Need some advice on DC Plumbing

[LCHIEN]

Thanks for all the great info guys, really helps alot. I'm now leaning towards just going with the 4" PVC rather than trying to hunt down the 5" ducting and fittings although 2.5 times the resistance is still putting me off a bit. At least I know now that just using the flex hose is now no longer an option.

In regards to the type of ducting availalbe at Home Depot, I originally looked at the white 4" S&D pipes. I noticed that the inner diameter was slightly smaller than the black PVC and the inside of the pipe had ripples rather than being completely smooth. That's why I was planning to use the black PVC which is the only other choice at HD. Even though the walls are thicker the inner diameter is slightly larger than the S&D pipes and the cost if I remember correctly is something like $13-18 for 10 foot section.

Well, I am no longer so convinced on the 2.5x figures.
Pentz has a spreadsheet in which you can estimate the losses of a duct run by entering the no. of 90's, Wyes, run length of smooth tubing, and run length of flex tubing. Some curious results:

Duct & fitting size 4" 5" 6"
90's 3 3 3 ea
Wyes 1 1 1 ea
run length 23 23 23 ft
Flex len 1.5 1.5 1.5 ft
SP Loss 2.93 2.36 2.0

Just Changing flex length to 6 ft causes a significant loss
SP Loss 3.88 3.09 2.36

So those of you dropping 4" Flex from the ceiling are incurring a heavy loss - nearly 1" S.P.

Other loss factors in your system:
Filtering
going from 30 u bag (2.5" S.P.Loss)
1 u Bag (1" S.P. Loss)
Pleated filter 225-300 sq ft (.5 to .3" S.P. Loss)

Depending upon whether you have open ports on your machine - the size and number of ports and hoods can have a big loss. Running 4" hose to a machine with 2.5" port is not much better than running a 2.5" hose, Pentz indicates. Loss at a well-ported machine could be 2-3 inches.

If you use a trash can pre-seperator, this imparts another 4.5" S.P. Loss to your system. THat's why they apparently work so well - they cause so much CFM loss, all the particles drop out in the can BUT the cost is so much CFM, you are not picking up all the fine dust at the source according to Pentz.
You can see from the performance CFM vs. S.P. I posted earlier in this thread that 4.5" additional loss will put you way down the curve on CFM if you already have 3-5" S.P. Loss from ducting and other hardware.



Conclusion #1 - According to Pentz's spreadsheet there doesn't seem to be a huge S.P. loss penalty running 4" instead of 5". Pentz's concern here would be not being able to get sufficient velocity at the pickup point to get all the fines. Going from 5" to 4" on a reasonable run, would cost about 1/2" S.P. Loss which on the blower performance chart, for the 1.5 and fudged 2 HP blowers would cost you about 100 CFM. BTW, I think maybe the "fudged 2 HP" DC is the H.F. unit.

Conclusion #2 - the Static pressure insertion loss of a Trashcan separator is huge and costs you in terms of air flow volume and velocity loss.

[Garasaki]

Wow, I seriously question the figure of 4.5" loss in a trashcan separator.

That's outrageous!! I'm gonna see if I can break into the calcs he uses...he has all those hidden in that spreadsheet but maybe I can get a peak at them.

One question I have, why aren't you guys considering 6" pipe for horizontal main runs?

Also, why are you limiting yourself to only buying stuff from the BORG? WHy not try some local plumb supply houses or directly from some plumbers?

[cgallery]

Well, I am no longer so convinced on the 2.5x figures.

That was an outstanding summary!

I guess if I had room for a 4" system I'd design a bypass blastgate that would allow me to continue using a separator w/ my jointer/planer, but bypass it for my other tools.

[cgallery]

Wow, I seriously question the figure of 4.5" loss in a trashcan separator.

That's outrageous!! I'm gonna see if I can break into the calcs he uses...he has all those hidden in that spreadsheet but maybe I can get a peak at them.

One question I have, why aren't you guys considering 6" pipe for horizontal main runs?

Also, why are you limiting yourself to only buying stuff from the BORG? WHy not try some local plumb supply houses or directly from some plumbers?

I would welcome more discussion about static loss on cyclone separators. I would imagine the math would be pretty interesting.

I think a lot of users shy away from 6" because velocity drops enough that chips may fall out of the airstream. That is what I've read. I have a real hard time believing it, but I've never had a real dust collector.

[LarryG]

One question I have, why aren't you guys considering 6" pipe for horizontal main runs?

