On Jul 20, 10:55*pm, Andy Dingley wrote:
On Jul 20, 12:33*pm, Jeremy Double wrote:

On 19/07/2011 23:43, Andy Dingley wrote:

Where is there a drop in pressure (required) where either (one of
which is also required) such a pressure drop approaches below
atmospheric pressures, or else the temperature is approaching the
steam temperature of the boiler?

There is a drop in pressure where the liquid accelerates on entering the
pump. *

Of course there is. If we're talking about a centrifugal pump, then it
might even get to the stage of cavitation.

I am however unaware of any *of Trevithick's engines, or even of any
steam locomotive, using such a pump.

Well it can happen in any sort of pump.

On 20/07/2011 22:55, Andy Dingley wrote:
On Jul 20, 12:33 pm, Jeremy wrote:
On 19/07/2011 23:43, Andy Dingley wrote:

Where is there a drop in pressure (required) where either (one of
which is also required) such a pressure drop approaches below
atmospheric pressures, or else the temperature is approaching the
steam temperature of the boiler?

There is a drop in pressure where the liquid accelerates on entering the
pump.

Of course there is. If we're talking about a centrifugal pump, then it
might even get to the stage of cavitation.

It's not only centrifugal pumps that can suffer from cavitation
(although it's more commonly experienced in that type of pump). A badly
designed suction line can cause cavitation in any type of pump. And
understanding of fluid mechanics was rudimentary at the time that
Trevithick was working (Osborne Reynolds hadn't even been born when
Trevithick died).

I am however unaware of any of Trevithick's engines, or even of any
steam locomotive, using such a pump.

No, but they will have had one-way valves to control liquid flow into
and out of the pumping cylinder (so that the liquid is actually pumped,
rather than just being moved backwards and forwards by the motion of the
piston). Such valves typically involve tortuous liquid flow paths that
will involve acceleration of the fluid flow...
--
Jeremy Double {real address, include nospam}
Rail and transport photos at
http://www.flickr.com/photos/jmdoubl...7603834894248/

On Jul 15, 11:20*am, Nick Leverton wrote:

Melting of fusible plugs (thus releasing boiler pressure steam into the
firebox) has occurred a couple of times in preservation, but the RAIB
don't seem to have reports on them for some reason.

There was also a case (Nene Valley Railway?) where the wrong taper
thread was cut for a fusible plug, which, held in by a minimal amount
of thread, came out at pressure. I think that killed someone.

Ian

On Jul 18, 8:26*am, Jeremy Double wrote:

It also gains them another 80 degrees or so of temperature difference
between the heat source and heat sink, which significantly increases the
maximum possible efficiency of the heat engine, according to the second
law of thermodynamics.

Enthalpy change from superheated steam at 10bar/500C to saturated
water at 1bar/100C: 3052.1 - 417.5 = 2634.6 kJ/kg.

Enthalpy change from superheated steam at 10bar/500C to saturated
water at 0.05bar/32.9C: 3052.1 - 137.8 = 2914.3 kJ/kg.

Extra enthalpy available: 2914.3 - 2634.6 = 279.7 kJ/kg ~ 10%.

Ian

In article ,
The Real Doctor wrote:
On Jul 15, 11:20*am, Nick Leverton wrote:

Melting of fusible plugs (thus releasing boiler pressure steam into the
firebox) has occurred a couple of times in preservation, but the RAIB
don't seem to have reports on them for some reason.

There was also a case (Nene Valley Railway?) where the wrong taper
thread was cut for a fusible plug, which, held in by a minimal amount
of thread, came out at pressure. I think that killed someone.

I think that's the example I was trying to recall. Certainly dropping
a fusible plug can lead to serious injury in the wrong circumstances,
so I'd hope it would come within the gambit of the RAIB (pace D7666),
but it's not there !

I remember reading of another incident with dropped plugs on a line in
the USA, run by a small team of volunteers on a shoestring like many
UK preserved lines. The sight gauges were furred up due to inadequate
procedures at overhaul IIRC, but as usual there was a catalogue of missed
opportunities to catch it. A good investigative report was printed
(don't remember if it was by the NTSC though ;-))

Nick
--
Serendipity: http://www.leverton.org/blosxom (last update 29th March 2010)
"The Internet, a sort of ersatz counterfeit of real life"
-- Janet Street-Porter, BBC2, 19th March 1996

Enthalpy change from superheated steam at 10bar/500C to saturated
water at 1bar/100C: 3052.1 - 417.5 = 2634.6 kJ/kg.

Enthalpy change from superheated steam at 10bar/500C to saturated
water at 0.05bar/32.9C: 3052.1 - 137.8 = 2914.3 kJ/kg.

