I am setting up a new shop (20′ x 24′, I’ve heard that size doesn’t matter it’s what you do with it). I have decided on an Oneida 3 hp cyclone collector. They sell their 24 ga ducting, but at a premium price. Their tech rep said that the Home Depot 26 ga duct will collapse. Call me skeptical, but with the $1200 outlay for the collector I would like to save some on the ducting. Has anyone used the slightly lighter gauge duct for their system and not have a collapse?
Thanks for any help, Greg Alexander
Replies
I'd think the only chance of collapsing any duct would be if you closed all the blast gates at the same time. If you make sure to keep a large opening to let air in, it should be fine. And what would be the point of running it if you didn't have a blast gate open? It might just mean you'd need to be a little more careful while switching from using one machine to the next.
white astm 2729 is much cheaper and works great. From our friend Bill Pentz
" I recommend the PVC ASTM 2729 “Sewer and Drain (S&D)” pipe for most small shop woodworkers. The 2729 PVC pipe and fittings cost far less than metal or standard schedule 40 PVC, are much stronger, don't leak like metal pipe, and have a much lower coefficient of friction than even spiral metal ductwork. The 2729 PVC is rated for many times the pressure that even large industrial blowers generate. I've seen no flex with my PVC pipe even when doing testing on 10 hp blowers driving a 16" impeller."
If you go to the home page here on the FWW site, then go to the workshop button you will find a great article on the use of PVC pipe vs. Metal pipe.
It states that you are unlikely to have any problems using PVC pipe on DC's of 1 1/2 h.p. and less. It also mentioned the cfm cut off as well. One of the guys involved with this article is a Prof, at MIT, fairly smart Gent.
They go on to say, that problems are unlikely, not that you will not have any problems.
I spent 27 years doing Sheet Metal, mostly doing blowpipe. Installing huge commercial DC systems. At 3 h.p. I would not be using 26 Ga. snaplock, stick to 24 Ga. the cost difference is not that much. And don't use screws for your connections, use SS pop rivets. Also stay away from duct tape it's a waste of money for sealing the joints. You could go to a HVAC supply hose in your area and pick up the sealant we use, or just use silicone.
Right now I am just finishing up moving into my new shop, and will be hooking up my new DC this weekend. I bought a old movie theater, after putting down a plywood floor I ended up with 4200 sqft. Of which a little over half will be my machine room. The DC I am putting in is a 5 h.p. Cyclone. For my system I am using 22 Ga. Spiral Lock pipe. I got out of the Sheet Metal trade 6 years ago, and working with this pipe reminds me why.
Good Luck on your installation, at least you have a good Cyclone to anchor your system.
Taigert
I'm just curious, but is there an issue with static electricity and wood chips flowing through a a PVC pipe. The recommended pipe sounds like a great thing, but I keep being surprised by what I don't know.And if it is strong and leak proof, perhaps even fire resistant, one wonders if you couldn't use it for a dryer vent as well. Now I am getting silly.Peter
There's a good summary on the subject on Bill Pentz's site:http://billpentz.com/woodworking/cyclone/ducting.cfm#StaticElectricityDr Rod Cole wrote an article for FWW:
https://www.finewoodworking.com/fwnpdf/011153048.pdf
http://home.comcast.net/~rodec/woodworking/articles/DC_myths.htmlIn over 5 years of regular use, I've never had problems with static electricity. An other advantage of PVC pipes, is the easy reconfiguration (it will happen). They're not glued or screwed.
I have a 2 1/2 hp Oneida and used the thin HD tubing. I have had no problems. I have all the joints sealed with either silicone caulk or aluminum HVAC tape and I can close all the blast gates and have never had a problem. I think the collapsing ductwork is an urban myth to get you to buy the heavy gauge ducting that the manufacturers sell. I do have some spiral 7" ducting, heavy gauge, in my system, but a lot of the balance is the cheap stuff.
In my opinion, save your money for wood!
Buce
I recently installed 60' of 7" and most 6" ducting with 8 blast gates for right around $400 from my local HVAC shop. All of the material is standard air-handling gauge metal and fittings and all of the seams are very well sealed. I can close all gates and it will stall the motor somewhat but not collapse the duct work.
I would have used thin-wall PVC but getting it where I live would have been more far effort and cost than I was willing to accept at the time. That would be my first choice were I to do it again. Your local plumbing supple or commercial irrigation supplier can get you everything you will need. A good heat gun will take care of mating the blast gates to the pipe opening.
"I can close all the gates and it will stall the motor somewhat but not collapse the ductwork."
