Welding cast iron

[Andy Breen]

Between 35 and 50 psi are the figures I've seen quoted. These were very high pressures for the day (and would remain respectable for another 35-odd years in railway applications).

It was geared down for low speed. Hauling unsprung waggons on plate rail, you'd not want to go faster. Speeds of 3-5mph or so were typical for plateway locomotives, certainly as long as cast-iron plates stayed in use (say

1850s at Dowlais). You'd not want to go faster, given that you needed to carry platelayers on the train to replace the rails that had broken under you..

It's often forgotten that the Pen-y-Darren machine was not designed as a locomotive, but was an adaptation of a multi-purpose stationary engine. Nonetheless, it managed the longest continuous run undertaken by any locomotive until 1825..

[Andy Breen]

Filling locomotive boilers against ~50psi pressures in the earlies was a problem. Trevithick seems to have tried a pump on the Pen-y-Darren machine, but makes much of not needing to use it (there were real issues with pump-feed until Stephenson's invention of the pet-c*ck to prevent locking, somewhere about 1820s - it may be Trevithick didn't want to risk working the pump..). The Middleton machines were filled before the start of a run, then blown down at the end of it and refilled. The refil /may/ have been with cold water at first, but the time needed to raise steam again (don't even think of the thermal stresses on a cast boiler being refilled with cold water!) meant that they shifted to boiling-water feed from lineside 'kettles' very soon. These 'kettles' seem to have been a common factor across most early locomotive applications, although Chapman and Buddle did use feed water heaters on the engine (as well as or instead?). Even after the pet-c*ck came in and allowed the boiler to be refilled while the engine was working, hot feed from a kettle to the feed-tank seems to have been the norm until the bigger and more efficient boilers introduced by Hackworth (1827 on Royal George) and Stephenson (1828-1829) came in.

There's a thought on operation: fill the boiler, wait until you have pressure. Now tie the safety valve hard down, get moving. At the end of it, release the valve, blow down the boiler and gravity-feed with boiling water. All with a cast boiler. The Middleton machines worked like that for over 20 years..

[Andy Breen]

Use of vacuum as an important part of the working cycle wasn't banished by Trevithick either: his most effective and longest-lasting engine type, the Cornish mine engine, used high-pressure steam on one side of the piston and vacuum on the other - made it a very efficient power source for its day.

[Jeremy Double]

The endothermic reaction of steam with hot coke is why a bed of hot coke cools down quickly when exposed to steam. But you're right, a byproduct is a lot of hydrogen and carbon monoxide...

C(s) + H2O(g) + heat -> H2 + CO

[Graeme Wall]

If I remember my schoolboy physics, it's 32ft of water and 15lbs/sq.in.

[Andy Breen]

They did, but there were still problems with the pump locking. To quote: "..an incurable defect in the feed-pumps of locomotive engines, for the pumps could not be made to keep in action, as they were fixed close to the boiler, and hot water entering from the leaking of the valves, causing them to be filled with steam instead of water at each stroke; thus preventing them forcing any water into the boiler.." (W.P. Marshall, writing in 1849 "under the direction of Robert Stephenson", and cite don p.310 of Andy Guy's paper in Early Railways 4)

The pet-c*ck, introduced - apparently by George Stephenson - in about 1815 (I mis-recalled above, when I said about 1820) allowed the pump to fill the boiler without pressure having to be blown down (though pumps were still regarded as "precarious" as late as 1857 - Templeton)

[dennis]

Remember that atmospheric engines worked on a partial vacuum not on a pressurised boiler or cylinder.

[Clive]

In message , Andy Breen writes

Any similarity between this and the modern clack valve?

[Andy Breen]

As I understand it, the pet-c*ck was for bleeding steam off from the pump: "by opening (the pet-c*ck) the steam in the pump was let out, and the action renewed" (Marshall, again).

I'd not expect a direct similiarity to anything on a "modern" steam engine, as even the ones that use hot feed and pumps have the pump well away from the boiler (and seals are much better, anyway)

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Matty F saying something like:

Taliban, Ahoy!

[Andy Dingley]

[Jeremy Double]

vacuum.http://en.wikipedia.org/wiki/Atmospheric_engine>>> FFS! Don't believe _anything_ on Wikipedia!

Wikipedia is a lot more reliable than many other sources of information, IMX, especially for non-controversial technological subjects. It stands up particularly well when compared with British newspapers, for instance.

[tony sayer]

And it took the Pikey's all of ten minutes to nick the lot;!...

[The Natural Philosopher]

32.2 & 14.4 rings a bell..

[Charles Ellson]

14.7 rings it better unless you're somewhere up a mountain.

[Jeremy Double]

Standard atmospheric pressure (but not for thermodynamic measurements) is 1.01325 bar, 760 mmHg or about 14.7 psi.

This will raise water about 10.2 m or 33ft 9in, assuming the figure I looked up for the density of mercury is correct.

Of course, actual atmospheric pressure varies from day to day.

[The Natural Philosopher]

Leading to the first recorded instance of the phrase 'wrong sort of weather' to explain the uselessness of the early steam engines, later used by every British railway (with variations) ;-)

[geoff]

In message , harry writes

Not french by any chance, are you harry?

[Andy Dingley]

Wikipedia can work well on narrow topics, usually where one or two competent editors have written an article from scratch and it hasn't yet been eroded. On anything broad-scale though, every idiot with a coffee table encyclopedia of steam engines gets to play with it. The top-level articles on Wikipedia are almost all dreadful - certainly those on broad engine types or boilers.

[Andy Dingley]

Have you read Rolt's Tools For The Job? A good explanation of just how difficult cylinders were to make, and why the inability to make them held up steam engine development for so long. For some years there was only one foundry (John Wilkinson) that could cast a cylinder that was acceptably cylindrical, and one boring engine that could machine them. Watt's first commercially working engine (at Kinneil) had a cylinder cast of block tin, rather than iron, because it was so difficult to make usable iron cylinders.