I was just reading the post about cyclone dust collectors and I have a question about ductwork. I’ve bought and assembled a 2HP Grizzly and now need to buy material for ducts. I’ve seen that some use HVAC pipe from Home Depot. I’ve heard that some use PVC pipe (with grounding precautions.) I’ve seen systems that you can buy which are custom made with spiral reinforced pipe. I’m sure there are other ideas too.
I’m interested in the opinions of the group on what would be the best way to go.
Thanks in advance for any advice/opinions.
Mark
Replies
Mark,
For my system I decided to use as much metal line as I could. For all of the 4" runs, I purchased 26 ga. gutter downspout in 10' lengths from my local hardware store. At $11 a stick, I was happy as a clam.
Have fun!
-Jerry
Jerry,
I think I'm headed towards metal too. I'm worried about the possibility of collapsing the tubes if the thickness of the walls isn't adequate and all of the blast gates are closed by accident. Also, I'll have an 6" main and some right near the collector that will be 8". Any thoughts on this?
Thanks!
Mark
Mark,
I don't know about the 6 - 8" line. The largest pipe in my setup is 5" which is the main trunk running down one side of the shop. I have not experienced any duct collapse; however, I generally have a blast gate open when the system is fired up. If crumpling the duct seems to be a serious issue, and saving some $$ using 26 ga. ductwork is an option, you could construct a blast gate for one tool that would always remain open when the system is first switched on. Just a thought.
-Jerry
Thanks Jerry. January is my target month for installing this. I'll let you know what I end up with!
Happy Holidays,
Mark
You may want to check out Taunton's book "Woodshop Dust Control" for good information on ducting types.
Three books I have read recommend at least 26ga for 5" or larger ducting. Be sure to use large radius elbows as well to minimize line losses.
stick with 6" ASTM 2729 all the way from the collector to the tool if you can ... Radius corners when you can, use 2 45's if you can't find the radius curves. Metal is un-necessary. Don't get me wrong: someone shows up with free spriral galvanized with fancy blast gates for free, sign me up! But at under $20 for a 10' piece the 2729 is fine. 45's and 90's range from $10 to $18. don't glue them - use duct tape if you change your mind or your needs evolve. You'll never collapse the plastic stuff, EVER.
Claims of explosive static in plastic ducting are theoretically possible, but as a professional engineer I've never heard of this in shops the size of ours. I've never known anyone hit by lightening or who's won Millions in the lottery either. In theory my clear-vue cyclone with a baldor 5 hp motor should create so much static in the cyclone alone that is is possible to blow the roof off of my shop. Hasn't happend, nor do I think it ever will. Grounding plastic is a fool's errand if you understand the physics of it all.
Two words: Bill Pentz. Man is my hero (obviously).
Edited 12/11/2007 12:50 am ET by BradG
I have been doing commercial sheet metal for about 31 years now, and a lot of it has been blow pipe. I have seen the results of PVC that was not grounded causing an explosion. It cost the guy the life of his son, and burnt his house down. Any dust collectiom system should be grounded. Some areas require you to pull a permit and have it inspected. If it's not properly designed and installed correctly you could have a hard time with your insurance company if you ever have to file a claim.
I personaly would stick with galvanized spiral lock pipe,with long radius ell's, & no 90' off the main line. Contact Penn they have a good Cyclone system, they will also help you with laying out your system. To do it properly you want to size the pipe for things like CFM' and Static Pressure.
Also put a good smoke detector near where your waste is collected. I have seen where someone has pushed on a dull saw blade and caused the plant to burn to the ground after every one went home. My system I have put in a sprinkler head in with a fuseable link. As well I can manualy turn on the water with a ball valve.
Depending on where you live think about where you want the exhaust to to be returned to the work space, or to the outside. If it's bak into th work space get really good canister filters. if your sending it outside give some though to it asto where the wind will be blowing. If your blowing it outside yur also removing you conditiond air heated or cooled. You also need to replace the air you remove, or the air will replace it self, such as reversing chimney flow on furnaces or water heaters. You ill quickly fin any air leaks in your shop.
Not saying it does not happen but can you give more info on where the PVC system caused a fire? I have seen articles of fairly recent vintage saying that they could find no evidence of this ever having happened.
Doug
I, too, would like to see more info documenting that PVC caused the fire. Even FWW has had articles about PVC pipe being okay in smaller shops.
Alan - planesaw
YOU CAN'T GROUND PVC PIPES! The fact that it holds a charge in the first place is linked to the fact that it doesn't conduct. You have a PVC pipe holding a charge, touch it with a wire, and the area in contact with the wire dissipates the charge, but everywhere else still holds a charge. Anyone with PVC pipes wrapped in a ground wire will see this in the dust pattern on the pipe.Now back to the dust explosion debate...
