PVC Duct & Static Electric Problems? - Page 2 - Woodworking Talk - Woodworkers Forum
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post #21 of 43 Old 03-03-2019, 04:05 PM Thread Starter
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My HF collector has a 5” inlet with a removable 5” to 4” Y. It allows for 2 4” runs. Remove the Y & you have the single 5” inlet.


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While out today we decided to make a trip to a Harbor Freight store. They have a unit on display which I had no problem taking apart and playing with. It did have the 5" inlet which was a good surprise. I'm still leaning towards using 4" pvc piping. I think I will get a much better sealed piping system than using the metal pipes. With the metal I'd have to tape all the joints and all the elbows and would probably tape the entire seam joint just to be safe. Also, sucking with a 5 inch inlet through a 4" hose I would assume I would get more sucking power at the tool end? Want to make sure it sucks up the small chips of wood and not have them rattle around in the vertical pipe. As for the static electric problem, do people get a shock when they touch the PVC pipe? Scott410 had the same idea I had.. Wouldn't attaching a metal screw to the outer wall of the pipe and attaching to a coper plumbing line OR the blower housing eliminate that problem?
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post #22 of 43 Old 03-03-2019, 04:09 PM Thread Starter
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Woodnthings: Thank you for the links! I've already thought about the impeller change as an option IF the HF unit doesn't perform well enough. Hope it's not needed but seems like a fun project if it does.
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post #23 of 43 Old 03-03-2019, 04:14 PM
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If you read any of the links .....

Quote:
Originally Posted by SteveKoz View Post
While out today we decided to make a trip to a Harbor Freight store. They have a unit on display which I had no problem taking apart and playing with. It did have the 5" inlet which was a good surprise. I'm still leaning towards using 4" pvc piping. I think I will get a much better sealed piping system than using the metal pipes. With the metal I'd have to tape all the joints and all the elbows and would probably tape the entire seam joint just to be safe. Also, sucking with a 5 inch inlet through a 4" hose I would assume I would get more sucking power at the tool end? Want to make sure it sucks up the small chips of wood and not have them rattle around in the vertical pipe. As for the static electric problem, do people get a shock when they touch the PVC pipe? Scott410 had the same idea I had.. Wouldn't attaching a metal screw to the outer wall of the pipe and attaching to a coper plumbing line OR the blower housing eliminate that problem?

There's a whole lot more to this than pipe diameter, although in any case "bigger IS better'.!



To summarize the 47 pages by Bill Pentz ... The home shop blowers do not move enough air. The impellers are too small as are the motors. They will collect chips OK, but not fine dust. The best plastic pipes are P &D sewer pipes. A 4" pipe is too small. etc.
http://billpentz.com/woodworking/cyc...ucting_diamter

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 03-03-2019 at 04:18 PM.
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post #24 of 43 Old 03-04-2019, 08:04 AM Thread Starter
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There's a whole lot more to this than pipe diameter, although in any case "bigger IS better'.!
OK.. so now I"m back to the 5" metal duct work. The impeller upgrade seems to make sense too. What got me wondering is that it seems a lot of HF owners are looking for upgrades which makes me wonder if the 5" duct is big enough? I've heard the 5" is better than 4" so 6" should be better than 5" as long as the blower can pull enough air. It's not about the pulling power but the volume of air moved is what I've been learning.. The question is that it all seems to connect to 4" hoses at the tool. Doesn't it loose volume of air movement when it's reduced to the 4" pipe at the tool? Does the 6 to 4 create better suction at the tool? I'm getting ready to order my piping and blast gates. Hate to purchase 5" if I'll be regretting not getting the 6 from the start. Thanks!
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post #25 of 43 Old 03-04-2019, 09:10 AM
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I don't have metal duct work .....

I don't even have much of a run of 4" PVC except what's under my 3 table saws, about 10 ft, which I do connect with a 5 ft flex hose directly to a Jet 1100 DC. So, I'm not your best source of advice, but I read a lot of Pentz's material just for the knowledge and pass that along here. According to his articles, even my Jet 1100 which has a "rating" on paper of 1100 CFM, it's only actually somewhere between 400 CFM and 800 CFM. All I know is they work OK when connected as directly as possible to my sanders and planers for one and the table saws and jointer for the other. I found it was much easier for my to get 2 Jet 1100's than run a bunch of pipe around a vaulted ceiling where it wouldn't look very good and it would be a pain to hang.


Just beware that any thin gauge metal duct from a home store may have flanges and seams which will collect the dust and if your blower id powerful enough, it may collapse, again I'm quoting/reading from Pentz's material. Also any transitions in sheet metal will be expensive for the slow curves. You may want to sketch out the layout form your system and post it here for us to comment on.
I don't have all the answers of course, since it is a science unto itself. Bigger Is better, but also more expensive......

