Workshop dust collection system design

[Scott Clark]

I am looking to upgrade my shop-vac based system that uses 2" hoses to a bunch of smaller tools so I can now attach the table saw, jointer, lathe and other larger tools that need 3-4" connections with larger CFM requirements. I am probably looking to install a 2-3HP system and want it plumbed around the shop.

What do most home built systems use for ductwork? I have looked at the clear flex-tubing to connect each machine. What about the main runs? Do most systems use flexible lines or rigid? Would you use 4" PVC (drain tile style) plumbing type material or 4" metal ductwork used for heating systems?

This is a good starter article from Rockler.... http://www.rockler.com/articles/getting-tough-on-dust.cfm

This seems to be a great place for a large diversity of gates, and other parts.... http://ahturf.com/store/index.php?route=product/category&path=5303

Any input or discussion about your setup would be appreciated. Thanks

[davestanton]

Wow, dust collection is a fine art and no one is going to be able to give you a definitive answer off the cuff. 4 inch is going to be ok if you have a strong impeller pulling around 2,000 cubic feet per minute. My suggestion is to use 6 inch sewer pvc for your main and use 6 to 4 inch y shaped t junctions off to the other machines and some 4 inch plastic blast gates. This is the cheap option. You could use a 2 horse dust extractor with this system depending on how long your lines are and also how many blast gates you keep open. There is heaps of reading out there on the web. The main consideration would be your jointer. It all depends on what type of blades you have on the jointer and their width as to if you are going to choke the system. The saw and lathe should be fine. Again this depends on the collection system you have at the source.

[Hybrid-woodworker]

I ran a 2 hp woodtek for about 8 years with 6" heating duct as the main line, only used Y branches and converted to 4" just before dropping down the the machines. Keep the number of 90s to a minimum and the flex to a minimum and you will be fine. The only place I ever had a problem was the joiner and I had too many bends close together and it would clog. I changed the main line angle, reduced the number of 90s and it was fine after that.

I upgraded to a 5 hp Clearvue and found that long runs of 6" heating duct could collapse if all the gates were closed before turning the system off. I built a vacuum breaker that opens before the duct collapses and have been fine since then. The metal duct is chaper and lighter. Use foil tape, not duct tape.

BRuce

[Scott Clark]

Thanks... I assume that grounding the pipes is a must with the metal ducting that is pretty easy.... How would you ground the PVC? Clamp a copper ground wire all along the outside of the ductwork?

I've heard others complain about the metal piping collapsing in the off chance that all the gates were closed. Do you have plans anywhere online for this vacuum breaker that you built?

I figure the source for the system will be in pretty close proximity to my jointer so that hopefully won't be an issue.

[dwacker]

I would not bother with thin hvac ducting, any well designed system 2hp or better will suck that stuff right down flat. I sucked down an entire shops worth with a 4" blast gate open. PVC is fine for any home shop. NO your not going to blow up that is a myth. If you design the system properly you will get shocked, thats not going to kill you. You can run grounds until your blue in the face if you have a well designed system with enough velocity you will get shocked. I wouldnt worry to much about design with just a few home shop machines. Just use some simple common sense and you will be just fine.

Don

[ChetlovesMer]

I would not bother with thin hvac ducting, any well designed system 2hp or better will suck that stuff right down flat. I sucked down an entire shops worth with a 4" blast gate open. PVC is fine for any home shop. NO your not going to blow up that is a myth. If you design the system properly you will get shocked, thats not going to kill you. You can run grounds until your blue in the face if you have a well designed system with enough velocity you will get shocked. I wouldnt worry to much about design with just a few home shop machines. Just use some simple common sense and you will be just fine.

Don

Don,

I love you man, but I do not agree with one thing you said. I just ran all my ducting. I put a 2" wide strip of aluminum tape through every pipe and every wye and elbow. Then I wrapped the same 2" wide aluminum tape around every union and every joint. When in doubt I put an extra piece of 2" wide aluminum tape. Anywhere I had a hose I jumpered past the hose with a wire outside the hose to the next aluminum tape. This way all of my aluminum tape is touching and connected to all the rest of my aluminum tape.

When I was testing my system I was getting shocked all over the place. Especially the table saw, the jointer, and I couldn't even think about the metal trash can without getting a shock.

Anyway, I just taped a wire to the first piece of aluminum tape and connected the wire to the ground on the motor on my ClearVue. Whalah! No more shocks. It was a bit of a challenge to add the aluminum tape as I went along. But I'm glad I did it. Besides I needed the aluminum tape to seal all the joints anyway. The only drawback was the 100 miles of aluminum tape backing that was left all over my shop (I probably should have thrown the stuff away as I went along, but anyway...) It looked like my shop had been TeePeed until I cleaned it up.

