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#41
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Emergency diesel shutdown
"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. |
#42
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Emergency diesel shutdown
"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. |
#43
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Emergency diesel shutdown
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 |
#44
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Emergency diesel shutdown
"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. |
#45
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Emergency diesel shutdown
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 |
#46
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Emergency diesel shutdown
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 |
#47
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Emergency diesel shutdown
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#48
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Emergency diesel shutdown
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 |
#49
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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. 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 |
#50
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Emergency diesel shutdown
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 |
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