On Wed, 24 Feb 2016 20:39:08 -0600, Leon lcb11211@swbelldotnet
wrote:

On 2/24/2016 8:06 PM, OFWW wrote:
On Wed, 24 Feb 2016 10:04:59 -0600, dpb wrote:

On 02/24/2016 1:38 AM, OFWW wrote:
...

In a vacuum strange things happen, given a spark, and a whoosh of dust
already suspended in the pipe (your cloud) and I can see things happen
that wouldn't happen in a positive pressurized pipe.

If it were a vacuum, there'd be no oxygen, hence no combustion.


At sea level the air pressure is 15PSI. Every 2" of vacuum is
equivalent to a 1 PSI drop in pressure. So at what point do you
consider a vacuum a vacuum? And how does a gasoline engine operate
when its intake manifold is in a vacuum if there was no oxygen?

Well hopefully there is no combustion inside of the manifold and having
said that, typically the fuel is combusted when it is under higher than
atmospheric pressure. And engines work better when the fuel bypasses an
intake manifold altogether and is atomized, by an injector, at the
optimum location and time inside the cylinder. BUT YES you need a
vacuum inside the manifold to draw fuel into the heads and cylinders
from a throttle body or carburetor. IIRC sometimes up to 15~30 lbs of
vacuum in the manifold at idle, considerably less during full throttle
with the butterflies fully open.


What you said brought back memories, old ones. Like the vacuum gauge
in inches of water column. Trying to use it for economy runs to save
gas for a race. Watching that sucker jump around made it all
pointless. In order to set injectors, or multiple carbs you had to use
a manometer to sync them up. On motorcycles and their smaller engines
and High rpms it was cortical, if a valve failed to seat or your fuel
system flooded out, it was a definite boom time in the intake
manifold. I've had more than one engine go up in flames, especially
with stromberg 97's.




IOW's how many inches of vacuum required before all oxygen is boiled
off, and that includes the oxygen from moisture.

Even in the highest CFM DC systems the air pressure is only a minimal
amount below atmospheric pressure; yes it's a big "vacuum" cleaner, but
there's really not a lot of vacuum, it's just slightly lower pressure
air moving at a pretty high velocity. Hence, there's not going to be
any strange things happening owing to anything other than that there is
a concentration of dust created and given a large enough ignition
source, one could potentially cause a boom. But, static electricity
from PVC for at least home-shop-sized duct work simply doesn't have
sufficient energy to do so. Metal hitting an iron impeller, _maybe_,
but still unlikely. More likely would be an overheated bearing or
another open ignition source like a steaming tube or the like that gets
away but getting it into the necessary location is the trick there...

An overheated bearing would have to be above 425 degF as I recall to
burn wood. A spark is a different animal. A spark hitting a muffler
packed with steel wool sets it on fire which sets the sawdust on fire
and minor implosion in a vacuum system, and hey! It was my imagination
so don't be a party pooper, K?


And I am not trying to argue with you at all here but there are a lot
other considerations to worry about that can make your DC combust aside
from static spark.


that's ok, I meant it as a joke, "in my imagination" just letting it
go wild to conjure up something. I believe that was first in response
to Mikes comment on using imagination. Guess it didn't come across
that way, sorry.

I cant tell you how many times I have cut through a finishing nail with
my TS. Surely there was a really hot spark that traveled into the
collector hose.

AND with marginal powered table saws or those with dull blades it is not
at all uncommon, at times, for the wood to actually get hot enough to
smolder and for the dust from that to go into the DC.


I've had that happen with skil saws, actually had glowing embers from
a dull blade.

I totally believe the static spark thing is a threat with any DC if the
DC is used to clean up something other than wood saw dust. I think the
caution labels are a blanket statement for what ever the DC might be
used for. Maybe some one uses them to clean up grain elevators. ;~)
I know I use mine to suck up anything that is on my shop floor including
my son's hair when my wife cuts his hair. Yeah is is 28 but sometimes
this is the only way we get to see him. LOL


As long as he doesn't ask for money too.

I finally picked up an 1 1/2" hose for some of my small stuff, then
realized I should cut that into smaller pieces and buy a few more
fittings for it. I mistakenly had my hand holding the 2 1/2 hose when
I hit to button to start the vac and boy did that hurt. that flex hose
slammed closed in a hurry, pinching my skin and gave me instant blood
blisters with that small hose hooked up. WOWEE! Then the small hose
started whistling and stuff. I'm not sure how long that hose is, but
it is so restrictive that I want to shorten it some to increase the
air flow and cut down on the whistling at the same time. I'm thinking
I am going to Rockler for those. they seem much better prepared with
the fittings and hose then woodcraft where I picked up the hose on a
whim. Where I am at there is only a woodcraft, and it is an
independent store. Rockler is about 50-60 miles away.