Emergency diesel shutdown
 

Ummmm...the normal shutdown of a diesel (like my Cummins equipped Dodge) IS
to
kill the electrical supply. Thereby closing the fuel shut off valve.

Most diesels, particularly older models, do not require electricity to supply
fuel to the engine.

Emergency diesel shutdown
 

On Thu, 11 Dec 2003 04:52:17 GMT, Rick wrote:

Steven Shelikoff wrote:


It would probably be better for you to define an absolute vacuum as 0
psi instead of -14.7 psig.

It is far better to describe it as it really is. An absolute vacuum (or
as close as we can get to one) is about .0049 psi.

No, an absolute vacuum is 0 psi. It doesn't matter how close we can get
to one. If 0.0049 psi is as close we can get to one, that only means we
can't generate an absolute vacuum.

There is no such thing as -X.X pounds per square inch.

There may not be an absolute -X.X psi, but there certainly is such a
thing as -X.X psig.

Steve

Emergency diesel shutdown
 

On 11 Dec 2003 05:36:39 GMT, (Karl Denninger)
wrote:


In article ,
Steven Shelikoff wrote:
On 11 Dec 2003 03:04:00 GMT, (Karl Denninger)
wrote:


In article . net,
Rick wrote:
Karl Denninger wrote:

(It will pull a near-zero-zero vacuum..... as will the fuel pump, in fact.
I've seen the fuel restriction gauge showing effectively a zero vacuum when
I foolishly started the engine without remembering to turn on the fuel
valves first....)

Cringe ... zero vacuum is one atmosphere, one Bar, or around 14.7 pounds
per square inch absolute, it is no vacuum at all.

The most complete vacuum you can produce will still only create a
pressure differential of 14.7 pounds per square inch at sea level, or
one atmoshphere.

Rick

"zero-zero" in my view means "absolute vacuum", or -14.7 psig.....

It would probably be better for you to define an absolute vacuum as 0
psi instead of -14.7 psig. Your way depends on your altitude, the
barometric pressure.

Steve

That only works if you have a gauge calibrated in psia instead of psig :)

Most gauges are calibrated in psig...

Then they're not giving an accurate absolute pressure reading if the
pressure of the atmosphere is not 14.7 psi. So you can't use one to
tell you whether you have an absolute vacuum unless you know exactly
what the atmospheric pressure is. That's why you can't define an
absolute vacuum in terms of psig unless you know what the reference is.

In other, more simple words...:) A reading of -14.7 psig only tells you
that the pressure the gauge is reading is 14.7 psi less than the
atmospheric pressure. It tells you nothing about the absolute pressure
you are reading. To know whether you have an absolute vacuum, you have
know the absolute pressure.

If you've defined an absolute vacuum as -14.7 psig and you're reading
that measurement at an atmospheric pressure of 14.71 psi, you still have
some gas in there so it's not an absolute vacuum and your definition is
wrong.

Steve

Emergency diesel shutdown
 

Emergency diesel shutdown
 

"Karl Denninger" wrote in message
...

You and I both know that's not correct - that their "zero" is really
14.7psi, but nonetheless, their "zero" is calibrated at 14.7psi.

No, their zero isn't calibrated at any pressure. "Gauge" pressure is always
a differential measurement, the difference between what the pressure
"outside" the gauge is and what the gauge is measuring.

The 14.7 value is only applicable at sea level. Go up into the mountains
and the difference between absolute and gauge will be significantly less.
Dunk the gauge underwater and it will be significantly more.

When working with physical characteristics of materials it is necessary to
work with absolute measurements: absolute pressure and absolute
temperature. On these scales, there is no negative. The lowest temperature
is zero, the lowest pressure is 0.

At least with temperature the convention is to use negative numbers when
referencing values below the datum on the "non-zero" scales. With pressure
and acceleration we have the unfortunate habit of giving a different name to
the portion of the axis that lies below the datum. The magnitude is usually
the same, however. A "zero" amount of "deceleration" is the same as a zero
amount of acceleration, that is, the velocity isn't changing. A zero amount
of vacuum should be the same as a zero amount of pressure (gauge).

"Absolute" or "total" vacuum are terms that are often used to represent as
low as you can go, or zero on the absolute pressure scale. What that
represents on the "negative gauge" scale is totally dependant on what the
pressure is that you are referencing as "zero".


Rod McInnis

Emergency diesel shutdown
 

On 11 Dec 2003 16:10:49 GMT, (Karl Denninger)
wrote:


In article ,
Steven Shelikoff wrote:
On 11 Dec 2003 05:36:39 GMT, (Karl Denninger)
wrote:


In article ,
Steven Shelikoff wrote:
On 11 Dec 2003 03:04:00 GMT, (Karl Denninger)
wrote:


In article . net,
Rick wrote:
Karl Denninger wrote:

(It will pull a near-zero-zero vacuum..... as will the fuel pump,
in fact.
I've seen the fuel restriction gauge showing effectively a zero
vacuum when
I foolishly started the engine without remembering to turn on the fuel
valves first....)