[ChetlovesMer]

Thanks... I assume that grounding the pipes is a must with the metal ducting that is pretty easy.... How would you ground the PVC? Clamp a copper ground wire all along the outside of the ductwork?

In my opinion forget the copper wire. Use aluminum tape.

[davestanton]

I hadn't considered the aluminium tape before. Glad it is working for you.

[dwacker]

Don,

I love you man, but I do not agree with one thing you said. I just ran all my ducting. I put a 2" wide strip of aluminum tape through every pipe and every wye and elbow. Then I wrapped the same 2" wide aluminum tape around every union and every joint. When in doubt I put an extra piece of 2" wide aluminum tape. Anywhere I had a hose I jumpered past the hose with a wire outside the hose to the next aluminum tape. This way all of my aluminum tape is touching and connected to all the rest of my aluminum tape.

To much aluminum tape is a serious NO NO with pvc dust collect and why it is against the law to use any period in pvc based vacuum systems in every state. To wide of a conductor creates a propigating brush charge turning your non conductive pvc pipe into a capacitor with enough of a charge to stop your heart. If you have a decently powered home system and you by chance happen to get enough dust flow from something like a drum sander the tape has actually done more harm than good. There are plenty of myths out there about dust collection explosion but aluminum tape is not one of them and you never know when the condition are going to be just right to put you 6ft under.

Don

[CessnaPilotBarry]

Exactly right...

Metal foil + insulator + metal foil = capacitor

[Hybrid-woodworker]

Don, you are wrong. I ran a 2hp system for years and before I hung all the 6" pipe I put 5 sections together straight off the DC, they were taped at the joints and nothing else. Glued a piece of closed cell foam to a scrap of plywood. Fired up the DC and when it was running top speed, slapped the plywood on the end... Nothing happened, just as I expected. Ran the 6" main line and 4" drops and used it without a problem for more than 5 years. Upgraded to the 5hp Clearvue and extended the main line with more 6" but 5 ft pieces, they collapsed but non of the original pipe did. As long as there is a fitting every 2' - 3' it wil holdup fine. This time I ran 6" down to the TS, miter saw and lathe. Makes a world of difference.

The HVAC pipe works and is lighter/cheaper than the PVC. Also no one argues with you about the potential of an explosion. :-)

I don't have a plan for the vacuum breaker but will take some pictures this weekend. It is just a Y fitting with a collar around the top end and a off enter balanced gate in the top. Too much vacuum will pull it open. I adjusted it so that an open 6" gate doesn't move it, an open 4" gate opens it a little and all the gates shut , open it fully and it self closes. I will post a picture of all 3 positions.

BRuce

[Hybrid-woodworker]

I don't believe in Santa, the tooth fairy or dust explosions in home PVC pipe. There is no first hand accounts, all the stories start with "a friend of mine". Also all the experts agree that the concentrations and ratios of dust to air just do not occursin the home shop and small pipe. Yes 4" and 6" pipe is small.

I do however believe in the Easter bunny. I'm not about to give up free chocolate ! :-)

BRuce

[Eric.]

I don't believe in Santa, the tooth fairy or dust explosions

Thanks for ruining it for me.

Pretty good trick with the valve thingamajigger you came up with.

[ChetlovesMer]

To much aluminum tape is a serious NO NO with pvc dust collect and why it is against the law to use any period in pvc based vacuum systems in every state. To wide of a conductor creates a propigating brush charge turning your non conductive pvc pipe into a capacitor with enough of a charge to stop your heart. If you have a decently powered home system and you by chance happen to get enough dust flow from something like a drum sander the tape has actually done more harm than good. There are plenty of myths out there about dust collection explosion but aluminum tape is not one of them and you never know when the condition are going to be just right to put you 6ft under.

Don

I don't understand. After all, its grounded.

You've got to be pulling my chain. After all, by that theory then every metal piped system in the world would be a giant capacitor.

[Chris H]

==> I don't believe in Santa, the tooth fairy or dust explosions in home PVC pipe.

Dust explosions are not really the safety issue… But static discharge can be…

Home shops typically don't segregate solvent storage, finishing areas, etc from the wood processing tools… Static discharge and finishes/solvents don’t mix…

I am certainly not reccomending inappropriate storage of solvents, but if your air is contaminated enough that a static discharge will ignite the solvents, then you are SOL when you turn the lights on. There is a spark in the switch everytime you flip it, and those $1 switches aren't air tight. Again, I don't reccomend bad storage, but there is a lot of leeway between not ideal solvent storage and static explosions. Let's not forget you risk static discharge everytime you take a step, especially in the winter months, or region of low humidity. Static will happen, and it's annoying, but that's about it.

