Another DC duct work question.

[Stan Welborn]

I'm in the process of planning my cyclone DC system, and find the availability and *cough!* cost:eek: of 6" the S&D PVC pipe and fittings to be very detrimental to my plans to say the least. To the point of "it ain't gonna happen scooter."

Where as on the other hand, 4" is both plentiful and comparatively mega cheap. As in -I can get it at a local plumbing supply for less than a 1/4 of what I can find 6" anywhere- cheap. So, as someone who has more time than money these days, after doing some calculations, I'm thinking that I can run a pair of 4" lines in lieu of 6" for quite a bit less than half the cost. 10' ceilings and plenty of room.

With 6" pipe having an area of 28.26, and two 4" combining to have an area of 25.12, I'm figuring this is close enough to the flow of 6" for government work, (or my lil' hobby shop.)

Thoughts?
Issues, with loss of flow through friction?
Way off base?
Crazy redneck has finally come unglued?
Somebody put a muzzle on this nut?...

[Jim O'Dell]

Stan, it would probably work, but it will create some extra problems with the hook up at the hoods, trying to get both to the machine without a weird manifold of some sort.
I finally found the pipe for about 21.00 per 10' length for the first 2, then the guy remembered me the next 2 times and sold them to me for just under 10.00 each! It can be found, it just takes leg work. Jim.

[Sean Troy]

The 6" S&D pipe is only 1.43 per ft. here.

[Stan Welborn]

Stan, it would probably work, but it will create some extra problems with the hook up at the hoods, trying to get both to the machine without a weird manifold of some sort.
I finally found the pipe for about 21.00 per 10' length for the first 2, then the guy remembered me the next 2 times and sold them to me for just under 10.00 each! It can be found, it just takes leg work. Jim.


Thought about that Jim, and you're right. I realize it will entail quite a bit more work, but I figure I can use a reverse wye 6X4X4 where needed at the tool if adding a 4" port isn't feasible. I also figure a double gate system wouldn't be any harder to construct than a single. Dual hookups in instances where I plan to split the flow anyway... at my router station, SCMS, etc, would be a breeze. I see most of it's disadvantages, I think, but can see a few advantages along with the cost savings as well. Or, maybe I'm out in la la land with the whole idea. What I DO know, is the 6" is anorexic scarce around here, and it is high as Tommy Chong's character on That 70's Show.

[Chris Friesen]

With 6" pipe having an area of 28.26, and two 4" combining to have an area of 25.12, I'm figuring this is close enough to the flow of 6" for government work, (or my lil' hobby shop.)

If I remember right, the additional wall surface area means that you have quite a bit more friction even though the cross-sectional area is similar.

I think it was about a third more resistance for two 4" vs a single 6".

[Wes Billups]

Stan, I called around to quite a few places and found the 6" PVC varied greatly in price. A 10' piece ranged from $24 to $12. I think the reason for this variation is some places only carry SDR 35 which is heavier than the ASTM D2729 I went with.

The fittings are the hard part to swallow. I paid $18/wye and $10/45° elbow. Hopefully this gives you some ballpark prices.

I can say don't use 4". I did this in my last shop and it kills airflow. If you're tight on money just do it as you can afford and use flexible hose to change out tools. Then add on as you can.

Wes

[Stan Welborn]

Stan, I called around to quite a few places and found the 6" PVC varied greatly in price. A 10' piece ranged from $24 to $12. I think the reason for this variation is some places only carry SDR 35 which is heavier than the ASTM D2729 I went with.

The fittings are the hard part to swallow. I paid $18/wye and $10/45° elbow. Hopefully this gives you some ballpark prices.

I can say don't use 4". I did this in my last shop and it kills airflow. If you're tight on money just do it as you can afford and use flexible hose to change out tools. Then add on as you can.

Wes
You used a dual 4" setup on your last shop and it killed the airflow? How did you measure this? Do you still have the figures? I can see where the friction can cause resistance, just as Chris stated he read it would be a third more loss over 6", but that's just one run, and only the percentage loss through friction. Not overall flow.

$18 per wye is a couple dollars less than I've found, but still far above the $7.12 I can get TWO 4" for.

