Piping in my HF Dust Collector

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ehpoole

Administrator
Ethan
Do you think the baffle takes away much power?

I assume that you are referring to the Thien pre-filter when you refer to a "baffle"? If so, then, yes, the extra stage you are adding inline with any pre-filter design will be robbing the system of power as it adds additional resistance and turbulence to the airflow (as well as the additional duct/hose length associated with inserting it inline), which does rob one of both static pressure and air volume versus no added pre-filter inline. It is impossible to say by how much as everyone builds their Thien pre-filter a bit differently and some are better built than others and some are better at designing for optimal airflow and alignment of the various components than others. But we can get some degree of a baseline by comparing them to the two-stage cyclone DCs that they are approximating.

A Thien-type pre-filter is essentially converting a single-stage dust collector into a two-stage cyclone-like dust collector but one which is not as well optimized and efficient as a proper two-stage cyclone dust collector. When comparing two-stage cyclone DCs to single-stage DCs one generally requires a cyclone DC to be equipped with a motor that is 30-50% more powerful in order to move a similar volume of air at similar velocity (e.g. typical shop suggested powers are 2-5HP for cyclones versus 1-1/2 to 3HP for single stage DCs). However, the true cyclone DC will be able to generate greater maximum static pressure on average, but that is due largely to differences in the impeller design since a two-stage cyclone DC can have tighter tolerances since there is no chance that large chunks of wood and other heavy debris, like screws and nails, striking the impeller, as will happen in single-stage DCs since all waste must pass through a single-stage DC impeller versus only fine dust in the cyclone. But that should give one some idea as to the probable insertion losses when adding a Thien type pre-filter inline as cyclone DCs are generally reasonably well optimized packages, so are something of a best-case.

So are Thien pre-filters necessarily a bad idea then? Not at all as they can potentially improve the waste capture volume (if you use a much larger bin) and/or can reduce (but not eliminate) the accumulation of fines that can clog the DC filter bags (not as great an issue if using a large pleated canister filter) which can potentially help to boost airflow between filter cleanings for a time. However. It does necessitate a DC that can move enough air to make up for at least sme portion of that insertion loss that is incurred by the addition of the Thien type pre-filter so that adequate airflow velocity remains.

As a 1HP DC is already fairly underpowered, and will loose additional power if upgraded with 1-micron filters (though a good pleated canister filter will have less loss than a 1-micron bag filter due to greater surface area) I, personally, would be hesitant to add a Thien pre-filter ahead of such a DC unless I were performing a task that was going to generate an enormous volume of fine dust (such as a belt sander). Most of our larger woodworking tools (tablesaw, bandsaw, planer, jointer, etc.) do not generate large volumes of very fine dust but can generate large volumes of heavier chips (particularly planers and jointers) that require good air velocity to effectively transport them without clogging the hose. In such cases, a Thien type pre-filter is only really an asset if it greatly expands the volume of chips and sawdust you can collect (that is, it's bin has far greater capacity than your DC -- keeping in mind that the Thien pre-filter will typically clog and cease to function effectively well before it's bin reaches full capacity and does not add significantly to your DC maximum volume since the DC generally only receives the fines) while still maintaining adequate airflow volume and velocity.

With a small DC I would opt for the 1-micron filter upgrade, using a good canister filter, for health and fine dust reduction purposes and likely skip the Thien pre-filter as you will want to maintain as much of your airflow as possible, which is already on the low side with an, at best, 1HP DC (I say "at best" as specs can often be fudged a bit and impeller efficiency can vary, hence the 5-micron filter they typically ship with), so as to capture as much sawdust and fines as possible and helping to ensure heavier chips do not fall out of the airstream and clog the hose. If it were a 1-1/2 to 2HP single-stage DC then I would be much more inclined to add the Thien pre-filter, particularly if it is designed with a large enough bin to expand the available collection volume. That said, if you do not upgrade to a 1-micron DC filter then I would probably go ahead and consider adding the Thien pre-filter, but upgrading to the 1-micron canister filter is a strong recommendation for both health and dust control purposes as such fine dust can remain suspended in the air for many hours and can foul finishes (and is very unhealthy), particularly if one does not have a good ambient air cleaner to scrub the air clean and help remove those fines from the air (but it is still best to try and capture such fines at the source before they become suspended in the air).