Extra enthalpy available: 2914.3 - 2634.6 = 279.7 kJ/kg ~ 10%.

---------------------------------------------

Huh? Wot's that in English then?


--
Cheers
Roger Traviss


Photos of the late GER: -
http://www.highspeedplus.com/~rogertra/

For more photos not in the above album and kitbashes etc..:-
http://s94.photobucket.com/albums/l9...Great_Eastern/

I remember reading of another incident with dropped plugs on a line in
the USA, run by a small team of volunteers on a shoestring like many
UK preserved lines. The sight gauges were furred up due to inadequate
procedures at overhaul IIRC, but as usual there was a catalogue of missed
opportunities to catch it. A good investigative report was printed
(don't remember if it was by the NTSC though ;-))


Most North American steam engine did NOT have fusible plugs, instead they
relied, if that's the right word, on low water alarms and crew vigilance. I
think the story you are referring to was the collapse of the crown sheet on
the Gettysburg Railroad engine number 1278, an ex Canadian Pacific 4-6-2 on
June 16th, 1995 while working a six-car train at about 15 mph near Gardners
Pennsylvania. The locomotive was not fitted with fusible plugs, a not
uncommon practice in North America.

http://www.ageofsteamroundhouse.com/loco1278.html



--
Cheers
Roger Traviss


Photos of the late GER: -
http://www.highspeedplus.com/~rogertra/

For more photos not in the above album and kitbashes etc..:-
http://s94.photobucket.com/albums/l9...Great_Eastern/

On Jul 24, 6:38*am, "Roger Traviss"
wrote:
Enthalpy change from superheated steam at 10bar/500C to saturated
water at 1bar/100C: 3052.1 - 417.5 = 2634.6 kJ/kg.

Enthalpy change from superheated steam at 10bar/500C to saturated
water at 0.05bar/32.9C: 3052.1 - 137.8 = 2914.3 kJ/kg.

Extra enthalpy available: 2914.3 - 2634.6 = 279.7 kJ/kg ~ 10%.

---------------------------------------------

Huh? *Wot's that in English then?

--
Cheers
Roger Traviss

Photos of the late GER: -http://www.highspeedplus.com/~rogertra/

For more photos not in the above album and kitbashes etc..:-http://s94.photobucket.com/albums/l99/rogertra/Great_Eastern/

Just think of it as energy. Near enough.

You get extra energy into the steam by conducting it away from the
boiler and heating it up some more. (Superheating)
This is done for virtually all steam engine/turbine applications.
But undesireable for steam heating.

On Jul 23, 11:18*pm, The Real Doctor
wrote:
On Jul 15, 11:20*am, Nick Leverton wrote:

Melting of fusible plugs (thus releasing boiler pressure steam into the
firebox) has occurred a couple of times in preservation, but the RAIB
don't seem to have reports on them for some reason.

There was also a case (Nene Valley Railway?) where the wrong taper
thread was cut for a fusible plug, which, held in by a minimal amount
of thread, came out at pressure. I think that killed someone.

Ian

So the whole plug can adrift? That would let a whole lot more steam
out than a melt.

On Jul 21, 2:51*pm, Andy Breen wrote:
On Fri, 15 Jul 2011 15:17:08 +0100, John Williamson wrote:
As far as I know, locomotives all had wrought iron boiler barrels from
the earliest days, with stationary engines using cast iron for parts of
theirs. Then again, early stationary engines normally ran at a maximum
of about 3 or 4 psi.

This set me off thinking and doing some reading up, and that's prompted
a couple of ideas..

Pre-1815 locomotives seem to divide pretty evenly between those with
cast iron and wrought iron boilers (with quite a few undetermined..).

* denotes locomotives built by well-established foundaries or engine-builders
with foundaries, # engines built by local workshops (e.g. colliery workshops)

Cast:
1802-03 Richardson Coalbrookdale machine (completion doubtful)*
1804 Trevithick Pen-y-Darren machine*
1805 Trevithick/Steele/Whinfield Gateshead machine*
1808 Trevithick Catch-Me-Who-Can*
1812-14 Blenkinsop/Murray machines at Middleton (first 3, certainly)*
1813 Hedley 'Black Billy' at Wylam# (boiler*)
1814-15 Blenkinsop/Murray machines in Prussia*

Wrought:
1813 Brunton engine at Crich*
1814 Blenkinsop/Murray machines at Wigan (built by Daglish, Haigh Foundary)*?
1814-16 Chapman Whitehaven locomotive#
1814 Chapman Wallsend locomotive#
1814-16 Hedley 2-cyl locomotives at Wylam#
1815 Stephenson locomotives (chain-coupled)#
1814-15 Brunton locomotive at Newbottle #?