[Jim O'Dell]

Stan, the other idea I just thought of is to contact Ed Morgano of Clear Vue. He is in South Carolina, and may have some ideas on a good place close to you for the pipe at a reasonable price. You can reach him through the contact page at clearvue dot com. Ed's a heck of a nice guy and will give you any information he has regardless if you buy his product or not. I know the place I got my pipe from locally is in all the states surrounding Texas, and several others have gotten pipe from them. Maybe there is a regional supplier you your neck of the woods that Ed knows about. Jim.

[Jason Beam]

I'm gonna stick my foot out there and ask ... Why PVC? Why not 26ga steel snap or spiral HVAC duct work?

I got the 6" snap in 5 foot lengths for about 7 bucks ... seems like a better deal, to me. The fittings are pretty inexpensive, too (though wyes are reversed for the airflow, but that's easily solved with some tin snips).

Static pressure increase would be a deal breaker to me. The sheer circumference differences:

4" pipe has 12.5" of circumference, two would have 25.
6" pipe has 18.8" of circumference.

As it was stated, about 1/3 more surface area. Air's picky, though. That extra surface area is going to have a dramatic impact on your air speed and consequently your CFM. Two 4" would be better than one 4", sure, but I don't think you're equal to 6" by any stretch. At best, i'd say you'd get closer to 5". It's better, but I'm not sure it's worth the hassle. And that's only straight runs. Imagine the added static pressure caused by double the elbows and such.

I'm thinking of it more like ... sure, you can break up a load into two small trucks and ship it across country, but going with a semi for a single load instead would be far more efficient. 6" carries with it a few other advantages that may be hard to quantify in terms of airflow. There's less "oomph" behind the air in a 4" pipe so it's harder to maintain a good airspeed. Proportionally, 6" of area gives you more mass or inertia to muscle through the bends better, too.

Then again, it's easy to be a critic. It seems like a bit more hunting around might get you into an easier price range for 6".

It'd sure bug the heck out of me if I put all that effort in only to find it doesn't work well enough.

[Sean Troy]

I'm gonna stick my foot out there and ask ... Why PVC? Why not 26ga steel snap or spiral HVAC duct work?

I got the 6" snap in 5 foot lengths for about 7 bucks ... seems like a better deal, to me. The fittings are pretty inexpensive, too (though wyes are reversed for the airflow, but that's easily solved with some tin snips).
Where did you find them for that cheap a price? I can't find any metal pipe for under 15.00 a 5' section. Thanks, Sean

[Jason Beam]

The snap stuff that most BORG's have was only about 7 for a 5' chunk. Not the spiral stuff, just the 26ga stuff. I just picked up some a couple weeks ago. Spent more on two elbows than I did on 2 5' sections.

[Sean Troy]

I'll have to check the local Borgs. Thanks for the info, Sean

[Jim O'Dell]

Be careful if you are using a high powered collector. I've heard stories of the snaploc collapsing from the negative pressures. It's designed to handle positive pressures, and low pressures and volume at that. Jim.

[Ed Bamba]

Be careful if you are using a high powered collector. I've heard stories of the snaploc collapsing from the negative pressures. It's designed to handle positive pressures, and low pressures and volume at that. Jim.

That's why the guy (DeHut, IIRC) on Woodworking at Home, a DVD magazine, made and installed a spring actuated flapper at the end of his duct run that opens when there is too much suction in the ducting. This prevents his thin-walled Borg ducting from collapsing when he closes off any of the blast gates, which is hardwired to the DC ON/OFF control. This is completly from memory BTW, it has been a few months since I viewed the story.

Ed

[Stan Welborn]

I'm gonna stick my foot out there and ask ... Why PVC? Why not 26ga steel snap or spiral HVAC duct work?

I got the 6" snap in 5 foot lengths for about 7 bucks ... seems like a better deal, to me. The fittings are pretty inexpensive, too (though wyes are reversed for the airflow, but that's easily solved with some tin snips).

Static pressure increase would be a deal breaker to me. The sheer circumference differences:

4" pipe has 12.5" of circumference, two would have 25.
6" pipe has 18.8" of circumference.