These are my thoughts and there is certainly room for disagreement as dust collection can be a very controversial subject for some. I tend to be more interested in achieving the best practical result rather than carrying things to either of the extremes that things can sometimes get taken to. Do the best you can with what you have available.
 

Alan in Little Washington

Alan Schaffter
Corporate Member
If so, then, yes, the extra stage you are adding inline with any pre-filter design will be robbing the system of power as it adds additional resistance and turbulence to the airflow (as well as the additional duct/hose length associated with inserting it inline), which does rob one of both static pressure and air volume versus no added pre-filter inline. . . . .

Oh, Ethan, I got crucified for saying as much some years ago. You would think I was casting dispersions on Santa Claus, the Easter Bunny, etc. How times have changed!

I would also like to add that everyone should remember why CFM and SP are important- it is important at the inlet end of a DC system, where the rubber meets the road- at the machine generating dust. The object is to collect as much of the chips AND fine dust before it escapes into the surrounding air where it can be inhaled. For that you need to move a lot air, a lot of CFM- there are tables showing the minimum recommended CFM for each type of woodworking machine, but more is always better. The equipment at the other (discharge) end- Thein baffles, cyclones, filters, etc. is only important if you are attempting to recycle (relatively) clean air back to your shop, which is seldom done in industry. SP is important, and is easily illustrated without a long discussion by looking at a fan curve- as SP goes up CFM goes down.

For a given motor/blower, dust dust collection (CFM) in order of best to worst is (1) a DC discharging directly to the outside (if you can do it is by far the best), (2) a DC with cyclone discharging air to the outside, (3) a DC with other separator (Thein, etc.) discharging air to the outside, (4) for all the others, add a filter so you can discharge the air inside. Filters of all types, even pleated cartridges with large filter areas, are a lose-lose situation. Regardless of common claims, they don't stop all fine dust and will clog because no cyclone or any separator will stop all the dust getting through. A clean-looking cartridge filter is not necessarily clean. It may have some varying amount of fine dust which may be impossible to see clogging (possibly permanently) the filter media. Cleaning may not eliminate all dust "captured" in the media and may also permanently damage it, reducing its effectiveness. For that reason, few, if any cartridge-type filters in any application are intended for continuous or multiple use (use-cleaning-use cycles). They are designed to be disposed of after a certain useful life. They start clogging the minute you start using them and it gets worse as time goes on. And why is a clogging/clogged filter important- it can raise SP and lower CFM in the entire system- from end to end- defeating the whole purpose of a dust collector- to capture as much dust at the source as possible. Remember, the volume of (dusty) air a DC pulls in is never greater than the volume of air it discharges!
 

stal023

New User
Stal
To clarify, my DC is 2 HP. That being said, does it make sense for me to finish making the thien baffle? The machines I plan to run duct work are: miter saw, table saw, planer and router table. Maybe in the future I will have more machine but doubt at this point due to the size of the space I have.

Sounds like my best option at this point is 4" PVC. I'm drawing out now how I think I can make this work and I am sure I will have questions to post along the way. Thanks for the help everyone!
 

Berta

Berta
Corporate Member
Just my 2 cents... Your shop is small, I would skip the baffle. That is space saved!
 

ehpoole

Administrator
Ethan
To clarify, my DC is 2 HP. That being said, does it make sense for me to finish making the thien baffle? The machines I plan to run duct work are: miter saw, table saw, planer and router table. Maybe in the future I will have more machine but doubt at this point due to the size of the space I have.

Sounds like my best option at this point is 4" PVC. I'm drawing out now how I think I can make this work and I am sure I will have questions to post along the way. Thanks for the help everyone!

Thank you for the correction in HP rating. Just be aware that if this is the 120V version of their 2HP DC then it is really a 1-1/2HP DC motor at best (they label it as a 20A motor, which would really be an overload on many 120V circuits, particularly if there are other appliances/tools running on the same 15 or 20 amp circuit -- a true 2HP motor would be around 24+A at 120V or 12+A at 240V). You have to watch out for such games when it comes to many imports, fortunately the voltage and amp specifications often yield a more accurate picture (though even those can be fudged).

