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Why no high pressure steam turbine?


Titan
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Clearly engineers thought there was enough potential in high pressure steam (Hush Hush, Fury etc) and also in steam turbines (6202) to spend a lot of money to build experimental locomotives.  I would have expected the combination of high pressure steam and turbines to have brought out the best of both of them and gain improved efficiencies compared to just trying one or the other.  The turbines could have been smaller and/or more powerful with additional stages to extract more of the energy from the steam.  What pressures are used in other applications - i.e. marine and power stations where the turbine was the engine of choice, and very successful?  Did anyone actually try a high pressure steam turbine locomotive?

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Power stations operate at pressures such as 17MPa, that's around 2400 psi. (170bar!) probaby OK for a static boiler/turbine system but maybe too dangerous for moving devices?

The temperatures are also very high.

The pipework isn't going to like the constant flexing it would get in a steam locomotive.

 

The highest pressure of the few rail steam turbines is around 300psi, the same as a reciprocating locomtive.

 

EDIT

Naval Steam Turbines started at around 300psi and never got beyond about 600psi

 

Edited by melmerby
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My memory is that, as stated above, the nature of a steam locomotive and vibrations etc., was not conducive to maintain steam tight joints. Experiments were made, case not proven for large scale adoption. The LMS turbine loco was eventually rebuilt when the supply of essential spare parts ran out Added were not remade.

 

IIRC similar issues with the actual delta diesel engine part within a Deltic locomotive; more reliable in a seagoing vessel than a locomotive due to several factors where the load on it on a vessel was more suited to the design’s capabilities than the operational needs of the ECML. A parallel scenario with Cl 50s on the Exeter run, usage patterns did not suit the design increasing failure rates.

 

 

Edited by john new
Updated - memory corrected by later posts
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The realistic highest pressure with a smoke tube boiler is about 300 p.s.i., after that you're into a water tube boiler and its associated problems. Turbines have many advantages but also many disadvantages:

 

(i) they are more efficient at high rpm so lose efficiency at low to medium speeds.

(ii) they can be made to be more efficient over a limited rpm range or, better still, designed to run at a set rpm, such as in a power station as already mentioned. A speed range from, say, zero to 100 mph is not good for a turbine.

(ii) a turbine cannot run in reverse, so you need either a reverse turbine; additional gearing; or electric transmission, all of which bring their own problems.

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7 hours ago, john new said:

The LMS turbine loco was eventually rebuilt when the supply of essential spare parts ran out.

Other than spares common to the other' Lizzles', no spares were kept for the turbine and transmission parts of 6202. Being entirely new, no-one knew which parts would be needed, they were expensive to make and hold on stock, possibly never to be used, so in the event of a turbine or transmission failure, those damaged parts would need to be remade from scratch. This is why the engine was stopped out of traffic for comparatively long periods: it was waiting for the replacement parts to be made.

 

By 1950, it was realised that the forward turbine was nearing the end of its life and would soon need replacement, so the engine was withdrawn before it failed on the road. A new turbine would be very expensive and the post-war situation was very different to that when 6202 was conceived, so the decision was made to rebuild as a conventional reciprocating engine.

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From what I have read, 6202 proved the concept of railway steam turbines but any chance of a full class of locomotives, where the economies of scale could be realised, was scuppered by WW2. It is considered to be pretty well the best application of the technology on a steam locomotive

It ran efficiently and was reasonably reliable and IMHO could have been successful as a class using the data gathered while in service to improve the design.

 

 

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9 hours ago, melmerby said:

 

Naval Steam Turbines started at around 300psi and never got beyond about 600psi

 

 

So it would seem that the boiler pressure of Hush Hush would have been right in the sweet spot. Perhaps that was why they were a popular marine boiler - ideal for turbines?

 

16 minutes ago, melmerby said:

From what I have read, 6202 proved the concept of railway steam turbines but any chance of a full class of locomotives, where the economies of scale could be realised, was scuppered by WW2. It is considered to be pretty well the best application of the technology on a steam locomotive

It ran efficiently and was reasonably reliable and IMHO could have been successful as a class using the data gathered while in service to improve the design.

 

 

 

It appears that 6202 adequately dealt with any shortcomings of the turbine, especially for a prototype locomotive.  It really would be fascinating to see what kind of locomotive 6202 would have been if it had had a Yarrow boiler.

Edited by Titan
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8 hours ago, john new said:

My memory is that, as stated above, the nature of a steam locomotive and vibrations etc., was not conducive to maintain steam tight joints. Experiments were made, case not proven for large scale adoption. The LMS turbine loco was eventually rebuilt when the supply of essential spare parts ran out.

 

 

I am really not sure about that bit at all. I understood that spares needed to be built when required, which would  account for its long periods out of service after each failure.

It was also a prototype, so they would not necessarily want to use like for like components; they would often want to re-design them.

It was re-built under BR. The Turbomotive was Stanier's experiment but he was not CME of BR.