My understanding (right or wrong) has always been that with this hobbyist class of 1.5-2HP units, a 4" duct is too small (increased resistance, as we've been discussing) but a 6" duct is too large (air velocity slows down to the point that the particles are no longer kept suspended in the airstream).

Loring's most recent post points to why I went with the economy of 4" pipe: this is a complex subject and I'm just not sure that it's even possible to get Pentz-approved efficiency with the DC units most of us own. It's maybe not quite an all-or-nothing proposition, but it's pretty close. You're either protecting your health adequately, or you're not, and the threshold is lower than one might think. I am persuaded that it takes a big investment in both dollars are shop space to get a system that will keep all the nasties out of one's lungs. I did not want to spend medium-size money on a piping system that ultimately would still fall well short of protecting my health.

[JR]

One question I have, why aren't you guys considering 6" pipe for horizontal main runs?

Also, why are you limiting yourself to only buying stuff from the BORG? WHy not try some local plumb supply houses or directly from some plumbers?

6" costs quite a bit more. And, IIRC, the input to the HF DC is 5", so running 6" doesn't seem to make much sense.

Buying from a plumbing supply is fine. You get more options. But you also lose the privilege of shopping on Saturday or Sunday (depending on the shop, obviously), when mosy hobbyists are doing their thing. Also, if you're not a contractor, pricing may not be advantageous.

JR

[THyman]

My understanding (right or wrong) has always been that with this hobbyist class of 1.5-2HP units, a 4" duct is too small (increased resistance, as we've been discussing) but a 6" duct is too large (air velocity slows down to the point that the particles are no longer kept suspended in the airstream).

Loring's most recent post points to why I went with the economy of 4" pipe: this is a complex subject and I'm just not sure that it's even possible to get Pentz-approved efficiency with the DC units most of us own. It's maybe not quite an all-or-nothing proposition, but it's pretty close. You're either protecting your health adequately, or you're not, and the threshold is lower than one might think. I am persuaded that it takes a big investment in both dollars are shop space to get a system that will keep all the nasties out of one's lungs. I did not want to spend medium-size money on a piping system that ultimately would still fall well short of protecting my health.

I agree with Larry. I'm about to hardpipe my DC as well. Larry can you post more photos especially areas that are tricky to connect or areas that you would do differently.

Thanks Todd

[Garasaki]

Well, I am no longer so convinced on the 2.5x figures.
Pentz has a spreadsheet in which you can estimate the losses of a duct run by entering the no. of 90's, Wyes, run length of smooth tubing, and run length of flex tubing. Some curious results:

Duct & fitting size 4" 5" 6"
90's 3 3 3 ea
Wyes 1 1 1 ea
run length 23 23 23 ft
Flex len 1.5 1.5 1.5 ft
SP Loss 2.93 2.36 2.0

Just Changing flex length to 6 ft causes a significant loss
SP Loss 3.88 3.09 2.36

So those of you dropping 4" Flex from the ceiling are incurring a heavy loss - nearly 1" S.P.

Other loss factors in your system:
Filtering
going from 30 u bag (2.5" S.P.Loss)
1 u Bag (1" S.P. Loss)
Pleated filter 225-300 sq ft (.5 to .3" S.P. Loss)

Depending upon whether you have open ports on your machine - the size and number of ports and hoods can have a big loss. Running 4" hose to a machine with 2.5" port is not much better than running a 2.5" hose, Pentz indicates. Loss at a well-ported machine could be 2-3 inches.

If you use a trash can pre-seperator, this imparts another 4.5" S.P. Loss to your system. THat's why they apparently work so well - they cause so much CFM loss, all the particles drop out in the can BUT the cost is so much CFM, you are not picking up all the fine dust at the source according to Pentz.
You can see from the performance CFM vs. S.P. I posted earlier in this thread that 4.5" additional loss will put you way down the curve on CFM if you already have 3-5" S.P. Loss from ducting and other hardware.



Conclusion #1 - According to Pentz's spreadsheet there doesn't seem to be a huge S.P. loss penalty running 4" instead of 5". Pentz's concern here would be not being able to get sufficient velocity at the pickup point to get all the fines. Going from 5" to 4" on a reasonable run, would cost about 1/2" S.P. Loss which on the blower performance chart, for the 1.5 and fudged 2 HP blowers would cost you about 100 CFM. BTW, I think maybe the "fudged 2 HP" DC is the H.F. unit.

Conclusion #2 - the Static pressure insertion loss of a Trashcan separator is huge and costs you in terms of air flow volume and velocity loss.