As it was stated, about 1/3 more surface area. Air's picky, though. That extra surface area is going to have a dramatic impact on your air speed and consequently your CFM. Two 4" would be better than one 4", sure, but I don't think you're equal to 6" by any stretch. At best, i'd say you'd get closer to 5". It's better, but I'm not sure it's worth the hassle. And that's only straight runs. Imagine the added static pressure caused by double the elbows and such.

An impact, yes. A dramatic one? I don't see it. Why did you choose more turbulant 5 ft HVAC sections over smother flow PVC if this is such an issue for you?

I'm thinking of it more like ... sure, you can break up a load into two small trucks and ship it across country, but going with a semi for a single load instead would be far more efficient. 6" carries with it a few other advantages that may be hard to quantify in terms of airflow. There's less "oomph" behind the air in a 4" pipe so it's harder to maintain a good airspeed. Proportionally, 6" of area gives you more mass or inertia to muscle through the bends better, too.

If it was 60% cheaper to send the two trucks, even if it were more of a headache to get them loaded, I'd send two.


Then again, it's easy to be a critic. It seems like a bit more hunting around might get you into an easier price range for 6".

It'd sure bug the heck out of me if I put all that effort in only to find it doesn't work well enough.
The way I look at it, I can't justify the extra expense over what is gained. Would 6"PVC be easier and better? Certainly. But so far, I've not seen anything that says two 4" runs won't be sufficent, and work, at less than 1/2 the cost.

[Jason Beam]

The way I look at it, I can't justify the extra expense over what is gained. Would 6"PVC be easier and better? Certainly. But so far, I've not seen anything that says two 4" runs won't be sufficent, and work, at less than 1/2 the cost.

I went with snap HVAC duct for the same reason you're thinking of double the 4" pvc. I'm certain that 6" snap duct is far less turbulent than two 4" pvc runs would be. Likely cheaper, it sounds. at $7 for 5 feet of 6" duct, I was hard pressed to find enough of a reason to go with PVC, very little bang for the buck in my research. It sounds like you feel the same about 6" vs. dual 4" and I don't feel it's as minor a difference. But, i'm hardly an expert. Just goin by gut on that one. I'd really try very very hard to find a 6" solution before i bothered with 4". If you're worred about turbulence, then dual 4" should be out right away, i'm just sayin :)

I guess my analogy got away from me with the trucks.... what I was trying to get across was that 4" pipe has considerably less than half the throughput of 6" at a lower static pressure.

It sounds to me like you have your mind made up already, though. So I hope you have good results and look forward to hearing how it worked out in the end!

[Mike Heidrick]

How does someone reverse the Wye on 6" metal duct work? Any pictures of this?

[Jason Beam]

Mike - the wyes are usually crimped on the two legs intead of the "stem" (for want of a better term). I took a tin snips and cut those crimped ends off. There's still plenty of ring left there for making the junction.

If you can gain access to a crimper, you can crimp the "stem" port so it can be inserted nicely into a non-crimped end. These crimpers ain't cheap, tho. I have a good friend with one that's really nice to let me borrow it. You can get away just fine with tin snips and making a half dozen or more 1" cuts in the end to get them to feather over one another to simulate a crimped end. It's not pretty, but it works perfectly fine for my non-glorious needs :)

[walter stellwagen]

Check with bill penz's website for the losses involved in using small pipe and an explanation of why the loss is so extreme. Snaplock comes in different gauges and the heavy guage stands up to plenty of pressure for home shop dust collection.
and as has been mentioned it is chap. If you insist on plastic ,again penz's site shows types cheaper than you mentioned .

Walt

[Noah Katz]

Not sure what people are basing the argument of catastrophic losses of dual 4" pipe over 6" pipe, but Bill Pentz's Static [pressure loss] Calculator (under Tests and FAQs here http://billpentz.com/woodworking/cyclone/index.cfm (http://billpentz.com/woodworking/cyclone/index.cfm) ) shows them as about equal.

