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Double heading GWR with none GWR and brakes

Discussion in 'Locomotive M.I.C.' started by odc, Oct 12, 2007.

  1. odc

    odc New Member

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    I have just been watching a video of 2968 and 7325 (SVRs Stanier and Collet Moguls) double heading on the mainline back in 1997 when air brakes were not even considered. 2968 was leading. My question is in this senario, double heading a vac braked train with a GWR loco as the train engine, how are the brakes managed.

    In FR practice at least the leading engine manages the brakes of a double header and the train engine dosen't run its ejector. If, when running like this, 2968 is controlling the brakes, how can it release the brakes on starting, as 7325's crosshead pump will have been drawing 25'' instead of 21'' and so the LMS ejector, not calibrated to run that high, would not be able to fully release the brakes.

    (My understanding is that the vac pump can not be "switched out" and that an ejector is colibrated so that it will have diffeculty drawing much more vac than the system intended)

    Of cause the solution is to run the WR engine on the front, but they didn't.

    Thoughts on a postcard...........................
     
  2. Nexuas

    Nexuas New Member

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    I would assume the the GWR engine would be in charge of creating the vacum, with the stainer engines ejector turned off. But with the stainer (leading engine) responsible for brake application. The brake valve should still destroy the vacum without the ejector running? This is only true if as you say the GWR crosshead pump can not be switched out of the system?
     
  3. John Elliot Jnr

    John Elliot Jnr New Member

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    Wouldn't the Stanier's vacuum relief valve restrict the whole train pipe pressure to 21", no matter whether it was pilot or train engine?
     
  4. JAmieNWR

    JAmieNWR New Member

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    You are quite right John, I was on the NVR's thomas last year during the "steam gala" and we topped and tailed the DMU with 9466.
    Thomas's vacuum relief valve held the vacuum at around 21-22 inchs of murcury whilst 9466's vacuum pump and ejector tried to pull the vacuum to 25 inchs.

    I am baseing this information on my first hand experiance at the NVR and the other railway's I've been involved with.
    please excuse my spelling as I cannot spell very well.
     
  5. olly5764

    olly5764 Member

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    Quite correct, the Pepper Box on the LMS engine will restrict the vacuum to 21 inches, irrespective of how the Vac Pump on the Great Western loco is running. It is possiable that the small ejector on the LMS loco may have been shut off, but on longer trains, i doubt it
     
  6. Dave Roderick

    Dave Roderick New Member

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    Don't know about the technicalities, but the same thing happened back in July on the East Lancs, when 60019 Union of South Africa and its support coach piloted City of Truro from Bury to Heywood in order to get a path back onto the main line. Seem to remember there's a picture of it somewhere on here.
     
  7. southyorkshireman

    southyorkshireman New Member

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    Okay next question, depending on how far the vacuum relief valve is from the pump, can this not lead to a variation in pipe / reservoir pressure along the length of the train?

    i.e. if the GWR is on one end and LMS the other, would the vacuum be greater at one end than the other?



    Hasn't there been instances of this on the mainline this year when 50049? was top and tailed with 5051 and 4965 at different times.
     
  8. Steve

    Steve Part of the furniture Friend

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    There is going to be a variation in vacuum throughout a train pipe, depending on where the vacuum is created and where it is measured. If memory serves me correctly, the rearmost guards van must register a minimum of 18" (17" on a goods train, or 16" if more than 20 fitted wagons), and the loco should not be creating more than 21" (GW locos excepted). The critical thing is whether the brakes come off fully, or not, and drivers soon get a feeling if the brakes are dragging.
     
  9. John Elliot Jnr

    John Elliot Jnr New Member

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    Quite possibly, if the tail loco had an air pump (never vacuum pump on the GWR! "You can't pump vacuum!" they always tell us.) The vacuum over the length of a long train is actually quite 'elastic'. The train pipe gauge on the locomotive of any train registers the pressure only on the locomotive. When blowing the brakes up after an application, although the gauge on the engine can quickly be back to 21", the pressure some 12 or so coaches back can still be at 10 or 15". A driver once told me that the train pipe pressure differential between the loco and the back end of the Bournemouth Belle set was so acute they had be careful not to pull the train in half when accelerating from a slack! So, with a long enough train and with a GW engine tailing I reckon you could achieve 25" at the rear and 21" at the front. Never thought of that one before...
     
  10. southyorkshireman

    southyorkshireman New Member

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    If the GWR was then taken off the back, would it possibly be necessary to pull the strings and recreate vacuum just to make sure the 21" at the front can release the brakes throughout?
     
  11. John Elliot Jnr

    John Elliot Jnr New Member

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    If the GW engine's managed to get more than 21" into the chamber side of the brake cylinders then the guard (not our problem, guv) will have to pull the strings.

    This isn't a situation I've ever experienced, but come to think of it surely the first sign of trouble would be binding brakes out on the road. There'd be problems immediately after the initial application if the reduction in speed meant that the crosshead pump was no longer working at a fast enough rate to maintain the vacuum differential. It wouldn't then be able to release the brakes it had previously charged to more than 21", and of course neither would the leading engine. It would be interesting to hear from anyone who's actually had this problem.
     