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 03-04-2019 at 09:18 AM.
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post #26 of 43 Old 03-04-2019, 07:13 PM
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The metal pipe you talked about is furnace duct. It is for pressure not vacuum. I watched a guy turn on his dust collector for the first time after installing furnace duct. A big part of it collapsed! Dust collection duct is the spiral stuff or the more ridged flanged stuff. PVC will work, just less than ideal. The elbows are pretty tight radius and will cause more drag than a proper duct elbow.
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post #27 of 43 Old 03-05-2019, 01:21 AM
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Simple PVC Static Discharge

I installed my central dust collection with PVC for several reasons, cost, ease of installation, future modification. I had previous experience with the static electricity build up when using any plastic type duct or hose. I looked at existing grounding systems available for purchase and home made systems. They were unattractive, difficult to install and rather expensive. I found a very simple and easy solution. Using aluminum foil duct seal tape, I adhered strips to the duct work while folding 1/3 of the strip back under its self to place the aluminum in direct contact with the exterior of the PVC. I then ran a second strip over the now 2/3 wide strip fully securing it to the PVC. You may have success just adhering the tape directly to the PVC, but I was uncertain about the rather thick adhesive interfering with the connectivity. I ensured I had continuous runs over all PVC duct, then attached an electrical eye connector and wire to the end of the tape near a grounding source. The other end of the wire is connected to the ground. I conducted multiple tests using various chip/dust particle sizes (MDF dust included) and have found the system is completely discharging all static.



The idea that you have to penetrate the PVC with connectors to capture the static charge is not correct. All that is necessary is to provide a discharge pathway that offers less resistance than the PVC.


Total cost, 1 large roll of aluminum foil tape, about $9. Installation time, 1 hour. (I connected all flex hoses internal wire frame to the system as well and they remain static free and very clean on the exterior.


I will try to upload some pictures tomorrow, but most the tape is out of sight.

- Greg


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post #28 of 43 Old 03-05-2019, 02:47 PM
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I ran some quick & dirty calculations for you. Based on half way between woodnthings 400 to 800 cfm real #s for the inflated 1100 claimed. I used 600cfm which seems about right. (normally around 1/2 of the free air #) So if we use the standard industry velocities of 3500'/min for horizontal runs and 4500'/min for vertical. Take a look at these #s. These would be the velocities right at the entry into the ducts at the collector. They do not include the losses from ductwork, bends, flex hose, dust hoods or dust loading of the bag, etc. One 5" duct 4400'/min, Two 4" ducts 3428'/min., One 6" duct 3061'/min. Flex hose and poor hood design will greatly reduce the actual results. Anything that creates turbulence drags the flow down.
I haven't gone into calculating the required suction level at the hoods. You can find the formulas for that one line. Most tools will require a minimum of 4" water column.

In a one man shop I would connect each machine to the collector with a run of duct directly to the collector, all the same size. You can use branches as long as you don't reduce diameter without a terrible loss of suction. Put the blast gates so they are easily operated at each machine. You can use extension rods to operate them so they can be in the best location with the fewest fittings. Get yourself one of the wireless remote switches so you don't have to run back to the collector each time you want to use it.

Do your layout taking into account likely tool changes, additions etc.
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post #29 of 43 Old 03-06-2019, 12:56 PM
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Stevekos: I think it will work. I have foundation bolts that hold my garage to the slab, I will use that as my ground.

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post #30 of 43 Old 03-06-2019, 04:24 PM
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I don't think your foundation bolts make a good ground connection.
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post #31 of 43 Old 03-06-2019, 05:26 PM
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interesting issue .....

Quote:
Originally Posted by Scott410 View Post
Stevekos: I think it will work. I have foundation bolts that hold my garage to the slab, I will use that as my ground.

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I don't think your foundation bolts make a good ground connection.

One may think that a foundation bolt would be a good ground, but how would you know/test it? I had to drive an 8ft rod in the ground for my system years ago and it wasn't all that easy in rocky soil. Then years later I learned about using an electric impact hammer to drive them in, may be on You Tube? I don't think the rod was copper, but some alloy maybe? The moisture in the soil would help conduction, but there wouldn't be any in a concrete slab. Interesting .....

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #32 of 43 Old 03-08-2019, 07:49 AM
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I used PVC on my whole system. It works great. I had to make a wood donut adapter for the PVC to fit the planner exhaust. But I was getting static sparks from the PVC to the metal part of the planner. That spark jumped about one inch or more. Some say the static won't start a fire, but I'm not taking a chance. If it started a fire in the PVC, and all that fresh air through the pipe it would fuel the fire very fast and very difficult to put out. So I took a rag, attached a small thin wire to it and sicked a wire trough the pipe. I then fastened the wire to the planner and the other end to the vacuum. I did this to each piece of equipment. Problem solved. No more sparks and I can relax while using it.

Some say the wood dust isn't like flour in a flour mill that causes explosions. If you don't think so, start a wood fire in your wood stove and after its going good through a shovel full in the fire. Stand back because it will flash back!!
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post #33 of 43 Old 03-08-2019, 08:39 AM
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Wood stove and flashback ....

