Discussion in 'Steam Traction' started by johnofwessex, May 17, 2017.
Not that I'm aware of.
I have read of the fitting of Ferodo lined blocks to the 7Fs and had assumed this was across all braked engine wheels, which would make sense at one level but perhaps not if selective fitting would deliver a cost saving. Do you know any more about this?
The 7F was very much a machine designed to carry out a specific job, it was regrettable that the design was not developed further, the act of improving the cylinder design and also the valve gear would have produced a more flexible machine. The exhaust system would stand some looking at but this would be most unlikely to occur. The attention to cylinders and valve gear would deliver enough of an improvement. The tractive effort was high enough, adhesion does not appear to be a major issue so far as I am aware, and those axle boxes are not so inadequate as some like to depict them. You can always look at the lubrication and that goes for any locomotive even to this day. Clayton did well in the circumstances that he found himself in, my view anyway.
I seem to remember 88 & 89 at Barry had Ferodo on all driving / coupled wheels.
Come to think of it, how would you deal with the different wear rates if you mixed CI and Ferodo. On modern wagons there is a move to eliminate CI brake blocks, due to noise. The composition replacements are known as 'K', which requires different brake rigging due to increased friction, and 'L' (low friction) which is a straight swap.
This is rather outside my chosen field but I'll do my best. As I understand it, the different wear rates between asbestos and cast iron blocks wasn't a problem as the engines needed reblocking so frequently, I remember reading every two days somewhere. Unfitted goods on 1 in 50 gradients tend to take their toll! As to the Barry pair, my understanding was that one had asbestos throughout but the other on the leading wheelset only; I don't know which way around. Although I saw both engines at Barry, I wasn't aware of the different materials so I didn't look - not at the brake blocks, anyway. I can't say except from second hand sources.
In answer to Dunfanagby Road, yes, I'd agree. I don't believe that the axleboxes were a problem with this class, but if the improvements you suggested had been carried out, would that have remained the case?
I wonder if revisiting the question of brake blocks might be worth while particularly with reference to locomotives in use on the mainline.
As far as I know, and I think this is right, the Ferodo blocks on the 7Fs were to overcome the iron brake dust causing wear to the slidebars and crossheads and was not an attempt to increase the brake force, although it might have done so. If you start increasing the loco's brake force beyond designed limits you run the risk of wheel slide under heavy braking and wheel flats as a result. Bear in mind that steam haulage on the main line is entirely passenger stock, and the braking effort from this is far higher than that from the engine, whatever blocks you use. I'd say that it was undesirable to have the situation where the loco leans on the stock when braking rather than stock have the stock maintaining tension in the couplings.
I agree with you that you do not want the wheels to lock yet modern friction compounds may well offer significant advantages over the more traditional cast iron block. The Ferodo lined blocks fitted to the 7Fs did, from what I have read, improve the braking of these engines and not just from the point of minimising problematic dust issues. The asbestos content would not go down particularly well today though.
Locomotive braking or the lack of it has always been something of an issue. A significant percentage of the weight of a locomotive can rest upon wheels that do not have brakes. The SNCF 231E had, and retained, front bogie brakes but such an application was seen as an unnecessary complication in the UK and in many countries elsewhere. The French system must have been well thought out to extract the optimum braking properties with minimum risk of lock-up and hence wheel flats if it survived for so long.
You also have locomotives where the speed of the actual application is a problem. This applied to the Std 9F when compared with the 7F.
I do not know the answer to this but you probably do not want your braking distances increased because the prime mover of your train has substantially inferior braking when compared with the vehicles that make up the train. There again it might, with all factors considered, be preferable to have this state of affairs rather than the reverse. Or maybe all components should be of equal capability.
One argument to consider in relation to improved braking performance is what happens when you head smokebox first down a steep gradient. All the water goes to the smoke box end, causing a fall in the level measured at the firebox end in the gauge glass. Add in braking and it exacerbates the effect. So if you have more efficient brakes the effect is potentially to further reduce the water level over the crown sheet when braking hard down a falling gradient.