Plus a lot of 'uncatagorised', though the only one of those built by
a major foundary seems to be the 1813 Chapman chain engine for Heaton,
built by Butterley.

With the exception of the Brunton engine at Crich and the Wigan Blenkinsops
(by Butterley and Haigh Foundary respectively), the wrought iron boilers
seem to mainly be the products of local workshops. The only country-built
machine that used a cast boiler was the first Wylam engine ('Black Billy')
- and that boiler was bought in (along with much of the machinery).

Hypothesis: in the early days of locomotive building cast iron was the
preferred material for boilers, but only a limited number of companies
could manufacture such large and complex items. As larger wrought iron
plates became available it became easier for colliery workshops and smaller
local foundaries to build boilers from wrought iron, avoiding buying in
large and expensive items from outside.
The emergence of George Stephenson as the dominant figure in railway practice
from 1816 established the use of wrought iron boilers (as in the Stephenson
standard locomotive) as the norm.

The hypothesis seems to fit available evidence, and oddly I've not seen it
suggested before. Have I missed anything obvious (e.g. actual costings..)..
Thoughts/comments welcome..

--
From the Model M of Andy Breen, speaking only for himself

You would still need some means of bending and forming flanges etc in
the plate.

On Jul 20, 10:55*pm, Andy Dingley wrote:
On Jul 20, 12:33*pm, Jeremy Double wrote:

On 19/07/2011 23:43, Andy Dingley wrote:

Where is there a drop in pressure (required) where either (one of
which is also required) such a pressure drop approaches below
atmospheric pressures, or else the temperature is approaching the
steam temperature of the boiler?

There is a drop in pressure where the liquid accelerates on entering the
pump. *

Of course there is. If we're talking about a centrifugal pump, then it
might even get to the stage of cavitation.

I am however unaware of any *of Trevithick's engines, or even of any
steam locomotive, using such a pump.

Steam locomotives often used axle driven or steam driven reciprocating
pumps, the latter were poplar in America. All liable to cavitation.
But as they used cold water, not a problem.

Found this BTW.
http://www.model-engineer.co.uk/foru...s.asp?th=38918

On Jul 24, 7:32 pm, harry wrote:

Just think of it as energy. Near enough.

You get extra energy into the steam by conducting it away from the
boiler and heating it up some more. (Superheating)
This is done for virtually all steam engine/turbine applications.

Does an 1891 Baldwin Steam tram have a superheater?

Matty F wrote:

Does an 1891 Baldwin Steam tram have a superheater?

Not if this page is correct, no superheating surface area shown for
"locobase 10029"

http://www.steamlocomotive.com/0-4-0/?page=unspecified

On Sun, 24 Jul 2011 00:36:18 -0700, harry wrote:

On Jul 21, 2:51Â*pm, Andy Breen wrote:


Hypothesis: in the early days of locomotive building cast iron was the
preferred material for boilers, but only a limited number of companies
could manufacture such large and complex items. As larger wrought iron
plates became available it became easier for colliery workshops and
smaller local foundaries to build boilers from wrought iron, avoiding
buying in large and expensive items from outside. The emergence of
George Stephenson as the dominant figure in railway practice from 1816
established the use of wrought iron boilers (as in the Stephenson
standard locomotive) as the norm.


You would still need some means of bending and forming flanges etc in
the plate.

For wrought iron boilers, I assume (in castings they'd be part of the main
lump out of the mould)?

You'd need flanges at the boiler ends, to attach the end plates. These
could be formed over a mandrel - within the expertise of a colliery
blacksmith? The makers of early wrought boilers don't seem to have been
bothered about having rivets through from outside to inside (nor, until
the 1840s, about having rivets from fire-side to water-side in the flue
or firebox), so the boiler plates could be either lap-jointed (overlapping
and rivetted through) or joined with a butt strap, with the rivets going
through the strap. Once again, within the abilities of a good colliery
blacksmith?
The result would be crude - but these locomotives were!

--
From the Model M of Andy Breen, speaking only for himself

On 23/07/2011 23:28, The Real Doctor wrote:
On Jul 18, 8:26 am, Jeremy wrote:

It also gains them another 80 degrees or so of temperature difference
between the heat source and heat sink, which significantly increases the
maximum possible efficiency of the heat engine, according to the second
law of thermodynamics.

Enthalpy change from superheated steam at 10bar/500C to saturated
water at 1bar/100C: 3052.1 - 417.5 = 2634.6 kJ/kg.

Enthalpy change from superheated steam at 10bar/500C to saturated
water at 0.05bar/32.9C: 3052.1 - 137.8 = 2914.3 kJ/kg.

Extra enthalpy available: 2914.3 - 2634.6 = 279.7 kJ/kg ~ 10%.

