Dust collection routing?

[Austin Richardson]

So I just got a 1.5 HP delta dust collector and want to hook it up to my table saw, router fixed into outfeed table, and miter saw. I am wondering if I should be running 4" pipe to all the locations or should I be decreasing the diameter of the pipe as I carry it past a certain distance.

Also, I have seen articles saying PVC is not recommended since the friction and static is higher so it will reduce the suction capacity more than metal duct. Is there much of a difference going from PVC to metal ducting?

Thanks!

[Bram]

I recommend using 4" (atleast) ducting for the whole dust collection system. Try not to reduce that diameter cuz that will decrease the suction a lot. Even not at the machine itself.

Also use blast gates to close off any non-used pipes.

For our small shops, PVC pipe is sufficient and cheaper than metal ducting. I think the suction would not decrease dramatically if you use pvc over metal piping.

For more info, I recommend reading Bill Pentz' website.

Good luck

[linkmx674]

im joining in on the topic- i just got me a dc unti as well and was wondering about using 90 deg bends and so forth in places, does that reduce air flow? where are the best places to use blast gates

[Beechwood Chip]

My understanding is that your curves should be as gentle as possible (ie, the largest possible radius). If you are using standard fittings you should use Y's and 45 bends, and avoid Tees and 90 bends.

The blast gates should be as close to the main trunk as possible, wherever you split off. But, you need to be able to operate the gates conveniently. Having a long tube with a closed gate at the end isn't as bad as having an open gate, but it does hurt the performance.

[konkers]

My understanding is that your curves should be as gentle as possible (ie, the largest possible radius). If you are using standard fittings you should use Y's and 45 bends, and avoid Tees and 90 bends.

I'm not sure how air works compared to water but it's better to use one 90 instead of two 45s when running water through PVC.

[Jfitz]

I'm not sure how air works compared to water but it's better to use one 90 instead of two 45s when running water through PVC.

I have never heard that before. Any idea why (other than cost)?

It's better to have 2 45's joined together to make a more gradual 90, rather than a regular 90; it cuts down on the resistance and turbulence of the air in the pipe.

[jsiard]

It's a little complicated but when dealing with dust collection you want to keep the air moving as fast as possible, therefore it is best to use the largest pipe your collector can handle. 90˚ degree bends should be broken into 2- 45’s with a short piece of pipe in between, wye’s in place of tees and so on. I would encourage you to visit Bill Pentz’ site, where he explains this in great detail.

[Vic]

If you're going to make a 90 degree turn, you should use a street 90. http://www.google.com/m/products/catalog?hl=en&client=safari&q=4+inch+street+90+elbow&gs_upl=31668l39965l0l41013l9l9l0l0l0l0l475l2284l0.1.7.0.1l9l0&um=1&ie=UTF-8&tbm=shop&cid=17887442781828220340&near=Pasco,%20WA&sa=X&ei=PbceT6f-EKXjiAKT7rX7Cw&ved=0CCsQ8wIwAQ

(null)

[linkmx674]

what about using vertical runs that go up the wall? or come down from the ceiling in the middle of the room to mt table saw

[Eric.]

It's a little complicated but when dealing with dust collection you want to keep the air moving as fast as possible, therefore it is best to use the largest pipe your collector can handle.

That's apparently a pretty common misconception. The largest pipe your DC can "handle" will give you your greatest CFM (volume of air moved), but the speed of the airflow will decrease with every step up in pipe size. From my understanding, using anything larger than 4" pipe for DCs 2HP and smaller will cause a decrease in air speed that will cause fallout, and consequently, clogs, especially in vertical drops.

As far as Bill Pentz is concerned, nothing short of a jet engine and pipe the size of bridge and overpass conduit will be sufficient, so take his expert opinion with a grain of salt. Many a woodworker has lived a full, healthy life with much less for DC. Get an air cleaner and some good respirators if particulates are a major concern...you should be wearing one anyway and it's much cheaper than Bill's advice. You can drive yourself nuts with this DC stuff. I'm over it.

[konkers]

I have never heard that before. Any idea why (other than cost)?

It's better to have 2 45's joined together to make a more gradual 90, rather than a regular 90; it cuts down on the resistance and turbulence of the air in the pipe.

According to my experience with saltwater aquariums, this is not the case. In Julian Sprung's mammoth 3 volume "The Reef Aquarium" series he lists the equivalent length of pipe for water flowing through PVC. For 2" PVC pipe it is as follows:

90 degree elbow: 5.5'

45 degree elbow: 2.8'

90 degree sweep: 4.3'

90 degree street ell: 8.6'

So two 45s to make a 90 gives you 5.6' instead of 5.5'. If you use a 90 degree sweep (gradual instead of sharp curve) you'll get down to 4.3'. So, two 45s does not make 1 gradual 90, just two sharp 45s.

