"Karl Denninger" wrote in message
...

In article ,
NetSock wrote:
There are specific cautions on doing this test at speeds above idle in
the
Detroit shop manual that I have, and the reason is the blower oil
seals.
The engine will draw vacuum against the shaft seals in the blower and
they
are not designed to seal against that.

2-stroke diesels do not produce a vacuum.

Bull****.

Sorry, but true.

The blowers on top of them are positive-displacement (well, close to it
anyway) devices.

In fact, without the blower the engine won't run.

Correct. The engine does NOT create a vacuum to displace the new air
charge...the blower forces the air charge in under pressure, when the
scavenging ports are opened by the pistons.

2-stroke diesels do not produce a vacuum.

"Rick" wrote in message
ink.net...
NetSock wrote:
2-stroke diesels do not produce a vacuum.

The Roots type blower used to provide scavenging air to many 2-stroke
diesels will produce a very high vacuum.

I can attest to the fact that a runaway 2-stroke will pull enough vacuum
to crush and collapse many feet of sheet metal intake trunking.

Rick

Oh! In that sense you are correct. I was referring to the internal (past the
blower) 2-stroke diesel engine. There is never a vacuum against the intake
ports, or in the cylinders. In fact, the plenum is always "pressurized" when
running.

Past the blower, a 2-stoke diesels do not produce a vacuum.

NetSock wrote:

Past the blower, a 2-stoke diesels do not produce a vacuum.

No one ever said they did. Karl was talking about the blower and what
occurred within the blower housing.

But since you brought it up ... 8-)

Quite a few early 2-stroke diesel engines produced a vacuum without
benefit of roots or any blowers at all.

Rick

"NetSock" wrote in message ...
There are specific cautions on doing this test at speeds above idle in the
Detroit shop manual that I have, and the reason is the blower oil seals.
The engine will draw vacuum against the shaft seals in the blower and they
are not designed to seal against that.

2-stroke diesels do not produce a vacuum.

There is a vacuum produced "upstream" of the blower - the fact that
the blower is sucking air into the engine tells you there is a vacuum
somewhere. It just isn't produced by descending pistons.

Karl Denninger wrote:

Actually, they can produce SEVERAL atmospheres of vacuum - those blowers
are pretty awesome, all things considered

You didn't REALLY write that did you?

Rick

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

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

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.

Rick

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. Had a
problem once with the starter bypass ckt once that required pulling the
electrical plug off the fuel valve to kill the motor. My owners manual does
say that the engine will run away if there is enough fuel vapor available in
the area and to remove the supply of air to stop things. Same with a bad turbo
seal that allows the motor to consume its own lube oil.
Mike

Karl Denninger wrote:

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

Yes there is Rick.

OK, Karl, anything you say.

Rick