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?
IOW's how many inches of vacuum required before all oxygen is boiled
off, and that includes the oxygen from moisture.
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?
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.
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.
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
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 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
Exactly the problem. You can't pull a vacuum higher than the outside
atmospheric pressure. That is, once you suck all the air out of the
room (14psi), you can't suck any more. Well, The Donald can, but...
OK, My mistake, not PSI, inches of vacuum. I was trying to recall what
the vacuum gauge on my first car indicated. I thought it was between
15~30 "inches".. apparently inches on the gauges are double actual PSI.
I questioned it because you said it and it was repeated. I didn't
know if you were talking about in.Hg, or what. Yes, PSI is half in.Hg
(though I hadn't thought of it that way) by the simple fact that
1ATM = ~14PSI = ~30"Hg.
You've mixed reference -- 1 atm is ~760 mm Hg (29.9"), 0" Hg _gauge_
pressure relative to atmospheric. Negative is then vacuum, positive is
pressure like 28 psi for tires is 28 psig(auge) or 28 psi _above_
Possibly, I didn't verify what ATM stood for, just accepted it as one
Atmosphere at sea level. I almost made the mistake of typing psig but
caught myself since that would be 14 above atmospheric pressure.
Now 0" is the equivalent to the air pressure at sea level. And yes, it
is gauged vacuum. since everything above 30" is actually positive
The air pressure at 20,000 feet is 6.8 Psi equivalent to 13.6" hg.
And yes, there is oxygen at that level. Maybe not enough to keep us
functional, but it is still there.
So if you want to dry out wood quickly run it up the mountain it would
be less expensive than pulling a vacuum on it. ;)
True, but I don't 0" should be understood as 14 psi since I know of no
zero measurement for board feet, etc. Since any identifying mark would
be larger than zero. Or maybe I am just used to say 0" as meaning no
vacuum in my old trade.
If you don't say it's 0" vacuum, then it isn't a complete specification.
Granted, if one is working within an environment where vacuum is the
norm it'll become a shorthand and will be understood
_in_that_environment_. But, it's still a shorthand and isn't precise
without the qualifier.
If you say so, "0" is neither pressure nor vacuum.
So, we can extend that out to making sure one specifies PSIA or PSIG
in all instances, and as there is no absolutes in vacuums it will need
to be specified in PSI? or PSI? if you know what I mean.
An interesting time wasting discussion. Along these lines I have
thought about the possibility of creating a near impossible large
diameter pipe. With the right diameter inside, and if it was created
with and interlock say 100 ft from its base. And a large door at its
base, one could put something inside, open the interlock and open
another door lower than the object and launch the object into space
with no energy consumed.
The only drawback would be if someone opened the door and left it open
all of the earths atmosphere would be sucked into space.
So that will be the last of my craziness for now. :)
Of interesting note for this topic, I found an addon for sketchup
which works with both Pro and Make.
It is like some add on libraries for AutoCAD and my understanding is
that it is free. There is an offline version, for downloading.
It has softwood libraries with the "finished " sizes, S4S, it has HVAC
and ductwork fittings and stuff.
It has various piping fittings for plastic, steel, copper, etc.
The wood sizing list is to me a bit on the weak side, but at least on
designs if you were to say a 4x4 it would give you the real s4s
Could be valuable for vacuum piping design.
Yes, apparently you are. That, as noted above, would be a shorthand
within that context that would be understood but is incomplete and
potentially misunderstood if translated to another context wherein the
missing reference units would not be automagically inferred.
0 "Hg Vacuum _is_ 14.7 psia by definition. It has to be else't the
weather measurements for barometric pressure would have to 0" plus/minus
instead of 30" plus/minus with fluctuations...and that isn't so.
Or another way to say it which I know you know innately is that no
vacuum is one atmosphere pressure.
You conflate two things of different relative measurements by comparing
to bd-ft (and yes, I know you were trying to somehow get it back to
w-working and that's a noble attempt) but there can be 0 bd-ft; you just
don't have any wood. But the difference is that you can't have negative
board-feet but you can have negative pressure or temperature or any of
several other physical measurements. It is simply what the definition
of the units reference point is.
Consider temperature, there are at multiple common scales, one of which
is absolute and the two other of most familiarity each have positive and
negative values but their zeros are at different absolute temperatures.
For pressure, simply for convenience, units were developed
historically from a mean atmospheric pressure and hence, are positive
and negative around that value. That was purely convenience as it's
nice when doing the ordinary things like tire pressure, etc., to not
have to worry about that background 14.7 psi. Similarly for vacuum
work, it was/is convenient to define a new zero at that point and
measure how far away from that point one is and in fact "inches of
vacuum" throws away the negative sign and speaks of less as
more...kinda' like scoring in golf! :)
So, currently barometric pressure is heading up and is about 30" Hg,
_not_ 15!!! :)
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