If you're going to make a 90 degree turn, you should use a street 90. http://www.google.co...ved=0CCsQ8wIwAQ

I think the street ells mention in the above table are more like http://www.bulkreefs...p-x-spigot.html . The one Vic points out is probably more like a 90 degree sweep.

[dwacker]

Comparing water flow to air flow is apples and oranges. Water flow uses head pressure of the liquid. Air does not care about head pressure or gravity. All we really care about is CFM. A straight 90 with planer shavings mixed with the air will cause turbulance at the bend especially when those shavings hit that sharp corner.. A longer sweep even if its 2 45's will reduce turbulance. But on the other hand the OP only has a small 1.5 hp dust collector so adding any ducting what so ever is really going to deteriorate the performance. These tiny little dust collectors are really made to hook up to a single machine. Id suggest just getting one of those really stretchy hoses from rockler and hook it up as needed. This way you will get the most out of your collector.

Don

[konkers]

Comparing water flow to air flow is apples and oranges.

I am by no means a fluid dynamics expert but according to Bill Pentz' site (http://billpentz.com/woodworking/cyclone/ducting.cfm#Resistance) "Air at the low pressures we use in dust collection, air is more like water, and does not compress. Any obstruction, small pipe, or tight turn will kill our airflow dramatically just like closing a water valve." I've also heard this from engineers I've worked with on thermal design and cooling of computers.

I also did a bit more digging to find the effective length HVAC ducting which should be a close approximation of dust collection ducting. According to http://www.ajmadison.com/ajmadison/itemdocs/ductworksheet.pdf a 6" 90 has an effective length of 15' and a 45 had an effective length of 9' making two 45s have an effective length of 18' vs 15' for the 90.

[dwacker]

I am by no means a fluid dynamics expert but according to Bill Pentz' site (http://billpentz.com....cfm#Resistance) "Air at the low pressures we use in dust collection, air is more like water, and does not compress. Any obstruction, small pipe, or tight turn will kill our airflow dramatically just like closing a water valve." I've also heard this from engineers I've worked with on thermal design and cooling of computers.

I also did a bit more digging to find the effective length HVAC ducting which should be a close approximation of dust collection ducting. According to http://www.ajmadison...ctworksheet.pdf a 6" 90 has an effective length of 15' and a 45 had an effective length of 9' making two 45s have an effective length of 18' vs 15' for the 90.

Water hits the flat 90 and creates head pressure or head loss (for the reef junkie). Any flats in the system create head loss. Head loss changes based on pressure. Using aquarium pumps as in your example. A non pressure rated pump would suffer extreme head loss at a 90 vs two 45's. Non pressure rated pump would be a closer comparison to a dust collector. Air and water flow comparisons would be real close if your talking about a pressure rated pump and something like an air compressor system. The smoother the transition from one direction to another the less head loss.

Hvac systems are backwards of a dust collector. With an HVAC system high pressure is on the input side of the impeller, atmospheric pressure is the driving force. On a dust collector the low pressure side is on input of the impeller also know as pressure difference or in laymans terms vacuuum. For example a closed loop in your aquarium system has the tanks volume applying the high pressure to the pump inlet vs your tanks overflow just flowing to the sump. The pump in the sump has little to no volume so has no pressure, so any flat wall is going to create serious head loss.

Don

[konkers]

Water hits the flat 90 and creates head pressure or head loss (for the reef junkie). Any flats in the system create head loss. Head loss changes based on pressure. Using aquarium pumps as in your example. A non pressure rated pump would suffer extreme head loss at a 90 vs two 45's. Non pressure rated pump would be a closer comparison to a dust collector. Air and water flow comparisons would be real close if your talking about a pressure rated pump and something like an air compressor system. The smoother the transition from one direction to another the less head loss.

Do you have any references to back this up? Bill Pentz says the opposite with respect to high vs. low pressure air flow. Also the stated effective lengths for HVAC fittings are at odds with the two 45 theory.

[dwacker]

Do you have any references to back this up? Bill Pentz says the opposite with respect to high vs. low pressure air flow. Also the stated effective lengths for HVAC fittings are at odds with the two 45 theory.

I edited my last post maybe that will make more sense. I had my origonal system designed by a computer. The CFM loss with two 45's was half that of a single 90. I had it run both ways to see which was more cost effective.

Don

[konkers]

Interesting. What software did you use? I curious why its results are different that what I'd expect based on the information I have. Maybe I'm missing some key assumption.

[dwacker]

Interesting. What software did you use? I curious why its results are different that what I'd expect based on the information I have. Maybe I'm missing some key assumption.