I have a longer reply on deck, regarding some of the reasons this analysis is hard, but I wanted to post this separately.

The numbers you have quoted for resistance are incorrect. I go into more detail about this, but the way Bill's calcs are set up are to assume you are getting the required airflow thru the pipe, regardless of your system.

The correct values for PIPE ONLY RESISTANCE and assuming the default 800 cfm (more on that later too) should be (according to Bill's spreadsheet)

4" 15.8
5" 6.75
6" 2.81

I'm really not kidding. Those are the right numbers. Directly from his spreadsheet.

What you have to do, is change the Delivered velocity numbers from 4000 (his target number) to whatever the calculated velocity is. Otherwise all calcs are based on the target velocity of 4000.

To be honest, it appears that unless you understand how it's set up, Bill's Spreadsheet does more harm then good

[LarryG]

Todd, I have a few more photos on hand but none of them show the system in its final form, or show anything more than broad, general views. I'll take some better ones, including some close-ups, tonight and will post them tomorrow.

None of the connections were especially tricky, but there are one or two portions of the runs I'd do a little differently.

EDIT: Before this thread goes any further, perhaps I should say ... my aim here is only to share what went into my own decision-making process, and to illustrate how I implemented my 4" hard-pipe system. It is not my intent to try to talk anyone into doing it "my way," nor is it to refute the excellent (and, I might add fascinating) legwork that more technically-savvy members like Garasaki and Loring are doing. On the contrary, I am trying hard myself to sort all this out, because I have dreams of building a larger, permanent shop of my own someday (so I can move out of the rented building I'm now in) and I want that shop to have a first-class dust collection system. In the meantime, given my current economic and spatial restraints, I have settled for a system that leaves me with a reasonably clean shop and have further accepted that I might well be running certain risks, health-wise. These are my decisions. They are not necessarily good decisions, applicable to or acceptable for everyone.

[Garasaki]

I found his calculations. (I apologize for the long post that follows)

Ok, look, believe me on this, everyone is chasing their tails looking at the math behind this. I was, in fact had part of it written out, going to do a long post with tons of equations and formula's and numbers, just to see where we ended up.

The problem is EVERY calculation is based on the volume of air moving thru your system.

All of Bill's calculations are too.

How do you know how much volume is moving thru the system?? The only way to even have a clue is to measure it.

We can sit here and guess 400 or 800 or 650 or whatever. The problem is it ain't right.

What makes it even more futile is when you discuss changing pipe sizes. Each time you change a pipe size, you change the volume of air moving. That means every calculation you've made gets thrown out the window.

Thats why my 2.5x number isn't true. It assumed constant airflow. The reality is that when you go from 4" pipe to 5" pipe, airflow increases. This increases velocity, which (if you recall) is SQUARED to get resistance. So it has an exponential impact on the actual value of resistance.

I have news for you guys...Bill Pentz's word isn't sacred. He's human too. Don't take everything he says to be concrete truth. I'm not discounting what he says, he has put a lot of time and effort into his website and there is a lot of good info there. But just because something is printed there, does not make it so. If something dosent make sense to you, really do the research and make up your own mind.

In regards to his spreadsheet, EVERY calculation within it is based on the CFM required cell. Good ole number D49. It's everywhere. So he assumes a constant velocity as well, and with it accompanies all the inheriant problems of that assumption.

However, he does get brownie points for looking at it "backwards" (sort of). He says "look here, this is WHAT YOU NEED FOR EFFECTIVE COLLECTION, now go build yourself a system based on these parameters and buy equipment that fits these numbers".

It (Bill's spreadsheet) is not intended to be a comparison tool, it's not intended to be "Ok, I have this dust collector, this separator, my runs are this long, and now I'm not sure if I should use 4" or 5" or 6" pipe...lets see what happens if I do".

In order to have that tool, you would have to take your dust collector fan curve, and input THAT into the "magical" D49 cell. Doing that would allow you to accurately evaluate different system designs based on actual numbers from a dust collector. I'm not a programmer, I don't know how to create a excel document with that degree of "life". But it would be really neat if someone could!

[LCHIEN]

My understanding (right or wrong) has always been that with this hobbyist class of 1.5-2HP units, a 4" duct is too small (increased resistance, as we've been discussing) but a 6" duct is too large (air velocity slows down to the point that the particles are no longer kept suspended in the airstream).

