Tornado

Foolish me for underestimating NP's aptitude for pedantry.

When is it or when is it not LCF? Are we going to have a discussion about musical theory next? When does a rhythm constitute music and when does it not...

250 odd Revs per mile?

At 90 Mph a mile is what, 45 seconds?

504 cycles on the combi lever, for every mile that the valve went from free to stuck?

How many miles do we reckon that took? 10? 20? 5?

It takes at least a mile to stop and my understanding is the brakes didn't go on until the Cross head made a bid for freedom after being let down and smacked in the face by one broken/free Combi lever/Union Link.

So we have a value bounded anywhere from 500 - 5000+ cycles on the combi lever.

Do please explain to me how that would not constitute fatigue?

 

This is getting crazy. One end of the combination lever became immovable, the other end didn't. Result-a combination lever in two pieces.

 

Never mind. I think you're getting the hang of it.

 

that's interesting . is that why she (46256) was laid up at the back of 1A in 1959/60 ? was there for about 2 months

 

Do I come in to your chats and undermine them? Why the hostility?

Same, why the hostility?

 

It may just be the absolutism of your responses? This outside observer, with no axe to grind about Tornado, and no real understanding of the detailed engineering principles, is thoroughly lost in the discussion of what does or does not constitute "fatigue".

 

I don't understand. Are you suggesting that the combination lever failed because of many cycles of increased stress, caused by the valve becoming stiff but not seizing completely?

 

The valve eventually became seized, that much we do know.

Does the valve instantly seize or does it go through a stages of reduced motion? Very difficult to say without actually measuring real time valve travel.

For every cycle the valve is refusing to sweep across its full range of motion, the combi lever gets progressively more stressed, until the valve seizes completely and the lever is just in pure bending. This is why the bound above is so wide.

It could be a few cycles (instant stuck valve - pure bending - few tens/hundred cycles - break) or it could be a progressive seize( thousands of smaller stress cycles followed by ever increasing amplitude leading to a break)

This is what creates the ambiguity of fatigue or not fatigue.

My point is you cant actually rule out fatigue as a failure mechanism, because you cant actually say when the valve began working at a reduced range of motion.

Yes this has become a highly technical theoretical discussion, but it makes a change from arguing over shades of black/blue/red/green which is a pointless discussion because everyone knows all locomotives should be battleship grey...

 

All true, but isn't the precise failure mechanism of the combination lever of purely acadamic interest, since the root cause of the failure lies elsewhere and it would be hard and arguably almost pointless to design a combination lever that wouldn't fail in one way or another given a seizure in the valve? Seems to me a lot of the sound and fury is people seeing the words fatigue failure and thinking that implies there was something wrong with the component.

 

Indeed. An infinitely stiff combi lever is a road to no where.

As I have said numerous times, the design and manufacture of the combi lever is NOT being critiqued here.

I would hazard a guess that this aversion to the F word stems from a generation familiar with the Comet which was a failure borne out of poor design. This is not that.

Perhaps the hostility I'm receiving both passive and directly is in exposing a concept that is clearly unfamiliar to most, that fatigue itself is not always a result of poor design, but can be when a component is placed into a situation beyond its design envelope.

 

A while ago I read Porta's tribology paper (sad but true).
He was maintaining that if things got too hot, the lube oil would just evaporate.
Could this be an issue with the Tornado failure?

 

I'm getting quite fatigued just reading all this.

 

I suspect there are a number of mechanisms by which the valve could have seized. And one tends to lead to another, since any significant problem is going to lead to excessive heat and problems with the lubrication. I've not been following this closely, but I'm not aware that a complete analysis of the failure mechanism has been published. It needs to be understood that it's not always possible to be confident about the root cause. I have no useful experience with steam engines, but my very limited experience with IC engines is that you may need to be lucky and catch a failure before it becomes catastrophic before you can be absolutely sure what the problem was. Difficult, for example, to detect that an oversize white metal bearing shell was used if the white metal has melted out of the failed bearing.

[Later] Just been reading the Tornado website fairly carefully. It states that there were four likely contributory factors to the failure, but isn't quite as precise as one might like about what they are. Maybe the for public version wasn't edited down as well as one might like. They suggest out of spec lubricating oil as one, they may be suggesting wear in the drive mech to the lubricator as another (I found the phrasing a bit contradictory), they're hypothesising piston ring fit (they were too damaged to test that theory), but I couldn't figure out what the 4th was. 29/10/2108 update on this page. https://www.a1steam.com/category/news/page/3/ .

 

Wasn't it imperfect alignment between the valve and the valve cylinder?

 

Can we have a separate thread for 'Tornado Failure' and keep this one for the activity of a wonderful loco.

 

Good idea. Then all the "experts" can gather together in one place and argue ad infinitum.

 

Very well said NeilL!

 

Don't worry, there wont be any more contributions from me.

 

Well, while you lot have been discussing the minutiae of the 'Ebor Flyer' failure, the Trust engineering team have completed a pretty thorough overhaul of the locomotive at the Wensleydale Railway, a plethora of updates have appeared on the A1 website and make interesting reading.

https://www.a1steam.com/2020/01/25/tornados-winter-overhaul/

https://www.a1steam.com/2020/02/21/february-news/

https://www.a1steam.com/2020/02/29/late-february-overhaul-progress/

https://www.a1steam.com/2020/03/06/early-march-overhaul-update/

https://www.a1steam.com/2020/03/25/late-march-overhaul-update/

https://www.a1steam.com/2020/03/30/overhaul-finale-and-move-to-york-for-storage/

Foxy.

 

Lots of very interesting reading there! An excellent insight into just how much work goes on to keep a Locomotive in operating condition. An absolute credit to the teamwork and hours spent on the Winter overhaul.

Richard.