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Dust collector hose size confusion

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Forum topic by JeffP posted 09-17-2015 09:42 PM 883 views 0 times favorited 15 replies Add to Favorites Watch
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JeffP

573 posts in 857 days


09-17-2015 09:42 PM

Topic tags/keywords: question

Let me start by apologizing for what is likely to be an over-long and somewhat disorganized posting. You see, as the title says…I’m confused.

Here’s the setup. I’ve been using a small “filter bag and plastic bag” style portable dust collector for awhile now, just hooked straight up to my saw with a 4” flexible hose.

With that setup, the suction and dust collection have seemed “adequate” or “expected”.

Now that I finally have my planer set up and in use, my shop is simply covered in chips…time to actually execute some of the plans I’ve had for dust collection for a long time.

Main plan is to put this unit outside the shop wall under a lean-to addition I just built, along with a trash-can style “cyclone” and remove the filter and the collection bag. That’s where this story actually begins…last couple days I’ve been throwing together a super-cheap and not very inventive trash-can separator. Confusion came from my testing of same.

I finished putting it together (just a Lowes $24 metal trash can – two 4” holes in the lid with one straight and one elbow – blow the dust around the perimeter and suck the air out the middle at the top). It works remarkably well…just sucked up enough stuff off the shop floor for about 3 inches of dust/chips in the bottom of the can…nary a dust mote in the plastic bag.

Now for the confusion, which as the title stated, has to do with hose size. When I went to test this thing I realized I only had ONE 4 inch flexible hose…needed two. Wanted to test it anyway, so I stole the remarkably whimpy hose from my shop vac (barely an inch diameter at the business end) and made a reducer ring out of plywood to make an air-tight connection between the separator and the little hose.

Well, I was absolutely shocked at how little suction power I had at the other end of that dinky hose! I stretched it out and peered down it to verify there wasn’t a mouse or something stuck in there…nope, can see daylight out the other end. What’s the deal? This big hefty dust collector isn’t pulling even a quarter of the air through that hose that a shop vac would pull?

If I take the reducer out and feel the air at the input of the trash can separator…seems about the same as what I get right at the “nozzle” of the dust collector. Not loosing it all in the separator as I feared. Verified by hooking dinky hose right up to the input of the DC. Same result.

So I’m confused. I wasn’t expecting as much air moving with the tiny hose…but I expected to feel good suction when I put my hand on the end of the tiny hose. Nope, wimpy. Sadness and confusion ensue.

It is messing with my mental model of how suction works. Just based on what happens with a shop vac when you put your hand over the end of the hose…seems like this big sucker should be at least comparable.

My plans for the larger system originally included putting in a blast-gated connection for this kind of a hose for general clean-up around the shop. This makes me think it would have to be hooked to a shop vac instead.

Can somebody clear this up for me?

-- Last week I finally got my $*i# together. Unfortunately, it was in my shop, so I will probably never find it again.


15 replies so far

View AandCstyle's profile

AandCstyle

2575 posts in 1723 days


#1 posted 09-17-2015 09:54 PM

Can you drive faster on a 6 lane highway or a 1 lane mountain road? It is the same principle. The narrow wavy shop hose creates a lot of resistance and turbulence that makes the vacuum virtually ineffective. A 6” PVC tube would be like the 6 lane highway and the air will will flow almost unimpeded. Does this answer your question?

-- Art

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JeffP

573 posts in 857 days


#2 posted 09-17-2015 11:06 PM



Can you drive faster on a 6 lane highway or a 1 lane mountain road? It is the same principle. The narrow wavy shop hose creates a lot of resistance and turbulence that makes the vacuum virtually ineffective. A 6” PVC tube would be like the 6 lane highway and the air will will flow almost unimpeded. Does this answer your question?

- AandCstyle

Thanks Art, appreciate you taking the time…but no, I’m still confused.

Why is it so wimpy with small shop vac hose compared to lesser wattage shop vac with small shop vac hose?

-- Last week I finally got my $*i# together. Unfortunately, it was in my shop, so I will probably never find it again.

View gfadvm's profile

gfadvm

14940 posts in 2156 days


#3 posted 09-18-2015 12:10 AM

A dust collector works on the principle of high volume air flow (which your small hose killed). The shop vac works on suction pressure (not high air flow). I know this doesn’t seem to make sense but that’s the difference. Some things you just have to accept on faith :)

This is a way over simplified explanation but I believe it’s accurate as it was explained to me by smart people.