Loring's most recent post points to why I went with the economy of 4" pipe: this is a complex subject and I'm just not sure that it's even possible to get Pentz-approved efficiency with the DC units most of us own. It's maybe not quite an all-or-nothing proposition, but it's pretty close. You're either protecting your health adequately, or you're not, and the threshold is lower than one might think. I am persuaded that it takes a big investment in both dollars are shop space to get a system that will keep all the nasties out of one's lungs. I did not want to spend medium-size money on a piping system that ultimately would still fall well short of protecting my health.

I reread a lot of Pentz's webpages carefully yesterday. There's some new stuff.

Pentz leaves no doubt that he thinks we all should have 5 HP blowers capable of true 1500 CFM with a cyclone and put full hoods on all our machines; his goal is to capture 100% of dust about 1-2 microns and up starting at the machine. (this for a small woodworkers shop in a garage)

So yes, he would unequivocally say your HF machine (usually tested at about 800 CFM completely uloaded) would be totally inadequate.

But I find it fascinating reading and it gives me a much better understanding of how dust collection systems work, sometimes even in a quantitative way from studying the spreadsheet on loss caclulations for example, in conjunctin with the typical blower CFM-SP plots.

Understand that to achieve Pentz' goal he has to capture all the fine dust being thrown off by table saws and miter saws and lathes, the saws turning 100 mph at the tip. You need a hood which sucks a sufficient quantity of air at some distance to overcome this speed. The velocity of air being pulled into an inlet goes down by the cube of the distance from the inlet working into a 3D space. So he says you need 4000 Ft/min velocity at the inlet. That's why the big hose, high velocity.



At least for an engineer like me I do not find it a waste of time at all reading his work; I do find it helps me decide how to get the maximum performance out of what I have.

[LarryG]

My use of the phrase "Pentz-approved efficiency" was somewhat tongue-in-cheek. Garasaki is right: he's as human as the rest of us, which makes him subject to error, and susceptible to his own biases. Many consider him to be a genuine fanatic (I've never run across anyone who'd call him a crackpot, though) and given his personal health problems, I suppose he is, with good reason. But implicit within that is the question, "Is what he preaches overkill for most people?" That, I just don't know. I really don't. I do know that many people read his web site and immediately scoff and claim it IS overkill. And maybe it is, for most of us. The problem there is the human tendency to assume that the really bad stuff is always going to happen to The Other Guy.

it helps me decide how to get the maximum performance out of what I have.

A nicely succinct way of saying exactly what I am trying to do, and what has driven my own decision-making process.

[LarryG]

Here's a Sawmill Creek thread a Google search led me to a while back, and which I bookmarked for future reference. It's now some 16 months old but it's far from outdated.

Much of it focuses on filtration rather than pipe size, but of course that's another important part of the equation. The one fellow who's a big proponent of bags over canisters certainly comes across as knowing his stuff, even though his position is a bit different than most of what I've read elsewhere. Most of us assume a canister is far superior to any bag; not so, says he.

[Garasaki]

I realized I should probably do this, as I feel it better illustrates the advantage of larger ducting/pipe:

Resistance values at 400 cfm (probably a more realistic number from the 1.5 HP to 2 HP DC's that we utilize)

4" - 3.84"
5" - 0.71"
6" - 0.16"

Lets assume there's about 3" static elsewhere in the system - stuff like filters, intakes, etc. So total system static, is like 6.8" SP for a 4" duct system, 3.7" SP for a 5" duct system, and 3.2" SP for a 6" duct system. So now you look at the fan curve



And for the Fudged DC, airflow is

4" - ~400 CFM (Hey we got lucky, this is what we assumed)
5" - ~650 CFM
6" - ~775 CFM

That illustrates what you gain with the bigger pipe.

Ok, hold on though. If you plug that CFM into the spreadsheet, it spits out 3.36" SP for the 5" system, making the system SP 6.4" SP, and according to the fan curves, the Fudged DC can't push 650 CFM at that SP.

I guess that's really what I'm getting at. This calculation dosen't really come full circle, well, not without a lot of iterations.

But, the point I'm trying to make is (and btw I'm not trying to tell anyone what they should or shouldn't do, and there is no doubt that something is better then nothing [btw I use a shop vac still...workign on getting a DC one of these days]) that increasing the size of your piping should result in some signifigant increases in real world airflow.

Think of it as getting more bang from your DC buck...

[Garasaki]

I was watching another DC thread over on woodnet, with a lot of people jumping down other people's throats....and lots of people relying on Bill's website as evidence.

I just wanted to bump this thread as a reminder that Bill's spreadsheet is NOT set-up to do what is intuitively obvious....