within a few feet. However I tested in the exact location as before which had a reducer at that point. Again I recorded another 50% increase in velocity and suction. That's a total of 125% increase from wher I started.

The problem with Bill's analysis if I remember correctly is it's based on agree systems I think 5hp which most home shops don't have. I also am a firm believer in results. My results are impossible according to his theory.

Architects and deign engineers design stuff all the time that I theory work but in reality it does not.

By using 6" main you move more air in the main line at lower velocity. When you reduce down to 4" the air velocity has to increase to keep up with the air volume in the larger duct. This will not work if you use a larger duct then what the DC inlet is.
 

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I understand where you gettting your ino but I tested my system made changes one at a time and tested again. Using just 4" duct and ports first.with a 1.5 hp DC and a standard crappy 30 micron bag filter.

I then changed to the Wynn canister filter leaving everything else the same. I recorded a 50% increase in velocity and the suction pulled 50 % harder.

I then changed out the duct to 6" all the way to each machine reducing down to 4" immediately at the machine or within a few feet. However I tested in the exact location as before which had a reducer at that point. Again I recorded another 50% increase in velocity and suction. That's a total of 125% increase from wher I started.

The problem with Bill's analysis if I remember correctly is it's based on agree systems I think 5hp which most home shops don't have. I also am a firm believer in results. My results are impossible according to his theory.

Architects and deign engineers design stuff all the time that I theory work but in reality it does not.

By using 6" main you move more air in the main line at lower velocity. When you reduce down to 4" the air velocity has to increase to keep up with the air volume in the larger duct. This will not work if you use a larger duct then what the DC inlet is.
One thing is easy to explain. The Wynn filters have a massive amount of filter area compared to a seasoned bag filter. If the Wynn filter will effectively decrease static pressure in the dust collector allowing more air to flow. You can expect to see a decrease in air flow as the Wynn filter becomes seasoned. Are you saying that initially you were pulling 400 cfm in a 4" duct and then started started pulling 600 cfm? or was it more like 300 then pulled 450 because the two are quite different. I expect the latter to be more realistic since the air is not that compressible. a 4" duct can support about 400 - 500 CFM. Without details about how the measurement was done I cannot provide an explanation.

I do agree that using a duct larger than the inlet on the DC does not make sense. Thats no different than runnign the collection system unconstrained. Not sure how running 6" everywhere except at the machine ports and the DC inlet would increase your air flow in the main duct. Something doesn't add up...
 
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