Is it really necessary to tape the pvc joints of your DC plumbing?

[Mike Dowell]

Provided you aren't rich and can't afford plumbing such as NordFab, do you tape the joints in your PVC pipe? I'm about to buy the Clearview 1800 DC, and most of the youtube videos I see portraying PVC plumbing show the joints being taped. Seems like they are a pretty good fit to boot though.

[Mike Henderson]

I taped mine but I don't think it's absolutely necessary. The only advantage I see is that any vibration would not cause the joint to come apart a bit and let air leak.

Mike

[Mike Dowell]

I taped mine but I don't think it's absolutely necessary. The only advantage I see is that any vibration would not cause the joint to come apart a bit and let air leak.

Mike
Makes sense. Well, I do have tape. Guess I'll use it.

[Bill Dufour]

Remember that duct tape is pretty much the worst possible thing to use to tape a duct. Any other type of tape is better according to government tests.
Bill

[Jim Becker]

Foil HVAC tape is the product to use regardless of the duct material (PVC or metal) and yes, I recommend you tape the joints.

[Andy Giddings]

I used mushroom head self tap screws to lock the joint together and then foil HVAC tape (3M) to make sure nothing leaked

[Larry Frank]

I used Gorilla brand white duct tape on my 6" DWV pipe. It is strong, and really sticks well. I can guarantee that it does not leak.

[Lee Schierer]

I taped some of the joints on my system where there were long runs prone to sagging or where there were tendencies for movement. I used foil tape. Duct tape dries out rather quickly and fails.

[Robert Engel]

I screwed all the joints. If they are seated down well there is virtually no air loss, but I taped them anyway.

I probably should have used foil tape but I used duct tape. My system works fine.

[Mike Wilkins]

I used short sheet metal screws to join pipes to elbows and Y-branches. During assembly I ran a bead of silicone caulk around the perimeter before sliding the joints together. Has worked well for a lot of years.

[Bill Dufour]

I think the following article is a well researched experiment showing duct tape does not work. The group did come up with a method that works well to pump an aerosol into the ducts it solidifies as it leaks out any bad joints sealing them permanently.
Bill

http://www2.lbl.gov/Science-Articles/Archive/duct-tape-HVAC.html

[Dan Friedrichs]

Silicone caulk. Easy to remove, later.

[Steve Peterson]

Silicone caulk. Easy to remove, later.

I like this idea if you feel the need to seal the ducts. Mine are completely unsealed. Most of them stay in place by being routed around the perimeter of the room. You can only dismantle the pipes from one end. A few places with hanging pipes have sheet metal screws to hold them in place.

Steve

[Larry Frank]

If you read the article about duct tape not working, you will find it is not applicable to dust collectors. The heat and or cold air from an HVAC system will cause duct tape to fail. For a dust collector where the air is room temp, the duct tape works fine. Mine has been on the DWV pipe for a year now and is still sticking fine with no leaks.

[glenn bradley]

No tape here and it passes the smoke test. If you have the tape I see no reason not to use it. Goodness knows I throw an extra clamp on here and there during glue-ups simply because I have them.

[Wayne Lomman]

Use silver/grey PVC tape. We call it duct tape here in Australia. It is flexible and behaves similarly to PVC electrical tape. It stretches into place and is easily removable if required with no residue. Keep it out of the sun and it is good for years. As an aside, what you guys call duct tape, we call 100mph tape and use it to patch bodywork on race cars. Cheers

[John K Jordan]

Provided you aren't rich and can't afford plumbing such as NordFab, do you tape the joints in your PVC pipe? I'm about to buy the Clearview 1800 DC, and most of the youtube videos I see portraying PVC plumbing show the joints being taped. Seems like they are a pretty good fit to boot though.

Who knows "necessary"? Taping/sealing could decrease losses but buy how much? It may be a matter of degree. My 5hp ClearVue is so powerful I can accidentally leave a second blast gate open and don't notice a big performance hit. I suspect that even if all joints leaked a little you would not detect a difference if measuring air flow/suction. Also, press 6" PVC into a fitting and it fits very tightly, quite difficult to get apart and the suction can only make it tighter.