Quote:
Originally Posted by tewitt1949 View Post

Some say the wood dust isn't like flour in a flour mill that causes explosions. If you don't think so, start a wood fire in your wood stove and after its going good through a shovel full in the fire. Stand back because it will flash back!!

That's a completely different set of circumstance, with the fire already started, tremendous heat already there are a draft going up the chimney to bring in combustion air. You have ffire, ignition and fuel in that case.


The wood and flour dust explosions occur only when the correct combination of the 3 elements are present and in the right proportions. In the case of flour dust, huge proportions of dust and volumes of air are present and in a wood manufacturing plant the same situation, huge volumes of dust and air combined.



I'm glad you have solved your static issue just like I did because it was real painful and annoying. It was a simple fix in both cases. I just ran a bare copper wire from the separator to the blower motor because the 6" clear plastic suction hose did not provide either a mechanical or electrical connection between them.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #34 of 43 Old 03-09-2019, 02:43 PM
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Just took this picture from a book I got from the library. Basically what I was going to do.

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post #35 of 43 Old 03-09-2019, 03:10 PM
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Annoying VS hazardous static ......

I solved my annoying, even painful static issue with a single bare copper wire from the separator to the blower motor housing. No more static shocks when I'm near the DC and it's running!



Wrapping the outside of the hoses and pipes with bare wire will do the same IF the one wire solution doesn't work. This is where it gets interesting .... running a bare wire inside the pipes and hoses will prevent a static discharge that could possibly be hazardous according to this rather scientific and scholarly article which I have quoted here many times:
http://www.waterfront-woods.com/
Quoting:
The primary point about dielectric breakdown, is that it takes far, far less voltage for a spark to jump through air, than it does to jump through PVC. This is the reason why it is absolutely pointless to wrap a ground wire around the outside of a PVC duct and expect protection against static buildup on the inside.


Another site that deals with debunking static explosions:
http://www.billpentz.com/Woodworking...ic_electricity

http://www.woodcentral.com/articles/...cles_221.shtml

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 03-09-2019 at 03:53 PM.
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post #36 of 43 Old 03-15-2019, 07:06 AM Thread Starter
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IT seems wrapping the wire on the outside of the pipe will take the static charge out of the PVC pipe while running a copper wire inside the pipe will prevent a static charge from building up. Plus it's hidden. If running inside do you drill a hole near the blower connection to bring the wire out of the pipe to ground? Guess it wouldn't hurt to bring it out at both ends instead of trying to attach the wire to the inside at the far end. What gauge copper wire is used or needed?
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post #37 of 43 Old 03-15-2019, 10:29 PM
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Grounding PVC the easy way

Thought I had already posted on this, but couldn’t find it. I grounded my PVC dust collection system using aluminum tape on the outside of the tubing. I folded the tape back onto itself 1/3 of the width, lengthwise. Thus 1/3 of the tapes non-adhesive aluminum surface was in direct contact with the outside of the PVC. I then secured the affixed strip with a second piece. All this is connected to the house grounding system. My flexible 4” ducts have the encased structural wire also attached to the ground. Total cost, about $6.99. Took about an hour to complete.

Works 100%. Zero static charge buildup. It is not necessary to ground the internal pipe. By simply providing a pathway with less resistance than PVC, the aluminum tape carry’s the system charge to ground. May not have been necessary to fold the tape so that th3 outer aluminum was in direct contact with the outside of the PVC, but I did not run my small test system with that setup. I wanted to eliminate any insulative properties of the ahpdhesive between the PVC and the tape’s aluminum backing.

Will try to upload a few pics after I get back from the PATINA auction tomorrow.

- Greg


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post #38 of 43 Old 03-15-2019, 10:32 PM
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PVC Grounding

BTW, I agree with those that have posted data on the almost non-existant threat of explosion from woodworking dust. I grounded my system mostly to avoid the buildup of charged dust particles all over the system, raining dust down as the charge dissipates and to avoid annoying static shocks. Success on both counts.

- Greg


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post #39 of 43 Old 03-16-2019, 01:26 AM Thread Starter
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Thought I had already posted on this, but couldn’t find it. I grounded my PVC dust collection system using aluminum tape on the outside of the tubing....
How many places did you wrap the tape on the pipe? I thought PVC was no conductive where just grounding one section would not ground the entire pipe?
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post #40 of 43 Old 03-16-2019, 06:52 AM
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I believe any wire or metal material will work. All I had available at the time was a small roll of piano wire. I don't know the diameter but it was about the size of kite string or 8 lb fishing line. I first sucked a small rag fastened to some chalk line then pulled the piano wire through the inside of my pipe. It just lays in the bottom of the pipe. I then drilled a small hole through the pipe for the wire to exit and fasten to the piece of equipment. I did this in every pipe. So far I'm very happy with it, no sparks or shocks anymore
. I had a shop burn down once (not from vacuum and saw dust) but it wasn't nice at all. Lost everything. So I'm very cautious now and go out of my way to prevent it from happening again.
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