 

As for the original question of why no high pressure steam turbines: They were slightly different eras.

Fury & Hush Hush were built in the late 20s. By the time it was decided to build 6202 as a turbine, the conclusion drawn from Fury was that its high pressure boiler required too much maintenance to be worthwhile.

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Another point is that both ultra high pressure and turbine  propulsion were highly experimental and you really need to keep them separate: you can't learn from one if it is being influenced by the other as you don't know which is cause and which is effect. This was probably Oliver Bulleid's mistake: he tried to cram too much innovation into one package, so the successful parts tended to be overwhelmed by those which needed a bit more thinking out. 

 

Very high pressure / temperature steam was used with turbine propulsion, most notably in the German navy prior to and during World War II. The result of over-rapid development was chronic unreliability and very heavy fuel consumption. The Americans went down a similar route but restricted the pressure and temperature and went through a proper development process, producing very reliable machinery with the low fuel consumption needed for Pacific operations.

 

Nigel Gresley was right to try the water tube boiler, Henry Fowler to try ultra high pressure, and William Stanier to try a turbine. Combining the three would have been a recipe for disaster.

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1 hour ago, Pete the Elaner said:

 

I am really not sure about that bit at all. I understood that spares needed to be built when required, which would  account for its long periods out of service after each failure.

It was also a prototype, so they would not necessarily want to use like for like components; they would often want to re-design them.

It was re-built under BR. The Turbomotive was Stanier's experiment but he was not CME of BR.

 

As for the original question of why no high pressure steam turbines: They were slightly different eras.

Fury & Hush Hush were built in the late 20s. By the time it was decided to build 6202 as a turbine, the conclusion drawn from Fury was that its high pressure boiler required too much maintenance to be worthwhile.

Original post re Lizzie spares now amended, fallible memory.

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Let's not forget that the LMS experiment with very high pressure (1400-1800 psi) in 6399 not only didn't produce any signs of additional benefits but regrettably killed somebody in the early testing phase when a leak in the high pressure section of the boiler caused a serious blow back.    True that didn't immediately end the experiment but clearly the additional costs and complications of the very high pressure experiment were not seen as offering any operational advantage.

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16 minutes ago, cheesysmith said:

Wasn`t one of the problems with the hush hush was the yarrow boiler was not designed for the pulses of the cylinders? It was designed for the smooth exhaust of the turbines?

 

This is I expect one big advantage of a turbine, the smooth exhaust allowing much better tuning of the drafting arrangements, resulting in better combustion, and therefore more power and/or less fuel for the same size fire.  We all know what working a conventional steam engine hard does to the fire.  I would also expect that the smooth flow would be better on the steam delivery side - less chance of priming and a steady flow through the pipes would see less restriction on the steam flow. Whether the smooth flow is enough to help make the life of the boiler significantly easier I don't know, but it would be unlikely to make things worse.

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It was the job of a CME of a railway to look for any technology that could improve the current range of steam locomotives.

As such Gresley's W1, Fowlers Fury & Stanier's Turbomotive were IMHO worthy trials of new technology.

Both the high pressure locos must be viewed as failures but Turbomotive was a good "near miss" that if development had proceeded and WW2 not intervened could have resulted in a class of reliable, smooth, efficient steam turbine machines.

 

BR was in no position to carry on with such experiments and we all know the fate of 6202, being rebuilt to bolster the stock of reliable LMR 8P locos.

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2 hours ago, LMS2968 said:

Another point is that both ultra high pressure and turbine  propulsion were highly experimental and you really need to keep them separate: you can't learn from one if it is being influenced by the other as you don't know which is cause and which is effect. This was probably Oliver Bulleid's mistake: he tried to cram too much innovation into one package, so the successful parts tended to be overwhelmed by those which needed a bit more thinking out. 

 

Very high pressure / temperature steam was used with turbine propulsion, most notably in the German navy prior to and during World War II. The result of over-rapid development was chronic unreliability and very heavy fuel consumption. The Americans went down a similar route but restricted the pressure and temperature and went through a proper development process, producing very reliable machinery with the low fuel consumption needed for Pacific operations.

 

Nigel Gresley was right to try the water tube boiler, Henry Fowler to try ultra high pressure, and William Stanier to try a turbine. Combining the three would have been a recipe for disaster.

 

This is quite true, but sometimes taking the conservative approach can also result in missing out on what could have been a a major step forward. Whilst trying out ideas separately is a good idea, and would probably been a better approach on Bullieds Leader, if one aspect has a significant effect on another, then testing them separately will not produce the same results as testing them together, and would lead to the wrong conclusions being drawn.

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I can't say I agree there. You get each system working correctly independently of others, and when this is satisfactory, then you combine them. If a problem then emerges, you know it's due to that combination and don't waste time trying to track down a fault which might be inherent in either the turbine, the water tube boiler or the high pressure steam system.

