Guy Gorton wrote:
On Fri, 15 Jul 2011 15:17:08 +0100, John Williamson
wrote:

Andy Breen wrote:
On Fri, 15 Jul 2011 06:12:52 -0700, harry wrote:

On Jul 15, 1:54 pm, Andy Breen wrote:
On Fri, 15 Jul 2011 05:05:17 -0700, Matty F wrote:
shurely shome mistake
Boilers are not cast iron just for starters
Not (usually..[1]) in locomotive applications for many years, but it
was the standard material for many boilers - including locomotive ones
back in the earlies.

The first commercially successful locomotives - and the first exported
- had cast iron boilers, after all..

[1] Does the replica of the Gateshead machine that masquerades as the
Pen-y-Darren machine have a cast boiler? Trevithick certainly used
'em..
I think you will find they were wrought iron for many years. Merthry
Tydfil was renouned for it's wrought iron.

Coalbrookdale, OTOH, was a specialist in casting. Pretty sure the
Trevithick stationary engine in the Sci. Mus. - that kissing-cousin
of Catch Me Who Can - has a cast boiler.


Don't forget that when that was designed, 10 psi was an amazingly high
boiler pressure. The replica of Stephenson's Locomotion on the Waggonway
at Beamish has a modern boiler made of modern materials but looks like
the old design, and runs at twice the original pressure. Its safety
valve is set to blow at 15 psi.

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.

That seems very low. My facts may be wrong but I think 30ft of water
creates 1 atmosphere of pressure, which is about 14 lbs/sq.in.
So the cast iron boiler on the ground floor of my house is under
about 15 ft of head from the loft cold tank, which equates to around 7
lbs/sq. in.
What have I got wrong?


I think you haven't got anything wrong at all.

Remember the very FIRST steam engines were atmospheric engines, So the
maximum cylinder pressure was about 14psi!

To go to a steam system at similar pressures was the obvious next step.

And there is no reason to go further if its a stationary engine with
plenty of water. And plenty of coal as well.

The need for pressure arises out of the need for efficiency so that a
locomotive can do reasonable distances carrying its own coal and water,
particularly water.

To put it simply there is more energy in high pressure steam than low.
And with the steam exhausting to atmosphere, and being lost, that means
there is more power and energy to be extracted from the coal for a
given amount of water, in a high pressure setup.

An ancillary consequence is that high pressure cylinders running faster
are lighter and more compact than low pressure ones All of which makes
sense for locomotion!



Guy Gorton