That said, I either glued or used aluminum tape all joins in my shop attic space. Since the most likely thing to need changes are the fittings and gates near the machines I fasten those with short self-tapping screws, three on each joint. Works for me.

JKJ

[Ole Anderson]

Provided you aren't rich and can't afford plumbing such as NordFab...
Many of us have used 26 gauge snap lock steel duct very successfully. Much less expensive than NordFab if you buy it locally from a sheet metal shop or an HVAC dealer, approaching the cost of thin wall pvc. AFAIK only hobbists use pvc for duct. Still baffled as to why so many think the only two choices are NordFab and pvc.

[Chris Padilla]

Silicone caulk. Easy to remove, later.

+1. One screw and smeared some caulk around the edge and called it done. No leaks.

[Andy Giddings]

Many of us have used 26 gauge snap lock steel duct very successfully. Much less expensive than NordFab if you buy it locally from a sheet metal shop or an HVAC dealer, approaching the cost of thin wall pvc. AFAIK only hobbists use pvc for duct. Still baffled as to why so many think the only two choices are NordFab and pvc.
Not sure that being a Hobbyist is linked to the choice of PVC :-) I changed from snap lock steel to PVC because it was cheaper, easier to assemble/cut and has a smoother, slightly larger internal bore resulting in better flow. If I were in business (assuming there was no issue with insurance) I would choose PVC for the same reasons

[Wayne Lomman]

Not too sure about this hobbyist and pvc connection either. It's a choice of cost vs return and that's all. In fact in my shops I have always used a combination because steel is cheap for the big bore stuff and pvc is cheap for the smaller stuff.

I tape joints so they don't rattle apart. However they are still easy to pull apart to clear the occasional blockage. Cheers

[Keith Outten]

I use three short sheet metal screws in each connection now. I used duct tape in the past but I got tired of having to clean the tape off of the fittings when I had to modify my system and the screws keep the joints tight even when there is vibration. I installed a DC swivel ball where my CNC Router hose connects to the pipe because the hose is constantly moving as the gantry moves all over the table. I also have a swivel joint at an overhead connection point that I use for my planer and other temporary connections like a long hose for floor sweeping.

When you have the proper penetration PVC pipe joints don't leak, the screws assure that they stay tight.

[Jim Becker]

Not sure that being a Hobbyist is linked to the choice of PVC :-) I changed from snap lock steel to PVC because it was cheaper, easier to assemble/cut and has a smoother, slightly larger internal bore resulting in better flow. If I were in business (assuming there was no issue with insurance) I would choose PVC for the same reasons
The issue you would run into as a business would be if you ended up with employees and came under the watch of OSHA...PVC isn't permitted for dust collection, if I'm not mistaken, in a commercial environment.

[Jim Finn]

Silicone caulk. Easy to remove, later.
I agree! Looks better too.

[Mike Heidrick]

Pvc tape is amazing stuff.

Also gorilla tape is amazing too.

I have not used either on ductwork but great products mentioned here.

Anyone use butyl caulk? That is some super gummy stick stuff. Harder to remove but sprsy technologies used some on this new to me cyclones fittings and it did a great job sealing the hoses to fittings.

[Chris Padilla]

Anyone use butyl caulk? That is some super gummy stick stuff. Harder to remove but sprsy technologies used some on this new to me cyclones fittings and it did a great job sealing the hoses to fittings.

Using a pure silicone caulk, it is easy to remove later if you need to modify things yet it seals nicely.

[Alan Schaffter]

100% silicone for sure. Do not use latex or siliconized latex- too hard to remove. 100% silicone rubs off easily. All you need is a small, thin bead on the outside of joints- remember your duct is under negative pressure which pulls the caulk tighter.

[Bill Jobe]

I'm not very learned on such things, but wanted to throw in my $.02.
It seems to me the far bigger problem is on the inside, turbulence and head.
I watched a show once where they demonstrated a new way to repair broken/cracked sewer/water lines with a membrane that they simply blew into an open end of the pipe and expanded it. The result was a pipeline as good as new.
Not having tinkered much with conduit to transport air, I have afair amount of experience dealing with head on the pressure side of a water pump.
For many years I kept koi and efficiently of the movement of the water column was where it was at.
Most "well designed" systems used as few fittings as possible to limit head. And, when possible, fittings are not used. The pvc would simply be heated slightly and bent into the position required.
Seems to me the membrane I mentioned would achieve nearly the same thing. This would also eliminate the need to tape anywhere on the outside.
Perhaps there are those here with the wherewithal to even apply a thin film on the inside of pvc,perhaps by spray gun to achieve the same thing
But as I said, we're talking water vs air.

