DC ducting

Chuck Beland

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Rhode Island
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OK, finally need some ducting advice. now I got some vaca time & the wife is away I want to get it finished. The first pic here is where I want to put my DC system. As you can see I got elect there already.






Next two pics is of the outside of the shed to the basement window I have to use.







As you can see the run will not be very long. I also know that you should use as little of the 90° elbows for good flow of air.


1. I was wondering if I should use instead of the 90 should I use two 45° elbows.

2. Should I use the thin walled PVC? I saw it has some type of black plastic inside of it will that do anything to the flow of air?

3. I'm not going to glue any joints just a pressure fit. Since we get some real heavy snow up here will the thin wall PVC have any type of cracking issue due to extreme cold?

4. I have the HF one., am I going to have to put it on a type of wood pedestal so the intake more lines up with the window? if so then I'm afraid of the height issue maybe to tall & the bag be constricted by the ceiling???

any advice is very welcome.

Chuck
 
lets see if i got this right so far chuck:) dense today:) your DC is gonna go in the shed and the lines are going threw the basement window?
if this is the case, then first of all a DC can only pull so much..depending on its size.. and the length of run affects that aswell..so you might be asking for to much for the DC to be in the shed and pulling from the basement..so we need to know the size of the DC and then what your plans are for distance and what you are attempting to do in the basement..
 
Chuck, if I understand you correctly, the shed is the structure on the left in this photo, and the basement window is on the right. I'm also assuming your Harbor Freight DC is going into the shed, with a pipe running from the shed, through the basement window, and into your shop. Is that all correct?

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If that's the case, I do think two 45º bends will be better than a single 90º elbow. I also think I'd look into running the intake pipe through the shed wall instead of the shed window. I think it'd be easier to get sealed up. I could be wrong on that, though.

On the PVC pipe questions, I'll let someone who knows more about the stuff chime in.
 

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1 If you only go with friction fit you are going to have too much loss from leakage at the seams.
2 Are you running two lines? one for the dust and one for the return air? for it to work the air needs to be returned to the room.
3 The 2 45's would be better than the 1 90 for air flow.
4 Be careful of static electricity build up in the pvc they dont recommend it for just that reason. You are a lot safer using metal pipe and grounding it.
 
...4 Be careful of static electricity build up in the pvc they dont recommend it for just that reason...

There's a lot of debate on that one, Rich. I know a number of experts are of the opinion that there is no risk, since they feel the right combination of dust density, oxygen, and airflow don't exist for dust explosion in a home shop DC system. It's my understanding that there has never been a documented case of PVC piping causing a dust explosion in a home DC system. On the other hand, there are a number of intelligent people who would prefer to avoid the chance entirely (however slight it may or may not be) by simply not using PVC piping in the first place.
 
use long sweep fittings and if you could use a y instead of the 45's you would have better flow.. i used pvc and havnt had any trouble and i used the schedule 40 rather than the S&D but if you seal the connection on the S&D you should solve rich point that he made..use the metal furnace tape to seal it..
if you were closer i got a batch of metal ducting and fittings that you could have:)
 
Larry,
I have this one HF 2hp DC Also I never heard of "long sweep fittings"?
The length of run is from the basement window Vaughn showed then it's only approx 8' to the lathe.


Vaughn,
You are correct the shed is to the left with the large windows & the basement is the one you said. Wife will kill me if I drill a 4" hole through the shed, sorry not a option.


Rich,
I thought being in the shed it would take air from the shed???


Question:
Do you think the metal would be cheaper or easier to use then the PVC?
 
There's a lot of debate on that one, Rich. I know a number of experts are of the opinion that there is no risk, since they feel the right combination of dust density, oxygen, and airflow don't exist for dust explosion in a home shop DC system. It's my understanding that there has never been a documented case of PVC piping causing a dust explosion in a home DC system. On the other hand, there are a number of intelligent people who would prefer to avoid the chance entirely (however slight it may or may not be) by simply not using PVC piping in the first place.

I agree with everything you said Vaughn, I have read both the reports that say its fine and the chicken little reports and several in betweens. I just felt it needed to be mentioned as there is always a chance. Even if it doesn't cause an explosion, just the stored up static on a dry cold February morning deciding it likes your flannel shirt better when you walk by and nailing you, or worse deciding to make the jump when you are operating a machine is more than enough to "not go there" for me....:eek:


A report I recently read said that "thorough testing" has shown that the danger doesnt manifest itself until cfm exceeds 1500 and then it's "rare"

Also, metal pipe, even though still a lot more expensive than pvc, has come down to the point where it is at least reasonably priced, and for most home runs you arent looking at a huge investment. Also, you can focus the pipe on the straight runs and use the flex hose which is very reasonable on the drops to the machines. and all can be grounded very easily.

But since whenever there is a 99 out of 100 chance something wont happen. I usally fall into the minority......:rofl::rofl:
 
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Larry,
I have this one HF 2hp DC Also I never heard of "long sweep fittings"?
The length of run is from the basement window Vaughn showed then it's only approx 8' to the lathe.


