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

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!

On Sun, 19 Dec 2004 21:02:18 -0500, wrote:

Motors driving fans work less when the
airflow is cut off, and conversely, are at risk of overload when the
airflow is too high.

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

"igor" wrote in message
...
On Sun, 19 Dec 2004 21:02:18 -0500, wrote:

Motors driving fans work less when the
airflow is cut off, and conversely, are at risk of overload when the
airflow is too high.

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. --

Its a fact that's true of the centrifugal type blowers used in dust
collection. Many electrical and mechanical facts are counter-intuitive.

Bob

On Mon, 20 Dec 2004 03:59:17 GMT, igor vaguely
proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

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.


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

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.

--
If at first you don't succeed, you're not cut out for skydiving


wrote in message
...
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

On Mon, 20 Dec 2004 14:56:38 GMT, "TBone"
wrote:

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.

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

"mac davis" wrote in message
...
On Mon, 20 Dec 2004 14:56:38 GMT, "TBone"
wrote:

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.

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


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.

--
If at first you don't succeed, you're not cut out for skydiving

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


On Mon, 20 Dec 2004 14:56:38 GMT, "TBone"
wrote:

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.

On Mon, 20 Dec 2004 03:59:17 GMT, igor wrote:

On Sun, 19 Dec 2004 21:02:18 -0500, wrote:

Motors driving fans work less when the
airflow is cut off, and conversely, are at risk of overload when the
airflow is too high.

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


house vacs are different. leave them blocked and they'll overheat.

On Mon, 20 Dec 2004 14:39:13 -0500, Bimmer wrote:
This is correct. A dust collector is a high-volume, lower-pressure
device.

Exactly.

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.

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

wrote in message
news
On Mon, 20 Dec 2004 03:59:17 GMT, igor wrote:

On Sun, 19 Dec 2004 21:02:18 -0500, wrote:

Motors driving fans work less when the
airflow is cut off, and conversely, are at risk of overload when the
airflow is too high.

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


house vacs are different. leave them blocked and they'll overheat.

That is because most of them use the air being drawn in to cool them and
when you block it, they overheat.

On Mon, 20 Dec 2004 14:59:54 GMT, "TBone"
vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email


I doubt that the hose would collapse, the dust collector just doesn't have
that kind of static pressure.

Less than a VC.

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.

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

"Old Nick" wrote in message
...
On Mon, 20 Dec 2004 14:59:54 GMT, "TBone"
vaguely proposed a theory
......and in reply I say!:

remove ns from my header address to reply via email


I doubt that the hose would collapse, the dust collector just doesn't
have
that kind of static pressure.

Less than a VC.

Considerably less.


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.

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

You are correct, induction motors run at a given speed. I stand corrected
here.

--
If at first you don't succeed, you're not cut out for skydiving

On Mon, 20 Dec 2004 22:24:39 GMT, "TBone"
vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email


The guy is confusing us all too much already! G

You are correct, induction motors run at a given speed. I stand corrected
here.

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:
On Sun, 19 Dec 2004 21:02:18 -0500, wrote:


Motors driving fans work less when the
airflow is cut off, and conversely, are at risk of overload when the
airflow is too high.


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