[Noah Katz]

Not sure what people are basing the argument of catastrophic losses of dual 4" pipe over 6" pipe, but Bill Pentz's Static [pressure loss] Calculator (under Tests and FAQs here http://billpentz.com/woodworking/cyclone/index.cfm (http://billpentz.com/woodworking/cyclone/index.cfm) ) shows them as about equal.

Put an equal number in the "Ft. of straight pipe" row in yellow and look at the loss numbers below.

Actually I wonder if the calculator is wrong; it actually shows a bit less loss for 2 4", ebven though the total area is less and the surface area is more.

[Steve Milito]

Not sure what people are basing the argument of catastrophic losses of dual 4" pipe over 6" pipe, but Bill Pentz's Static [pressure loss] Calculator (under Tests and FAQs here http://billpentz.com/woodworking/cyclone/index.cfm (http://billpentz.com/woodworking/cyclone/index.cfm) ) shows them as about equal.

Put an equal number in the "Ft. of straight pipe" row in yellow and look at the loss numbers below.

Actually I wonder if the calculator is wrong; it actually shows a bit less loss for 2 4", ebven though the total area is less and the surface area is more.

The surface area to volume ratio of 6" pipe is 2/3's that of dual 4 inch pipe. The will also be more turbulence and greater loss at the junction of the two 4" pipes. Bill's spreadsheet shows a 10% reduction with dual 4", but it doesn't include the junctional loss.

FWIW, every time I start calculating the cost of a fixed piping system, I conclude that the cost of the fittings is what really drives the cost. You need to look at the additional cost of all the extra Y fittings you are going to need. It's also impossible to find odd sized PVC fittings. So if you have any 5" ports on machines, good luck with PVC.

[Jason Beam]

My gut still says it's not gonna be good enough (or cheaper in the long run) to use in place of true 6" all the way to the tool. If Stan gives it a try, we'll know for sure!

I was just playing around with my DC the other day and should have given it a go ... laziness won out, i'm afraid. That, and I don't think I have enough wyes and reducers to do an adequate job. Plus, all i have is steel, so apples/oranges, i suppose.

Wanna save money? 26ga snap steel hvac is the cheapest I've found. If you can find cheaper, go for it. Bet they'll perform comparably in the end.

[Andy Calenzo]

Stan,

I am an engineer here at Oneida Air Systems. Our company philosophy is that the woodshop should be operated in as safe a manner as possible. This is why we pioneered the use of cyclonic dust collection systems in home woodshops. Our cyclone systems minimize fire hazard by capturing and containing most, if not all of the wood dust/chips generated by woodworking tools. As such, we feel that the issue of the use of non-electrically conductive PVC pipe in a dust collection system should be addressed. It is evident to us that there is a fair amount of skepticism out there as to whether the buildup of static electricity in dust collection systems represents a real hazard. This topic is addressed in the following safety standard written by the National Fire Protection Association: NFPA 664, 'Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities'. Specifically, please see Section 8.2.2.2 on page 664-13 entitled 'Duct System'. Their philosophy here is that electrically conductive metal piping is always preferable to non-conductive PVC in minimizing the potential hazard that could be caused by a buildup of static electricity in a dust collection system.

[Jim O'Dell]

Andy, do you have a link to that publication online that the general masses can access? I'd like to see how it is worded, and what situation it applies to. I'm going to guess that it is written to commercial operations, and yes, those installations should be metal for fire safety. Would it be best for homes to do the same? Possibly. Is the same risk there for problems as in a commercial situation? Have there ever been any substantiated explosions from dust concentration and static spark in a home environment. I can see a fire break out if metal was being collected, which is why I chose not to put a pick up at my drill press or the grinding wheel. These questions aren't to challenge what you say, but I would like to see the documentations if it has happened so I can gain a better understanding and further weigh the risks for myself. Yes I chose to use PVC for my ductwork. I've had mine up and running for about 8 months. I've yet to empty the barrel. It doesn't get a lot of work.
Anyway, I hope you can point to a website we can read up at. Who knows, it might change some of our ideas. Jim.