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56 minutes ago, LMS2968 said:

I can't say I agree there. You get each system working correctly independently of others, and when this is satisfactory, then you combine them. If a problem then emerges, you know it's due to that combination and don't waste time trying to track down a fault which might be inherent in either the turbine, the water tube boiler or the high pressure steam system.

 

And if they are unable to work independently what do you do?  A steam turbine won't work without a supply of steam it is dependent on it,  and if the ideal pressure for running a turbine is 450psi, then compromising it's performance by testing it on a lower pressure would also be a waste of time.

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Then you get your boiler right first. Meanwhile, you can run your turbine at reduced pressure and sort out the problems there before moving on, and extrapolate results to a higher pressure, even if it means building a test vehicle. This is basic R&D.

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10 minutes ago, LMS2968 said:

Then you get your boiler right first. Meanwhile, you can run your turbine at reduced pressure and sort out the problems there before moving on, and extrapolate results to a higher pressure, even if it means building a test vehicle. This is basic R&D.

And if you can't get the boiler right because it needs the steady flow of a turbine instead of the pulses of a reciprocating engine?  The characteristics for turbine operation are different, a boiler that works well on a reciprocating engine may be no good for a turbine, and vice versa.  To get the best out of a turbine superheating between stages is required, this would require a different superheating set up which again means getting the boiler "right" first would be nullified.

Edited by Titan
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Wikipedia actually summarises the history fairly well https://en.m.wikipedia.org/wiki/Steam_turbine_locomotive

 

The most promising were probably those that came closest to being a power station on wheels, so using electric, rather than mechanical, transmission, but power stations are easier to keep happy when standing still, and become thermally much more efficient at sizes, temperatures, and pressures too great for locomotive use, so railway electrification is usually the better idea, and where that isn’t viable, then diesel.

 

In the U.K. context, I’m not sure the country is long enough for a steam turbine electric locomotive anyway, because one would be most suited to steady running, for a long period, at almost fixed output. Our railways are too full of humps, bumps, corners, and stations, which be bedevilled gas turbine too, and even made life for diesel fairly tough.

 

 

 

 

Edited by Nearholmer
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We aren't going to agree on this. Not only have I been involved in R&D but I also taught mechanical engineering and design to undergraduates studying for a degree in manufacture. If you put all the unknowns together into a single package and it all goes pear shaped, you'll have to think up some pretty good answers to your employer's questions as to why it's taking so long - and costing so much - to find the answers. Stanier had this problem with poor steaming on his new 5XP class in 1934: there were multiple problems so even if one was cured, it didn't necessarily effect an improvement so that this cure could be discarded. And that was entirely known technology; there was nothing experimental about it, but it took a couple of years to find the answers.

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Around the end of the war Mum joined Brush at Loughborough as a steam turbine designer, she had a maths degree she did during the war.  She left after a while as men returned from the services when they were demobbed.

 

Even now at the age of 97 she talks about her work which was partly investigating fatigue failures causing blades to shear off in ships' turbines.  You can imagine what a loose blade can do!  Usually most of the other blades are destroyed.

 

She points out that there were limits as to what was known about metal fatigue at the time.  Some blades ended up being heavier than needed, others sadly failed quite quickly by not having enough metal in critical places.

 

If a steam turbine loco was being built now the turbine might be quite different from the one Stanier used as so much more is known about blade design. This might bring about a change in size and potential power output.

 

David

Edited by DaveF
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41 minutes ago, DaveF said:

Around the end of the war Mum joined Brush at Loughborough as a steam turbine designer, she had a maths degree she did during the war.  She left after a while as men returned from the services when they were demobbed.

 

Even now at the age of 97 she talks about her work which was partly investigating fatigue failures causing blades to shear off in ships' turbines.  You can imagine what a loose blade can do!  Usually most of the other blades are destroyed.

 

She points out that there were limits as to what was known about metal fatigue at the time.  Some blades ended up being heavier than needed, others sadly failed quite quickly by not having enough metal in critical places.

 

If a steam turbine loco was being built now the turbine might be quite different from the one Stanier used as so much more is known about blade design. This might bring about a change in size and potential power output.

 

David

That's very interesting.  I was also involved in failure investigation.  Metal fatigue was known about in the 50s and 60s, and indeed Griffiths had done some fundamental work in the 1930s, but it was still in early days in the design offices, especially in marine engineering. I read C.C Pounder's book on diesel engines (the authority in the 1960s) and was puzzled by what he called "creeping cracks".  It took me some time to realise that these were fatigue cracks. Mind you in retrospect, I should have been suspicious of anyone who could inflict double-acting opposed-piston heavy oil engines on marine engineers.

Peterfg

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I recall my materials lecturer at uni describing - IIRC - how useful early data about fatigue cracking was collected by a crew member on board a ship who had noticed a crack in a bulkhead, and kept a record of its growth up until the point when it failed catastrophically and the ship sank!

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