Which ones? Most of Trevithick's had cast iron shells (still with a wrought iron endplate), but I can't think of any others, or of any "first exports" (which one?) that were cast iron. Certainly the Tyneside builders were using wrought iron from the outset - although they still managed to have boiler explosions, including Locomotion itself.
There is some possibility that Brunton's Mechanical Traveller (the one with the walking legs) was built with a cast boiler, but it had been fitted with a wrought iron boiler just before it was destroyed by a boiler explosion.
There's a well-known period illustration of a Blenkinsop machine showing a boiler that's clearly riveted from plates.
Puffing Billy & Wylam Dilly survived a long time, along with their wrought iron boilers. I don't know which you mean by the "Gateshead Trevithick", but none of the Gateshead-built locos have any evidence for using cast iron.
Price didn't change significantly - although everything, and especially provender or iron goods, became cheaper after Napoleon, hence the number of cast iron bridges dated 1816. What did happen is that ironmasters could make _bigger_ plates, allowing the introduction in the mid-1830s of the "long plate" boiler. This had plates long enough that a whole boiler barrel could be made of four parallel staves, without the need for either endwise joints or else very short barrels (as Stephenson used with Rocket & later).
According to several operating practices (depending on whether you're boat or rail, US or UK) they're inspected monthly and may be _replaced_ every six months (depending on the number of days in steam).
Yep. Just checked in the ER procs., and there seems to have been a change in boiler construction between the first two and later engines at Middleton. The first engines there certainly had cast boilers (from both illustrations and contemporary descriptions).
The 1808 machine ordered(?) by Wylam but never delivered and subsequently used to drive the foundery blower. Black Billy was the 1813 Wylam machine
- single cylinder and flywheel, possibly built on the 1812/13 test chassis. Puffing Billy and Wylam Dilly came in 1814, after Black Billy had been working more or less unsatisfactorily for a while. Checking the ER procs. suggests that Black Billy may also have had a wrought iron boiler, so the date for suitable boiler plates becoming available may be more like 1812-13 than 1813-14.
Point of order Harry, Zimbabwe is one of a very few commercial railways to run steam locos in continuous line service until now. Most steam preservation outfits would give their eye teeth for Bulawayo shed's facilities. Steam overhauls are (AFAIK) contracted out to ZECO Engineering but repairs are still dealt with on shed. Bulawayo shed takes safety seriously. However I don't think NRZ goes back to the days of cast iron steam manifolds.
We shall have to add a new 3'6" gauge chapter to the Afghan Railways handbook.
Fusible plugs are to put the fire out and shouldn't cause a blow back. I've only seen one example of where the plugs melted, and put the fire out efficiently is what they did, without a blow back. It was an 82xxx on a Bristol TM to Bath Green Park train, and the incident happened at Mangotsfield where the rising gradient from Bristol suddenly becomes a falling one towards Warmley, causing the boiler water to slosh to the front of the boiler and uncover the plugs.
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?
No, this was the sort of pressure used. Early boiler feedwater wasn't pumped in, it was fed by a gravity cistern up in the rafters of the engine shed (it was raised here by the pumping engine itself).
The distinction in strength between Newcome or Watt's boilers and the first high-pressure boilers (such as Trevithick''s "strong steam" of
25psi) is that the newer boilers also had a margin of safety over- design to them. Trevithick knew that safety valves were unreliable and often adjusted by enginemen (this wasn't even seen as a bad practice at the time), so he not only designed for 25psi, but he designed to not fail at 25psi, and to survive overpressure too.
The first haystack or balloon boilers used by Newcomen and Watt weren't even iron, they were copper brewer's mash tubs with lead lids fitted. These had a fairly benign failure on over-pressure, as their seams would leak or split without causing the whole pressure vessel to explode. As a result, fear of boiler explosions was much less in the early days, despite them being more common, as the injuries would only be scalding (possibly fatal) to a few enginemen, rather than the expensive destruction of the engine house. The real concerns over boiler explosions didn't begin until pressures had raised and engines were working as expansion engines.
Yes, they could only be cast by a few expert foundries (Coalbrookdale being the obvious example), owing to their large size. Coalbrookdale could cast these because of their past experience making try pots for whaling. Even then, it was only the outer shell and cylinder being cast - the inner flue was sheet iron work (being of smaller diameter, it was inherently stronger).
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!
Very low pressures are entirely feasible considering that the steam was only used to raise a piston which through a beam allowed what it was working on (Man engine etc.) To drop, the steam was the condensed by spraying in cold water and the atmospheric pressure on the other side of the piston did the work.
Why? They don't seem to have had any trouble doing so in 1808?
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hard is it to cast a cylinder anyway? They'd been doing it for years. Cast one big cylinder for the casing, a U-shaped one for the flue, bolt on (cast) end-plates and bolt the flue into the end plate. Voila. A vey sophisticated boiler for the day.
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