[Brian Backner]

One option to the high cost of PVC fittings it to MAKE your own. I found this very interesting software that prints out templates for making T's and Y's for any diameter, angle of take-off, or offset. For instance, you could design a Wye - 6" main pipe with a 4" takeoff at 37.4 degrees with a 2" offset (so the 4" takeoff will be flush with the back of the main duct and the whole thing will sit flush to the wall):

http://harderwoods.com/pipe.html

Brian

[Jim O'Dell]

Brian, someone on one of the forums gave a link to a program that does that, and I down loaded it. I have a couple questions: What did you use to cut the holes? Did you cut them at the bevelled angle that the wye exits on? What did you used for glue? Thanks for any help you can offer! Jim

[Andy Calenzo]

Jim,

Thanks for your reply to my post. Regarding the link that you requested, please note the following:

http://www.nfpa.org/freecodes/free_access_agreement.asp?id=66407 (http://www.nfpa.org/freecodes/free_access_agreement.asp?id=66407)

This link will take to the exact spot on the NFPA website where the 664 standard can be read free of charge (requires Java software). We feel that this document, for the most part, offers valuable safety information that is applicable regardless of the size of the woodworking operation.

[Jim O'Dell]

Thanks Andy!! I'll start on it this evening. Jim.

[Brian Backner]

Brian, someone on one of the forums gave a link to a program that does that, and I down loaded it. I have a couple questions: What did you use to cut the holes? Did you cut them at the bevelled angle that the wye exits on? What did you used for glue? Thanks for any help you can offer! Jim

Jim,

The program prints out a full size pattern - you tape it around the main pipe. The pattern is made up of two roughly parallel lines - you cut through the wall of the pipe along the inner line and then bevel the resulting hole to the outer line. Any sharp saw that will cut through pvc pipe will work fine - I drilled a hole and then used a fine tooth sabre saw. The beveling was done with a medium cut curved file.

The website not only creates templates for you, which you can then print out, there is also a tutorial that shows how to do it step by step.

A second template is for the "fish mouth" of the intersecting take-off pipe. Once you get it close, glue a piece of 150 grit sandpaper to a section of the main pipe and rub back and form 'til you get a decent fit. Then use pvc pipe cleaner (either the purple or clear stuff) and finally fuse them together with pvc thick bodied pipe cement. The only disadvantage is that you have to hold the pieces together for several minutes until everything sets up enough to be self supporting.

Brian

[Jim O'Dell]

Thanks for the info Brian!. Yes, that sounds like the same program I down loaded, I just wasn't sure what to use to cut the hole. I was thinking a hole saw that was close in diameter, and get a long pilot bit, but then I'd go right through the other side! :eek: :D The program I have lets you dictate the outside diameter of both pipes so it makes it easy to do a 6-6-2 wye if you want. I'm guessing your's is the same setup.
Thanks again. I may try it as I do need a small diameter pipe off of a 6" to go to a MS blade guard and/or RAS blade guard hook up, that could also be used with hand held power tools. Jim.

[Brian Backner]

Andy,

Without having read the link the to NFPA 664 reference you cite, I would agree that electrically conductive dust collection piping would always be preferable. That said, how do you rate the use of conductive "raceways" to be built into a pvc system - I have seen systems with bare copper ground wire loosely draped inside the pipe, and I have also seen steel screws driven though the wall of the pipe at regular (6-9") intervals all bonded together by a ground wire spiral wrapped around the outside of the pipe.

Also, how do recommend grounding flexible plastic pipe for that last several feet where the ductwork connects to a machine?

Brian

[John Schreiber]

This sounds like a stupid idea, but I can't quite decide why it is so stupid. Has anyone tried making square tubing out of sheet goods? 1/2" ply or something. I guess if your time has any value, it wouldn't make sense, but would it work?

[Tom Veatch]

Thanks for the info Brian!. Yes, that sounds like the same program I down loaded, I just wasn't sure what to use to cut the hole. ....

Did you download a program to run on your local machine? The links I've seen appear to be for an online application that runs on the server and downloads only the results. That requires internet connectivity each time the program is executed. I'd prefer a local application if such is available. Might even be willing to contribute a few dollars for a version with a local executable.

