Steam Loco Power Classification questions, etc

[grumpyxch]

I was at Swanage Railway Station yesterday and saw 34028 Eddystone. I noticed on the cabside, just above the number, it had "7P 5FA". Now, I know what the 7P and 5F refer to, but what does the A mean?

On the sublect of Steam Locomotive Power Classification, how do they work out what the P figure should be for a loco type - same question really for the F figure, and for MT?

Also, on the cabside, there was a yellow circle. I assume this was for Route Availability. Is there a published list that states what each Route Availability actually means when they are working them out? Otherwise, how do they work out what the Route Availability figure is for a particular line?

 

[DelW]

I was at Swanage Railway Station yesterday and saw 34028 Eddystone. I noticed on the cabside, just above the number, it had "7P 5FA". Now, I know what the 7P and 5F refer to, but what does the A mean?

On the sublect of Steam Locomotive Power Classification, how do they work out what the P figure should be for a loco type - same question really for the F figure, and for MT?

In my reprint of the 1963 Ian Allan ABC, the light Pacifics are listed as 7P5F and 7P5F*, with the asterisk denoting rebuilt locos. Might the "A" also indicate that?

Such designations weren't fixed, as the 1950 version shows them as 6MT, possibly a leftover from the justification for their construction during WW2. I imagine the classification was an assessment by the CME's department rather than a hard and fast calculation.

 

[Snow1964]

Wasn't the split designation also related to brake force, the lower freight rating applying in those days of lots of unbraked trains

 

[hexagon789]

I was at Swanage Railway Station yesterday and saw 34028 Eddystone. I noticed on the cabside, just above the number, it had "7P 5FA". Now, I know what the 7P and 5F refer to, but what does the A mean?

On the sublect of Steam Locomotive Power Classification, how do they work out what the P figure should be for a loco type - same question really for the F figure, and for MT?

Also, on the cabside, there was a yellow circle. I assume this was for Route Availability. Is there a published list that states what each Route Availability actually means when they are working them out? Otherwise, how do they work out what the Route Availability figure is for a particular line?

BR adopted the LMS system.

The LMS used the calculated tractive effort at 50mph for passenger and 25mph for freight to determine power category.

The GWR used a system of coloured discs to indicate axle load restrictions. Yellow was 14-16 imperial tons. Yellow was the lowest given restriction, below that was only unrestricted locos. (Ie - no colour; yellow; blue; red; double red.)

Wasn't the split designation also related to brake force, the lower freight rating applying in those days of lots of unbraked trains

Yes, FA / FB related to permitted loads dependent on brake force of the loco.

 

[etr221]

On the Southern, the Yellow circle (or spot or disc) on the cabside was to do with water softening treatment (TIA or BR system) a triangle was also used for similar purpose, but I don't know details. (Not to be confused with GWR/Western Region RA system, using similar discs, of various colours for completely different purpose)

 

[norbitonflyer]

Also, on the cabside, there was a yellow circle. I assume this was for Route Availability. Is there a published list that states what each Route Availability actually means when they are working them out? Otherwise, how do they work out what the Route Availability figure is for a particular line?

The RA system adopted by British Railways was that previously used by the LNER (just as the power classification was inherited from the LMS, whilst carriage design, particulatly EMUs, initially closely followed Southern practice). The route availability of a rail vehicle is defined mainly by axle load, although axle spacing may be taken into account for short-wheelbase vehicles (as two axles simultaneously on the same span of a structure may overload it). The RA of a route is based on the strength or structures such as underbridges, and the condition of the track (in particular the weight/unit length of the rails). For a vehicle to travel over a route, the vehicle must have an RA no higher than that of the route. (So an RA 5 route may only be traversed by vehicles of RA0-5, and an RA5 vehicle may only travel over routes with RA 5-10)

The actual axle load figures are quoted concisely in Wikipedia, with copious references to official documents https://en.wikipedia.org/wiki/Route_availability

 

[Rescars]

BR adopted the LMS system.

The LMS used the calculated tractive effort at 50mph for passenger and 25mph for freight to determine power category.