[ChetlovesMer]

I am certainly not reccomending inappropriate storage of solvents, but if your air is contaminated enough that a static discharge will ignite the solvents, then you are SOL when you turn the lights on. There is a spark in the switch everytime you flip it, and those $1 switches aren't air tight. Again, I don't reccomend bad storage, but there is a lot of leeway between not ideal solvent storage and static explosions. Let's not forget you risk static discharge everytime you take a step, especially in the winter months, or region of low humidity. Static will happen, and it's annoying, but that's about it.

I realize you were going for humor here, but did you know you get a much bigger arch in your light switches when you turn the lights OFF? Braking the flow of electricity actually produces a larger spark than starting the flow. That's why if you call the gas company and say "My house smells like gas". They tell you to leave and NOT TO SHUT YOUR LIGHTS OFF.

[ChetlovesMer]

Exactly right...

Metal foil + insulator + metal foil = capacitor

Ha! that's Re-Gosh-Darn-Diculous!

Firstly, Capacitance is most successful when the conductors are large and the dialectric is very thin. In this case you'd need aluminum tape amounting to the surface area of the state of Texas to push accross the dialectric created by a 3/16" inch walled piece of PVC.

Second, to build enough charge on the "Inside" of the pipe, inorder to jump over to the "outside" of the pipe and kill me is impossible. There will always be great charge on the OUTSIDE of any PVC pipe. So if I could create enough voltage to jump through the 3/16" dialectric of the PVC pipe the charge would go INTO the pipe not out.

Third, because you always build more charge on the outside of the pipe (which is true of metal pipes too by the way, they are generally easiser to sink to ground.) The only risk I have is the same shock I'd get if I had no metal tape at all, only in my case I've sunk the tape to ground so the build up of charge on the tape is sunk, this would not be possible without the tape as you cannot "GROUND" an insolator like PVC.

Forth, I cannot built up a voltage differential in my aluminum tape as it is all connected. Therefore it is the same node. Therefore equal voltage drop throughout which does not a capacitor make.

Fifth, My aluminum tape is sunk to ground. You cannot build a capacitor that's tied to ground at either leg... nothing less both legs tied to ground. You cannot develop a voltage drop when sunk to ground.

So, I say again: That's just re-gosh-darn-diculous!

[Chris H]

I realize you were going for humor here, but did you know you get a much bigger arch in your light switches when you turn the lights OFF? Braking the flow of electricity actually produces a larger spark than starting the flow. That's why if you call the gas company and say "My house smells like gas". They tell you to leave and NOT TO SHUT YOUR LIGHTS OFF.

Yeah, the point was only that you are constantly surrounded by things far more dangerous than static discharge. The size of the arc would be irrelevant in such a shop that was chalk full of volatile vapors.

Same point you are making about the capacitor. It's only with bad math, and mythically imperfect situations that greater harm would be caused.

[davestanton]

I want to step back from the stand off that is developing here and ask a silly question. Why do I need to earth the inside of a pvc pipe. Surely a grounding copper wire running full length wrapped around the outside of the pvc vac line and earthed correctly will suffice?

[dwacker]

Ha! that's Re-Gosh-Darn-Diculous!

Firstly, Capacitance is most successful when the conductors are large and the dialectric is very thin. In this case you'd need aluminum tape amounting to the surface area of the state of Texas to push accross the dialectric created by a 3/16" inch walled piece of PVC.

Second, to build enough charge on the "Inside" of the pipe, inorder to jump over to the "outside" of the pipe and kill me is impossible. There will always be great charge on the OUTSIDE of any PVC pipe. So if I could create enough voltage to jump through the 3/16" dialectric of the PVC pipe the charge would go INTO the pipe not out.

Third, because you always build more charge on the outside of the pipe (which is true of metal pipes too by the way, they are generally easiser to sink to ground.) The only risk I have is the same shock I'd get if I had no metal tape at all, only in my case I've sunk the tape to ground so the build up of charge on the tape is sunk, this would not be possible without the tape as you cannot "GROUND" an insolator like PVC.

Forth, I cannot built up a voltage differential in my aluminum tape as it is all connected. Therefore it is the same node. Therefore equal voltage drop throughout which does not a capacitor make.

Fifth, My aluminum tape is sunk to ground. You cannot build a capacitor that's tied to ground at either leg... nothing less both legs tied to ground. You cannot develop a voltage drop when sunk to ground.

So, I say again: That's just re-gosh-darn-diculous!

