Saint Class 135 ish mph

Depends whether it has piston or slide valves. Quite possible with the former; a challenge with the latter.

 

That's interesting. Can you elaborate?

 

Slide valves have a high degree of friction, even with steam shut off, so moving the lever with the loco moving at high speed has a tendency for the valves to stop and the movement instead transferred to the lever via the reach rod.

 

Query: Doe this apply to just traditional, or also the balanced slide valve? (I'm still trying to get to grips with the balanced flavour.)

 

LMS 2968 has explained it succinctly. On larger slide valve locos, any attempt to alter the cut off whilst the regulator is open is usually a fight that the driver will lose. A 10" x 12" slide valve with 160 psi has over 8 tons pressing it against the port faces. However, in my experience with lever reverse piston valve locos (admittedly confined to GWR 2-8-0 and 0-6-2 tanks) it takes no undue effort to alter the reverser. Indeed, I have been known to hold it between notches to get the cut-off I want.
The difficulty of altering the cut-off on slide valve locos is one reason why they are invariably driven on the regulator with a fixed cut-off. You get the train on the move in full gear, shut the reg and put the lever where you want is then open the reg, again. The lever then tends to stay untouched.
As for balanced slide valves, I can't comment as I've no experience but I suspect they are not as balanced as a piston valve.

 

You can move the valves on a slide valve engine with open regulator if you have a steam reverser Though even there, my experience on Chatham engines is that on starting, the reverser may be notched up in a two or three increments as speed increases, but once you get to a reasonable running position, as you say, driving is largely on the regulator and the reverser isn't touched. The exceptions being either when the regulator is closed, or it is desired to go into the big valve (for which you have to notch right up to a very short cut off; move into or out of the big valve, then back to the desired cut off, then adjust the regulator to the desired level on account of the regulator being otherwise impossible to move beyond first valve with a normal running cut off).

One reason I think slide valve engines tend to be driven that way, apart from the effort of moving the valves, is that typically slide valve engines are also unsuperheated. If you drive on a partially-open regulator and a longer cut off, there is a pressure drop across the regulator where the steam is throttled, but because there is no temperature drop, the result is a mild degree of superheating which helps prevent condensation in the cylinders.

Tom

 

Being pedantic, a steam reverse doesn't count as a lever reverse but, otherwise all you've said is very true. As for not adjusting the steam reverser once set I'd suggest that it is probably down to the difficulty in finessing them.

 

I see, thanks chaps.
On a slide valve the pressure difference is pressing the valve onto the port, while on a piston valve the pressure difference acts perpendicular to the port opening?

 

Sort of. With a piston valve arrangement there are two valves, one for each port at the ends of the valve chest. The steam pressure is acting on both valve heads but in opposite directions, so cancel each other out. There is therefore no pressure acting on the valve spindle.*

*Note: the front valve was sometimes made slightly larger than the rear to make fitting the valves into the steam chest easier.. This produced a slight forward thrust on the valve spindle.

 

Of course! Your explanations are always clear, you should have been a teacher

 

A fair summary in my opinion.

BTW I've seen nothing in Mallard's dyno roll to suggest a speed as high as 125 - as mentioned earlier it gives me no pleasure to be providing evidence that perhaps 05 002 (with its notorious passengers) was faster. The next question would be how accurate was the German record - which was measured in a similar way.

 

Not necessarily so. The first supersonic flights were achieved in a dive and even world speed records for aircraft - certainly in the early jet era - used a dive to build up speed before flying the level measured course.

 

Quite so but just quoting from Roly Beamont's book about the time he was on the RAF High Speed Flight.

 

If Charles Rous-Marten had only left us the final quarter mile timing then it would be impossible to say anything certain - it would be too easy for one timing to be wrong. However he published nine timings, 8 quarter mile timings over the previous two miles and a timing of the final mile. You can plot a theoretical curve through that scatter plot, one that obeys the laws of physics - and it strongly suggests a speed of 100 mph. None of the points is further from the line than the likely error (human reaction time plus error of a fifth second stop watch).

You cannot plot believable curves that match the speed curves published by the LNER. For instance FS accelerating from 96 to 100 mph in half a mile after taking three miles to get from 90 to 95. If we had the original dyno roll, or even CJ Allen's stopwatch timings we could try to make sense of that run - but the lack of data brings you to a dead end. That was the point I was trying to make.

The Mallard dyno roll shows a believable speed profile - without the rapid fluctuations in the LNER curve.

Regarding the 1964 Darlington report - I did quote the relevant sentence. The original report is in the NRM - kept with the dyno roll and some other papers - but there is a transcript in Rutherford's "Mallard - the record breaker".

No one claimed 135 mph for 2903 - that is a red herring. In Collett's account he states they timed the locomotive at 120 mph - and quoted the signal box times just as supporting evidence that a high speed had been attained. As discussed higher up this thread, timing a loco at high speed from the footplate is not an exact art - but it seems fair to say that a speed well over 100 mph was attained - as it was in 1927 in a similar run.

I understand Edward Thompson was an admirer of GW practice, perhaps you should follow his example

 

I would be interested to look into this further - call me nothing if not fair if I am able to look at the same evidence and admit I am wrong (if I am of course).

Actually he was an admirer of the Great Eastern Railway. This is borne out by his choice of livery for Great Northern, his work at Stratford and some GER items within his personal collection.

Stanier's work on the LMS developed from the GWR was also something he looked closely at. It is interesting to note in my research that the only reference to the GWR came from hearing the "bark" of engines at Paddington whilst living there in the 30s.

There's no evidence to suggest that he actually followed GWR practice, but he and AE English did pay particular attention to valve events and the size of chimney orifices with their rebuilds of B12/3 and D16/3. This also seems to have followed through into class B1 (compared to a Hall or Black Five) and some of his standardisation policies.

 

When I wrote that I was half in jest and half thinking of his 4 cyl layout with inside cyls to front and outside ones to rear.

Just noticed that he was a Wiltshire lad - from Malborough. We are all influenced by what we see in our childhood - but this is seldom recorded. You wonder what locos he admired as a boy - was he a fan of the GW - or perhaps he preferred the Midland and South Western Junction Railway?

 

He was also one year below...Herbert Nigel Gresley, whilst at Marlborough. It is astonishing how parallel and yet how different lives Thompson and Gresley led.

Also - Thompson liked divided drive in his 3-cylinder machines in a way, as you say, not dissimilar to GWR practice. Outside cylinders power middle drivers, inside cylinder powers the front axle. Hence the longer front end and shorter connecting rods. Interesting that he refers to Chapelon rather than the GWR though.

 

I'll try to put this politely as I mean it politely, but online things tend to sound less courteous than intended...
I'm afraid my problem with all of your arguements in this regard over various threads are twofold:
1. (the important one) you seem to think you can somehow apply "the laws of physics" to something as complicated and varied as *transient* (non-steady-state) thermodynamics, mechanics, kinetics and dynamics of a steam locomotive with a train on non-level ground, and then use your "laws of physics" to *correct* actual measured data from 80-120 years ago better than the people present who collected it. If so, you are the greatest scientist the world has ever seen! And, from an engineer, I mean the word scientist as an insult...
2. (the silly one) it's remarkable how all your arguements go to support the claims of a certain railway you were already very partial to while scoffing at those of other railways you aren't so partial to.
Personally, I think you're wasting your time. The claims of CoT, FS, Papyrus, Coronation, Mallard and the German loco are all matters of *historic* fact, regardless of their *scientific* merit... Just love 'em all and have done with it...