Ideally you would plumb with 6" PVC pipe (which may require enlarging the inlet opening on the DC if the main inlet is not already 6"), then drop down to 4" flexible hose or PVC (whichever is most practical) for the shortest practical distance at each tool. You can also opt to go 6" all the way to each tool, but that usually requires enlarging the opening on each tool. Look for broad sweeping right angle fittings (such as used in waste lines), or make the turn in two steps using 45-degree fittings, rather than the abrupt right angle fittings typical of plumbing for water to help reduce turbulence at each turn. When you need to branch off a main line use Wye fittings and not Tee fittings, ensuring that the orientation of the Wye flows in the direction of your DC (if you get it turned around it will be oriented upstream instead of downstream towards the DC).

As mentioned a number of times, you will likely wish to upgrade the DC filtration to a 1-micron canister filter. If you need specific recommendations then there are a number of HF DC users on this forum whom can likely suggest appropriate sources for such should you wish.

Regarding floor sweeps, they are worth installing if your shop is fairly open and you regularly sweep your floors. If your shop is more crowded and broken up, like mine, then vacuuming is usually more practical and a floor sweep is useless. So it really comes down to whether or not you ordinarily sweep your floors versus vacuuming. Though vacuuming has the added benefit of not stirring up the dust nearly as much as sweeping.

As to whether to build a Thien pre-filter, it is really up to you. Since you have 1-1/2HP (real) to work with it is at least doable. However, for the tools you will be operating I do not see a big advantage to the pre-filter as the Thien pre-filter nearly always reduces the effective capacity of your DC unless you use an incredibly large dust bin for the dust collection. Most Thien pre-filters immerse the "top hat" inside of the bin, which already costs one all of that lost volume, plus you need room for the vortex/cyclone to form within the bin in order for the heavier dust to fall out of the air stream as intended. Once the collection area of the Thien pre-filter has filled your DC system has reached capacity (you do not typically get to overflow into the DC's bag as airflow largely chokes off once the pre-filter has filled). Personally, I would rather have the 1-micron canister filter and preserve greater air velocity and static pressure for my dust collection plumbing and tools than the Thien pre-filter, but that is just me personally. I would likely feel differently if I were running a drum/band sander and an argument might be made for locating such a pre-filter directly at your thickness planer's outlet if the pre-filter is easier to empty (but only for that reason on a planer) so long as there remains sufficient airflow to keep up with the waste production as no tool generates a greater volume of waste in a short period of time then a thickness planer. Again, that is my personal opinion on this question and there will likely be many who disagree.

As you get further into woodworking you may wish to add a jointer (6" or 8") and bandsaw (a heavy duty 14", perhaps) to your lineup so that you may efficiently dimension lumber to custom sizes, but only you can make the determination of what works within your shop and/or workflow. But you may wish to design in the opportunity for such additions to be made at a later date while plumbing your DC system.

Good luck and keep us up to date on your progress.
 

stal023

New User
Stal
Ideally you would plumb with 6" PVC pipe (which may require enlarging the inlet opening on the DC if the main inlet is not already 6"), then drop down to 4" flexible hose or PVC (whichever is most practical) for the shortest practical distance at each tool. You can also opt to go 6" all the way to each tool, but that usually requires enlarging the opening on each tool. Look for broad sweeping right angle fittings (such as used in waste lines), or make the turn in two steps using 45-degree fittings, rather than the abrupt right angle fittings typical of plumbing for water to help reduce turbulence at each turn. When you need to branch off a main line use Wye fittings and not Tee fittings, ensuring that the orientation of the Wye flows in the direction of your DC (if you get it turned around it will be oriented upstream instead of downstream towards the DC).

Thanks for this. I've read in numerous places that installing larger main lines than your DC inlet does not increase efficiency and is not the way to. Now, that being said, if your DC has a 4" inlet (as mine does) but enough power to move the air in 6" lines (does mine being a true 1.5 HP), is that the way to go? Of course $$ is always an issue but this is something that I see being used for a very long time, so if I should run 6" main lines, that is what I will do.

Now I have made a dust "hood" for my miter saw, so running 4" is fine to that, but the planer outlet is not 4". How does one handle this? Same with the router table and actually the table saw. I have seen some mods out there to make for better collection on these 3 machines I mention...A dust hood for the table saw, and some other creative ways to help capture dust (https://www.pinterest.com/pin/470344754807520195/ ; https://www.ridgidforum.com/forum/p...rum/36538-shop-built-table-saw-upgrade-ts3650). So I guess I bring in a whole new topic...how to reduce your runs to each machine??
 

ehpoole

Administrator
Ethan
Thanks for this. I've read in numerous places that installing larger main lines than your DC inlet does not increase efficiency and is not the way to. Now, that being said, if your DC has a 4" inlet (as mine does) but enough power to move the air in 6" lines (does mine being a true 1.5 HP), is that the way to go? Of course $$ is always an issue but this is something that I see being used for a very long time, so if I should run 6" main lines, that is what I will do.

