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Bluebell Motive Power

Discussion in 'Steam Traction' started by Orion, Nov 14, 2011.

  1. Hampshire Unit

    Hampshire Unit Well-Known Member Friend

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    Just a slight diversion, 92212 is now in steam at Ropley and due to run on the dining train tonight (2FO's a MK1 Pullman, two MK1 kitchen cars and a BG) without diesel assistance
     
  2. green five

    green five Resident of Nat Pres

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    "Just a slight diversion, 92212 is now in steam at Ropley and due to run on the dining train tonight (2FO's a MK1 Pullman, two MK1 kitchen cars and a BG) without diesel assistance"

    Good to hear. I hope the crew have snorkels as the weather is very foul. I thought they would use the U-boat tonight! Looking forward to the food tonight.
     
  3. Big Al

    Big Al Nat Pres stalwart Staff Member Moderator

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    No problem. Keep it in Sussex and Kent where it's probably one of the only SR locomotives that could go everywhere.
     
  4. david1984

    david1984 Resident of Nat Pres

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    Would you really want to trust a Schools in autumn with NR's linear jungle ?.
     
  5. Big Al

    Big Al Nat Pres stalwart Staff Member Moderator

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    Well, if you overload a Stanier 5 then it won't climb in the autumn. Tangmere is Tangmere and these are the 'go anywhere in Kent' engines so a Schools would be no worse. There is of course the other nine or ten months available, so I don't see the problem, other than, of course, the added cost of getting a Schools main line ready.
     
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  6. david1984

    david1984 Resident of Nat Pres

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    I suppose, just thinking I woulden't envy someone who had the task of restarting a 4-4-0 on a gradient on NR, I remember City of Truro put up a bit of a fight trying to get out of Stratford on Avon.
     
  7. Jamessquared

    Jamessquared Nat Pres stalwart

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    The factor of adhesion on a Schools is pretty low (i.e. adhesion weight divided by tractive effort) - it works out at 3.74. (Low numbers mean lots of force in a small loco, but conversely, put you closer to the edge of adhesion.

    The only loco that I can find that comes close (admittedly a non-exhaustive survey) is a LSWR T3 at 3.87.

    Steve put up some comparable numbers for the NYMR fleet from which:

    Schools - 3.74
    LSWR T3 - 3.87
    LNER K1 - 4.02
    LNER A4 - 4.17
    BR 9F - 4.37
    Maunsell S15 - 4.45
    BR 75xxx - 4.52
    Bulleid WC/BB (*) - 4.53
    LMS Black 5 - 4.64
    BR 80xxx - 4.65

    (*) With 250-psi pressure; with 280psi pressure as built, that number would be close to 4.

    (Steve quotes the reciprocal of these numbers, e.g. TE over adhesion but the principle is identical).

    Of course, the factor of adhesion isn't the only issue - the evenness of torque (e.g. three cylinders vs. two cylinders) and the way the springs are set up and the propensity to transfer weight from front to back on starting will all have an impact. But clearly the raw numbers would tend to suggest that the reputation of the Schools class for being a bit slippery was probably well founded. But you can't have everything - if you want to pack that much power into so small an engine, something is going to give.

    (PS - anyone note the dinky windscreen wipers on the Schools video? :) )

    Tom
     
  8. Seagull

    Seagull Member

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    On the K&ESR we have had problems with poor quality springs and without knowing the history of the Mid Hands 9F I can't possibly comment as to whether that was the cause or not. I'd be a bit surprised if the Bluebell track was an really issue on a loco with a 10 coupled loco as it's not likely to ride badly on dropped joints in the same way that a four or six coupled loco would. I suspect that the more likely cause would be getting on or off the low loader. During loading/unloading there is usually a point where most of the weight of the loco is on one axle. Some owners put wooden blocks between the top of the axlebox and the horns to limit spring movement caused by this, but I've no idea what would have happened in this particular case.
     
  9. John Petley

    John Petley Part of the furniture

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    That's interesting Tom. There's a fascinating anecdote in "SR150" by David St John Thomas and Patrick Whitehouse of an Adams X2, with 7ft driving wheels (and therefore with a lower adhesion factor than the smaller-wheeled T3s) deputising for a failed "Lord Nelson" on the Atlantic Coast Express at Woking in the 1930s. The driver started a 13-coach train without slipping. "They didn't slip, the X2s", was the writer's comment, which seems rather surprising in view of the data you posted above. Perhaps Adams 4-4-0s were more sure-footed than the adhesion factor might suggest. Regrettably, it's unlikely 563 will ever steam again for us to find out.
     
  10. Jamessquared

    Jamessquared Nat Pres stalwart

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    It would certainly be high on my fantasy restoration list...

    I suspect one reason for the relative sure-footedness of the Adam's 4-4-0s, despite the low factor of adhesion, would be because they are not superheated. So you have a relatively direct passage from regulator to cylinders and a small steam chest volume: those factors would tend to give a very direct relationship between opening regulator and steam reaching the cylinders. So the degree of control afforded to drivers is quite precise.

    On more modern and bigger engines, with big superheaters, you can open the regulator and nothing happens for a while until the steam flows through the superheater and steam chest pressure builds. Then, if the loco slips, you can shut the regulator but there is a relatively big volume of steam that has to be used before control is regained. So the prudent driving technique on starting is to open the regulator and then almost immediately shut it until the engine starts to roll, then open it again - there is a big lag between what you do on the regulator and what the engine does. I suspect the more direct relationship between regulator movement and power changes on a small engine like a T3 also gave more confidence for starting big loads.