Yes, and looking at the Carnot cycle efficiency (i.e. using the second
law of thermodynamics rather than the first law), using your figures:

Theoretical maximum efficiency = 1-(Tc/Th)

For 33 deg C sink temperatu efficiency = 1-(306/773)= 61%
For 100 dec C sink temperatu efficiency = 1-(373/773)= 52%

(Real efficiencies are considerably below the theoretical maximum Carnot
cycle efficiencies, but these indicate the trend).

Getting down the cold sink temperature of a heat engine really improves
its efficiency.
--
Jeremy Double {real address, include nospam}
Rail and transport photos at
http://www.flickr.com/photos/jmdoubl...7603834894248/

On Jul 24, 9:29*am, Matty F wrote:

Does an 1891 Baldwin Steam tram have a superheater?

I would doubt it. There are two reasons why not.

Firstly, not much in 1891 was superheated. Superheating in steam locos
appeared slowly, from 1900. It appeared according to the preference of
CMEs, some embracing it, others avoiding it. They mostly recognised
the efficiency advantages, but the problem was cylinder lubrication.
The high temperatures of superheating tended to break down the
lubricants of the period, leading to varnish buildup and sticking
pistong rings and valves. This was particularly a problem with slide
valves - why the piston valve also started to become popular around
this time.

Secondly, superheating still doesn't work well in trams or shunters,
even today. Superheating requires a hot superheater element, which
requires gasflow past it. Fine on a long-haul run, but hard to achieve
with stop-start work, or long periods standing idle. Some superheater
designs also suffer if cycled between hot & cold and may start to
leak. A more common arrangement for donkey engines (and this might
have applied to trams too) was the "steam drier". This was a very mild
superheater whose purpose wasn't to change efficiency by shifting the
enthalpy significantly, but merely to heat the steam enough to ensure
that thoroughly dry steam was delivered to the cylinders, and that it
would avoid condensation during expansion - even when these were
distant, or went cold between operations. For intermittent use,
condensation and wet carry-over (even though this wasn't as bad as
priming) was a problem. Steam driers were particularly common in small
vertical boilers, which otherwise tended to deliver wet steam.

On Sun, 24 Jul 2011 02:45:43 -0700, Andy Dingley wrote:

On Jul 24, 9:29Â*am, Matty F wrote:

Does an 1891 Baldwin Steam tram have a superheater?

I would doubt it. There are two reasons why not.

Firstly, not much in 1891 was superheated. Superheating in steam locos
appeared slowly, from 1900.

Tried out much earlier, of course - possibly in the middle 1830s[1], certainly
in the 1840s - in locomotives. By that time it was moderately common in
marine and stationary plant (IIRC first application of superheating in a
stationary engine was about 1801). It provided a much greater boost to
efficiency in a low-pressure engine, of course.

It appeared according to the preference of
CMEs, some embracing it, others avoiding it. They mostly recognised the
efficiency advantages, but the problem was cylinder lubrication.

Again, less of an issue at low pressures, where steam temperatures were lower.
Most of the early (pre-1880s) attempts on locomotives were smokebox
superheaters, probably providing a fairly low order of superheat. Reasons
for non-adoption varied, but generally seem to come down to greater
maintainance costs and poorer reliability - much the same story as with
piston valves in locomotives in the same period (first adopted in a locomotive
in 1826, but in use in stationary plant slightly earlier).
All these early superheaters seen to have been mainly intended to avoid
condensation in the cylinder (Ahrons 1825-1925 is a good starting source
on them).
The smoke-tube superheater did, as you say, place much more severe demands on
lubricants.

The
high temperatures of superheating tended to break down the lubricants of
the period, leading to varnish buildup and sticking pistong rings and
valves. This was particularly a problem with slide valves - why the
piston valve also started to become popular around this time.

There'd been a brief flurry of piston valves on (UK) locomotives in the 1870s
- the younger Beattie on the L&SW and Bouch on the S&D notably[2], but none
were free of problems (piston valves on locomotives go back much further,
to Wilson's engine for the S&D in 1826). Interestingly, builders of lower-
pressure engines in marine and stationary applications seem to have made
piston valves work well much earlier than locomotive builders really did,
even though I'd have expected condensation in the valve to be more of an
issue with low pressures..

Secondly, superheating still doesn't work well in trams or shunters,
even today. Superheating requires a hot superheater element, which
requires gasflow past it. Fine on a long-haul run, but hard to achieve
with stop-start work, or long periods standing idle. Some superheater
designs also suffer if cycled between hot & cold and may start to leak.

Good summary.

[1] It's been suggested that the re-entrant smokebox fitted to the Dundee
and Newtyle locomotive "Trotter" in 1834 may have been a low-order superheater,
similar to some used in Germany later (can't recall ref. for this..)

