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Swanage Railway General Discussion

Discussion in 'Heritage Railways & Centres in the UK' started by Rumpole, Oct 10, 2012.

  1. green five

    green five Resident of Nat Pres

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    4270 did the same thing when it was visiting the MHR for a Steam Gala. I travelled behind it and attempted to film a video from the window of the climb up Medstead bank but gave up as the train was rocking about so much. My Dad had half a cup of tea which ended up over the table as it was spilling over the top of the cup. None of the other GWR loco's visiting for the same Gala were rough riding like 4270.

    Sent from my D6603 using Tapatalk
     
  2. John Petley

    John Petley Part of the furniture

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    When 5643 was hired by the Bluebell about 3 or 4 years ago, I had a run behind her and this was one feature I wanted to observe. I didn't experience any of the to-ing and fro-ing which was a feature of my trips behind 6695, especially downhill.
     
    Last edited: May 1, 2017
  3. johnofwessex

    johnofwessex Resident of Nat Pres

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    I suggest then that this is an issue the WSR would be well advised to look into and attempt to correct then................
     
  4. twr12

    twr12 Well-Known Member

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    Depends on the driver.....

    To reduce train shagging by gWR locos with Mr Stroudley's crank axle, don't pull it up too much, too soon when powering; drift it where it feels comfortable rather than coasting; and don't go above 20 Mph.
     
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  5. johnofwessex

    johnofwessex Resident of Nat Pres

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    The Mind Boggles...............
     
  6. gwr4090

    gwr4090 Part of the furniture

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    Strong fore-and-aft oscillation is a feature of all 2 cylinder locos to some degree. Two cylinder locos can not be perfectly balanced - There is always a compromise between residual for-aft out-of-balance forces and vertical forces leading to track hammer blow. Most GWR engines were balanced for low hammer blow, but this leads to shuffling which often coincides with a resonance of the coupling/buffer system at around 20mph unfortunately. It can be reduced to some degree by setting of the regulator especially when coasting. I remember some of the BR Standards (especially the Britannias) were quite bad for this when new, but the balancing was presumably altered.
     
  7. Jamessquared

    Jamessquared Nat Pres stalwart

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    I seem to recall at the time that the preference was not to use 5643 on dining trains unless absolutely essential, as the motion transferred to the leading carriage was considered not ideal. I think the root cause was that they were balanced in a way to minimise hammer blow on possibly poor quality colliery tracks. You don't get anything for nothing though, and minimising up and down hammer blow ends up increasing the fore-and-aft imbalance. Not a problem for their original use, but not especially pleasant on passenger trains.

    Tom
     
  8. paulhitch

    paulhitch Guest

    I am absolutely in no position to comment on technical matters about locomotive balancing and the pros and cons of inside or outside cylinders, Stroudley counter balancing or so on. However for a person with neck vertebra problems (I know one such) an engine like the 0-6-2 tank in question is not only uncomfortable but really painful. Not really suitable for a longer journey IMHO.

    PH
     
  9. Martin Perry

    Martin Perry Nat Pres stalwart Staff Member Moderator Friend

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    I have read elsewhere that the fore and aft motion imparted by some 2-cylinder locos could be alleviated by not tightening the coupling shackle as tightly as possible; rather leaving it a turn or two looser.
     
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  10. paulhitch

    paulhitch Guest

    As I said previously, I am not in a position to comment on the engineering background to this unfortunate problem. However, I have been present when empirical trials of this sort were carried out. Alas, they brought about no improvement.

    PH
     
  11. lil Bear

    lil Bear Part of the furniture

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    Such a method can help soften the effects, but end of the day it all comes down to how the loco is driven.
     
  12. paulhitch

    paulhitch Guest

    Sorry to disagree but at the end of the day it has to be the loco. Otherwise they would all do it which they don't

    PH
     
  13. lil Bear

    lil Bear Part of the furniture

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    Sorry, you've misinterpreted me. It's as per twr12 post #924, whilst a feature of the class the actual impact can be controlled by how the loco is driven. Let them plod and you rarely feel it, I rode behind 6619 at NYMR lots and can't remember ever experiencing her shuttling on that line - but then again she rarely got above 20mph whilst slogging it out up there.
     