-- " I'll try to be nicer, if you'll try to be smarter" gfadvm

View rg33's profile

rg33

83 posts in 1467 days


#4 posted 09-18-2015 06:25 AM

Like Art and gFad commented above, flow and “suction/pressure” are not intechangeable nor comparable; we can get into the specifics like how they are related by bernoulli’s equation etc, but that would be overkilll here. Let it suffice that Dust collectors work on the principle of moving large volumes of air but with little change in pressure. A shop vac on the other hand, like most other vaccum cleaners move a relatively small amount of air but with a large amount of differential pressure. I’ll make an analogy here hopefully it will clear things somewhat. Think of a dust collector as a car battery. It’s only 12 volts (analogous to pressure or suction) but it can flow a large amount of current (analogous to volume of air flow) needed to start your car. if for example you were to put two nine volt batteries in series you’d get a whopping 18 volts right? But if you tried to start your car with them you’d find that they cant push enough current (flow) to crank your starter.
The analogy here is that you expected to get more suction out of your dust collector by putting a smaller hose. That would be like expecting your car battery to give you say 50 volts by changing your thick battery cables to thinner cables. At the end of the day all you did was limit the air flow.
The reason why we use dust collectors rather than shop vacs for dust control is that they are able to move large amounts of air. But the downside as you found out is that their use is very prone to inefficiencies when flow is restricted. Things like bends in tubing, or smaller diameters kill volume flow and indirectly affect “suction”.

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jonah

687 posts in 2764 days


#5 posted 09-18-2015 11:28 AM

What he said ^^^

Shop vacs = high static pressure, low air flow volume
Dust collectors = low static pressure, high air flow volume

View JeffP's profile

JeffP

573 posts in 857 days


#6 posted 09-18-2015 11:33 AM

Thanks rg33. This helped me get it more straight in my head. My mental model of the system is catching up with reality now.

Since my background is electronics, my mental wanderings had already started down the path of this electrical analogy, but you certainly helped to solidify this new mental model for me.

While I understand that the “important” part of dust collection centers on keeping/cleaning the tiny particles out of the shop air, I find myself wondering at this point if somewhere back down the line a bad engineering decision was made to try to combine solutions for both the visible and the invisible “dust”?

Combining removal of the visible and the invisible “dust” may have been a false economy dreamed up a long time ago and never really tested. The inefficiencies you mentioned and general costs involved with trying to hook one large “flow centric” system to a bunch of tools may outweigh the benefits of having better invisible dust handling at each machine. Having 6” and larger smooth pipes with no right angles running to a dozen machines is both costly and inconvenient. Moving enough “low pressure” air through such a system to pull along big heavy shavings and planer crumbs requires a large and costly “air pump” that may be a significantly inefficient way to achieve the goal.

Maybe a higher-pressure/lower-volume (think big shop vac) system plumbed to all the machines inexpensively would leave more money for a larger and more efficiently designed (but not connected to the machines) “flow centric” air handler to clean (out of the ambient air) what the “shop vac” missed at the machines.

Might get more bang for the buck by using a more “suction centric” system connected to the tools, and a more “flow centric” system cleaning very large volumes of shop air but not hooked to the machines that make the dust.

I’m just saying maybe focusing on airflow is not the best way to go for the machine-connected dust handling. Maybe somebody just went down that path without much experimentation a long time ago and then the industry just kept ramping that same plan up and up and up in size over time without re-examining the alternatives.

Unfortunately, actually testing all of this is expensive and time consuming. Most of us would rather spend that time making sawdust rather than dealing with it. :)

-- Last week I finally got my $*i# together. Unfortunately, it was in my shop, so I will probably never find it again.

View jonah's profile

jonah

687 posts in 2764 days


#7 posted 09-18-2015 01:05 PM

Some good thoughts there, but the main thing to keep in mind is the differences in the kinds and quantity of waste produced at each tool. For example, a jointer or planer produces huge quantities of relatively large (and benign) wood chips, while a sander produces a comparatively small amount of very fine (and dangerous) dust.

For the former type, you actually need big pipes and lots of airflow just to keep up with the quantity produced. Anyone who has tried to hook a shop vac up to a planer quickly finds out that the shop vac can’t keep up. Yet that same shop vac is ideal for sucking the fine dust produced by a small random-orbital sander.

The ideal circumstance is what many of us can’t afford: a very large motor turning a very large impeller sucking lots of air very fast through a large smooth pipe to a dust hood/downdraft table at each tool. Smaller tools get point-of-use dust collection via a shop vac.

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JeffP

573 posts in 857 days


#8 posted 09-18-2015 01:25 PM



For the former type, you actually need big pipes and lots of airflow just to keep up with the quantity produced. Anyone who has tried to hook a shop vac up to a planer quickly finds out that the shop vac can t keep up.
...
- jonah

Thanks Jonah. Just based on my “gut”, I would not have guessed a shop vac would work poorly hooked to a planer. I actually (after yesterday’s disappointing experiments) was thinking of changing my plans in that direction.

I will say that I have, for a year or more now, had an “on paper” understanding of air-flow vs pressure difference between a DC and a shop vac (I’ve been reading here and elsewhere about DC for about a year now)...until you stand there in your shop with your hand over the end of the hose…it is just that…”on paper”.

While I have a lot of my own experimentation ahead, the one thing I think I can say I have demonstrated pretty well:

No matter how “technical” you think you are and no matter how much you have read/heard/seen-on-youtube about DC…you haven’t met Jack until you have stood in your own shop surrounded by hoses and trash cans and “suckers” of various kinds and actually witnessed what they do when hooked together in various ways.

