DSK wrote:

Nav wrote:

... It was Doug who said there was no bypass valve.


I didn't say anything of the kind, you clown.

Go back and re-read my posts. I said that a turbine will not be stopped
by opening a bypass valve, which is what you claimed was the summ &
total of how to reverse the Titanic's engines.


Isaid nothing about summ and total. the first act in stopoong the
turbine was to open the bypass valve. Ask Rick he really knows about
steam plants. Let me remind you of what you said in your usual sneering
tone:


"Please tell me what ships you've steamed where the engine could be
stopped by "opening a steam bypass valve." Also please tell me where the
steam is bypassed to... are you suggesting dumping main steam directly
into the condenser? "


Another point I'd like you to explain is how do you stop the engine and
not the shaft. Push in the clutch, maybe?



It was you who is quoting a psia figure and confusing it with psi.



No confusion at all. The pressure is exactly as I stated it. It was you
who claimed that the oiperating pressure was 11 psi(a). (Which is wrong
anyway you look at it). All I was doing was quoting data that you said
was wrong because somehow you know more about the Titanic plant and how
it works than anyone else. Strange that you don't know that steam bypass
vlaves are standard in multiple engine plants... Maybe they never let
you run the engines on the ship you served on.


Cheers

Rick wrote:
Well, in the mode and condition which I described, I KNOW that the
engines can run indefinitely without exceeding the condenser capacity.

OK. I'm a bit surprised to hear that, since it's definitely not true of
most plants I know about. Otherwise loss of condenser vacuum wouldn't be
given such a prominent place in the drill book.


... The circulator pump moves more water than is required to remove
the heat leaving the turbine. Reduced power operation might have been
required, just as modern plants - even military plants - but there is
no time limit associated with that condition.



???


What part of steam plant operation and construction elicited the "???" ?
Most condensers and circpumps have a larger capacity than required for
normal operation up to a sea temperature around 85* F. Under some
conditions of sea temperature and load, reduced power operation may be
required to match condenser capacity. Once the balanced is achieved
there is no time limit to operation.

Well, that's what I meant. You're taking that balance very much for
granted. "Under some conditions, reduced power operation may be
required" is definitely true, but an understatement IMHO. Sometimes you
have to shut down and start over, to restore vacuum!

Run that by again ... "compression" of the shaft? I would love to see
the figures on that one ...

Sorry about that.... got it backwards... in stopping the shaft against
the momentum of the ship, the shaft would be in tension... not going to
produce much axial load that way! Make that strain on the couplings, not
the line bearings

BTW I wonder why our brilliant Navspritjax didn't catch that mistake?

Interesting discussion, thanks for joining in.

Fresh Buckets O' Steam
Doug King

Nav wrote:

Often HP steam was bled to the LP cylinders to start big marine steam
engines? Do you do you do that on your tug?

Steam was admitted directly to the condenser via a "snifter valve" in
order to raise vacuum enough to allow smooth starting, never heard of
admitting drum pressure steam to the LP, it would sure jerk the poor
engine around.

My tug has a very large for its power and quite elderly diesel. I only
operate other people's steamboats for a living.

Rick

DSK wrote:
Nav wrote:

At that time the reliability of the turbine was in question so that
the plant was designed to run without it indefinitely.


Oh really? Perhaps you can produce a reference to that?

Yes. http://www.dellamente.com Here you a

"Harland & Wolff were quite limited technically, with only their own
experience to draw on. They were aware of the power and economy the
turbine offered, although still unsure of its reliability, and chose to
play it safe ..."

Or is this another site that knows less than you about the Titanic?


... If I recall, the bearings proved to be a problem on a sister ship.


Care to produce a cite on that? Or did you just pull that out of thin
air, like almost everything else you've said so far in this thread and
many others?


Good lord. Are you seriously suggesting that turbine bearing failure did
not occur in that era? I'd say that your behaviour is exposing your true
nature quite nicely -just for the record.

Cheers

Nav wrote:

But I'm puzzled by your statement that recips don't need as great a
vaccum for peak efficiency. Isn't thermodynamic efficiency directly
related to the inlet and outlet pressures -or do you mean that most
reciprocating engines run at higher outlet pressures?

Reciprocating steam engines alternately see cool steam and hot steam on
the same end of the cylinder. As the steam expands during the stroke it
cools. As it cools, it cools the cylinder and some of it may condense on
the cylinder walls.

When steam is admitted to the previously exhuast side some of it
condenses immediately then reevaporates as the cylinder temperature
rises again. This phenomenon is exaggerated at the low pressures and
temperatures associated with greater vacuum. The thermodynamic
efficiency of a recip steam engine is limited due to this effect.

That is why steam turbines like superheated steam and exhaust into the
greatest vacuum obtainable. The only place we want steam to condense is
in a condenser and the only place we want to evaporate feedwater is in
the boiler.

Rick

DSK wrote:

Rick wrote:

We determine condensate depression and other operational factors by
calculating condenser vacuum based on exhaust temperature.


Here's a good homework question for Navvie/Navjax/Navsprit:

Define "condensate depression" and explain it's significance in steam
plant operations.


Good lord. How childish. No wait, it's a genuine question right? Well
Doug, it's a temperature difference that is impoertant to overall
thermodynamic efficiency which can be defined as P/Qh-Qc. For a steam
plant, the steam temperature and it's dryness fraction times the mass
flow rate determine heat fluxes in that equation.

Yes Doug, I did freshman thermodynamics. Did you?

Cheers

DSK wrote:

Rick wrote:

Well, in the mode and condition which I described, I KNOW that the
engines can run indefinitely without exceeding the condenser capacity.


OK. I'm a bit surprised to hear that, since it's definitely not true of
most plants I know about. Otherwise loss of condenser vacuum wouldn't be
given such a prominent place in the drill book.

Drill book?

What drill book?

Cheers

Rick wrote:

Nav wrote:

Often HP steam was bled to the LP cylinders to start big marine steam
engines? Do you do you do that on your tug?


Steam was admitted directly to the condenser via a "snifter valve" in
order to raise vacuum enough to allow smooth starting, never heard of
admitting drum pressure steam to the LP, it would sure jerk the poor
engine around.

Well it was bleed only. I looked and found this description:
http://www.johnforester.com/Maritime/SEB2.htm

"When the engineer needs to start the engine, and it won't start just by
opening the throttle valve, he can open either of these bypass valves to
let a little steam into the valve chests of the other cylinders just to
get the engine moving. Once it is turning, he then closes the bypass
valves to stop wasting high-pressure steam in the low-pressure cylinders. "

Cheers

Rick wrote:
otnmbrd wrote:

Interesting .... thanks. I would have thought, considering the mass
involved that you would have had to reduce "ahead" steam first, prior
to "pulling one lever".

Sorry, I neglected one point of your post because it is so much a part
of normal or emergency operation as to require no thought ... of course
the throttle is closed prior to changing direction, no marine steam
engine is routinely started at full throttle. The shaft speed may not
change much when and as the throttle is closed rapidly but closing the
throttle is part of the sequence of operation.

Rick


Thanks. That was/is the point I was looking for.

otn

Nav wrote:

Good lord.

That may not be the response you were looking for ...

You guys have fun, it is time to bow out of this one.

Rick
USCG Chief Engineer
Steam/motor/gas turbine