Jones1945Did PRR [buy] valves which had metallurgy issues, or [were] the issues was caused by constantly speeding of T1 so that the valves needed to use higher strength alloy to replace the mild steel provided by Franklin?
Remember that it is not difficult to figure out that the "140mph" speeds recorded by the Franklin test engineers had nothing to do with road speeds; they were rotational measurements in sustained slipping (perhaps otherwise undetected by enginemen). This of course made no difference to the magnitude of valve contact and inertial issues, which were precisely as expected not only for high rotational speeds (at full mass flow) but at high potential rate of change.
The first issue that had to be fixed was to 'debounce' the valves, which was essentially done by increasing the spring return pressure without introducing single-spring-rate resonance effects. This eliminated much of the cam and follower issues, but introduced much harder seat contact, much of it just at the time the valve was subject to severe superheating conditions. One potential solution to this would be to use the kind of seat on the LP valves in a Skinner Unaflow engine, where steam essentially cushions the seat a few thou against high-momentum impact. The 1948 change would have involved centrifugal casting and better alloy composition and some detail design of the seat regions. I see nothing particularly "impossible" about fixing the valves for reliable high-speed service within a relatively short time in the late Forties; all that happened was functional and commercial obsolescence.
LMS Turbomotive was built about 10 years before PRR S2, it was working fine in UK, probably because she only needed to handle passenger stock loads which was equal to merely 30% of loads in America.
M636C will have much to contribute here, but in my opinion the turbine was 'rightsized' to give comparable output to its conventional four-cylinder 'sisters' (and Guy and Metropolitan did a really, really good job on the design for the 'ahead' turbine and its control). The principal problem was that it appears (to me at least) that no one really understood that part of the locomotive's regular service involved backing full consists up a considerable grade, so the reverse turbine arrangements were pretty inadequate (and not susceptible of any cost-effective fix).
The big problem was that, when the turbine mainshaft fractured and took out the blading, there wasn't any even remotely cost-effective way to rebuild the locomotive in-kind -- I always found it interesting that it was economical to rebuild her completely as a piston engine, but not with any kind of turbine.
Just as a peripheral comment: Turbomotive 2 was NOT intended as a 'replica' of the original. It was a new approach to the design of an express locomotive that would fit British loading gage and esthetic criteria.
PRR S2 was about 300% more powerful than LMS Turbomotive but she only lasted 4 years with cracks all over the firebox, leaking steam pipes, leaking turbine casting etc.
S2 was no more a 'foreign concept' copying of the Turbomotive than it was a copy of the Swedish LGOJ turbines. And yes, most of the detail-design issues could either have been solved with the same level of attention as the T1s actually received in that period, or as part of a redesign for production. In my opinion at least some of the difficulties involved compromises due to wartime restrictions.
Overmod Remember that it is not difficult to figure out that the "140mph" speeds recorded by the Franklin test engineers had nothing to do with road speeds; they were rotational measurements in sustained slipping (perhaps otherwise undetected by enginemen). This of course made no difference to the magnitude of valve contact and inertial issues, which were precisely as expected not only for high rotational speeds (at full mass flow) but at high potential rate of change.
Jones 3D Modeling Club https://www.youtube.com/Jones3DModelingClub
The first thing to say about 6202 was that while it was technically successful, it spent about half its life in workshops either under repair or, most often, awating parts for its one-off turbine. It regularly ran between London Euston and Liverpool. Both of these stations were at the foot of inclines that were both originally worked by rope haulage, and which were by British standards severe gradients, which had to be tackled from a standing start.
I suspect the main problem with the reverse turbine was that it had to be clutched in and out. If it was possible for the main turbine, which was permanently connected, to be spun backwards in reverse, it must have been possible for the reverse turbine when running forward. While the reverse turbine had far fewer stages than the forward, it didn't need to be economical and could have been more powerful than the number of stages suggest.
I remember awakening one morning on an aircraft carrier to unusual vibration, I found that the ship was running astern at full power. The officer's wardroom was getting the worst of it. The point of the test was that the astern turbines were much less efficient than the forward turbines and the ability of the newly fitted condensers to take the hotter steam from the astern turbine was being tested. I still can't think of any possible use to which that information could be put, but the small astern turbines had the ship up to fifteen knots if I recall correctly, and watching the bow wave from the admiral's stern walk was worth the effort.
But back to 6202. It was found in tests to be more economical than the equivalent four cylinder Pacifics and was capable of good performance in the hands of a sympathetic driver. A problem in service was if the main turbine was damaged, no provision had been made to disconnect it, so the rods had to be removed and the lead driving axle raised above rail level before the locomotive could be moved. That would not have endeared it to train controllers (dispatchers).
It should be recalled that after its final failure as a turbine, it was now the property of British Railways rather than the LMS and Br management was more conservative. The two LMS main line diesels were kept in service but were not repeated for ten years. The new management probably thought one more "Princess" would be more useful.
In fact, a new frame was built to the later Duchess design, to which the original bogie and coupled wheels were fitted. The extension frame under the firebox and the trailing axle were retained. But the new four cylinder Pacific now had evenly spaced driving wheels and outside Walschearts gear with rocking levers to the inside valves. But the original boiler was used giving a locomotive of unique appearance.
When the rebuild was destroyed in the Harrow accident ater only a few months in service, the locomotive was not rebuilt but a replacement to a new design was authorised (71000 Duke of Goucester). The turbine boiler was repaired and became a spare for the Princess class.
The turbine boiler was different in that it had 40 superheater elements, compared to 32 for the standard boiler (and only 16 in 6200 and 6201 as built). So the boiler, and its double exhaust were tailored to the demands of the turbine. As rebuilt, 6202 had a single exhaust, although all the other locomotives with its cylinder arrangement had double exhausts.
How did we get to turbies in the steam railcar thread?
Peter
in my opinion the turbine was 'rightsized' to give comparable output to its conventional four-cylinder 'sisters'
I realise I didn't address this aspect. Indeed the turbine was rated at 2600 HP at 62mph (which sounds a lot like 1940kW at 100km/h) but this was, I think a bit more than a "Princess" could do under normal conditions. Against this was the limitation of six "throttle" settings, but reports from experienced train timers suggest that when working, 6202 was slightly better than a standard Pacific. It wasalso slightly more economical, no doubt assisted by the reduction in internal resistance provided by four cylinders and four valve gears.
But I imagine the cost was much higher. At the time of building, the locomotive might have been subsidised by the British Government, as were the majority of the LNER A4s, as a Depression "stimulus" initiative.
One of the things that might have caused the demise of the turbine was the fact that unlike 1935, in 1949 Metropolitan Vickers would have had much more work in hand and the costs of building a new turbine would have been relatively higher. At the time M-V were building a gas turbine locomotive for BR Western Region which worked relatively well but could never be run on heavy oil and proved far too expensive on kerosene.
Clearly BR thought that 6202 would be better as a conventional loco, and the actual cost of the rebuild may have been higher than simply replacing the turbine. The intention (in 1949 at least) was to get another "Princess". By 1952 when it was completed and placed in service, things had moved on, and after the Harrow accident it was replaced by 71000, basically as an excuse to build the only BR Class 8 pasenger locomotive.
Both direct-drive steam turbine engines almost shared the same fate......
Besler High Pressure Streamliner No. 9610, "The Blue Goose." Click to enlarge.
Found this in Hagley Digital Archive.
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