Now I have made a dust "hood" for my miter saw, so running 4" is fine to that, but the planer outlet is not 4". How does one handle this? Same with the router table and actually the table saw. I have seen some mods out there to make for better collection on these 3 machines I mention...A dust hood for the table saw, and some other creative ways to help capture dust (https://www.pinterest.com/pin/470344754807520195/ ; https://www.ridgidforum.com/forum/p...rum/36538-shop-built-table-saw-upgrade-ts3650). So I guess I bring in a whole new topic...how to reduce your runs to each machine??

Larger lines reduce the frictional losses incurred for a given length of pipe. A 6" line can move twice the volume of air as a 4" line at a given velocity with less static pressure loss over that distance. As long as the air velocity remains high enough to keep the waste suspended it is indeed advantageous so long as you do not carry such to such an extreme that the air velocity drops too low too keep the waste suspended along it's journey (which can then lead to clogs). It also affords you the opportunity to serve a pair of outlets concurrently where needed, such as at a router table (or a tablesaw with added overhead dust collection, or a bandsaw with lower cabinet and under table outlets) where you typically require dust collection both above and below the table. But that does assume a 6" inlet at the DC inlet, a 6" main line will work against you if you starve it at the beginning by reducing it to 4" at the DC inlet (if necessary, you can often enlarge the DC inlet fairly easily in many cases...it may already be 5-6" since it has the Y adapter attached to the inlet, so such is worth measuring if you have not already). Often times all you need to enlarge the opening is a jigsaw or tin snips to cut a 1" thick band out around the circumference of the existing 4" hole to make it 6", then buy a bolt-on 6" fitting (or make one from wood) to receive your 6" pipe or hose.

What size outlet is your planer? Most that are not 4" to begin with include an adapter that steps it up or down to the common 4" size. Sometimes they will be 2-1/4" or 2-1/2", sized for a shop vac hose (which is silly as shop vacs will fill quickly) but still ordinarily include an adapter that steps the outlet up to 4".

If it is one of the common shop vac hose sizes then you can get a conical reducer that will reduce 4" down to 2-1/2" and use a very short length of hose to connect the conical reducer to your planer outlet. However, if your planer does not include a blower fan (like the DW735) then the restricted outlet may starve your DC of the required air volume to do its job most effectively, in which case you can either drill some vent holes into the reducer or leave a blast gate further down the main line partially open to admit the necessary makeup air so as to maintain sufficient air volume and velocity.
 

Rwe2156

DrBob
Senior User
So, let me back up and ask specific questions;

1. Is it recommended to have sewer grade PVC or metal piping? Why?
1a. If you say PVC, I've seen video of grounding a copper wire and wrapping around the pipe. Needed, or waste of time?
Direct answer: You don't need it to do that. I did, however, ground the blast gates to each machine.

2. Size of pipe? Do I run 6" as the main pipe and have reducers to each machine?
Yes. I have 6" mains and drops then reduce to 4" w/ 4" blast gates, then 4" flex to machines. Keep the flex as short as possible and buy the best quality you can with a smooth inside surface. BTW contrary to what a lot of guys say 4" pipe is NOT adequate. 6" is pretty much a minimum size for any collector in the 1 1/2 - 2HP range. 3HP and up you are looking at 7-8" pipe.

3. Blast gates....matter where they are installed?
They say the further up the trunk at possible but I don't think there's an appreciable performance difference. I prefer to have the gates close to the machine for easy reach.

3a. Metal, plastic or spend the time making your own?
IMO you can buy them too cheap to warrant building them. Plastic gates are too cheap. I got the metal gates PennState Industries. Got my flex there too.

Other comments:
I was going to do the Thein baffle, but went with a cyclone (Super Dust Deputy, Oneidea) instead.

If you can vent your collector outside eliminating the filter will increase performance. However, in a small shop replacement air and heating can be an issue.

Couple other things: make sure your DC is on a dedicated circuit and get a remote.