[Stan Welborn]

This sounds like a stupid idea, but I can't quite decide why it is so stupid. Has anyone tried making square tubing out of sheet goods? 1/2" ply or something. I guess if your time has any value, it wouldn't make sense, but would it work?
No reason why that wouldn't work IMO. Time consuming maybe, but it'd work. I would keep away from 90 angles though. Which would make it even more time consuming.

[Jason Beam]

No reason why that wouldn't work IMO. Time consuming maybe, but it'd work. I would keep away from 90 angles though. Which would make it even more time consuming.
I agree - it might take some time, but it'd work. I've seen it done some place. Though, the shape isn't the MOST optimal for airflow - I think i saw a page somewhere on the web somewhere that explained square vs. round for airflow. But unless it was very smooth (maybe melamine?) it'd probably impart quite a bit more drag than sheet metal or pvc.

Then again, it may not be a factor in this application. Square duct work has been used in the HVAC world ages. The air is not moving very fast, though, so maybe that's the limiting factor? Beats me!

Now ... would it be cheaper? I dunno .. your big troubles are gonna be transitions to machines unless you can modify the machine to take the square duct and doesn't need to move. At $20/sheet the straight runs would probably be pretty economical. Getting to the machines, i dunno ... sharp 90s into round holes for flex tube would be pretty turbulent, methinks.

It's an interesting exercize, to say the least. :)

[Andy Calenzo]

Brian,

On the subject of trying to ground a PVC piping system, NFPA 664 states that 'a ground wire or other grounding system for PVC pipe is not acceptable' (see page 664-31 of NFPA 664). I think that their reasoning is that trying to ground a plastic piping system is somewhat unreliable. I believe that this is because if any of the ground connections become faulty a year or so after installation, it won't function and you wouldn't necessarily be aware that this ground fault occurred.

Regarding a recommendation on grounding the flexhose typically used over the last few feet between the ductwork and the tool port, I would prefer that 'static dissipating' hose be used. This type of hose is commercially available (I found it when I conducted an internet search earlier today) although it's probably expensive. I will say from experience that if the flexhose is connected to an all metal piping system, 4 to 5 feet of flexhose at each tool drop doesn't seem to create much in the way of static electricity buildup. Also, NFPA 664 allows for the use of short runs of flexhose at tool drops to make it easier to make the connection(s).

Andy C.

[Noah Katz]

"I do need a small diameter pipe off of a 6" to go to a MS blade guard"

Don't bother; it'de be far better to hook a shop vac to that sized port.

But there will still be a spray of material that the port won't get; I'd (and it's on my list) run the full 6" to a large hood around the MS.

[Jim O'Dell]

Did you download a program to run on your local machine? The links I've seen appear to be for an online application that runs on the server and downloads only the results. That requires internet connectivity each time the program is executed. I'd prefer a local application if such is available. Might even be willing to contribute a few dollars for a version with a local executable.

Tom, I can't remember now if it was a down loadable program, or one that you just plugged your info into online. I'll have to do some searching to see if I can find where it came from. I'll post the link in this thread if I find it. Jim.

[Tom Veatch]

Tom, I can't remember now if it was a down loadable program, or one that you just plugged your info into online. I'll have to do some searching to see if I can find where it came from. I'll post the link in this thread if I find it. Jim.

Thanks, Jim. I'll keep an eye out. I've got a computer in the shop for CAD type stuff and suppose I could network it to the office machine and share the internet connection. Probably ought to do that for a lot of reasons, but that's one of those "roundtoits". Besides, not having direct internet connection in the shop keeps my Lee Valley/Rockler/etc. bill a little more manageable. My wife already thinks I'm having an affair with the UPS delivery lady.:)

[Jim O'Dell]

Thanks, Jim. I'll keep an eye out. I've got a computer in the shop for CAD type stuff and suppose I could network it to the office machine and share the internet connection. Probably ought to do that for a lot of reasons, but that's one of those "roundtoits". Besides, not having direct internet connection in the shop keeps my Lee Valley/Rockler/etc. bill a little more manageable. My wife already thinks I'm having an affair with the UPS delivery lady.:)

Well unfortuanately, it's not a stand alone program, so you'll just have to have a little will power, and your wife will just have to trust you!!:D :D
Luckily I found the site here at work. Go to: http://www.harderwoods.com/pipetemplate.php It's simple to use.