Vaughn,
You are correct the shed is to the left with the large windows & the basement is the one you said. Wife will kill me if I drill a 4" hole through the shed, sorry not a option.


Rich,
I thought being in the shed it would take air from the shed???




Question:
Do you think the metal would be cheaper or easier to use then the PVC?

It would release the air from your shop into the shed. The air needs to be returned to the room it was removed from to work properly, also if that is where your furnace is (if you have gas or oil) the dc can potentially create the path of least resistance for the exhaust gasses and draw them into the shop instead of letting them release through the chimney
 
rich, why does the air that has been sucked in the DC need to be brought back into the shop except for the possible heat and cooling issues you mentioned? in my case and i have seen others this way as well its ducted outside..:huh:
 
what are your primary tools that you use regularly chuck? if its the lathe and your getting mostly chips till the sanding begins then i would think you would be better off having it move tot he machine your using.. see how vaughn has his setup.. he does both flat and spinny stuff and can give you some insight on the whole deal he even has the same DC i think, his is purple though:)
 
I believe it has to do with the static pressure and air flow. By returning the air to the room it keeps the draw constant. By exhausting it outside or to another area you create a pressure loss as well as the heat/cooling issues.
Of course if you have a fresh air supply running into the room and can exhaust the air being drawn into the shed so you dont get into over pressuring the system at that end then you can have it flow fine but still need to address heating and cooling issue and costs.

Just look at how much pressure your dc drops when the bag reaches half full.
It's like a line gets crossed. I really notice it when I am running my planer. All is great till that point then I start seeing the shavings coming out the end of the planer.

In the shops I have worked in, if the dc was outside the building it always was ducted back into the shop with filters at the end to catch the fines. If the entire system was inside there was no issue.
 
I'm no expert and probably not even knowledgeable, so take my comments with a grain of salt.... I use the 2hp HF DC in my shop. I have mine in a separate shed outside the shop with a hole through the wall... my shop is a 12 x 24 shed... the lathe sits in the middle of the shop about half the distance from the end wall where the DC is sitting. I have my piping along the floor until it passes my work bench then it goes up overhead to the lathe and over to the band saw. I also have another pipe running on the floor over to my table saw. I have two lathes, the band saw and the table saw all piped into the DC... I also have gates before each tool so I can effectively shut off the suction before each tool and only open the gate at the tool I am operating. I seem to have a pretty good draw... it doesn't catch all of the chips coming off the lathe, but a good percentage of the lighter stuff... the heavier pieces all fall to the floor.

I need to make a couple of changes to mine... I used the flex dryer hose for the run behind the work bench... I've notices a couple of dents in the light aluminum and may have some vacuum leak.... need to put a good piece of pvc in there.

I built the shed almost like an out house... it's about 40 x 40 x about 6 ft high... just accommodates the DC... wish not I had allowed a little extra room for a compressor... OH WELL...

I looked for pictures of the current configuration, but just changed some of the routing of the piping and haven't taken pictures yet... these pictures do show the location of the DC and the aluminum pipe under the workbench... the WB hasn't been set in place yet.

To answer your comments about the sweeps... it's probably best that you use gentler 45 angles rather than sharp 90... my opinion and only my opinion with no scientific back up, but asking for a sharp turn in the suction is a potential for a clog. I use "Y" fittings and flexible tubing for my runs so I can make gentler turns... only place I seem to get a clog is at the grid covering over the entry to the impeller cage... if my DC picks up a lot of long shavings, they'll catch on the grid and stack up... I have a clean out cap (actually another "Y" fitting that would allow you to hook two different runs to the DC, but I only use one.. the other is capped) at the front of the impeller cage and I can take the cap off and reach in to clean out any clog there.

BTW, this seems like a good unit... only 2 problems I've ever had with it... I burned up a switch on the motor... thinking it was a motor called HF and complained.. (I had had the unit only about 10 months) they sent me a new motor... sans switch, so when I took the switch off to put it on the new motor discovered it was shorted... bought a new switch and the original motor works great now and has for last 4 years. and I now have a new unused 2 hp motor.
The other problem, I got some critters in the shed that liked the felt materials from the bags to make nests... I had about a half bushel of acorns stored under the DC unit and they ate holes in the top bag for their nesting materials....
 

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It doesn't have to come back from the shed into the shop, but you do have to have a source of makeup air. Best to control where it comes from, as pulling exhaust gas from a vent back into the basement can be dangerous. Outside air is fine, as long as a window is cracked or something to allow it to come in freely.

On the elbows your 2x 45 elbows can allow a bigger piece to pass through without clogging than a single 90 elbow.


You want the path into the DC the most direct as possible, if that means elevating the DC a little that would be best. I don't think having the filter bag touching the ceiling a little is a big problem, but you don't want to hold it 1/2 collapsed. If it's needed, 1-2' of flex at the end of the pvc isn't that big of a a deal to hook up the dust collector. You just want to minimize the amount used, as it's around 3x the pressure drop per foot as hard duct.
 