[2] Bouch's machines for the S&D[3] in the early 1870s seem to anticipate
(or exceed!) best practice of 50-60 years later, with 13" diameter long (6.5")
travel, long lap piston valves serving 17" cylinders. Sadly, metallurgical
and lubrication problems with the valves made them near-useless, and Fletcher
rebuilt them with slide valves and inside cylinders, after which they did well
(obviously no problems with the boilers..).

[3] OK, strictly for the NER (Darlington Committee) by then.

--
From the Model M of Andy Breen, speaking only for himself

On Jul 24, 6:38*am, "Roger Traviss"
wrote:
Enthalpy change from superheated steam at 10bar/500C to saturated
water at 1bar/100C: 3052.1 - 417.5 = 2634.6 kJ/kg.

Enthalpy change from superheated steam at 10bar/500C to saturated
water at 0.05bar/32.9C: 3052.1 - 137.8 = 2914.3 kJ/kg.

Extra enthalpy available: 2914.3 - 2634.6 = 279.7 kJ/kg ~ 10%.

---------------------------------------------

Huh? *Wot's that in English then?

Too complicated to explain in a throwaway usenet post, sorry.

It's also wrong to use these simplistic enthalpy calculations to
explain engine efficiency, especially the importance of condensers.
Improvements to the low end of the cycle that appear to be unimportant
from a simple linear calculation actually turn out to be very
important when you integrate over the cycle. This is why stationary
engines, and marine engines, and especially turbines, all make the
effort to run condensers.

This is overlooked for locomotive practice - probably because the size
& weight of condensers would be so impractical anyway. I know of no
English language descriptions of steam locomotive performance that
explain this properly, or give it the due importance. The only real
treatments of it are by Chapelon and Porta. If you want such an
explanation (like I said, I don't have time to write it) you'll
probably find it best explained by a good book on beam engines and
especially something heavily theoretical on the Cornish engine (which
isn't just an engine in Cornwall).

On Sun, 24 Jul 2011 05:28:06 -0700, Andy Dingley wrote:

[snip]

This is overlooked for locomotive practice - probably because the size &
weight of condensers would be so impractical anyway.

Surely the biggest factor would be the reliance of the Trevithick/Hackworth
/Stephenson line of locomotive on exhaust steam blast to stimulate the
fire and draw it through the flue/tubes? In a stationary engine the only
limitation on chimney height is cost and structual limits of materials, and
in marine applications uptakes can be carried high - and there's likely
to be significant air movement over the top of the uptake anyway. If neither
of these suffice, then there's more space available to provide forced
draught (either in a closed-stokehold or open-stokehold arrangement) than
there is in the limited loading gauge of a locomotive.
Another factor would be that a stationary engine can have a very large cooling
pond to keep the condenser water cool (a sea-going steamship, of course, has
an effectively limitless cool sink available!), whereas a locomotive with
a limited on-board water supply will gradually heat that up, reducing the
effectiveness (in thermal terms) of the condenser. From what I've read,
(virtually?) all usage of condensers on locomotives was aimed at either
reducing steam emission (underground locomotives, tram engines) or reducing
water consumption, rather than enhancing thermal efficiency.

--
From the Model M of Andy Breen, speaking only for himself

On Jul 24, 2:14*pm, Andy Breen wrote:
On Sun, 24 Jul 2011 05:28:06 -0700, Andy Dingley wrote:

[snip]

This is overlooked for locomotive practice - probably because the size &
weight of condensers would be so impractical anyway.

Surely the biggest factor would be the reliance of the Trevithick/Hackworth
/Stephenson line of locomotive on exhaust steam blast to stimulate the
fire and draw it through the flue/tubes?

An issue, but you can do it as Seguiin did, with a mechanical fan.
The few condenser locos (mostly turbines) tended to do just this, with
a separate little steam engine and a smokebox fan. Several of the
turbine locos, mostly the Swedes, did indeed use condensers for their
cycle efficiency.

On Jul 24, 1:28*pm, Andy Dingley wrote:

It's also wrong to use these simplistic enthalpy calculations to
explain engine efficiency, especially the importance of condensers.
Improvements to the low end of the cycle that appear to be unimportant
from a simple linear calculation actually turn out to be very
important when you integrate over the cycle.

I'm not sure what any of that is supposed to mean. The enthalpy
figures I gave were certainly not in any sense linear, and by looking
at the difference from maximum to minimum enthalpy I was indeed
"integrating over the cycle".

This is why stationary
engines, and marine engines, and especially turbines, all make the
effort to run condensers.