Noah, you're probably right about the small pipe thing, but I really don't want the cyclone and the shop vac on at the same time.:eek: Jim.

[Brian Backner]

Brian,

On the subject of trying to ground a PVC piping system, NFPA 664 states that 'a ground wire or other grounding system for PVC pipe is not acceptable' (see page 664-31 of NFPA 664). I think that their reasoning is that trying to ground a plastic piping system is somewhat unreliable. I believe that this is because if any of the ground connections become faulty a year or so after installation, it won't function and you wouldn't necessarily be aware that this ground fault occurred.

snip

Andy C.


Andy,

Thank you for the response. As I said, I appreciate the prudence of using conductive duct work but I had never realized that NFPA 664 existed. For non-commercial applications, I can see the higher cost creating a great incentive to use PVC.

Over the years, I have seen more than a few professional cabinet shops, typically one to three man operations, using PVC or other types of plastic pipe. I wonder what OSHA has to say about such installations? I also wonder what their insurers would do in the case of an explosion/fire; would they be criminally/civilly liable in the event of an injury or death that could be traced to that piping?

Brian

[Jim Kountz]

Im just gunna chime in here with my own experience. I have had both 6" systems and now two 4" runs in my shop and I suppose if someone hooked some measureing gadget to it and conducted some tests they would find some loss of pressure and suction but the bottom line is I didnt notice a thing. One of my runs is over 16' long while the other is about 12'. My dust collector came with a double 4" to 6" wye and thats why I used it like that. This setup allowed me to make two separate runs to various points in the shop. Everything has a blast gate (shop made) on it with low voltage switches and turns my DC on when open and off when shut. This way I dont leave a gate open by accident. This setup works well for me but Im just a one man show. I suppose if there were multiple machines running at the same time the system may not be up to job. However along those notes I do often have the planer and table saw going at the same time and this works fine in my shop. I suppose every setup is going to vary but so far so good with the 4" duct. One more thing, use the thin wall PVC drain, its even cheaper and so are the fittings.

Jim

[Stan Welborn]

Im just gunna chime in here with my own experience. I have had both 6" systems and now two 4" runs in my shop and I suppose if someone hooked some measureing gadget to it and conducted some tests they would find some loss of pressure and suction but the bottom line is I didnt notice a thing. One of my runs is over 16' long while the other is about 12'. My dust collector came with a double 4" to 6" wye and thats why I used it like that. This setup allowed me to make two separate runs to various points in the shop. Everything has a blast gate (shop made) on it with low voltage switches and turns my DC on when open and off when shut. This way I dont leave a gate open by accident. This setup works well for me but Im just a one man show. I suppose if there were multiple machines running at the same time the system may not be up to job. However along those notes I do often have the planer and table saw going at the same time and this works fine in my shop. I suppose every setup is going to vary but so far so good with the 4" duct. One more thing, use the thin wall PVC drain, its even cheaper and so are the fittings.

Jim

Good to hear. I had decided on this route strictly as a $ decision thinking it would work. Or at least no one could tell me conclusively that it would not. I can get the 4" S&D pipe and fittings to run dual runs much cheaper than I can do 6" in anything else. INCLUDING the HD snap-lock stuff at my local borg. Good to hear from someone who has a system like that already up and running.
Thanks for posting Jim.

[Jason Beam]

Im just gunna chime in here with my own experience. I have had both 6" systems and now two 4" runs in my shop and I suppose if someone hooked some measureing gadget to it and conducted some tests they would find some loss of pressure and suction but the bottom line is I didnt notice a thing. One of my runs is over 16' long while the other is about 12'. My dust collector came with a double 4" to 6" wye and thats why I used it like that. This setup allowed me to make two separate runs to various points in the shop. Everything has a blast gate (shop made) on it with low voltage switches and turns my DC on when open and off when shut. This way I dont leave a gate open by accident. This setup works well for me but Im just a one man show. I suppose if there were multiple machines running at the same time the system may not be up to job. However along those notes I do often have the planer and table saw going at the same time and this works fine in my shop. I suppose every setup is going to vary but so far so good with the 4" duct. One more thing, use the thin wall PVC drain, its even cheaper and so are the fittings.