The GWR used a system of coloured discs to indicate axle load restrictions. Yellow was 14-16 imperial tons. Yellow was the lowest given restriction, below that was only unrestricted locos. (Ie - no colour; yellow; blue; red; double red.)


Yes, FA / FB related to permitted loads dependent on brake force of the loco.

Leading on from these details about how passenger and freight power classifications were calculated, does anyone know how MT classifications were calculated and, for that matter, why some locos were classified as MT whilst others were classified with separate P and F ratings?

 

[norbitonflyer]

Leading on from these details about how passenger and freight power classifications were calculated, does anyone know how MT classifications were calculated and, for that matter, why some locos were classified as MT whilst others were classified with separate P and F ratings?

I stand to be corrected, but I have always understood that an MT rating simply meant they had the same rating for both passenger and freight (so 5MT was the same as 5P5F)

 

[grumpyxch]

The RA system adopted by British Railways was that previously used by the LNER (just as the power classification was inherited from the LMS, whilst carriage design, particulatly EMUs, initially closely followed Southern practice). The route availability of a rail vehicle is defined mainly by axle load, although axle spacing may be taken into account for short-wheelbase vehicles (as two axles simultaneously on the same span of a structure may overload it). The RA of a route is based on the strength or structures such as underbridges, and the condition of the track (in particular the weight/unit length of the rails). For a vehicle to travel over a route, the vehicle must have an RA no higher than that of the route. (So an RA 5 route may only be traversed by vehicles of RA0-5, and an RA5 vehicle may only travel over routes with RA 5-10)

The actual axle load figures are quoted concisely in Wikipedia, with copious references to official documents https://en.wikipedia.org/wiki/Route_availability

This is just for information, but apparently, back in the days before Nationalisation, the line into London Fenchurch Street station from Gas Factory Junction was owned by the Great Eastern and then the LNER. This line had several weak bridges. However, the main users of that stretch of line were the London, Tilbury & Southend Railway, which was bought by the Midland in 1912, which then became part of the LMS. The LTS/MR/LMS trains were getting too heavy for the LTS locos, but the LTS locos were already pushing the weight limit of the bridges. Double-heading was out because of the short platforms at Fenchurch Street, and the intensive rush-hour traffic. The Great Eastern/LNER refused to let the LTSR/MR use heavier, more powerful locos because of the weak bridges. During the 30's, the LMSR tried to use a couple of Fowler 2-6-4Ts, but when the LNER found out, they soon told them to stop. The LMS then designed the Stanier 3-cylinder 2-6-4T, which were above the LNER permitted axle load for the line, but the LMS got around that restriction because they argued that with 3 cylinders, the hammer blow was much less than other locos on the line, so they would be better than locos the LNER used. The LNER accepted this argument, and the Staniers started work. Eventually, the bridges were strengthened, so the problem was solved, but that may have been post-nationalisation, and may have been to allow the Standard 2-6-4Ts to be used too. Therefore, there can be other things than axle loads that affect locomotive Route Availability

 

[etr221]

The Great Western Railway sytem is described here https://en.wikipedia.org/wiki/Great_Western_Railway_Power_and_Weight_Classification .

Power classification was always something of a black art: the process may have started with nominal tractive effort (which could be calculated from loco dimensions), but there was then a lot of consideration given to practical considerations, and how locos actually did. Steam loco horsepower ratings are rarely published, as very difficult to understand and calculate... As Sturrock of the GNR said, it was function of how much water you could boil - which in turn was a reflection of the fireman's capabilities.

 

[Taunton]

This is just for information, but apparently, back in the days before Nationalisation, the line into London Fenchurch Street station from Gas Factory Junction was owned by the Great Eastern and then the LNER.

Not wanting to be pernickety, but the Fenchurch Street line was, up to 1923, actually owned by the London & Blackwall Railway. They had leased out operation of all their trains to the GER, but they also had, separately, negotiated with the LT&S to use station as well, so the latter's presence there was nothing to do with the GE. Come the LNER and the same concession was carried forward. Of course, by the time these large tank locos arrived it was indeed an LNER issue.