The extra efficiency is certainly worth having, though of course it
gets less and less as the boiler pressure and superheat increase.
There are other factors too, though. In general marine engines have to
recycle their water and the same goes for stationary engines with
specially treated water. Doing that means a condenser and if you're
going to have a condenser you might as well use it to suck a bit more
power out of the system. While locomotives could also benefit from the
water recovery, the power gained in the cylinders would be dwarfed by
the loss of draught from losing the blast pipe.

Ian

On Jul 24, 2:14*pm, Andy Breen wrote:
...rather than enhancing thermal efficiency.

Surely thermal efficiency has almost always, for locomotives, played
second fiddle to maximising power?

ian

On 24/07/2011 13:28, Andy Dingley wrote:
Too complicated to explain in a throwaway usenet post, sorry.

Try this for the idiots guide.

The exhaust pressure of a steam loco is atmospheric pressure. The
engine actually has to work to push that atmosphere out of the way when
getting rid of the used steam. Add a condensor, and the exhaust pressure
is near-as-dammit zero. The engine doesn't have to push air out of the
way to get rid of the used steam.

Alternatively - the condensor drops the exhaust pressure to nearly zero,
and it sucks the steam out.

In practice of course it isn't that good because (a) you have to pump
water out of the condensor (b)there's always a bit of air in there, and
you have to pump that out too (c)the pressure isn't actually zero...

Andy

On Jul 24, 6:38*am, "Roger Traviss"
wrote:
Enthalpy change from superheated steam at 10bar/500C to saturated
water at 1bar/100C: 3052.1 - 417.5 = 2634.6 kJ/kg.

Enthalpy change from superheated steam at 10bar/500C to saturated
water at 0.05bar/32.9C: 3052.1 - 137.8 = 2914.3 kJ/kg.

Extra enthalpy available: 2914.3 - 2634.6 = 279.7 kJ/kg ~ 10%.

---------------------------------------------

Huh? *Wot's that in English then?

"Enthalpy" is the combination of energy contained by virtue of being
hot and energy contained by virtue of being compressed.

Ian

In article ,
Roger Traviss wrote:
I remember reading of another incident with dropped plugs on a line in
the USA, run by a small team of volunteers on a shoestring like many
UK preserved lines. The sight gauges were furred up due to inadequate
procedures at overhaul IIRC, but as usual there was a catalogue of missed
opportunities to catch it. A good investigative report was printed
(don't remember if it was by the NTSC though ;-))


Most North American steam engine did NOT have fusible plugs, instead they
relied, if that's the right word, on low water alarms and crew vigilance. I
think the story you are referring to was the collapse of the crown sheet on
the Gettysburg Railroad engine number 1278, an ex Canadian Pacific 4-6-2 on
June 16th, 1995 while working a six-car train at about 15 mph near Gardners
Pennsylvania. The locomotive was not fitted with fusible plugs, a not
uncommon practice in North America.

http://www.ageofsteamroundhouse.com/loco1278.html

Thanks Roger, that's no doubt why I couldn't find it then !
The NTSB report is at
http://www.docstoc.com/docs/45374631...-Railroad-Near
amonst other locations.

Nick
--
Serendipity: http://www.leverton.org/blosxom (last update 29th March 2010)
"The Internet, a sort of ersatz counterfeit of real life"
-- Janet Street-Porter, BBC2, 19th March 1996

On Jul 24, 12:11*pm, Andy Breen wrote:

Secondly, superheating still doesn't work well in trams or shunters,
even today. Superheating requires a hot superheater element, which
requires gasflow past it. Fine on a long-haul run, but hard to achieve
with stop-start work, or long periods standing idle. Some superheater
designs also suffer if cycled between hot & cold and may start to leak.

Good summary.


Cox tells of a post-war project, never implemented, to provide extra
superheating in stop-start working by winding electric coils around
the superheater elements and powering them from an adjacent diesel-
electric shunter. It was abandoned before it was actually built
because, whatever its thermal advantages, it was hard to see how you
would practically use that efficiency.

On Jul 24, 3:15*pm, Andy Champ wrote:

In practice of course it isn't that good because (a) you have to pump
water out of the condensor (b)there's always a bit of air in there, and
you have to pump that out too (c)the pressure isn't actually zero...

On the other hand you have to pump water into the boiler anyway, and
pumping it from below atmospheric pressure doesn't take much more
power than pumping it from atmospheric pressure, since the bulk of the
work is getting from 1 bar to boiler pressure.

The pressure in the condenser is set by the temperature at which you
can keep it. If you have a large sink at 10C available, the pressure
will be 0.015 bar or so. That's pretty low.

Ian

Too complicated to explain in a throwaway usenet post, sorry.

Try this for the idiots guide.

