Posted by daestrom on March 26, 2009, 10:32 pm
Another one of the killers for small scale turbines is the inlet valves.
Large steam turbines will have four or more valves in parallel (sometimes
separate, sometimes in a common steam chest, some marine units were as many
as seven in a common steam chest).
When you throttle a valve down to drop the pressure to the turbine, you have
a lot of 'throttling losses'. Large units get around this by completely
shutting some valves and leaving others full open. This reduces the steam
flow without a lot of losses.
In most small scale systems just one valve is probably all that is used so
whenever it's operated at partial load, the turbine becomes quite
inefficient due in part to these throttling losses.
Water turbines have a similar issue, but I don't think they call it
'throttling losses'. But unless you have some fancy wicket gates, it's
better to use several valve/nozzle pairs and shut off completely the ones
you don't use.
With piston engines such as locomotives, they got around such losses by use
of the cutoff (or 'Johnson bar'). Of course they still had a throttle
valve, but ideally you would have that open as far as you could and control
speed by controlling the cutoff. So the steam would enter the piston at
nearly full boiler pressure (little pressure drop through the throttle) and
be allowed to expand in the cylinder where it would do the most good.
Newbies would leave the cutoff lever in 'full forward' and control speed
with just the throttle valve. Very wasteful.
Posted by Lord Gow333, Dirk Benedict's n on March 26, 2009, 1:26 am
Actually most three and four cylinder locomotives were of the 'simple' type,
using high pressure steam (up to 300 psi by the end) in all equal sized
cylinders. Union Pacific Challenger #3985, active in excursion trains most
summers, is of this type.
The 'compound' double expansion types were slower and more complicated, but
were great luggers and so found some favor with mountain railroads. The most
notable of these was probably the Norfolk & Western Y6b.
It feeds the high pressure steam to the rear cylinders, and then passes it
on to the impressive 39 inch diameter front cylinders! (I stood next to one
of these out in Illinois... astounding!)
There were also a few 2-8-8-8-2 six cylinder monsters which I believe tried
using high pressure steam in the middle cylinder and low split between the
front and back. Besides the usual problems with compound locomotives they
tended to exhaust their steam supply in very short order.
(top one. the small stack on the tender exhausted the rear engine's steam)
And therein lies the rub...
"Keep it simple. If it takes a genius to understand it, it will never work."
- Clarence Leonard "Kelly" Johnson
Posted by daestrom on March 26, 2009, 10:22 pm
Nice pics. So what gauge are those first ones? Pretty nice weathering.
I'm sure I've read of using a 'helper' that was in the truck under the
firebox on some locomotive, although the details escape me at the moment.
Re: the last (2-8-8-8-2), I think if you look hard enough, you can find just
about anything was tried at one point or another. Baldwin or Lima would
build almost anything you asked for.
I've always been fascinated by Shay's and Climax's
For those of you laughing right now, get your mind out of the gutter ;-)
The Climax was the name of an obscure locomotive that had the pistons
arranged in a 'V' turning a crankshaft that went lengthwise under the boiler
and then used bevel gears to turn the motion 90 degrees to drive the wheels)
Posted by Lord Gow333, Dirk Benedict's n on March 27, 2009, 3:32 am
Both HO I believe. I debated going wth model photos but they showed better
details than most of the full size pics I found.
Boosters. I'm not sure of the specifics either, but they were usually used
for starting out and then thrown out of gear when the train got up to speed.
I think some were on tender trucks too, if I'm not mistaken.
Indeed. They both had their gems tho. Baldwin had the rack drive Pike's Peak
engines (still in use I think), Southern Pacific Cab Forwards, and the heavy
lugging Duluth, Missabe & Iron Range Yellowstones, and Lima cranked out the
mighty C&O Allegheny 2-6-6-6s and Nickel Plate's 2-8-4 Berkshire racehorses.
(just Googled these as I was curious)
Actually that's a Heisler, "The Bull of the Woods". The Climaxes had
cylinders angling down on the sides to a crossways gearbox which then drove
the wheels via the centerline driveshaft. Always seemed like an extra step
to me. If you ever make it to Corry, Pennsylvania (and really, I don't know
why you would) where Climaxes were made the historical society has one as
the centerpiece of their museum.
But, that said, really any steam engine is a good steam engine. Personally
I'd like to see a Beyer Garrett someday.
LG (honestly not trying to be a know-it-all)
"The United States is like a giant boiler. When the fire is finally lighted
under it, there is no limit to the power it can generate." - Winston
Posted by daestrom on March 28, 2009, 9:05 pm
Ah Heisler! That was the third type, I couldn't remember that name. All
three (Shay's, Climax, and Heisler) were interesting units. As I recall all
three were for tortuous track of dubious quality (logging or perhaps
mining?). The geared, independent trucks were for very tight radius.
Actually, I've been to Steam Town near Scranton a couple of times and the
Strausburg RR too. May have to lookup Corry, PA sometime.