Power Classifications, how and why?

There is no reason that a recently overhauled engine will have had new tyres, if there was plenty of meat on them they probably were just turned down, the same applies to the cylinders, they may or may not be at nominal size. As you imply an engine in good condition with smaller wheels and over-size cylinders will have more power than originally designed, up to about 10% from memory if both wheels and cylinders are near the limits of wear.

Baldric

 

Are you not forgetting that 45699 had one brand new wheelset fitted.

 

They could be but, if you are spending £½m plus on a resotration that required one new set of tyres, would you not re-tyre the other four? I don't know what was done but, looking at photos, 45699's tyres seem fairly thick, if not exactly new. The cylinders would certainly need re-boring and a liner fitting so likely to be to spec. but I'm speculating.

 

If the remaining 4 tyres had had one turning it would be a waste to scrap those to buy 4 new tyres instead of loosing 1 turning from 2 the new tyres on the new axle.

Re-boring a cylinder does not mean it has to have a new liner fitted.

I have no detail on the particular locomotive I am just saying you can't assume some of the things stated, an overhaul does not need to make it back to original specification, the limits and fits should be however in an ideal world.
Baldric

 

Why some locos carry a freight power classification and some do not there are pictures of castles pulling freight trains mainly fitted but no classification and the other way 9fs have not passenger classification a guess maybe 7 p.
How do you define a mixed traffic loco wheel size.

 

I've also wondered what passenger classification a 9F would have had according to the formula. 5 or 6 perhaps? Also as with steam locomotives there are so many variables to power output i suppose the classifications were just a general guide.

It's a shame the only source of the information for the power classifications is in a single publication. You would of thought something like that would of been more widely known about. Also as steam locomotives are so many variables to power output i suppose the classifications were just a general guide.

I know on the Somerset and Dorset each locomotive was given a tonnage figure, so the light pacifics had the same weight (or near enough) limit as a black five,albeit down to adhesion rather than a lack of power. Was this a universal set up with loco limits for all lines or more unique to the line and perhaps other challenging routes?

 

I've seen similar locomotive - tonnage tables for Ilfracombe - Barnstaple (both directions) and Exeter St Davids - Central, though both of those would definitely be in the "challenging" camp! I suspect it was more universal, but it is just the interesting lines that get quoted in modern-day enthusiast histories.

If you read the older literature, often loads are expressed in number of vehicles rather than tonnage, both for goods and passenger working. There were equivalences in which heavier vehicles were equated to multiples of lighter ones. So you might see a report in which a passenger train was "11, equivalent to 13 1/2" which means 11 vehicles, but some of them (perhaps six wheelers) heavier than a standard (at that time) four wheel carriage. Or in goods working, a mineral wagon might equate to "1 1/2" indicating that a loaded mineral wagon is heavier than a normal loaded wagon. I guess counting things that way was quicker for the guard to work out than trying to add up weights and assess how loaded each wagon was. Instead, he could just count wagons and then add an allowance for any of the known types of heavy wagon, and then give the driver a load such as "30 equivalent to 38" or whatever.

Tom