    Just a theory - would love to have a play on one to find out!

    Tom
     
  11. John Petley

    John Petley Part of the furniture

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    Well, Tom, even if you never have a crack at driving 563, if you stay involved at the Bluebell long enough, you should eventually get a turn on 488, for I'm sure that it will return to steam one of these days. Given it is also unsuperheated and its sure-footedness on the 1 in 40 gradients of the Lyme Regis branch, it presumably also offers that same degree of control for the driver as the 4-4-0s. You wouldn't naturally think of a 4-4-2T, with such a low adhesion weight, as being suitable for such a fiercely-graded line.

    Still, if you ever drive it, you'll need a decent fireman! I recall having a couple of "third man" turns on this engine during my brief time in the loco dept, and when I was given a chance to fire, I found the injectors really awkward compared with those on the rest of the working fleet at the time, and inevitably needed a bit of help fom the fireman who was showing me the ropes (Maybe I was just stupid!). Those were the days! Wish I had as much free time now.
     
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  12. Steve

    Steve Resident of Nat Pres Friend

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    I'd suggest that three cylinder locos are more likely to slip on starting that two cylinder ones. There's a lot said about the more even torque of three cylinders, which is of course true, but only when the loco is on the move. At the point of starting, a three cylinder loco is more likely to be on a low point of the torque curve than a two cylinder loco and, all other things being equal, that low point of torque is much lower than that of a two cylinder one. The peak torque is also much lower. To illustrate this, I designed(?) a three cylinder Black 5 and, to get an equivalent tractive effort it had 15.1" cylinders. It was discussed further on Nat Pres a couple of years ago. Why are they more prone to slipping at starting? To get the starting TE necessary to get a train moving from rest, you probably have to have full pressure of steam in the cylinder and, as soon as all three cylinders are doing their bit, you have too much TE, which on a slippery rail, leads to the inevitable. With two cylinders, you stand more chance of getting away with a lower steam pressure. As I said then, Harry Holcroft certainly appreciated the poorer starting characteristics of a three cylinder loco. (See Locomotive Adventure)

    You can see more of the detail by going to http://www.national-preservation.com/threads/2-cylinders-v-3-cylinders.34703/#post-460256
     
  13. jma1009

    jma1009 Well-Known Member

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    hi steve,
    as a devout harold (not harry) holcroft devotee, i think you have mis-interpreteded what he wrote about 3 cylinder locos. he was a fervent advocate of same. the problems with the SCHOOLS class at London Bridge were due to the piston valve design. hence the subsequent alteration to the piston valves. it stands to reason that a 3- cylinder loco with a more even turning movement is much easier to start .
    cheers,
    julian
     
  14. Big Al

    Big Al Nat Pres stalwart Staff Member Moderator

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    I agree that regulator technique is the secret to starting a heavy train. Given the fact that, for example, Clan Line regularly moves around 500 or so tons it is interesting that she seldom does much more than turn the wheels around a couple of times when getting under way rather than some of the more spectacular and seemingly uncontrolled slips that YouTube is full of. Good crews understand and know how to handle steam flow and the purpose of the steam chest gauge is to use it to do just that as well as control what is going on at high speed. It makes for the more efficient use of steam and that, of course, is why it is on the driver's side! Stowe has one of these so as I said earlier, whilst the adhesion of a Schools may be lower than others, slipping and grip shouldn't be a problem for those who can.
     
  15. green five

    green five Resident of Nat Pres

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    "Just a slight diversion, 92212 is now in steam at Ropley and due to run on the dining train tonight (2FO's a MK1 Pullman, two MK1 kitchen cars and a BG) without diesel assistance"

    92212 didn't make it on to the MHR Dining train last night. She was standing cold in the yard at Ropley. 31806 and a Diesel top and tailed the dining train.
     
  16. Steve

    Steve Resident of Nat Pres Friend

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    Agreed that the particular problem with the Schools getting started at London Bridge was largely put down to the valve design but, as Holcroft stated, the effort also required high steam pressure, which was the essence of my argument. At starting you effectively only have one cylinder producing most of the torque and that cylinder, being one of three is smaller than the equivalent cylinder of a two-cylinder loco so you need a higher steam pressure in the cylinder. Once on the move and the other cylinders kick in, you have a lot more torque and a greater propensity for slipping. You need to be a dab hand on the regulator to control the steam because of this characteristic. I'm sure that Holcroft also made comment about Gresley three-cylinder locos but I can't find it. Perhaps it's in an ILocoE paper discussion somewhere.
    The Bulleid Light Pacifics have a relatively high factor of adhesion yet they have a reputation for slipping at starting and my contention is that it is due to having three cylinders rather than anything else. In a similar way, I find 61994 to be much more temperamental at starting than 62005 but, once on the move, they are both sure footed.
     
  17. banburysaint

    banburysaint Member

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    A schools is pretty capable once set up correctly, Repton on the NYMR seemed to be able to cope, plus it went mainline even if Whitby might be considered as cheating! Good news is that she is being assessed for overhaul too.
     
  18. 21B

    21B Part of the furniture

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    It wasn't rostered to the Dining train to start with. It was being warmed through.
     
  19. green five

    green five Resident of Nat Pres

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    "It wasn't rostered to the Dining train to start with. It was being warmed through."

    Sorry 21B, only going by what Hampshire Unit posted on the thread.
     
  20. Paul.Uni

    Paul.Uni Well-Known Member

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