Power Classifications, how and why?

PS does anyone know if the new build B17 is planned to run on the main line? I assume so as I believe it will be built with roller bearings. Also are any other performance enhancements planned?

I hope the project makes good progress as I like the B17s, although they had all gone before my spotting days so I never saw one. Will be a useful engine I would have thought, both for ML and heritage lines.

Dave

 

But the B17/6s were with 225psi boilers from 1943 onwards and are much closer in leading dimensions to the Jubilees than the loco involved in the 1936 tests.

 

Aye, B17/6s had 100A boilers, which were the same boilers that were fitted to the B1s and O1s.

 

The ministry of supply 0-6-0 ST (J94) were called 3F by the LMS and had a higher TF than their LMS 3F tank, but the LNER called them 4F and BR also called them 4F

 

Perhaps my post was poorly worded, because I thought the test results were impressive. So the performance from a B17/6 would potentially be even better?

Dave

 

An extra 25 psi is going to make an impact on performance level. The reduction of working pressure to 180 psi during WW2 as an economy measure took the edge off performance and the engines were only rated at 4P. Those with 225 psi boilers were updated to 5P and 5F on fully fitted freight. So bearing this in mind, and having a test report to guide thinking (there are performance logs that confirm the abilities of the class) what should the power classification of the Jubilee be?
I would say 5P and not 6. True not all engines in a class are created equal but the power classification should reflect the average capability to be found within that class and Galatea is certainly not Leander.

 

Jubilees were classed as 5XP until the early 1950s. They were called 5X's by loco crews until their demise.

 

5XP you could have little disagreement with. I suppose that BR could be considered as having been a little muddled when it came to the classification of the LMS 4-6-0s. The Scots were 6P until 1955, in this year the Jubilees became 6P5F though they continued to display the 1951 6P classification. If the Jubilee class had been rated as 5P, which given what we know about the performances of the 5MT seems more than fair, that would leave the 6P slot filled with the Patriot class.

 

The massive OQ class Peckets were 0-6-0STs, but had a similar tractive effort to a Black 5, but could they exceed 20mph?.

 

For some reason I had it in my my mind that the original boilers were 220 psi. Yes another 25 will certainly make a difference. I didn't know about the war time reduction. Was this applied to other classes also? I was aware of a 60mph blanket speed restriction, but wouldn't reducing the boiler pressure also result in lower efficiency?

So it wasn't that that the B17s were under-rated, but the Jubilees were probably over-rated. Makes sense to me.

Dave

 

I suppose that what I am getting round to is saying that application of the formulas quoted earlier would logically lead to the Jubilees and the B17/6s being in the same power classification. As they were not one is bound to wonder whether the reason is that the ex-LNER officers were conservative about their power or whether the ex-LMS officers were bullishly confident about their beast. There seem other anomalies such as both the Hughes-Fowler and the Stanier 2-6-0s being 6P5F and the Gresley K3/K5s and K1/K4s being 5P6F. I can't see a shedmaster willingly sending out a Crab on a turn rostered for a Jubilee. It would get there but a little late.

 

The Jubilees were Stanier's version of the Patriots, the first ones being built in place of more Patriots. So they ought to have been equally powerful. If only some of them achieved that, on a good day, that would imply that neither the LMS nor BR ever got the design quite right.

 

The LMS rated the Jubilees and Baby Scots as 5XP, i.e. a passenger rating, and in this they were definitely superior to a Black 'un. BR simply moved the classes up to eliminate the X, which wouldn't exist on the other regions, but the class was certainly still superior on passenger workings. As I said somewhere else, a driver at Liverpool Exchange told me in in 1968, "Unless it's an express passenger working, I'd rather have a Black 'un than a 5X any day." But the point is that, on an express turn, he preferred a 5X. Don't underestimate them.

The 6P5F rating for the Crabs and Stanier Crabs was purely a beauracratic issue: these were basically goods engines, specialising in Fast Fitted Freights. At summer weekends in particular, they were frequently found at the head of excursion traffic, and while this wasn't fast, the trains could be very heavy, and some went into the 6P area. There simply weren't enough Baby Scots and 5Xs to cover the work, which the Crabs were quite capable of working anyway. The answer, to satisfy the Rules, was to uprate them to 6P5F, probably on the basis of Nominal Tractive Effort. No-one, and certainly not the running foremen, were under any illussions about their being the equal of a 5X on an express turn, or a Black 'un, for that matter, and throughout the week, they spent their time, as before, mostly on goods traffic.

 

I think that history shows the Jubilees to have been good locos once the initial steaming problems were sorted. Admittedly, they could be shy for steam if not fired correctly but that can be said for many locos. They were certainly on top of the jobs they were given to do and the very fact that they lasted to the final days of steam shows that they were well liked by those running the railway. If a 5X is virtually no better than a Black 5, they would have gone long before that.
As for why 45699 is presently regarded as poor, I don't have an answer as I have no knowledge of its use in service. There can be a whole host of reasons, from the driver, through the fireman to out of line blast pipe. All performance logs tell you is what the loco did, not why it did it and that must be speculation without frst hand knowledge of what is happening on the footplate. It should also be remembered that 45699 is fresh out of works after a total rebuild and will almost certainly be to 'spec' with new 6'-9" wheel tyres and 17" dia cylinders (possibly slightly less). A Jubilee that has been around in traffic for a while will have had tyres turned and cylinders bored out. That can make a huge difference to power output and performance as long as the boiler will produce the steam, which a 5X boiler can.

 

That was the case only pre-war. The Baby Scots were an excellent design but flawed in some - important - details, although these didn't necessarily show up until the class had been many years in traffic. Post war, they were far less highly rated than 5Xs. There was something of a role-reversal: the 5Xs by then generally would steam alright, if not brilliantly, but the Baby Scots were often shy for steam, largely due to air leaks into the smokebox which proved impossible to cure in the long term.

Similarly, the Stanier 2-6-0s did not represent a massive leap above the Horwich Crabs, from which they were developed, and the two classes maintained more-or-less equal merit to the end. The Crabs were excellent engines, but there was no deterioration in their condition or abilities over the years, being L&YR inspired rather than Midland.

 

Power depends on the amount of steam coming from the boiler and on the efficiency with which that steam is used in the cylinders. The efficiency depends on the steam chest pressure (hence the trend over the years to higher and higher boiler pressures) the cut-off setting, and several other factors. A reduction in actual wheel diameter and an increase in actual cylinder diameter make a difference to the tractive effort at any given speed and setting of the controls. That in turn demands different settings of the controls for the same speed and load, which can make a slight difference to the efficiency. But that is only slight, and consequently makes only a slight difference to the available power if the boiler performance remains the same.

If the control settings and other conditions are unchanged, the loco will deliver more power, but only as long as the boiler delivers more steam.

 

What were the differences between the original and re-built boiler/firebox for Jubilees and Royal Scots ?

 

I'm not sure that that's what was meant, Martin. The 5X's 3A boiler and the 2A boiler of the all the rebuilds, Jubilee, Baby Scot and Royal Scot, were in size and heating surface, The 2A boiler was larger diameter, hence the wider smokebox ring, allowing for a greater number of tubes and flues. Surprisingly, the grate area went up by only 0.25 sq.ft.