I didnt. I paid pacific air systems to come to my shop and do it for me. It worked so well that the system imploded and crushed all the pipe that most people are using for their dust collection systems. Basicly I wasted a bunch of money and said the heck with it and just replaced it with pvc. Off the top of my head one very big reason not to use a 90 is a stick getting stuck in the corner. Those little off cuts 6" -10" long are not going to make it through a 90 but they pass easily through a pair of 45's.

Don

[jsiard]

That's apparently a pretty common misconception. The largest pipe your DC can "handle" will give you your greatest CFM (volume of air moved), but the speed of the airflow will decrease with every step up in pipe size. From my understanding, using anything larger than 4" pipe for DCs 2HP and smaller will cause a decrease in air speed that will cause fallout, and consequently, clogs, especially in vertical drops.

I agree that you can drive yourself nuts with this stuff but I have to disagree with you on the pipe size being a common misconception. I have a Delta 50-850 with an aftermarket cyclone, 6" duct off the cyclone 26' of pipe with 2-45's, 2 wyes and a long sweep elbow to an 8" jointer, 32' of pipe with 2-45's, 2 wyes and 2 long sweep ell's to a 13"planer both have 8' drops with 6" pipe and experience no "fallout" or clogs. Conventional wisdom dictates that this scenario should not work but it does, and very effectively. Would it work with just 4” pipe? I don’t know. I’m not saying that I buy all the information gleaned from Mr. Pentz but the guidance derived from him helped me put together a very affordable and effective system.

[linkmx674]

i have been racking my brain with all this info- too much! i just need to know if i am using 4'' pvc and the wyes and 45s to fit the 4'' pipe in the plumbing section at menards- how does my blast gates and 4'' hose fit into that system. are the not different sized id and od diameters? how will they go together properly? do u use and 3'' reducers or couplings of that sort?? does anyone have any pics of there blast gates and wyes connected to give me a visual of setups? thanks

[Eric.]

On 1/25/2012 at 8:25 PM, jsiard said:

I agree that you can drive yourself nuts with this stuff but I have to disagree with you on the pipe size being a common misconception. I have a Delta 50-850 with an aftermarket cyclone, 6" duct off the cyclone 26' of pipe with 2-45's, 2 wyes and a long sweep elbow to an 8" jointer, 32' of pipe with 2-45's, 2 wyes and 2 long sweep ell's to a 13"planer both have 8' drops with 6" pipe and experience no "fallout" or clogs. Conventional wisdom dictates that this scenario should not work but it does, and very effectively. Would it work with just 4” pipe? I don’t know. I’m not saying that I buy all the information gleaned from Mr. Pentz but the guidance derived from him helped me put together a very affordable and effective system.

 

 

I'm surprised to hear your 1.5 HP DC pulls hard enough to keep 6" pipes clear, but I'm happy to hear it, too.

[dwacker]

i have been racking my brain with all this info- too much! i just need to know if i am using 4'' pvc and the wyes and 45s to fit the 4'' pipe in the plumbing section at menards- how does my blast gates and 4'' hose fit into that system. are the not different sized id and od diameters? how will they go together properly? do u use and 3'' reducers or couplings of that sort?? does anyone have any pics of there blast gates and wyes connected to give me a visual of setups? thanks

You can take a look around my shop. You can sort of see its kind of patched together. The blast gates go right into a piece of 4" pipe. Tool connection can be just the hose or a quick disconnect stuck in the hose.

You can make use of those stretchy hoses. The one that drops from the ceiling to my table saw will cleanup the whole shop and I move it to the bandsaw as needed everything else is dedicated. I stuck a sheet metal screw through the pvc pipe into the metal blast gates. They are a snug fit but will fall out eventually. You also want to run a ground wire so that your not constantly getting shocked by the static made by the pvc. When I talked to the air handling company about using pvc he told me that static was normal. In fact if your not getting a big static charge your collector is to small for the ducting. The shock gets old quick so get a ground.

Don

[ChetlovesMer]

Don,

Sweet shop. It does not look patched together.

It looks great.

Have you heard of people running their PVC with some aluminium ducting tape stuck to the inside wall to reduce that static charge? To me that seems easy to do.

[linkmx674]

all 4'' hose and pipe? any 3'' couplings at the end of your runs or anything special?

[dwacker]

Don,

Sweet shop. It does not look patched together.

It looks great.

Have you heard of people running their PVC with some aluminium ducting tape stuck to the inside wall to reduce that static charge? To me that seems easy to do.

Thank you. I really dont know. I bought a roll of bare copper wire from home depot and used a wire fish. It was real easy, then screwed to the dust collector motor ground. I should have done it when putting in the pipe but wanted to see how much static it produced. Enough to jump 1" from my finger to any metal.

Don