By the way, this may be common knowledge here at Sawmill Creek because there seems to be an unusually high number or great minds here, and this really has nothing to do with pulling/pushing air, but race boats do not strive for a perfectly smooth hull
They use a specific grit of sandpaper to create an environment for air to accumulate. So, the boat skims across the water on a very thin layer of air, reducing drag.
May not be worth $02, but wanted to throw my thoughts out there.

[Alan Schaffter]

There isn't much you can do about internal turbulence and static pressure other than design duct runs as best as you can with minimal bends and fittings, optimize duct size, and use a blower designed to achieve the desired CFM with the duct SP restrictions.

There are a whole host problems with a "liner"- first and most important- liners are designed to seal against leaks with pressure on the inside of the pipe- dust collection systems work with negative pressure on the inside. You seal the joint to keep air from leaking into the duct. It is most likely too difficult and I'm sure way too expensive to install a liner that would need to be rigid so it won't collapse, and frankly that level of sealing is just much easier and cheaper to do by other means from the outside. What do you do about openings for branch ducts and drops? How does it handle bends and wyes? Won't it be difficult to disassemble to change your duct configuration (a fact of life in most shops as people get more machines). And last but not least, high velocity wood chips would likely wear it out or tear it up in pretty short order. Also, a liner reduces the effective I.D. of the duct. I've never heard of any hobby or commercial use of such a liner in dust control ducting.

[Bill Jobe]

I'm not trying to be contentious....just thinking out loud.:)
I know koi keepers who would chase ideas to the ends of the Earth.

[Brian Henderson]

While I'm sure you can get away without it, all of my joints are screwed and taped, just to make sure they never come loose or leak. If you're sure about your setup, you can always just glue it together and ignore the rest. PVC glue is cheap.

[Alan Schaffter]

While I'm sure you can get away without it, all of my joints are screwed and taped, just to make sure they never come loose or leak. If you're sure about your setup, you can always just glue it together and ignore the rest. PVC glue is cheap.

PVC glue is kinda permanent! :eek:

My horizontal runs didn't need little screws, but I used them on a few of the short 45° runs connecting to the machine ports in my shop above. Most ports are in the knee walls except for the ones servicing the tablesaw and jointer, which are in the floor. The 4th photo is a very old one showing manual blast gates on the tablesaw and jointer. All gates were converted to autogates and relocated behind the knee walls or below the floor.

http://www.ncwoodworker.net/pp/data/1329/medium/P10100902.jpg

http://www.ncwoodworker.net/pp/data/1329/medium/P1010091a1.JPG

http://www.ncwoodworker.net/pp/data/1329/medium/P1010088a1.JPG

http://www.ncwoodworker.net/pp/data/1329/medium/P3070165.JPG

http://www.ncwoodworker.net/pp/data/500/medium/P3080015.JPG

http://www.ncwoodworker.net/pp/data/500/medium/P4060034.JPG

http://www.ncwoodworker.net/pp/data/500/medium/P4280022.JPG

[Brian Henderson]

PVC glue is kinda permanent! :eek:

That's why I said if you're really sure of your setup, that will solve the problem and it's cheap.

[Alan Schaffter]

Yes, but what if you suck up a stick (done that), tape measure (done that too! :) but it made all the way to the blower, Yikes!), or something else that can't be retrieved unless you disassemble the duct? Saw time?

[lee cox]

I thought with 6 inch pipe you were suppose to leave 2 blast gates open? I don't have my DC finished yet.

[Ole Anderson]

I thought with 6 inch pipe you were suppose to leave 2 blast gates open? I don't have my DC finished yet. Where did you hear that? All it will do is reduce the suction at the machine in use. Suction is the name of the game.