I’m off to Lowe’s now to buy some more hoses and adaptors and duct tape. This is fun, and as the Mythbusters often say “For Science!” :)

Thanks for all the helpful replies here. This forum rocks.

-- Last week I finally got my $*i# together. Unfortunately, it was in my shop, so I will probably never find it again.

View AZWoody's profile

AZWoody

697 posts in 689 days


#9 posted 09-18-2015 01:40 PM

Collection of fine particles and large particles is possible at the machine, but it requires spending the money on a true dust collector meant for that job.
Most of what’s marketed and called dust collectors are realistically just chip collectors.

You need the higher air flow to get the finer dust particles and that requires larger motors and impellers and ducting at the minimum of 6”.

If you really want to read up and try to wrap your head around all the numbers and the explanations of everything, go and read Bill Pentz’ website. He’s long winded and prone to some exaggeration but he lays out all the details and principles that go into setting up a true dust collection system.

View jonah's profile

jonah

687 posts in 2764 days


#10 posted 09-18-2015 03:01 PM

By the way, you want foil HVAC tape, not duct tape.

View JeffP's profile

JeffP

573 posts in 857 days


#11 posted 09-18-2015 03:13 PM



By the way, you want foil HVAC tape, not duct tape.

- jonah

The duct tape is for experimental purposes only…but since you brought it up…why would it matter?

thanks.

-- Last week I finally got my $*i# together. Unfortunately, it was in my shop, so I will probably never find it again.

View buildingmonkey's profile

buildingmonkey

242 posts in 1013 days


#12 posted 09-18-2015 05:37 PM

What size shop do you have, and what equipment are you using? My 15” planer is easy to collect the chips from, I have a 2hp cyclone, and find the chips are easy to pick up, what is hard is sander dust. If you use your shop a lot, it is easy to spend quite a bit on good dust collection, but worth it for your health,

-- Jim from Kansas

View NoSpace's profile

NoSpace

73 posts in 706 days


#13 posted 09-18-2015 06:14 PM

Maybe a higher-pressure/lower-volume (think big shop vac) system plumbed to all the machines inexpensively would leave more money for a larger and more efficiently designed (but not connected to the machines) “flow centric” air handler to clean (out of the ambient air) what the “shop vac” missed at the machines.

Might get more bang for the buck by using a more “suction centric” system connected to the tools, and a more “flow centric” system cleaning very large volumes of shop air but not hooked to the machines that make the dust.

I’m not sure but what I think you’re saying is something like the setup I have. I have a Fein Turbo1 that I really like, great suction, quiet, and OK CFM for its tiny size, and a chip bucket with Thien baffle. With the exception of my new Laguna 14-12, the only 4” dust port I have is on my dewalt planer. just like your hose killed suction to the DC, the dust hood/port on smaller tools plus poor or non-design of dust collection on my open table saw means that a proper DC I doubt will help much with fine dust for table saw/miter saw.

But what about bandsaw and planer? Others have pointed this out, but since I have a Dylos laser particle counter I can say my planer produces so little fine dust that I don’t even wear a mask (probably should anyway). So a huge DC might leave fewer chips on the floor and save me 1 minute of vacuuming but major space cost. After resawing 8” walnut on my 14-12 yesterday for 20 minutes, my dylos read about 850 small particle, in relative terms, that’s average for a hot SC day. my dewalt table saw with one rip shoots the dylos up to 2400. so what it comes down is in my opinion, if you has space issues etc., the DC really earns its keep once you’ve got a table saw properly designed for dust collection. Even then, you still want to wear a mask.

I have a jet air filtration system that will have my shop air cleaner than the air I breath in the office I work at after 5-10 minutes of running. my only lingering problem is I don’t have enough power to run the jet while I cut. So I have a bit of a visible dust problem but 10 minutes a week running through with an air compressor and the jet on high fixes most of that.

I’d love to have a DC, but I just don’t see the ROI until I have some significant tool and shop upgrades.

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splintergroup

829 posts in 688 days


#14 posted 09-18-2015 07:55 PM


By the way, you want foil HVAC tape, not duct tape.

- jonah

The duct tape is for experimental purposes only…but since you brought it up…why would it matter?

thanks.

- JeffP

Duct tape dries up and falls off after a few years. The foil tape is designed to seal and stay put. Duct tape will work for a while, but if you want things to last…

View AandCstyle's profile

AandCstyle

2575 posts in 1723 days


#15 posted 09-19-2015 12:41 AM

I have used this caulk and like it a lot. If you ever want/need to redesign your tubing configuration, this caulk is much easier to remove than the metal tape. It was still flexible after 7 years in the high desert of NM. Also, I used Gorilla tape to wrap the ends of some tubes to get them up to the proper diameter for some fittings and it was fine for that purpose, but I haven’t tried to remove it. It might be somewhat porous but it is fine to use as I have.

-- Art

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