Cringe ... zero vacuum is one atmosphere, one Bar, or around 14.7 pounds
per square inch absolute, it is no vacuum at all.

The most complete vacuum you can produce will still only create a
pressure differential of 14.7 pounds per square inch at sea level, or
one atmoshphere.

Rick

"zero-zero" in my view means "absolute vacuum", or -14.7 psig.....

It would probably be better for you to define an absolute vacuum as 0
psi instead of -14.7 psig. Your way depends on your altitude, the
barometric pressure.

Steve

That only works if you have a gauge calibrated in psia instead of psig :)

Most gauges are calibrated in psig...

Then they're not giving an accurate absolute pressure reading if the
pressure of the atmosphere is not 14.7 psi. So you can't use one to
tell you whether you have an absolute vacuum unless you know exactly
what the atmospheric pressure is. That's why you can't define an
absolute vacuum in terms of psig unless you know what the reference is.

In other, more simple words...:) A reading of -14.7 psig only tells you
that the pressure the gauge is reading is 14.7 psi less than the
atmospheric pressure. It tells you nothing about the absolute pressure
you are reading. To know whether you have an absolute vacuum, you have
know the absolute pressure.

If you've defined an absolute vacuum as -14.7 psig and you're reading
that measurement at an atmospheric pressure of 14.71 psi, you still have
some gas in there so it's not an absolute vacuum and your definition is
wrong.

Steve

True.

SOME gauges are referenced to atmospheric, some are sealed units

Those would read psig.

(referenced to whatever atmospheric was when they were manufacturered) and

Those would read psia and the calibration of the scale would depend on
what the atmospheric pressure was when they were sealed.

some are referenced to absolute vacuum.

The latter are pretty rare; you certianly don't seem them in your local
welding or hardware store.

Referencing it to absolute vacuum is the same thing as a sealed unit
with a known absolute pressure sealed in. You only have to change the
scale to whatever you want. You could make is read 0 at whatever
absolute pressure you want, either 0 psi (absolute vacuum) or 14.7 psi
(to simulate psig even though it isn't really psig) or whatever.

Steve

Emergency diesel shutdown
 

Rick wrote in message link.net...
Steven Shelikoff wrote:


It would probably be better for you to define an absolute vacuum as 0
psi instead of -14.7 psig.

It is far better to describe it as it really is. An absolute vacuum (or
as close as we can get to one) is about .0049 psi.

There is no such thing as -X.X pounds per square inch.

All depends on the reference. If you are measuring with a gauge where
"zero" is atmospheric pressure then you would see it go below zero
PSIg when suction (vacuum) is applied. If your reference is actually
zero, then yes, there is nothing below zero PSIa.

But then again we are talking about the vacuum (or low pressure) in
the intake of an engine. Intake pressure is normally measured in
inches (Hg) --- perhaps to avoid this arguement altogether.

Emergency diesel shutdown
 

I suggest you guys find a textbook or look up vacuum or metrology on Google.

Rick

Emergency diesel shutdown
 

On Fri, 12 Dec 2003 02:08:36 GMT, Rick wrote:

I suggest you guys find a textbook or look up vacuum or metrology on Google.

Why? Did you find somewhere that says an absolute zero/zero vacuum is
0.0049 psi?

Steve

Emergency diesel shutdown
 

On 12 Dec 2003 01:36:58 GMT, (Karl Denninger)
wrote:


In article ,
Steven Shelikoff wrote:
On 11 Dec 2003 16:10:49 GMT, (Karl Denninger)
wrote:

Those would read psia and the calibration of the scale would depend on
what the atmospheric pressure was when they were sealed.

some are referenced to absolute vacuum.

The latter are pretty rare; you certianly don't seem them in your local
welding or hardware store.

Referencing it to absolute vacuum is the same thing as a sealed unit
with a known absolute pressure sealed in. You only have to change the
scale to whatever you want. You could make is read 0 at whatever
absolute pressure you want, either 0 psi (absolute vacuum) or 14.7 psi
(to simulate psig even though it isn't really psig) or whatever.

That's only true if the scale is calibrated or even extends to the right
place (e.g. there is no "pin" at zero in the case of a gauge that reads
psig as opposed to psia)

Well, sure. The point is that if the gauge has a sealed reference, it's
reading an absolute pressure no matter what it's calibrated to. If the
calibration is off, the reading will be wrong. But it's still reading a
wrong "absolute" pressure. That is, the reading (correct or not) will
not change as the atmospheric pressure changes.

If the reference it open to the atmosphere, it's reading a gauge
pressure, or relative pressure, no matter what it's calibrated to. If
the calibration is off, the reading will be wrong. But it's still
reading a wrong "gauge" pressure. That is, the reading (correct or not)
will change as the atmospheric pressure changes. Unless, of course, the
needle is at the stop and has to go further in that direction.

Steve