[John K Jordan]

I thought with 6 inch pipe you were suppose to leave 2 blast gates open? I don't have my DC finished yet.

I've never heard that either. The amount of air and suction will depend on the type and power of the DC. The only time I leave a second blast gate open on purpose is when I want more airflow in the main line when I use a shop vac hose to clean up dust around the bandsaw and lathe.

JKJ

[Jim Becker]

Where did you hear that? All it will do is reduce the suction at the machine in use. Suction is the name of the game.
Actually, "suction" isn't where it's at for dust collection...exactly the opposite. :) Dust collection is about air movement at low static pressure. The more air you move from a CFM (cubic feet per minute) perspective, the more dust and chips get moved with it. That said, I agree that opening up multiple blast gates generally will reduce performance in the smaller systems we use in a typical one-person shop. Ideally, the air movement needs to come from the tool being serviced. Having a 6" port for a 6" drop is ideal, but even a smaller port where the reduction is right at the machine still benefits from the larger duct size because of venturi effect.

[lee cox]

I guess I should qualify if you are using a 6 inch pipe with a 4 inch end then it is best to leave 2 4 inch open ports. One 4 inch open port does not feed a 6 inch pipe properly. I only have 4 inch ports on my tools.

[Andy Giddings]

I guess I should qualify if you are using a 6 inch pipe with a 4 inch end then it is best to leave 2 4 inch open ports. One 4 inch open port does not feed a 6 inch pipe properly. I only have 4 inch ports on my tools.
Depends on what you are trying to achieve - I would agree that 2 x 4 is about the same as the 6 in area, but if you only have one open, its not going to cause an issue - just means the DC motor is not going to work as hard (draw as many amps). As others have pointed out, your duct should collect from the machine in use and only that machine

[Ole Anderson]

Actually, "suction" isn't where it's at for dust collection...exactly the opposite. :) Dust collection is about air movement at low static pressure. The more air you move from a CFM (cubic feet per minute) perspective, the more dust and chips get moved with it. That said, I agree that opening up multiple blast gates generally will reduce performance in the smaller systems we use in a typical one-person shop. Ideally, the air movement needs to come from the tool being serviced. Having a 6" port for a 6" drop is ideal, but even a smaller port where the reduction is right at the machine still benefits from the larger duct size because of venturi effect.

Yes, it is all about air flow volume, measured in cfm for us in the states. For a given size pipe, the more suction (static pressure) you maintain, the more air you are going to flow as you try to offset the pipe and entrance losses with horsepower and static pressure. The very high static pressure you get from a shop vac is needed to get a decent airflow from a small hose. The same principal applies to the larger pipes in a dust collection system, except instead of a 2" hose and 100" of static pressure, we deal with a 6" pipe and hopefully 8" or 10" of static pressure. By opening a second gate, you are splitting the available airflow between two ports, reducing the airflow at the tool being used. As far as opening a second port to maintain adequate flow in a main duct, which is more important: collecting dust as the source or keeping the inside of your pipes squeaky clean? All you need to clean the pipes is a quick opening of the second gate when you are done using the dust producing machine.

[Bill Jobe]

From what I've read here there are a lot of members that use 2 45s to make a 90 degree turn as opposed to a long sweep 90. I'm curious to know if anyone has actually ran tests on the 2 and came away with real numbers to back the choice up.
My guess is that a long sweep 90 would come out on top, but I don't know that.
For one thing, using 2 45s would double the cavities that create turbulence.

Also,and this may sound a bit silly, but have any of you tested some type of vortex generator, such as the Tornado they used to advertise on tv to increase gas mileage in an automobile.
I've read some reviews that stated they actually lost milage using one.
But I can't help but wonder if such a device was placed shortly before a turn in a pvc run that it might reduce the loss of flow created by the cavities at the union.

[Peter Christensen]

BobL on the woodwork forum in Australia discussed a PDF engineering book from a US company with a lot of data on duct, elbow, wyes, etc. It showed that 2 45s did have more drag than a tight 90 elbow. A 1.5 x diameter radius 90 was best. Using the cell or I would link the PDF.


PDF is Loren Cook Engineering Cookbook (http://www.lorencook.com/PDFs/Catalogs/Cookbook_Catalog.pdf). Page 54.