If you go with PVC be aware the money is in the fittings. I found there are cheap ones and expensive ones. For example, don't get a sweep T get a Y fitting. For a 90 degree turn, don't use 1 - 1/4 bend (90) use 2 - 1/8 bends (45's) with a short run between.

Do not glue the fittings. I rivetted mine and wrapped with duct tape.

Did I answer your questions?
 

Alan in Little Washington

Alan Schaffter
Corporate Member
I have problems with some of your statements:

Yes. I have 6" mains and drops then reduce to 4" w/ 4" blast gates, then 4" flex to machines. Keep the flex as short as possible and buy the best quality you can with a smooth inside surface. BTW contrary to what a lot of guys say 4" pipe is NOT adequate.

You are rigtht, 4" is not adequate, so why did you reduce! The only reason to ever reduce is if you have and under-powered DC and plan to have more than one gate open at a time.

6" is pretty much a minimum size for any collector in the 1 1/2 - 2HP range. 3HP and up you are looking at 7-8" pipe.

It REALLY depends on layout- number of bends and length of ductwork. Actually the typical 1-1/2 to 2 hp DC can't move enough CFM through a 6" duct, no less a 4" line, especially it has a small diam. impeller (10" - 11").

They say the further up the trunk as possible but I don't think there's an appreciable performance difference. I prefer to have the gates close to the machine for easy reach.

Who is "They?" In almost every case it just doesn't matter where you locate a blast gate- at the end middle or start of a drop. Air will not flow anywhere in the duct if there is a closed gate blast gate, regardless of the location of the gate, so there is no impact on SP or DC performance elsewhere in the system. Locate gates where they are easy to reach.

If you can vent your collector outside, eliminating the filter will increase performance. However, in a small shop replacement air and heating can be an issue.

This is not as a much a consideration as many think. The amount of air lost has minimal thermal mass compared to the shop structure and its contents which have over 100 times more thermal mass and will warm the new shop air quickly. It only becomes an issue if you discharge outside and run the DC continuously for extended periods.

If you go with PVC be aware the money is in the fittings. I found there are cheap ones and expensive ones. For example, don't get a sweep T get a Y fitting. For a 90 degree turn, don't use 1 - 1/4 bend (90) use 2 - 1/8 bends (45's) with a short run between.

The difference is in the type of pipe and matching fittings. You must get the correct PVC - "thin-walled" S&D (ASTM 2729) (or the thicker-walled, but heavier SDR35 (the blue/gree stuff which has the same O.D. as ASTM 2729) is the correct stuff to get instead of Sched 40 (standard residential plumbing grade). A 6" X 6" X 6" ASTM 2729 PVC wye (usually marked ASTM 3034, 3035) will typically run $16 to slightly over $20 while Sched 40 (and most good metal) wyes of the same size can run $35, $40 on up!

Do not glue the fittings. I rivetted mine and wrapped with duct tape.

Rivets are a pain to remove same as duct tape- very few people ever install a DC without changing the duct layout or duct size fairly soon. Just use one or two short tapping screws at each joint- with metal or PVC duct. In view of the way standard "duct tape" deteriorates over time (fabric self-destructs and falls off while the adhesive hardens and is difficult to remove) and despite its name, regular duct tape is not recommended. If you plan to use tape, you should use HVAC metal foil-backed tape specifically designed for ducting. Better yet, with both PVC and metal duct- just apply a small, thin bead of pure silicone sealer (not latex caulk) to the outside of each joint. It sticks and since the duct is under negative pressure stays in place, but can be easily removed by rubbing it gently with your fingers.
 

Rwe2156

DrBob
Senior User
I have problems with some of your statements:

You are rigtht, 4" is not adequate, so why did you reduce! The only reason to ever reduce is if you have and under-powered DC and plan to have more than one gate open at a time.
Because DC connections to ww'ing machines are usually 4". For a lot of machines fabricating a DC shroud to fit 6" is neither practical or necessary because reducing the last 3-4 feet does not affect performance enough to matter.

Actually the typical 1-1/2 to 2 hp DC can't move enough CFM through a 6" duct, no less a 4" line, especially it has a small diam. impeller (10" - 11").
I don't have performance curves (nor do I undertand them) but I will say from my research almost any DC 100CFM and up will perform better with 6" ducts. In my case its a 1 1/2HP Jet DC. I haven't measured the actual CFM at the machine, but in real life it pulls very well from my table saw which is 25 feet from the DC -- and that's with a cyclone. Before I remodelled my shop I had (incorrectly) piped with 4" ducts all I can tell you is the difference before/after was remarkable.