I don't think this was mentioned yet, but I have a thought: Since your DC will be higher than the room in which your lathe and other equipment is located, you might consider a chip collector in the DC pipe in the basement. The heavier chips end up in a garbage can in the basement and only the lighter dust has to be drawn uphill.
 
Dust Collection Miscellaneous

OK fasten your seatbelts, here I go again, long winded and opinionated as usual.

Let’s start off with this. I spent a whale of a lot of hours over a period of months reading everything I could find about dust collection. I did the calculations for air flow, static pressure, duct size, duct type, etc. I read what Bill Penz had to say, I purchased books, I had the library get books from other libraries, I was just plain old DC saturated.

My own personal system seems to be working quite well. I do a lot of duct rearranging every time I purchase a new major tool.

In general keep in mind that anything that gets in the way of the airflow in a DC is going to cost you. Air has to come in EASILY to replace air that goes out. Straight lines of air flow are most efficient. Use the shortest runs practical. Pipe size needs to be large enough to move the air freely. Pipe needs to be smooth, not rippled like flex pipe.

My response to Chuck’s original questions:

1 Definitely use two 45* (* means degree) ells to make a 90* turn. This disrupts the air flow much less than a 90*. Use a Wye instead of a Tee for the same reason. Two HP units should not have to cope with 90* turns.

2. I have not used thin wall ducting. From ignorance I did overkill and used SandD schedule 35. I could not find anything that told me how strong the duct walls needed to be. I did find references that stated the thinner venting ducts would collapse in a DC situation. However, that was it.

Some thin wall PVC has rippled interior walls, like flex ducting. DO NOT use it. It has triple the drag of smooth wall.

3. I have used only friction fitting of joints in my DC. It is quite satisfactory. I have no leakage. My son Glenn has done the same. Neither of us has taped any connections.

4. I am not familiar with the HF dust collector. I will try to see one tomorrow. In my opinion, HF stuff can be a tremendous bargain or junk.

Sorry Rich but the air does not need to be returned to the DC room. However, some way the air that is removed has to be replaced with more air or the expelled air. I built an addition onto my shop to house the DC. I did it specifically so that the filtered air was NOT returned to my shop. I did not want the invisible pollutants returned to my shop.

There was a several page technical report about static electricity causing a problem with wood dust. It was on Saw Mill Creek about the time FWW was started or it might be on FWW back then. This was a report by a chemical engineer on what it takes to make a fire/explosion with wood dust. According to all of his technical jargon and research references, it cannot be done with static electricity. The result was that I used PVC and I did not run wire along the outside of the PVC.
Metal ducting was VERY much more expensive than PVC. One joint I purchased for my system was less than $15.00. In metal it was $90.00 plus.

We think and talk about vacuum with vacuum cleaners, shop vacs, and DCs. We are not dealing with vacuum. We are dealing with air movement. The air movement, if correct, will carry the wood dust and the pollutants with it.

There is a kind of dance going on, very similar to sewage movement. If the water moves too fast, it will run off and leave the solids behind. If the water moves too slowly, it will not carry the solids with it. We have to move the air fast enough that the solids will not settle. We have to move it slowly enough that wood chips do not become bullets and ruin the system.

Recently I moved part of my DC ducting. The duct had been in place over four years. The inside of the pipe was sparkling clean except at joints. There was a little ring of dust that smoothed off the area where the pipe met the elbow (or whatever). That ring of dust was packed quite solidly. It was less than half a teaspoon per joint.

Remembering that the job of the DC system is to move air, we do not want to do anything that slows that air as it goes down the tube. We do not want it turbulent the way the rings in flex, make it turbulent. We want the plumbing to be large enough that air friction along the tubing walls is not a problem. We want the gentle turns (and as few as practical) so the air molecules are not crashing into each other slowing down the flow.

Jonathan is correct. You do not want the DC unit “…anywhere near the furnace/boiler.”

Looking at the pipe there are a couple places you will note the slight dust ring. The ring forms where the end of the pipe is tapered for easier insertion into the fitting. It can be as wide as 1/8 inch and at worst 1/16 inch thick.

These pics are old. There is more pipe now. There is less flex now.

At the bottom end of the drop to the lathe there is a 2 1/2 inch wye. From it two of the adjust and let go type ducts run under the lathe bed. I can pull them up with the end(s) into the dust and chip stream from the lathe. This is quite effective.

Enjoy,

Jim
 
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Larry,
I would only use it for sanding on my lathe. For my Rigid contractors saw I use a shop vac I just received a dust deputy to hook to my shop vac. I just have to install it.


JIm,
The reason I got the HF one is that Vaughn has had good results from his. I couldn't afford a brand name at the time just to much money. I trust Vaughn opinion & went with the HF one. I also crossed my fingers I got a good one. I did buy the extended 3 year warranty if anything happens to it they just replace it no questions asked. To me it was worth the extra $25


Ok so next to the boiler is a bad idea then I'll have to make a base on wheels & when I need to use it then roll it into the room when done roll to the other room then the run will only be about 6' for that I should be good to go using only flex hose correct???
 
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