[Bill Jobe]

Thank you, Peter.

[Chris Padilla]

BobL on the woodwork forum in Australia discussed a PDF engineering book from a US company with a lot of data on duct, elbow, wyes, etc. It showed that 2 45s did have more drag than a tight 90 elbow. A 1.5 x diameter radius 90 was best. Using the cell or I would link the PDF.


PDF is Loren Cook Engineering Cookbook (http://www.lorencook.com/PDFs/Catalogs/Cookbook_Catalog.pdf). Page 54.

Peter,

Looking at the PDF you attached on Page 54, a 3-piece 45 is 15' and a 2-piece 45 is 20'. An R/D of 0.75 gives a best case of 37' (tightest on the chart) for a smooth, 90.
I assume it is fine to simply double the 45 to get a 90 and that gives 30' and 40', respectively. However, I wonder about the R/D ratio for the 45s as they claim the same numbers regardless. Two 45s look like fine to me. Long-radiused 90s are usually more expensive than two 45s--at least in 6" DWV PVC fittings last I built my system over 10 years ago.

That is a great PDF...lots of information in there!

[Peter Christensen]

Look at the 3 piece 90, 1C on the chart which is essentially what you make with a couple 45s. It has a resistance of 61', 48', 39'. So the best you'll get if there is some space between them will be 39' but perhaps more because there are the 4 ridges where each pipe to elbow joint is.

I've been looking at PVC for my system (CV-Max) but here we can't get much DWV in 6" and nothing in 8". Only Schedule 40 which is $10' for 6" pipe and $16 for 8" and that was the best I could locate. Spiral pipe starts at $3.50' for 6" and that's more than I would prefer to spend. Nothing for the cheapskate. ;)

[Wade Lippman]

Grizzly recommended I leave another gate open on a different branch than the tool i was using on my 3hp cyclone. The increased air flow would let the rotor spin up to full speed and actually increase the air flow from my tool.

I tried it with an anemometer and found it didn't make much difference either way. So now I try to close other gates, but don't spend much time on it.

If having a gate open doesn't hurt anything, a little leakage from joints can't be so bad.

[Ole Anderson]

Grizzly recommended I leave another gate open on a different branch than the tool i was using on my 3hp cyclone. The increased air flow would let the rotor spin up to full speed and actually increase the air flow from my tool.

I tried it with an anemometer and found it didn't make much difference either way. So now I try to close other gates, but don't spend much time on it.

If having a gate open doesn't hurt anything, a little leakage from joints can't be so bad.

That doesn't make sense and is just bad advice. The impeller/motor will spin faster when there is little airflow, as it is spinning in a higher vacuum and there is less air resistance. Look at any fan curve and more static head (vacuum, suction) means less airflow. Put your hand over a shop vac hose and you will hear the motor speed up as it has no air to move. The motor does the most work, and will therefore spin slightly slower when it is under maximum load, and that is when it is moving the most air with the gates open.

[Ole Anderson]

I've been looking at PVC for my system (CV-Max) but here we can't get much DWV in 6" and nothing in 8". Only Schedule 40 which is $10' for 6" pipe and $16 for 8" and that was the best I could locate. Spiral pipe starts at $3.50' for 6" and that's more than I would prefer to spend. Nothing for the cheapskate. ;)

There are obvious choices other than PVC and spiral steel (Nordfab) that can give you economy and steel ducting at the same time. I am not even going to mention what it is for fear of sounding like a broken record.

[John Jenkins4]

I've been looking at PVC for my system (CV-Max) but here we can't get much DWV in 6" and nothing in 8". Only Schedule 40 which is $10' for 6" pipe and $16 for 8" and that was the best I could locate. Spiral pipe starts at $3.50' for 6" and that's more than I would prefer to spend. Nothing for the cheapskate. ;)

And just a reminder that DWV and Sch 40 aren't interchangeable (different ODs) so once the choice is made, there's no mix and match.

[Peter Christensen]

............ I am not even going to mention what it is for fear of sounding like a broken record.