Who is "They?"
Bill Pentz's website and talking to DC engineers at Oneida and Penn State Industries.

In almost every case it just doesn't matter where you locate a blast gate- at the end middle or start of a drop. Air will not flow anywhere in the duct if there is a closed gate blast gate, regardless of the location of the gate, so there is no impact on SP or DC performance elsewhere in the system. Locate gates where they are easy to reach.
Isn't that what I said? But in actuality, if you read what the experts say, it actually does make a difference, but to me not a practical one.

This is not as a much a consideration as many think. The amount of air lost has minimal thermal mass compared to the shop structure and its contents which have over 100 times more thermal mass and will warm the new shop air quickly. It only becomes an issue if you discharge outside and run the DC continuously for extended periods.
If you check you will see I was referring to exhausting outside.

The difference is in the type of pipe and matching fittings. You must get the correct PVC - "thin-walled" S&D (ASTM 2729) (or the thicker-walled, but heavier SDR35 (the blue/gree stuff which has the same O.D. as ASTM 2729) is the correct stuff to get instead of Sched 40 (standard residential plumbing grade). A 6" X 6" X 6" ASTM 2729 PVC wye (usually marked ASTM 3034, 3035) will typically run $16 to slightly over $20 while Sched 40 (and most good metal) wyes of the same size can run $35, $40 on up!
I assumed everyone knew I was talking about S&D pipe.

Rivets are a pain to remove same as duct tape- very few people ever install a DC without changing the duct layout or duct size fairly soon. Just use one or two short tapping screws at each joint- with metal or PVC duct. In view of the way standard "duct tape" deteriorates over time (fabric self-destructs and falls off while the adhesive hardens and is difficult to remove) and despite its name, regular duct tape is not recommended.
Yes screws are better I've done it both ways. Guess the point is don't glue it. I've tried using caulk and had it fail. This is why tape is recommended. HVAC tape is fine but I've always used duct tape. Used it on 3 different DC systems and never seen it deteriorate as you describe (one system was >10 years) even if it did, so what?

I'm sorry if you had problems with what I've said but I believe if you do the research you'll find overall it follows recommendations of the experts. Don't know why, but DC seems to be a subject that sparks debate (I suspect because guys have built a system and reading something that says its incorrectly designed). I've read a LOT of posts on forums about DC and there is a LOT of bad info out there. I based what I said on both practical experience and hours of research. Before building my new system I talked to people at both Oneida and Penn State Industries.

Bottom line: there is a lot of nuance and hair splitting that won't make a practical difference but the biggest mistake I see guys make is undersizing their ductwork. I've seen guys use nothing but a shop vac and 2" pipes running all over the shop and think it works great!
 

Jeremy Scuteri

Moderator
Jeremy
I love dust collection discussions. As others have said, and as you can plainly see, there is not a consensus on this topic. There is quite a bit of debate. Listen to what people say, but don't take anything as the gospel. Allow discussion to complement your own research and experiments and make up your own mind.


Here are some experiments and measured results that I have conducted. Maybe you will find them useful.
http://www.ncwoodworker.net/forums/...&page=2&highlight=dust+collection+experiments
 

Alan in Little Washington

Alan Schaffter
Corporate Member
Because DC connections to ww'ing machines are usually 4". For a lot of machines fabricating a DC shroud to fit 6" is neither practical or necessary because reducing the last 3-4 feet does not affect performance enough to matter.

I can't understand why you would say that. It may take a bit of work, but 6" ports are both practical and advised. It doesn't matter where you have 4" duct, it will ALWAYS affect performance because max CFM possible through a 4" pipe is SIGNIFICANTLY less than through a 6" pipe! Do the math.

I don't have performance curves (nor do I undertand them) but I will say from my research almost any DC 100CFM and up will perform better with 6" ducts. In my case its a 1 1/2HP Jet DC. I haven't measured the actual CFM at the machine, but in real life it pulls very well from my table saw which is 25 feet from the DC -- and that's with a cyclone. Before I remodelled my shop I had (incorrectly) piped with 4" ducts all I can tell you is the difference before/after was remarkable.