PVC Pipe Dangers Debunked
FWW no. 153
For those who missed it.------------------------------------
It would indeed be a tragedy if the history of the human race proved to be nothing more than the story of an ape playing with a box of matches on a petrol dump. ~David Ormsby Gore
Just to clarify this a bit. I do think that the metal is a better idea (as long as it is strong enough to hold up, some metal is just to thin) But I personally do not think that PVC is all that big a deal. The articles I have read seam to agree with me on this and no one has ever (in anything I have seen) ben able to specify any instances of PVC DC ducts being involved with a fire in a wood shop. All the cases I have ever heard of were the friend of a friend kind of thing. So if someone know and can give facts on a case this would be a big deal in this debate.
The only issues I have with metal (and why I have PVC) is simply cost. I looked into metal and it was going to be a lot more money. So if their is a true safety issue it would be nice to know about it.
I sometimes wonder about submitting the PVC DC saw dust explosion to those guys on Myth Busters to look into. I can just see them blowing up a shop to test this out.
Doug
Doug,
"Myth Busters" did do a test on this ,on a smaller scale, and they couldn't get any kind of explosion to happen. Can't remember when this aired, but do remember seeing it. I suppose if one were to do a search this episode could be found. Although I'm not sure that they used PVC, but they did use sawdust and introduced an electrical charge in various ways.
Danny
Edited 12/12/2007 11:13 am ET by brownman
Cool, I will have to look for it. I am still in aww of the hot water heater test.
Doug
I think the MythBusters episode is "Bug Bomb."
Dust explosions (of any combustible dust, not just wood) are fairly common in industrial settings. There are even records of powdered milk explosions. What we usually call "saw dust" isn't finely divided enough to explode, because the substance has to be suspended in a fairly high concentration in the air.
The powdery dust you get from milling MDF would certainly qualify, if you could make an appropriately thick cloud of it. And that's really the challenge: You have to have a lot of dust in the air in order to reach the lower explosive limit (LEL). It varies from one substance to another, but is generally in the range of 10-100 grams per cubic meter. Unless you were doing it on purpose, it would be difficult to put that much dust in the air under normal wood shop conditions. But if you did manage to do it, just about anything would set it off. Static-laden PVC pipe would be no more likely to cause an explosion than any of a number of other sources (e.g., a spark from the brushes in a universal motor).
-Steve
Yeah I am familiar with the dust explosion idea, I have seen the remains of a grain bin that did not do so well when I was much younger.
Also I have tossed the saw dust onto the fire bit a few times. I don't do this now with the fine stuff. May as well toss a cup of gas as a cup of really fine saw dust. Now I put it on before starting the fire and let it go from that point. Not enough air to burst into a large fireball that way. More exciting the other way but I am getting old enough that I could do with a little less excitement.
Doug
The only real advantage of metal over PVC that I can see i sthe ability to ground it. I've been shocked enough...
dgreen,
Thanks. I knew I had seen the FWW article and read it a couple times. Just didn't remember which issue.
Alan - planesaw
I got lucky... I was doing a quick search for dust collection mishaps involving pvc and came across the reference.------------------------------------
It would indeed be a tragedy if the history of the human race proved to be nothing more than the story of an ape playing with a box of matches on a petrol dump. ~David Ormsby Gore
I really could care less about what anyone doe's or doe's not use. Fact is I would not have a PVC system if you gave it to me. I have spent over 30 years as a Commercial Sheet Metal J/M. Most of that time was spent doing blow pipe and installing bag plants in Saw Mills & Pulp and Paper Mills. About any place you have dust, smoke, odor, grease or need to move something with air, such as grain.
Most times when you have a fire in a system in starts in the collecter bin or bag house. Because som one was pushing on a doll blade or bit. Almost all of the fires that happen inside the pipe are caused by the system being shut down without emptying the pipe. When you shut the system off evrything in the run drops where ever it's at at the time. You keep doing this and its amazing how much will build up. I have seen one commercial job that had 12" pipe where it was so built up you couldn't even see a fashlight shining from 10' away. If you get debris from MDF, Particle board built up and keep shuting down ealy your askig for all kinds of bad things to happen.
I your confident about PVC chek with your omeowners insurance and the Fire Marshall. If you ever have to file a claim to have your house rebuilt after a fire you maybe in for a suprise.
If I had any plastic dust line I'd ground it. Maybe it isn't much risk but I have sure enough been smote by lightning. If nothing else it will convince you it can happen to you.Retired until my next job.
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