I'm new here so haven't heard the playlist. If you don't want to say then how about a link to the tunes?
Thanks

[Chris Parks]

BobL on the woodwork forum in Australia discussed a PDF engineering book from a US company with a lot of data on duct, elbow, wyes, etc. It showed that 2 45s did have more drag than a tight 90 elbow. A 1.5 x diameter radius 90 was best. Using the cell or I would link the PDF.


PDF is Loren Cook Engineering Cookbook (http://www.lorencook.com/PDFs/Catalogs/Cookbook_Catalog.pdf). Page 54.

BobL has done his own testing and it showed that a single 90 performs better than two 45"s which when you think about it sort of makes sense. The first 45 degrades the flow then the second 45 does the same to the already reduced flow whereas a single 90 only affects the flow once without the compounding loss. The figures are all there and illustrated for those who are curious about these things.

[Ole Anderson]

I'm new here so haven't heard the playlist. If you don't want to say then how about a link to the tunes?
Thanks Many of us have used 26 gauge snaplock steel HVAC duct very successfully. Slightly more than PVC, but way less than spiral pipe. But stay away from the much thinner 30 gauge stuff you may find at the BORG, it can collapse with a strong suction. You will generally find it cheaper at an HVAC supply house or local sheet metal shop than online. No issues with static. And it looks professional.

[Carl Kona]

Just to be clear about the 2-45s vs 1-90 (apples to watermelons comparison). The idea of using 2 45s instead of one 90 will always increase flow if it increases the radius. That is how the suggestion first started. Most snap lock and pvc fittings have inexpensive 90s, but come with a small <1 radius. If in those situations when you use 2-45s and make a longer radius 90 you will increase flow (as shown in this video https://www.youtube.com/watch?v=oXd6YlCnyzQ). If available a smooth long sweep 90 will always be better, which was the goal of 2-45s. Unfortunately long radius pvc or snap lock 90s are not readily available and usually significantly more expensive. Somewhere along the way the point of increasing radius in the curve has been lost and it has become a 2-45 vs 1-90 (apples to watermelons) comparison.

Ole is correct about the possibility of long straight 30 gauge snap lock (from big box stores) collapsing under pressure. However a simple wooden ring around the mid-span of long straight ducts will eliminate the issue and add a mounting point for you.

Hope that helps.

Carl

[Chris Padilla]

BobL has done his own testing and it showed that a single 90 performs better than two 45"s which when you think about it sort of makes sense. The first 45 degrades the flow then the second 45 does the same to the already reduced flow whereas a single 90 only affects the flow once without the compounding loss. The figures are all there and illustrated for those who are curious about these things.

Carl just said it above me but one must CLARIFY what the radii are when comparing the "2 45s" vs. "1 90" flow question. I'm not sure if 45s come with different radii but certainly 90s do. When I was picking up my SDR35 (DWV, S&D, not Sch40) fittings from McMaster-Carr a decade+ ago, two 45s were significantly (IMO) cheaper than the long-radiused 90 so I went that route. And as it turns out, for my situation, having 2 45s in place of 90 was handy for directing my pipe.

[John K Jordan]

... And as it turns out, for my situation, having 2 45s in place of 90 was handy for directing my pipe.

Same here. In fact, in snaking my 6" pvc through the trusses above the ceiling I had several places where four 22.5-deg elbows made the installation easier. By rotating some a few degrees the pvc almost turns into flex! Who knows what efficiency, but with the 5hp clearvue I have a clear excess of capacity at the machines according to the particulate counter.

JKJ

[Chris Parks]

Who knows what efficiency, but with the 5hp clearvue I have a clear excess of capacity at the machines according to the particulate counter.

JKJ

That small point escapes a lot of people. It also depends on the configuration of the Clearvue and the speed it is running at. Never the less it is good to know these things and keep up to date with what others are finding.

[Bill Jobe]

This ain't much, but I've been shopping online for ways to build my duct system and it occured to me that, if in fact the cavities created by pvc joints does reduce flow, by simply belt sanding an angle on the end of the pipe equal to the angle inside the fitting, applying silicone, sliding it in and wiping the eccess silicone off, the smoother joint should result in improved flow.

Like I said....not much, but if you cannot afford to overcome inefficiencies with hp, why not?