Not so! 6" duct will flow more CFM but there are two other factors to consider if you use large (6") and long ducting with too small of a DC- first, velocity will likely be insufficient to adequately keep large particles suspended in the stream, while long runs (regardless of diam.) will drive up SP. That is the reason why a 1 1/2 hp DC, especially one with a small impeller, is not suited to be plumbed in a fixed installation.

Bill Pentz's website and talking to DC engineers at Oneida and Penn State Industries.

A 100 CFM DC is not going to do anything, even move chips! 100 CFM only works in shopvac installations where you have SP's in the range of 80" and such a system is totally inadequate for big machine dust collection. Show me where you read this on Bill's site. I understand fan curves and been doing this for over 15 years, and by the way I know Bill personally (we were in the initial stages of writing a DC book together about 10 years ago.) And frankly, I doubt you talked to DC "engineers" at either place- more than likely you talked to sales or CS people, since I doubt either company, has more than one or two real engineers in the company, especially PSI which likely doesn't have any.

Isn't that what I said? But in actuality, if you read what the experts say, it actually does make a difference, but to me not a practical one.

Do you have a link for that?

I assumed everyone knew I was talking about S&D pipe.

I joined this forum back in 2005, not long after it was established, and believe me, many people still don't know the difference between "thin wall" S&D and other types of PVC sewer and drain pipe. There are still a large number of people who think any PVC pipe used for sewer or drain lines (Sched 40) is the S&D best suited for DC ducting. Even (the blue/green) SDR35, which has the same O.D. and can use the same fittings as ASTM 2729 thin-walled S&D, is much heavier, has thicker walls, and small I.D.

Yes screws are better I've done it both ways. Guess the point is don't glue it. I've tried using caulk and had it fail. This is why tape is recommended. HVAC tape is fine but I've always used duct tape. Used it on 3 different DC systems and never seen it deteriorate as you describe (one system was >10 years) even if it did, so what?

You've been lucky then. You are saying pure silicone which is typically guaranteed for 15 or more years has failed? By your statements you sure don't sound like you've had 3 DC systems, at least ones that were well designed.

I'm sorry if you had problems with what I've said but I believe if you do the research you'll find overall it follows recommendations of the experts. Don't know why, but DC seems to be a subject that sparks debate (I suspect because guys have built a system and reading something that says its incorrectly designed). I've read a LOT of posts on forums about DC and there is a LOT of bad info out there. I based what I said on both practical experience and hours of research. Before building my new system I talked to people at both Oneida and Penn State Industries.

I agree, there is a lot of bad info out there, but I don't believe you've been reading or at least understanding the right stuff, especially if you don't understand fan curves, and so continue to promulgate some of the same bad info. Besides Bill Pentz, who do you consider to be the experts- hopefully not Sandor Nagyszalanczy nor Rick Peters.

Bottom line: there is a lot of nuance and hair splitting that won't make a practical difference but the biggest mistake I see guys make is undersizing their ductwork. I've seen guys use nothing but a shop vac and 2" pipes running all over the shop and think it works great!

There certainly is a lot of nuance, but it does make a difference! And yes under-sized duct it a big mistake. 2" is only adequate for a vac based system designed for small power hand tools, etc. But you must do the math. I think you will find if you compute SP and CFM at the tool end of the 25' run in your 1-1/2 hp system, you will not have enough CFM with your 4" drops to meet minimums for any typical machine (see the tables on Bill's site)

This post is way too long, but let me give you two examples of the problem I have seen with DC discussions over the years-

Let's say a woodworker has a mobile, low hp (2 hp, probably generating 1-1/2 hp or less) DC that he plans to turn into a fixed, ducted system. Right now it is connected to one machine at a time using 5" flex. When he converts it to a fixed installation he uses 4" PVC because that is a common size and available. But now the air has 20'+ of pipe and a couple of turns to negotiate so he is notices he is not collecting as much dust from the machine. He reads somewhere that 6" pipe is better, so replaces the 4" pipe with 6" but still has 4" drops and/or tool ports. He "assumes" dust collection (CFM at the machine) is better when in reality it isn't because of the 4" drops and ports. In fact he may end up with problems- while the velocity in the 4" is adequate to keep dust in suspension in his system, as soon as the air enters the 6" pipe it will slow down which could cause trouble if dust begins to settle and accumulate in the duct. Another woodworker has the same DC but runs 6" all the way to the machine. He notices it is not picking up all the dust either, so for some reason ne reduces the drop to 4"- boy does that 'sound' better so he assumes collection is better- not so, CFM will be reduced and all he is observing is the increased noise and what he calls improved 'suction' due to higher air velocity and SP- not an actual increase in CFM. See the problems?
 