  12. Steve

    Steve Part of the furniture Friend

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    Vacuum problems with the GW tanks are quite common on the NYMR. Being alien things we probably don't know how to use them properly (!) but life is much easier with the more conventional arrangement of large and small ejectors. If we are simply double heading there is generally no problem as the 21" loco will control the vacuum. If the locos are top and tail with the GW on the back then the driver will just crack the realease cock to stop it over creating. The biggest problem I find with the GW ejector/pump arrangement is that the ejector will over create if it is left on, say whilst the guard is doing a brake test, and can get up to 27" and the pump will under create at lower speeds, only managing about 23-24. You then have to keep supplementing it with bursts of using the ejector to stop the brakes from dragging. The other horror, when light engine, is that the GW chamber side vacuum leaks off very quickly and, if the retaining valve doesn't change over you soon lose your braking if you don't keep a very watchful eye on proceedings. Do the more GW orientated lines (ie WSR & SVR where they are more used to the system) have this problem?
     
  13. olly5764

    olly5764 Member

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    This is quite true, it is not unknown for a loco to apply the brakes on approaching a signal, only for the peg to come ofdf, and the loco to be busy trying to re-create the vacuum, and for the guage in the van still to be falling!
     
  14. jtx

    jtx Member

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    Yes, mate. Can be a bit scary, if you're not alert. I was shunting stock in Eardington siding (1 in 100) a few years ago with Bradley Manor and the reservoir was leaking off quite rapidly. It means your fireman has got to be a bit bloody quick with the handbrake, when all the vehicles in front of you are loose-coupled wagons and your shunter has got to have his wits about him. As has been said earlier, when working double-headed LMS and GW, the LMS engine's pepper-pot valve will regulate vacuum to 21", regardless of what the G.W. engine's vacuum pump does.
     
  15. hassell_a

    hassell_a New Member

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    I'd echo John's comments about the resevoir side leaking off - they shouldn't in practice, so if it is it should be booked/investigated. Like most things, it varies from engine to engine - the last few times I was on 7802, the resevoir wasn't holding up well at all; whereas on 5164 there is still 17" on it 10 mins after you destroy the train pipe side.

    Vacuum pumps, should maintain 25" once you get to 10 or 15mph, but when doing the 1st brake test of the day, I tend to only create about 23" with the ejector, so if the pump is an inch or 2 short, you haven't over created. If all is well, the pump will soon pump up to 25".

    Traditionally the pump should be lubricated with neat lube oil, but at the lower speeds preserved lines operate at, I find a 50/50 mix of lube with paraffin works well as the pump doesn't get as warm. If cold thick oil gets right around it, that is when 1 or more of the air clacks may stick - then you definitely won't get 25"! If a stuck clack won't clear,a squirt of neat paraffin in it will often work. I have seen people put neat paraffin in the pump lubricator, but I would think that this would have the effect of flushing all of the lubrication out - which doesn't sound like a good idea to me!

    Likewise, the retaining valve can be prone to collecting gunk (shavings of rubber brake hoses and the like) around it - it is usually fairly easy on a pit to undo the cap on it and clean it out if this is happening. If it sticks while you are out on the road, opening the resevoir relief valve with the train pipe at 25" should free it - not to be tried in the light engine scenario above though!!!

    Like most things with steam engines, when the pump/resevoirs are set right, they are great - when they're not, it's a pain in the a*se!

    Adrian.
     
  16. boldford

    boldford New Member

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    Adrian
    I think you'll find a number of our retaining valves are getting a bit ropey now (so much mileage!) hence the new'un(s) been machined by Harold after I'd got the main body pattern to work properly.
    Brian
    Known to lead to brown trouser moments!
     
  17. Steve

    Steve Part of the furniture Friend

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    I guess I'm comparing the longevity of chamber side vacuum with our other vacuum braked locos, such as the Schools and S15, where you'd normally expect to have 10-15" still in the chamber the next day! Just been on 61994 and that holds up for ever, as well.
    It can take several minutes to carry out a full brake test, during which the ejector has to be on whilst the guard checks all the brakes have released properly, so it's quite difficult and time consuming to fiddle with the ejector to keep it down to less than 25. Plodding up to Goathland the speed is generally around the 15mph mark so the pump doesn't really get into its stride.
    We use a 50-50 mix on our GW locos. Often wonder whether a straight hydraulic oil would do a better job, though.
     
  18. hassell_a

    hassell_a New Member

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    Not being overly familiar with most Southern or Eastern (it's been 10 years since I was on the Marquess) engines, do you know if the brake cylinders have a rolling rubber ring like mk 1's or a trapped IR band like Western machines - just curious really, as that could be why the resevoir on Western engines seems to leak off quicker. Or it could all be down to maintainence! How do you WSR/Llangollen crews find them?
     
  19. Steve

    Steve Part of the furniture Friend

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    Don't know is the answer but I'd bet a king size Mars Bar that they're rolling rings! Can someone else confirm or do I have to ask others who've stripped them down next time I'm at Grosmont?

    I'm full of respect for those poor GW drivers who had to take a 56XX down the Valleys with a few hundred tons of minerals behind them! Rather them than me.
     
  20. P&JR

    P&JR New Member

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    As far as I'm aware it was only the GW who had the obsession for rubber flaps rather than rolling rings. Certainly never come accross them on LNER/Southern/LMS rolling stock. Only got a few GW style vac cylinders on the TR and they're the ones that give the agro - although I have to admit they are running at 21in now.
     

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