 

[Rescars]

I stand to be corrected, but I have always understood that an MT rating simply meant they had the same rating for both passenger and freight (so 5MT was the same as 5P5F)

This certainly makes sense. Thank you!

 

[The Crab]

Then you oddities such as the LMS "Crab" 2-6-0s being classified as 6P5F for a while. Why they should be "More P" than a Black 5 is beyond me but I did read somewhere that it was to justify their (overloaded) use on summer extras.

 

[Taunton]

The Great Western Railway system is described here

The GWR coloured disc scheme (which carried on through to BR Standards, and indeed WR diesel hydraulics) was subject to all sorts of exceptions. There was a somewhat creased official map on the shed foreman's office wall at Taunton with it all, which dated back to GWR days. A discussion here a while ago was about how a "Blue" Prairie tank was long-term allocated to Cardigan, end of a "Yellow" long branch. Other cases required the water tanks to be only part-filled to trespass on tracks of a lower category.

An amusement was how the classic 57xx Pannier Tanks were put back, around nationalisation, from Blue to Yellow, thus allowing them to go anywhere, while the supposedly more modern 94xx Panniers being introduced then, often disliked in comparison by the crews, were stubbornly stuck at Red, which enabled many sheds to deny having them allocated there. The water tanks of the latter had already been cut back at the front end of the loco to prevent the first axle being overloaded.

 

[grumpyxch]

Not wanting to be pernickety, but the Fenchurch Street line was, up to 1923, actually owned by the London & Blackwall Railway. They had leased out operation of all their trains to the GER, but they also had, separately, negotiated with the LT&S to use station as well, so the latter's presence there was nothing to do with the GE. Come the LNER and the same concession was carried forward. Of course, by the time these large tank locos arrived it was indeed an LNER issue.

Yes I knew about the L&BR, but the GER had a 999 year lease so as good as owned it, and both the L&BR and GER disappeared as companies when they were absorbed into the LNER in 1923. Putting the history into words was complicated enough in what I was trying to describe, so I wasn't too bothered about not mentioning the L&BR

 

[Irascible]

The GWR coloured disc scheme (which carried on through to BR Standards, and indeed WR diesel hydraulics) was subject to all sorts of exceptions. There was a somewhat creased official map on the shed foreman's office wall at Taunton with it all, which dated back to GWR days. A discussion here a while ago was about how a "Blue" Prairie tank was long-term allocated to Cardigan, end of a "Yellow" long branch. Other cases required the water tanks to be only part-filled to trespass on tracks of a lower category.

An amusement was how the classic 57xx Pannier Tanks were put back, around nationalisation, from Blue to Yellow, thus allowing them to go anywhere, while the supposedly more modern 94xx Panniers being introduced then, often disliked in comparison by the crews, were stubbornly stuck at Red, which enabled many sheds to deny having them allocated there. The water tanks of the latter had already been cut back at the front end of the loco to prevent the first axle being overloaded.

It always amused me that the Tiv Jct - Tiverton line was rated as Red. Sadly never seen a photo of a Castle at Tiverton! the Exe Valley line was most definitely not Red, so diverted trains got large Praries ( Blue, I think? which I guess isn't bad for a branch ).

 

[chorleyjeff]

Then you oddities such as the LMS "Crab" 2-6-0s being classified as 6P5F for a while. Why they should be "More P" than a Black 5 is beyond me but I did read somewhere that it was to justify their (overloaded) use on summer extras.

The Crabs were 6P only for ordinary ( slow ) passenger trains. "F" engines on ordinary passenger trains were allowed 10% heavier loads than equivalent number "P" engines. No idea why.

 

[Taunton]

The Crabs were 6P only for ordinary ( slow ) passenger trains. "F" engines on ordinary passenger trains were allowed 10% heavier loads than equivalent number "P" engines. No idea why.

Smaller driving wheels give greater tonnage hauling capacity, at the expense of speed.

 

[Bevan Price]

The power classification (PC) was roughly derived by using a formula

PC = Drawbar horsepower (dbhp) / x,
where x was something around 200-250 dbhp

but I cannot remember if the applicable dbhp related to "at starting" or "continuous" .