You will find that the motor runs most freely when all the blast gates are closed. Try holding your hand over the hose end of your vacuum cleaner and hear it speed up. Running the fan with all the ductwork removed may not stall the motor but could overload it to the point of blowing a breaker or burning it out. Beware!
Edited 11/20/2009 11:24 pm ET by Tinkerer3
"Stall" was the wrong word but couln't think of how else to state it. You are correct closing all of the gates for any prolonged amount of time can ruin the motor and your caution is well advised.
How fortunate to have such a diverser and knowlegeable group of fellow woodworkers to draw upon. This has given me a lot to digest and apply. How critical is it to use 6" duct for the main run and dropping to 4" for the individual tools. Could I just use (what I already have on hand) 4" for the main and drops?
Thanks again everyone.
Greg Alexander
You want to take the 6" all the way to the tools and use the largest possible port. If you have to choke-down to 4" blast gates, use a reducer and place it as close to the tools as possible. The smaller the diameter ducting the more static pressure which means less efficiency. Many of the larger tools can be easily adapted for larger ports and I would recommend that you do that.
If you are talking about a DC with an induction motor, then no, you will not wear out your motor my closing the ducts. Your motor will have less wear and tear with the gates shut. An induction motor should run at a constant speed, with the power draw varying to keep it there. When you close the gates it has less air to move, so it requires less power. A universal motor is different. To quote wikipedia: "Motor damage may occur due to overspeeding (running at an RPM in excess of design limits) if the unit is operated with no significant load." A vacuum cleaner with such a universal motor may be damaged when you close it off for this reason, and because the air pulled through can also be used for cooling the motor. So it's not overloading the motor, but unloading this type of motor that can be a problem.
Now I'm going to really expose my ignorance about things electrical: are most DC motors induction or universal? What is the differrence?
http://en.wikipedia.org/wiki/Induction_motorThe powerful motors on stationary machines are induction, while the lighter ones on portable tools are universal motors. Universal motors are less efficient, but tend to operate at high speed so you an get a fair amount of power in a compact lightweight package. Induction motors don't have brushes to wear out, and tend to last longer.
I have about 30' of the big box store ducting mixed in with the expensive stuff. I added the cheep stuff when I got a new tool. They both work fine for me. I have the 2hp gorilla. The only time that I open a gate is when a machine is running. The collector is at idle a lot with all gates closed.
For all the information you need and more on dust collection, go to http://billpentz.com/woodworking/cyclone/index.cfm. A great site and a must read.
I have a cyclone with 5 HP motor. I used PVC for ducting. The 6" pipes are fairly inexpensive, but I found that the Ys, elbows, etc were expensive and adding rapidly to the cost.
To save on those go to http://www.harderwoods.com/pipedocs.html. You will find a free pipe joint template software that you can use online.
When a 6" flexible hose needs to be attached to a 6" PVC pipe, the hose is just a bit too large. I made a simple jig to remove some of the PVC with a router.
I built modified versions of the blast gates shown here: http://benchmark.20m.com/articles/BlastGate/blastgatebuilding.html. They've been working very well for over 5 years now.
Good look with your project.
When I sealed my duct work, I used clear plastic wrap. The same stuff used at home centers for bundling items together. It was very inexpensive, sealed the duct work completely, and can be removed very easily if needed.
As far as using light gauge duct work, if the fan has a high enough static draw, it might collapse the ducting.
One thing to remember about collapsing ductwork is that the pressure will never be more than atmospheric pressure - something like 13 or 16 lbs per square inch. Unlike a fluid pressure inside the pipe, it makes no difference whether a blast gate is closed gently or slammed shut, it will not exceed that atmospheric pressure. If in question about a material, buy one section, close the end and see if you can collapse it. If you can keep the pipe perfectly round, it will stand much more negative pressure than if flattened somewhat. Also remember it is the velocity of the air that moves the dust along with it. Not the pressure. For instance, if you are collecting dust from a 4" supply and run it into a rediculously large 2' pipe, the dust will stop right there as the velocity will be so reduced that it will not carry the dust along.
Duct work
I have a 3hp Grizzly cyclone and when then gates are all closed I have collapsed the duct I just reinforced it with a wooden ring around it and was good to go. Just make sure you have at least one gate open.
OK finally
Interesting to finally hear someone say that they personally collapsed a piece of ducting. Up until now all I ever heard was hearsay. Thank you for your input. Can you tell me what gauge of hvac ducting you had fail. I have a 2hp cyclone and have some of the cheap hvac ducting and have never had a problem. But, obviously you are drawing more amps with your 3hp than me.
I'm useing 24 gauage duct work.
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