My understanding is that Collett did some tests and found that bogie brakes [later clarification - which were fitted to Stars, Saints, the Bear and early Castles] made little or no difference to the distance run after a full brake application on passenger trains. (Its in Holcroft) Little surprise really ! And I suspect with loose coupled freight trains the difference would have been no more than applying the hand brakes on one extra wagon, so of little benefit either. In other words fitted trains were too well braked to be worth bothering with bogie brakes, and unfitted freight too badly braked...
I thought that the S&D 7Fs were working unfitted mineral trains, so the braking performance of the trailing load was limited to the guard's van. Did I once read the claim that the CI blocks got so hot that the glow could be seen at night, or was that a bit of leg-pulling?
Continental railways may have been better able to fit brakes to bogies and trucks by virtue of having air brakes. Much easier to mount the brake cylinder, I imagine. Certainly the Germans did it.
Would Tom's point about the movement of water in a boiler leading going downhill explain why the South Wales Valleys were worked bunker first downhill?
As Jimc inferred above Churchward fitted brakes to all wheels of his express locos, the bogies requiring an additional 13"(?) vacuum cylinder. The only exception being The Great Bear where, unlike the Atlantics, the trailing axle had 4.5" side play and the weight of another (18") cylinder was unacceptable. The similar radial axles on the tank engines weren't braked nor were the leading trucks.
Might have been necessary if his locos were running around at 130mph light engine
With unfitted mineral trains the braking performance was governed by the number of wagons that had their brakes manually pinned down when the train was stopped at the crest of a gradient to do so. Stopping to individually put the brakes on and take them off again at every serious gradient was scarcely an efficient way to run a railway, and no doubt did its share in moving freight traffic to the roads.
I can't comment on 7F's in general but regarding 53808 it had fibre (Ferodo) brake blocks when it came out of Barry and at least one of those still exists as a sample of an original. During it's service on the WSR it ran with a more modern non-asbestos version of the of the original Ferodo block. These were made by Transport Brakes Ltd (TBL) in Bristol and required a special mould for the purpose. Every few years we would purchase a batch of 16 blocks from TBL to keep the locomotive in service. Unfortunately around 2010 TBL closed down it's plant in Bristol and the moulds were lost, we only found out about the closure a couple of years later when we tried to re-order some more blocks. We approached other fibre block manufacturers but either the block was too large for their machines or they did not want to be involved for the small numbers required. The result is that 53808 now runs on standard cast iron blocks.
Since the change from fibre to cast iron on the WSR slide bar wear on 53808 has increased but not dramatically, with the fibre blocks it was virtually non-existant. I would not expect slide bar wear to be the reason for the original change, other bits give far greater problems on 53808 and they never addressed those!
The braking system of the 7F's is very powerful, 3 brake cylinders on the loco and the usual one on the tender. Two cylinders under the cab apply the brakes to 6 brake blocks on the intermediate coupled, driving and trailing coupled wheels. One cylinder under the smoke box saddle originally applied the brakes to the leading coupled and the pony truck, the brakes on the pony truck were removed sometime pre-BR service.
A characteristic of cast iron brake blocks is that as the rotational speed of the wheel increases the coefficient of friction between the brake block and the wheel reduces. This means that the faster you go the less effective the brakes become. The effect is most noticable as a steam era passenger train comes to a stand at the platform with a jerk, unless the driver has come to a stand with a "rising brake' or taking the brake off as the train slows to a stand.
Heavy unfitted trains would often have to stop at the top of a steep down grade to have sufficient brakes pinned down on the wagons, to few wagons and as the speed rose the train would become uncontrollable and run away, to many wagons and the locomotive would be unable to start the train moving.
Thanks for all that, Aberdare. Now we have the story from someone who does know!
We have a either a like or a reply option, some forums have a thanks option. I think that this might be a useful addition. In the absence of this, thanks to Aberdare.
Also the Southern W class, the LSWR G16 & H16s, the NER Y & X, the GCR 1N and the LNER L1
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