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Rwe2156

DrBob
Senior User
William you're obviously much more knowledgeable than me. That was a typo I meant 1100CFM, not 100 ;-)

I followed basic principles from what I learned and now my system works great.

I'm sorry I came across the wrong way or pushed a button with you.

I think any further posting will serve no purposes so I've unsubscribed to the thread.

Have a good day.
 

stal023

New User
Stal
Larger lines reduce the frictional losses incurred for a given length of pipe. A 6" line can move twice the volume of air as a 4" line at a given velocity with less static pressure loss over that distance. As long as the air velocity remains high enough to keep the waste suspended it is indeed advantageous so long as you do not carry such to such an extreme that the air velocity drops too low too keep the waste suspended along it's journey (which can then lead to clogs). It also affords you the opportunity to serve a pair of outlets concurrently where needed, such as at a router table (or a tablesaw with added overhead dust collection, or a bandsaw with lower cabinet and under table outlets) where you typically require dust collection both above and below the table. But that does assume a 6" inlet at the DC inlet, a 6" main line will work against you if you starve it at the beginning by reducing it to 4" at the DC inlet (if necessary, you can often enlarge the DC inlet fairly easily in many cases...it may already be 5-6" since it has the Y adapter attached to the inlet, so such is worth measuring if you have not already). Often times all you need to enlarge the opening is a jigsaw or tin snips to cut a 1" thick band out around the circumference of the existing 4" hole to make it 6", then buy a bolt-on 6" fitting (or make one from wood) to receive your 6" pipe or hose.

What size outlet is your planer? Most that are not 4" to begin with include an adapter that steps it up or down to the common 4" size. Sometimes they will be 2-1/4" or 2-1/2", sized for a shop vac hose (which is silly as shop vacs will fill quickly) but still ordinarily include an adapter that steps the outlet up to 4".

If it is one of the common shop vac hose sizes then you can get a conical reducer that will reduce 4" down to 2-1/2" and use a very short length of hose to connect the conical reducer to your planer outlet. However, if your planer does not include a blower fan (like the DW735) then the restricted outlet may starve your DC of the required air volume to do its job most effectively, in which case you can either drill some vent holes into the reducer or leave a blast gate further down the main line partially open to admit the necessary makeup air so as to maintain sufficient air volume and velocity.

The inlet on my DC is 5"...and I guess I am not understanding how to make a 5" hole 6" easily??

My planer fits a standard shop vac hose.
 

Michael Mathews

Michael
Corporate Member
Stal,
I used 4" PVC everywhere for my system. I also built a Thein Separator and it works fantastic! I removed my blower assy and mounted it on the wall about the Thein unit. I blow directly outside with the outlet and so far don't see any signs of any dust getting out. I have a Wynn filter that I used to use and works very well. But by completely opening up the outlet with no restrictions, I greatly improved my dust collection at all my drops. I built my shop (approx 800 sq.ft.) and embedded 4" PVC under the concrete. I don't know where you are located but you're welcome to come to my shop here in Chapel Hill and check out my system.
 

Jeremy Scuteri

Moderator
Jeremy
Stal,
I used 4" PVC everywhere for my system. I also built a Thein Separator and it works fantastic! I removed my blower assy and mounted it on the wall about the Thein unit. I blow directly outside with the outlet and so far don't see any signs of any dust getting out. I have a Wynn filter that I used to use and works very well. But by completely opening up the outlet with no restrictions, I greatly improved my dust collection at all my drops. I built my shop (approx 800 sq.ft.) and embedded 4" PVC under the concrete. I don't know where you are located but you're welcome to come to my shop here in Chapel Hill and check out my system.


How do you handle make up air? A vent that you manually open or some other method?
 

Michael Mathews

Michael
Corporate Member
I haven't done anything so far. After setting it up, I wasn't sure if I'd need a make up air port, so I just turned it on. I do have some air gaps around the doors that go into the garage, so I'm sure I'm pulling air from there. May be pulling it from around the overhead door in the garage.
 
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