Jim


Just so I'm not misunderstanding .. I get from this post that you have two 4" runs to different tools. NOT two 4" pipes going to a single port on one tool, right?

Just wanna makes ure i'm comparing apples to apples here.

The OP's question wasn't about stepping down to 4", it was about ganging two 4" pipes to take the place of a single 6" run to a single machine. It sounds like the airflow would be similar. I think we've all understood it'd be less, but nobody seems to know how much less.

Someone should do it and find out ... take 6" down to two 4", run some length of dual 4" pipe and then recombine them to 6" again at the other end and compare that performance with that of a 6" duct. I'm especially concerned with the fact that you're doubling up your elbows at every turn. So it'd e really nice to see if someone could test wtih some real-world duct runs to see if the elbows are as big a factor as some of us suspect.

Something tells me that by the time you get enough wyes and fittings to pull this off, you'll be in nearly as much money as if you just did it with 6" to begin with.

Stan are you saying that buying two of everything in 4" pvc is cheaper than buying one of everything in 6" steel (snappy or not)? Prices must be quite different between you and me because two of each 4" would be about 40% more money around here.

I'll be the first to admit i'm speculating ... i was just working on my DC ducting and considered doing a test, but I don't have enough 4" fittings to conduct a useful test. My opinion stands that it wouldn't be "good enough" and if it were my system I would later regret trying to pinch pennies.

[Jim Kountz]

Jason you are absolutley correct. I read the original post wrong. My apologies group!

Jim

[glenn bradley]

http://www.taunton.com/finewoodworking/Workshop/WorkshopPDF.aspx?id=2756

[Tom Veatch]

Thanks for the link, Glenn, but to read the entire article, one has to be a paid subscriber to the online service.

The back 'n' forth on this subject will probably never be settled to anyone's satisfaction. The truth is, dust explosions can and do happen. June 8, 1998, the DeBruce grain elevator (http://www.google.com/search?hl=en&newwindow=1&rls=com.microsoft%3A*&q=DeBruce+grain+elevator+explosion+wichita&btnG=Search)within 5 miles of my house exploded with several fatalities. I definitely felt the shock wave when it happened.

However, the danger of a dust explosion in a hobbiest shop DC setup is badly overblown (pun not intended). The conditions have to be just right (or wrong, depending on the point of view) for a self sustaining flame front to develop and progress to an explosion. If I'm not mistaken, there has never been any reports of such an occurence in a home workshop. Unlike grain elevators, most small shops simply don't produce enough fine dust in heavy enough aerosol concentrations to create explosive conditions. There is a much higher danger of fire in the collection bin from sparks or chips of hot metal from accidental encounters with metal in the wood than from dust explosions generated by static discharges.

Don't get me wrong, I'm not recommending either that you do or don't ground pvc ducting. I am saying that, in my opinion, for whatever that might be worth, you're not flirting with disaster if you don't.

[Noah Katz]

"June 8, 1998, the DeBruce grain elevator (http://www.google.com/search?hl=en&newwindow=1&rls=com.microsoft%3A*&q=DeBruce+grain+elevator+explosion+wichita&btnG=Search)within 5 miles of my house exploded with several fatalities. "

Is that relevant? Was there any PVC piping w/3500 w/high velocity airflow involved?

[Tom Veatch]

"June 8, 1998, the DeBruce grain elevator (http://www.google.com/search?hl=en&newwindow=1&rls=com.microsoft%3A*&q=DeBruce+grain+elevator+explosion+wichita&btnG=Search)within 5 miles of my house exploded with several fatalities. "

Is that relevant? Was there any PVC piping w/3500 w/high velocity airflow involved?

The only relevance is to show that I am well aware that dust explosions can and do occur.

[Alan Schaffter]

Stan, sent you a PM.