Can I dual function a dust collector to be a home central vacuum??????

Just a thought. My wife's vacuum went on the blink today so I thought about extending the dust collector ductwork behind the drywall and using it for a central vacuum. Comments appreciated. mike
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Somebody posted that same question to PennState. The answer was that dust collectors and vacuums are very different and you will burn the motor out if you try it.
Let us know if they are right!
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I'd imagine that it has something to do with the *much* higher resistance to flow in the small-diameter hose that's used with vacuum cleaners vs. the large-diameter hose in a dust collection system. The motor just has to work too hard.
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wrote:

Regardless of the fact that I'm not a mechanical engineer, I'm going to guess that the dust collector motor wouldn't have much work to perform in this situation. Motors driving fans work less when the airflow is cut off, and conversely, are at risk of overload when the airflow is too high.
However, the use of a household vacuum hose might result in too much pressure drop, and the hose would simply collapse - unless it's a very stiff hose.
Hope this helps, John Sellers
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snipped-for-privacy@bellsouth.net wrote:

In a central vacuum system there's usually rigid pipe to the outlets. I suspect most of the pressure drop would occur there leaving the hose fairly safe. But I may be in error.

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Talk about counterintuitive. Hmmmm? So, if I take a house vacuum, run it, and put my hand over the end for 30 minutes, the motor hardly works, but if I hook up the outlet of my shopvac to blow into the vacuum's hose the motor has to work very hard and will overload? Sorry, but I don't get that. -- Igor
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wrote:

Its a fact that's true of the centrifugal type blowers used in dust collection. Many electrical and mechanical facts are counter-intuitive.
Bob
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proposed a theory ......and in reply I say!:
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No. You have taken it to the extreme. More counter_productive_ than intuitive. The "up its bum" idea you have mentioned will simply complicate the issue. It _may_ work, but I feel that the restricted flow from the vacuum's own tubing will simply as a blockage. Also you are blocking the outlet as much as the inlet.
What happens is that you block the flow of air _to the inlet_. The machine has to move no air. It cannot do any work. It is actually spinning in its own vacuum, effectively. If you block the outlet the effect is not the same. The machine is still trying to blow the air up against pressure.
What people are saying applies to a DC. But a vacuum cleaner usually uses vacuumed air flow over the motor to cool it. So the motor will do less work but still overheat.
Try it with the shop vac. Start it up and then put your hand over the inlet tube. The motor will speed up. Simply put, it's doing less work, so it can. But if you left it blocked it would still probably get hot.
But a DC usually has a centrifugal blower, and the motor has its own fan. So the motor will speed up some, and heat up _less_.
But the difference between vacuum cleaners and DCs is that VCs are "high vacuum" low volume. DCs tend toward less vacuum, much higher flows. My gut feeling is that the DC will speed up less if impeded than the VC. It will also react badly to being restricted, and not act very well as a vacuum cleaner. Interestingly your normal fan will _labour_ and slow down if you block the back side of it.

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house vacs are different. leave them blocked and they'll overheat.
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That is because most of them use the air being drawn in to cool them and when you block it, they overheat.
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Okay I'm coming in the middle here but, there is some truth in that. But not blowing into the hose part.
Listen to the shopvac when you put totally cover the hose end. You wil notice the rpm's increase.
The blades stalled and are no longer moving air.
Now slowley cover up the hose and you will notice the rpm's drop as load increases. But again if you totally cover it....
Having the fan blades act like a wing and move air is a load on the motor. But when the airflow is choked off enough the airflow ceases and the blades spin with air swirling around them and this has actually less resistance than when pumping air.
Related reading; compressor stall, blade stall, wing stall, how a wing works, cavitation.
John
igor wrote:

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I doubt that the hose would collapse, the dust collector just doesn't have that kind of static pressure. It may cause the dust collectors motor and blower to overspeed with the lack of air but I don't know what if any harm would come from that.
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vaguely proposed a theory ......and in reply I say!:
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Less than a VC.

Highly unlikely. Most of them are synchronous, and will simply rotate at no load speed (1750-3500 RPM)
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Considerably less.

You are correct, induction motors run at a given speed. I stand corrected here.
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vaguely proposed a theory ......and in reply I say!:
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The guy is confusing us all too much already! <G>

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It simply will not work. They are two very different machines. A vacuum puts it's strengths into a very high static pressure required to pull dirt and such from the floor thru small hoses and because of the small hoses and designed use, is not big on air volume. A dust collector OTOH, is trying to catch large volumes of flying dust and chips in large hoses and keep them suspended until it captures them and for this, it depends on massive amounts of air flow and not so much on static pressure. The closest combination to this would be a good shop vac but even there, they lean more to the vacuum side than the dust collector side of the fence. If you hook up a DC to a 1 1/2 or 2 inch vacuum hose, you will see that you will get very little suction compared to either a shop vac or a vacuum cleaner.
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wrote:

I had the opposite problem, T.... when I first got my DC, I put an adapter on it and attached a 2 1/2 vac hose and floor nozzle.. I had good collection power, but the suction seemed to be dropping off... I looked toward the DC and saw that when I dropped the hose from 4" to 2 1/2", the plastic garbage can part of my cyclone collapsed like it was made out of paper.. lol
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LOL, I said that it didn't have as much as a house vacuum, not that it didn't have any at all. There is a lot of surface area on those plastic lids so even with a reduced static pressure, the area that it can act on more than makes up for it. If you could get an air-tight seal on it, I bet that your shop vac would collapse it even further. To get around that, I set up two floor sweeps for the main stuff and just used my shop vac for the rest at teh house in NJ. I am still building the shop here in NC and will probably do the same thing. I also have one of these lids but never got the chance to use it but now with your warning, I'll make sure to have at least one blast gate open before starting the DC when I set it up.
Since you seem to know something about turning (and anything would be more than I do) what would a beginner need to get started with wood turning. I did turn a salad bowl once but that was well over 20 years ago in high school (and it actually came out great) so anything I might have know is long gone now. I am looking toward the Grizzly G5979 for the lathe since it seems to be a sturdy unit that won't hurl pieces at me and at around $300, won't break the bank but what do I really need to get started besides that such as tools, books, accessories? Like I said, I have little knowlege in this area.
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This is correct. A dust collector is a high-volume, lower-pressure device.
My father and I tried this as an experiment and proved it to be correct. You could barely feel the air draw at the end of the vacuum pipes.
...R
wrote:

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Exactly.
As did I, maybe 5 years ago. It's counterintuitive but flow vs. pressure makes a huge difference.
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