Tank v Tender Locos

Under what conditions, i.e. tanks full? half full? empty?

An 84xxx tank had 1350 gallons of water, which I make to be roughly 6 tons, and apparently 3 tons of coal - so the variation between full and empty is about 9 tons, spread over 5 axles (3 of which are driving axles); whereas the adhesive weight of the 2-6-0 variant presumably wouldn't change appreciably during the course of its day.

Tom

 

The first two of the Brighton "L" tanks (4-6-4T) were said to roll appreciably at speed. They were soon modified (and the subsequent ones built) with the side tank capacity severely curtailed, with a well tank being squeezed in between the frames to make up for the lost capacity. For purely aesthetic reasons, the outer sides of the tanks on all the locos maintained their original external size, just the actual tanks inside were only 15" high!

Tom

 

3150: 9-15 + 19-0 + 19-5 + 19-5 + 14-7 total 81-12, adhesive 57-10 (post 1919-1922 bunker enlargement)
4300: 10-0 + 17-2 + 17-13 + 17-5 total 62, adhesive 52-0 (post 1917 weight distribution). Weights were different again with the 8300s, 9300s and 7322s
Source: RCTS vol 9
All figures tons-cwt

Not sure how seriously the LMS formula was taken at Swindon, who continued to use the GWR classification in service. In any case it produced odd results with GWR design decisions.

 

Thanks Jim.

So, like for like, it looks like a tank engine makes for a better freight engine then. More adhesive "bang for buck" as long as you don't need to go too far...and the PW can handle it.


Edit: found these at random whilst down the rabbit hole...

LSWR/SR G16 4-8-0t 7F later 8F
LSWR/SR H16 4-6-2t 5F later 6F

 

No. As I said in post 18, you were deficient in brake power. Getting them moving was one thing, but stopping again was more important.

 

And also the Z class 0-8-0T, which were 7F.

But notably, the G16s were built for hump shunting at Feltham, and rarely needed to exceed walking pace; nor - pace @LMS2968 - did they really need to stop a train on a regular basis. The Z class were also shunting engines, where the high adhesion helped (and the boiler was chosen, in Maunsell "bitsa" fashion, to have a large reservoir capacity but small firebox so as to minimise standby losses). The only one that did significant traffic mileage was the H16, which was used for cross-London traffic.

Tom

 

Ok, I see how stopping might be important!

 

I think the statistics are taken with full tanks and bunker/tender and a boiler with half a glass of water but happy to be told I'm talking rubbish.
You are right about the variation in axle load over the day. I've never noticed any problem with this on the NYMR but admittedly, the significant hill climbing is generally done with full -ish tanks and bunker. However, as I said in an earlier post, the tanks have the advantage of not having to drag a tender around so, when hauling identical trains, they have a significant advantage. IMHO, the Standard 2-6-4T's ride a lot better than their 4-6-0 & 2-6-0 equivalents, as well. A day on 80135 (and n0w 80136, as well) is generally referred to as a day in the office and for good reason.

 

My what if might be stanier 2-6-4 T's going to the S&D instead of Black 5's in 1938 After all the original locomotives provided by the Midland for through trains were tank engines

 

It would depend on what the engines were intended to do. As well as passenger, the Fives also worked goods over the S&DJR, and I again return to the braking effort. The 8Fs went to the S&DJR only quite late when the very heavy goods trains were pretty much over; prior to this the S&D men had rejected them. The 8Fs had a very good brake, but it wasn't as effective as the native 7Fs', so failed the test. The Class 4 tanks would fall at the same hurdle. In this respect, although the line received Standard 9Fs, they were used only on passenger turns. Their braking was inferior to the 8Fs', so they were not allowed on goods traffic.

 

The Irish ones also suffered in this regard.
Serious consideration was given to rebuilding them with larger (parallel) boilers to the Irish loading gauge, but the resulting increase in axle load would have reduced their operating range considerable. As it was, there was never the money.
The frames on the Irish ones were at a disadvantage as they skimped on frame stretchers when widening the gauge...