That would be incorrect and has been proven time and time again. Folks the whole Easter bunny thing is concerning dust explosion. Where talking about shock hazard a propagating brush discharge Non arcing. Completely different animal, going nuts with aluminum tape on pvc is a risk that's just plain fact. The larger the conductor the higher the risk. The more dust volume the higher the risk. I agree 100% with the fact that your a$& is not going to go up in flames but you may get shocked enough to stop your heart. In order for an explosion to happen you would need a bulk of material flowing through the pipe that no home shop is capable of producing with every machine working at once. Secondly you need an arc. A propagating brush discharge is non arcing.

Chet

This is just plain fact. It takes a single strip inside and out of one inch aluminum tape in 2" pvc to create enough of a charge to stop your heart in a residential central vac system. I just went to a seminar 3 weeks ago put on by eurovac and they demonstrated how easy it was to create this charge even though they were selling their pipe the demonstration was real. Your grounding theory is off in order for it to happen the conductors have to be grounded. Your metal pipe statement is irrelevant. We use metal pipe as the standard for one reason only and that is because it is a conductor. You could use carbon fiber if you were made of money because it is a conductor and can be grounded. You can't ground pvc ever, pvc can't be grounded thus why it is not legal for duct work. Even though you can run a wire with a screw every few inches the only way for static to discharge is an arc discharge. The reason running a wire doesn't work well is the charge has to build to the point that it can discharge. At this point the conductor has to be close enough to cause an arc discharge. The wire is never going to be in the right place at the right time, thus why the standard is metal with 100% surface area. The only reason your seeing results with the tape is you increased the surface area and made it more likely to produce a discharge arc. You simply increased the odds that the ground and charge are going to meet at the right time. In turn you changed the dynamics and created the opportunity for a NON arcing propagating brush discharge.

Hybrid

No offence but I sucked down my entire the first time I fired my brand new 3hp cyclone with a four inch blast gate open. All the pipe was brand new from pen state industries. Iirc there may be photos posted here somewhere. I'm not the only guy that has done this I was the guy that ignored the advice.

Don

[dwacker]

I want to step back from the stand off that is developing here and ask a silly question. Why do I need to earth the inside of a pvc pipe. Surely a grounding copper wire running full length wrapped around the outside of the pvc vac line and earthed correctly will suffice?

Dave,

It's simply opportunity. In order to get rid of static there has to be an arc. Pvc can never be grounded. The charge has to be in the right place at the right time to discharge / arc. A wire may or may not be in the right spot for the charge to occur depending on where the majority of fines are in the pipe. If your system is moving air fast enough you will not get a charge discharge event at a consistent enough rate to prevent minor shocks to yourself. This is why the drum sander is always the culprit that wakes you up. The dust is so fine and it has the bulk to keep a constant charge going from one end to the other wire or not. Sort of a double edge sword you want your drum sander connected to you most powerful ports and in my case two ports, same goes for the planer especially wide boards that are loading the system with bulk material, a 15 or 20" wide board loads the pvc somuch that a tiny wire just doesn't have a chance at getting all the charges. Think of it this way. When your system is flowing and you have a wire, you may have thousands of tiny arcs before the material hits the can or bag.

Don

[Pbmaster11]

I ran a 2 hp woodtek for about 8 years with 6" heating duct as the main line, only used Y branches and converted to 4" just before dropping down the the machines. Keep the number of 90s to a minimum and the flex to a minimum and you will be fine. The only place I ever had a problem was the joiner and I had too many bends close together and it would clog. I changed the main line angle, reduced the number of 90s and it was fine after that.

I upgraded to a 5 hp Clearvue and found that long runs of 6" heating duct could collapse if all the gates were closed before turning the system off. I built a vacuum breaker that opens before the duct collapses and have been fine since then. The metal duct is chaper and lighter. Use foil tape, not duct tape.

BRuce

I would love to see your vacuum breaker!

[Eric.]

I still don't get it. Good thing I don't really care.

My duct is out of my way, along the ceilings and walls, so I rarely come in contact with it unless I'm pulling a blast gate. And when I do, I rarely get shocked. And when I do, it's not that bad. Sounds like much ado about nothing to me. Maybe other guys' systems are worse with static shock than mine.

[dwacker]

I still don't get it. Good thing I don't really care.

My duct is out of my way, along the ceilings and walls, so I rarely come in contact with it unless I'm pulling a blast gate. And when I do, I rarely get shocked. And when I do, it's not that bad. Sounds like much ado about nothing to me. Maybe other guys' systems are worse with static shock than mine.

I just deal with it. Gave up. A lot has to do with your machines, most don't have dual drum sanders and the like.

Don

[davestanton]

Thanks for the advice Don.

Am I correct to assume that if no grounding on the lines would only give you a zap on the lines, not on the machines because they are already earthed? If yes, I think maybe the thing to do would be to keep the dust lines out of touch.