The exhaust pressure of a steam loco is atmospheric pressure. The engine
actually has to work to push that atmosphere out of the way when getting
rid of the used steam. Add a condensor, and the exhaust pressure is
near-as-dammit zero. The engine doesn't have to push air out of the way to
get rid of the used steam.

Alternatively - the condensor drops the exhaust pressure to nearly zero,
and it sucks the steam out.

In practice of course it isn't that good because (a) you have to pump
water out of the condensor (b)there's always a bit of air in there, and
you have to pump that out too (c)the pressure isn't actually zero...

Andy

Thanks Andy.


--
Cheers
Roger Traviss


Photos of the late GER: -
http://www.highspeedplus.com/~rogertra/

For more photos not in the above album and kitbashes etc..:-
http://s94.photobucket.com/albums/l9...Great_Eastern/

On Jul 24, 4:29*pm, The Real Doctor wrote:
On Jul 24, 3:15*pm, Andy Champ wrote:

In practice of course it isn't that good because (a) you have to pump
water out of the condensor (b)there's always a bit of air in there, and
you have to pump that out too (c)the pressure isn't actually zero...

On the other hand you have to pump water into the boiler anyway, and
pumping it from below atmospheric pressure doesn't take much more
power than pumping it from atmospheric pressure, since the bulk of the
work is getting from 1 bar to boiler pressure.

The pressure in the condenser is set by the temperature at which you
can keep it. If you have a large sink at 10C available, the pressure
will be 0.015 bar or so. That's pretty low.

Ian

Condenser reject a lot of energy. There is no place to reject it to
on locmotives. (Always done at sea.)
I think there was an experiment in Siberia with air cooled condensing
steam locos. Only worked in Winter.

On Jul 24, 3:14*pm, The Real Doctor wrote:
On Jul 24, 2:14*pm, Andy Breen wrote:

...rather than enhancing thermal efficiency.

Surely thermal efficiency has almost always, for locomotives, played
second fiddle to maximising power?

ian

True but the greater the efficiency the less coal was needed and the
fewer stops needed to get more.
Some loco were double expansion just to improve efficiency.
(Marginally)
The overall efficiency is in the order of 2%. Pretty crap. Loco
boilers are exceeding crap efficiencywise
Marine engines had to be more effiicient some were triple and
quadruple expension plus condensers. This extended the range of ships.

On Sunday 24 Jul 2011 20:28, Andy Breen wrote:

These would be easier to bend to "near enough round"
than the large "belt" plates used at a later date,

Had rolls not been invented by then? No need for "near enough" if they
had.

--
Alex

On Sun, 24 Jul 2011 12:07:53 -0700, harry wrote:

On Jul 24, 2:14Â*pm, Andy Breen wrote:

Surely the biggest factor would be the reliance of the
Trevithick/Hackworth /Stephenson line of locomotive on exhaust steam
blast to stimulate the fire and draw it through the flue/tubes? In a
stationary engine the only limitation on chimney height is cost and
structual limits of materials, and in marine applications uptakes can
be carried high - and there's likely to be significant air movement
over the top of the uptake anyway. If neither of these suffice, then
there's more space available to provide forced draught (either in a
closed-stokehold or open-stokehold arrangement) than there is in the
limited loading gauge of a locomotive.

Forced (or induced) draught becomes an issue in "economic" style
boilers, ie ones where there is high resistance to combustion gas flow
due to multiple small firetubes. In early boiler where there was just a
furnace tube the resistance was low so natural draught would suffice.

Originally introduced in warships as a source of short-term "sprint" power,
IIRC (late 1870s, I think. Iris-class rings a bell here but I'm not going to
go and pull Brown off the shelf to check..). Had the added advantage of
allowing fuel saving the rest of the time by reducing the weight of machinery
needed for sprint power. Got adopted widely (over-widely, and over-ambitiously)
in warships after CALLIOPE sustained 110% of 1-hour power for 23 hours
while escaping the typhoon at Apia in 1889 - she had a very good set of
boilers and engines by Maudsley (and a very good chief engineer).
As you say, the advantages were restricted to boilers with a more restricted
draught path than the old large flues (where forced draught would simply
have sucked the fire straight through [1]) - warship use of forced draught,
and subsequent civil maritime use - followed the introduction of multitubular
fire-tube boilers in place of the old flue type, and snowballed with the
appearance of water-tube boilers (Bellevilles, and such..).
For a bit of uk.r topicality, the multitubular fire-tube boilers were
referred to at the time as "locomotive" boilers, even though - with the
grate in a large flue - they were unlike anything used in main-line locomotives
after the 1850s (apart from some L&Y 0-8-0s in the 1900s, I think...).

[1] which happened later, where boilers were over-forced. To a spectacular
degree at times, such as in WW1 battlecruisers.