 

And the Decapod?
@Steve how were the 8 coupled GW tanks when they were at the NYMR? Given your above comments regarding not having to drag a tender, and presumably having plenty of power I'd have thought they would be pretty well suited?

Chris

 

4277 & 5224 were well up to the job of hauling heavy trains and steamed well enough to do the job. And so they should be. They weren't allowed on diners except in an emergency for the usual reasons with GW tank locos. They seemed to drink a lot of water (could be due to the ashpan sprinkler).
6619 was a good loco but it was a plod up the bank with 7 coaches on the 1 in 49. No matter where you tried putting the lever it never seemed to go above 15 mph. Certainly steamed well for me and would start 7 on the 1 in 49 with no problem.

 

I think I have to burst the myth bubble about 9Fs not working freight trains on the S&D as it simply is not true. Bath's No 1 diagram, which 9Fs regularly worked consisted of the 2.40am so called "Down Mail", which was in effect a freight working, followed by the up then down "Pines", returning home on the heavy 8.10 pm freight from Poole yard. This was the only freight working that ran the entire length of the line and thus the only one suitable for a 9 as they could not be turned intermediately at either Evercreech or Templecombe where most freight diagrams worked to. Of course there is scant photographic evidence of 9s on S&D freight workings because people rarely took pictures of night time workings in those days, but turning issues rather than braking problems were the dictating factors here.

Anyway back to the topic in hand

Peter James

 

A couple of points. Firstly when one gets up to the big tank engines such as the 4-6-4s rigid body length starts to be a problem with overhang and the risk of buffers locking. When Fairbairn continued the basic LMS Fowler/Stanier 2-64s he managed to reduce length and weight. Secondly, in relation to power classification, if one looks at the locomotives on last week's "Pannier Ramble" the 5700 class is 3F and the 9400 class is 4F despite having the same leading dimensions. The 9400 is some 6 tons heavier and it must be the additional adhesion that justifies the higher rating.

 

The extra weight is presumably due to a bigger boiler, which would also mean more available power, despite the same TE.

 

Here's an interesting snippet from Wikipedia:

"The Midland Railway introduced a system of locomotive classification based on the power output represented by a locomotive's tractive effort at 50 mph (passenger locomotives) or 25 mph (goods locomotives). This is the continuous tractive effort and is much lower than the starting tractive effort which is the figure usually quoted in technical publications.

This system was adopted by the LMS and also, from 1948 the nationalised British Railways. The classification was made up of a number (representing the power output - 0 being low power and 9 high power) and a letter (representing the type of work the locomotive was intended for), e.g. 4F. Over the years there were some modifications to the system, but the basics remained the same."

 

Wikipedia is almost definitively unreliable... I did try to research the LMS system on line earlier, and what I found was fragmentary and contradictory, with loads of people promoting their own methods of calculating BR power classes (!) and others, like the wikipedia entry, spectacularly incomplete.
Information in this thread on RMweb seemed more credible and complete than some, but has still some big gaps.

http://www.rmweb.co.uk/community/index.php/topic/3790-steam-loco-power-ratings/

Amongst others it states: "For freight locos ... the BR classification was based on the LOWER of the nominal tractive effort or the adhesion weight divided by 4.5."

 

I think the 5700s were originally classified 4F. The strangest anomaly seems to be that all the GWR 2-6-2Ts apart from the 4400s were class 4, from the small 4500s up to the 3150s etc with no 4 boilers.

 

The RCTS book on the BR Standard locomotives gives a substantial amount of information on the MR/LMS/BR power classification system, which did vary over the years and, indeed, did end up as the lower of nominal T.E. or factor of adhesion for freight locos. There was also a caveat that locos that were known to be better or worse than the classification the system gave them could be up or downgraded accordingly. The WR seemingly used this to class their 57XX Panniers as Class 4 but the LMR took a different view and classed them as class 3. I've said in an earlier post that the 56XX were rated at Class 5 but there is no way that they could match a Class 4 tank, never mind a Black 5 (or even a Manor.)
I've re-drawn one of the power classification charts. Input your favourite loco statistics and see where it ends up.