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  14. Nigel Clark

    Nigel Clark Member Loco Owner

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    The class were renowned for it (there's an article in a 1960's issue of The Railway Magazine which alludes to this) but driving technique can soften the effects substantially. In fact most of the GWR 'goods' engines are prone to it and I've had some 'interesting' rides behind 5224 and 5239. 3850 used to do it but mainly at 24mph +. As has been said drifting with a little extra steam on and also keeping an eye on speed (plus not screwing up the coupling really tight) can alleviate the worst effects. Loco's are individual, some are more prone than others, but I've heard reports of 5643 shuttling badly whilst on the SVR. There is nothing really that can be done mechanically to alter the situation, what would you have, all such engines stuffed and mounted? It really is up to the driver to handle the engine sympathetically. To close, 6695 has worked WSR trains quite a lot during the 2008/2009 period with no apparent issue and the railway approached us to discuss this long term hire so they must be happy with her. I'm sure that during post overhaul testing we will attempt to find the critical speed where the shuttling kicks-in and then advise the crews accordingly. As I mentioned earlier, the same situation was evident with 3850 but this was dealt with in a similar way.
     
  15. Jamessquared

    Jamessquared Nat Pres stalwart

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    It's some of both. Some locos are worse than others, but as @lil Bear says, driving also has an impact - most Stephenson valve gear locos can be made to hunt back and forwards if driven in a certain way; in particular, trying to run in too short a cut-off at low speed. On the other hand, driving at a longer cut-off often cures the problem and gives a smooth ride.

    As I understand it, the lead (i.e. pre-admission of steam in advance of the piston reaching the end of its stroke) on Stephenson valve gear increases as cut off is shortened. In normal practice (in which cut off would be progressively reduced as speed increased), that is useful, since the lead steam helps cushion the reversal of the piston. At high speeds, the valve is open for lead steam for only a short period of time, so having it open earlier in the stroke before the piston reverses is useful to ensure there is sufficient steam to cushion the change in direction of the piston, which becomes a progressively bigger change of momentum at higher speeds.

    If you run at short cut off but low speed, the valve opens early (because the lead increases with short cut off) but the low speed means that the valve is open for lead steam for a long period of time. The result is an excessive amount of lead steam, which goes beyond simply cushioning the reversal and actively tries to stop the piston moving forward at all. That is felt in a distinct shaking of the loco - the solution is to let the valve gear out to a longer cut off and, if that results in too much power, reducing the regulator opening. In other words, you have to drive with part-open regulator and long cut off, rather than trying to drive with wide open regulator and short cut-off.

    The effect is more pronounced on locos with large wheels, because at equivalent forward speed, the angular velocity of the wheels is less and therefore even with valve gear of equivalent geometry, the length of time in which the valves are open is longer. As an example, on the Bluebell, the P class locos with 3'11" wheels will run quite happily at 25mph and 25% cut-off, but the H class with 5'6" wheels complains if you try to link up beyond about 35% - 40% at the same speed - but at that cut off, it is as smooth as a coach, even with the regulator wide open in second valve.

    Tom
     
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  16. paulhitch

    paulhitch Guest

    Not so dissimilar to ensuring a motor car is driven in the correct gear I suppose. However the problem can be observed with the regulator shut at least as much as open.

    Looking back, the common factor for the offenders encountered was Stephenson valve gear with the worst offender having inside cylinders and the second worse, outside ones. I suppose this js another argument for guards to take the odd trip on the locomotive, with footplate staff riding in the van just so that each may determine the problems they can cause the other

    PH
     
  17. Matt37401

    Matt37401 Nat Pres stalwart

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    WD 600 Gordon wasn't allowed to work the Limited on the SVR for the same reason.
     
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  18. John Petley

    John Petley Part of the furniture

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    In spite of the shuttling issue discussed above, like you, I'm sad 6695 won't be returning to Swanage. It certainly did what was asked of it. Still, like many others, I'm sure, I have some good pictures to remind me of its time in Dorset and enjoyed some good runs behind it too, shake rattle and roll notwithstanding.

    Anyway, living in East Sussex, if I am suffering form 56xx withdrawal symptoms, there's two of them not far away on the K&ESR, although 6619 needs an overhaul and 5668 won't be going anywhere any time soon!
     
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  19. Nigel Clark

    Nigel Clark Member Loco Owner

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    Paul

    It is indeed coasting/drifting when the worst effects become apparent, unbalanced reciprocating masses without sufficient cushioning, but a little extra steam when drifting can significantly reduce the unpleasantness. Under power (unless pulled up too far as mentioned by Tom) there is usually little to notice.
     
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  20. gwr4090

    gwr4090 Part of the furniture

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    As Nigel says, it is more of a problem when coasting than when under power. I don't believe it is anything to do with Stephenson valve gear, crank axle configuration or position of the cylinders, but to do with the wheel balancing. On some engines it is exacerbated because the frequency coincides with a resonance in the buffer/coupling system about 20mph, hence the importance of not overtightening the coupling. I remember the Britannia Class were very bad when first introduced.
     
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