--
From the Model M of Andy Breen, speaking only for himself

In article ,
harry wrote:
On Jul 24, 4:29*pm, The Real Doctor wrote:

The pressure in the condenser is set by the temperature at which you
can keep it. If you have a large sink at 10C available, the pressure
will be 0.015 bar or so. That's pretty low.

Ian

Condenser reject a lot of energy. There is no place to reject it to
on locmotives. (Always done at sea.)
I think there was an experiment in Siberia with air cooled condensing
steam locos. Only worked in Winter.

South African Railways had a large and successful class of air-cooled
condensing steam locomotives, and they worked in the desert not Siberia.

Nick
--
Serendipity: http://www.leverton.org/blosxom (last update 29th March 2010)
"The Internet, a sort of ersatz counterfeit of real life"
-- Janet Street-Porter, BBC2, 19th March 1996

harry wrote:
[snip]

Condenser reject a lot of energy. There is no place to reject it to
on locmotives. (Always done at sea.)
I think there was an experiment in Siberia with air cooled condensing
steam locos. Only worked in Winter.

I can find a list of Seven classes of air cooled condensing locomotives.
Five from the UK, two from South Africa, none from Siberia.

Heck, Harry caught talking ****, again.

On Sun, 24 Jul 2011 22:43:38 +0000, Nick Leverton wrote:

In article
,
harry wrote:
On Jul 24, 4:29Â*pm, The Real Doctor wrote:

The pressure in the condenser is set by the temperature at which you
can keep it. If you have a large sink at 10C available, the pressure
will be 0.015 bar or so. That's pretty low.

Ian

Condenser reject a lot of energy. There is no place to reject it to on
locmotives. (Always done at sea.) I think there was an experiment in
Siberia with air cooled condensing steam locos. Only worked in Winter.

South African Railways had a large and successful class of air-cooled
condensing steam locomotives, and they worked in the desert not Siberia.


Yes, but the aim there was to conserve water supplies, not improve efficiency.
So long as the the steam could be condensed, it was enough in that application.
IIRC the Siberian experiment was to try and reduce coal(?) consumption by
improving efficiency, and it was found they only got a measureable improvement
in winter.


--
From the Model M of Andy Breen, speaking only for himself

In message
,
Andy Dingley writes
For intermittent use,
condensation and wet carry-over (even though this wasn't as bad as
priming) was a problem.
Priming is normal for any engine with an over full boiler, indeed before
a steep bank that the fireman would have to watch the water very
carefully, it wasn't unusual for the injectors to be kept going long
after the water disappeared out of the top of the glass until priming
started, then you knew you had a full boiler.
--
Clive

In message
,
harry writes
So the whole plug can adrift? That would let a whole lot more steam
out than a melt.
Yes. Whilst a lead plug looks to be entirely of lead, it is in fact
mainly steel with a bored core and this restricts the amount of steam
and water needed to put out the fire.
--
Clive

On Jul 25, 2:03*am, Clive wrote:
In message
,
Andy Dingley writesFor intermittent use,
condensation and wet carry-over (even though this wasn't as bad as
priming) was a problem.

Priming is normal for any engine with an over full boiler, indeed before
a steep bank that the fireman would have to watch the water very
carefully, it wasn't unusual for the injectors to be kept going long
after the water disappeared out of the top of the glass until priming
started, then you knew you had a full boiler.
--
Clive

Priming is never "normal". If you'd ever seen it you'd know why.
Significant priming would wreck the superheater (if fitted) and damage
the steam engine.
No-one in their right mind is going to lose sight of the water level.

On Jul 25, 1:20 pm, Clive wrote:
In message
,
harry writesSo the whole plug can adrift? That would let a whole lot more steam
out than a melt.

Yes. Whilst a lead plug looks to be entirely of lead, it is in fact
mainly steel with a bored core and this restricts the amount of steam
and water needed to put out the fire.

Why is there such a steep taper on the thread on the plugs?
Wouldn't that make the whole plug fall out more easily?

On Jul 25, 2:20*am, Clive wrote:

Yes. * Whilst a lead plug looks to be entirely of lead, it is in fact
mainly steel with a bored core

"Lead plug" isn't the most helpful term anyway.

They're not lead, they're tin (with obsessive purity standards,
depending on your regulatory body)

They're not steel bodies, they're a cuprous alloy so that they don't
rust in - they are removed and replaced fairly frequently.

The "plug" isn't solid either. It's (an improved design, although not
universal) a brass plug thickly soldered in by the tin plug around it.
The idea is that once the plug softens, this core is blown out and
then the whole plug is open. If it's a literal "lead plug", as for the
older ones, then a small pinhole melts first and (if not too
overheated) then jet of escaping steam can be enough to chill this and
re-freeze it, so the plug never opens fully.