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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. pseudonym

    pseudonym New Member

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    Would it be possible to simplify things and reset ex-GWR engines to 21"? Or, would this have detremental ramifications such as seriously reducing the brake force?
     
  2. Kerosene Castle

    Kerosene Castle Well-Known Member

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    Experience at Didcot has shown that when putting engines through the works, unless absolutely necessary, leave the pump alone!

    Regarding reservoirs leaking off, there is a minimum recommended time for this to occur in, but for the life of me I cannot remember what it is. I believe it may be 45 seconds, but in any case it's probably in MT276 (or whatever it's called today). About 18 months ago there was trouble with the res leaking off very quickly on 5051. It took an age to find the cause, in the end I recall it was just a duff O-ring on top of the brake cylinder. This of course was after the band had been replaced, hoses changed, and endless use of a flare lamp...
     
  3. howardw-s

    howardw-s New Member

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    The problem we have on the KESR with 1638 is that if we reduce the setting on the vacuum relief valve to 21" so that it isn't possible to over create with the ejector then the tension on the valve spring is so low that the valve pops open and closed as the air pump reciprocates and we can't get 21" with the pump! I suppose a non GWR relief valve would help.
     
  4. Steve

    Steve Resident of Nat Pres Friend

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    If I remember correctly, in its first return to service 6619 ran with 21" vacuum and didn't present too much of a problem. The theoretical reduction in brake power is about 20% but as GW loco vac brakes are next to useless anyway, that didn't make too much difference! Having 25" gives you a few moments longer before the brake leaks off!

    Just wonder how things would work the other way round and standardise on 25". I believe that the BR standards and other locos operating on the GW lines were set to 25". Am I right in this ? Certainly mk1 coaches are no problem!
     
  5. howardw-s

    howardw-s New Member

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    The problem there is that many ejectors struggle to reach 21", let alone 25! We wouldn't get a reduction in brake power on 1638, she has a steam brake, the vacuum is only for the train.
     
  6. Rumpole

    Rumpole Part of the furniture

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    This reminds me of a question someone posed a while ago about the times that pannier tanks were doing ECS workings between Clapham Junction and Waterloo, which I don't recall being answered at the time.

    Were they modified in any way to prevent them creating more that 21", or were they forever being cursed by the traffic department for all that string pulling at such a busy terminus?
     
  7. standardman

    standardman New Member

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    According to GWR literature, locos regularly working with other regions stock could be (and were) fitted with a differerent vacuum relief valve which retained vacuum at 21"
    Instructions for double heading stated that the GWR loco should restrict the amount of vacuum created in the train pipe by partial opening of the vacuum release cock in the cab thus preventing over creation of the vacuum and risk of the brake dragging.
    It was always preferred that the GWR locomotive was leading, to minimise the risk of overcreation of the trainpipe (the Vacuum relief valve on the train engine restricting the vacuum in the train behind it to 21")

    I used to think that it was just because the GWR thought they were superior and therefore their locomotives should lead out of principle!
     
  8. George

    George New Member

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    According to GWR literature, locos regularly working with other regions stock could be (and were) fitted with a differerent vacuum relief valve which retained vacuum at 21"
    Instructions for double heading stated that the GWR loco should restrict the amount of vacuum created in the train pipe by partial opening of the vacuum release cock in the cab thus preventing over creation of the vacuum and risk of the brake dragging.
    It was always preferred that the GWR locomotive was leading, to minimise the risk of overcreation of the trainpipe (the Vacuum relief valve on the train engine restricting the vacuum in the train behind it to 21")

    I used to think that it was just because the GWR thought they were superior and therefore their locomotives should lead out of principle!,

    Hi, would it be possible to get a copy of the literature to which you refer?, I am happy to meet all costs etc,

    regards, George
     
  9. tuffer5552

    tuffer5552 Member

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    Double heading is easy, it doesnt matter which engine makes the brake, the pepper pot on the non superior....sorry i mean non GWR engine, would keep it down to 21 inches. If the gear is set right and working reliably then it'l work right.
    The problem is when a GWR engine has worked a train single handed and then a non GWR engine joins or replaces it. In this occasion the "strings" on the coaches would have to be pulled to release the vacuum from the top of the cylinders. This is the vacuum that holds the brakes on. If this isnt done, then on a good system, when the brakes are blown off to 21 they will still hold a little, as there are 4 inches on the other side. This may make the wheels drag, at best just making the train heavy, and at worst sliding the wheels, etching flats into them.
     
  10. twr12

    twr12 Well-Known Member

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    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.[/quote:21h56v5l]

    220 general lube, completely useless in gWR vacuum pumps. Tried that 50/50 paraffin/gen. lube mix. All that happens is the trimming picks up the paraffin in the morning, then the general lube in the afternoon, and the pump stops working because the clacks stick.

    Compressor or vacuum pump oil works nicely. Thin oil that can take loads of heat. Available from your usual oil supplier.
     
  11. Jimc

    Jimc Part of the furniture

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    Back in the day AIUI there was also the question of running costs. Again AIUI an ejector pulling 25" would use a shed load of fuel, whereas a Vac pump pulling 25 was cheaper to run than an ejector pulling 21...
     
  12. Pannier Man

    Pannier Man Member

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    Don't forget the delights of having your steam brake come in hard on a GW loco with a combination brake when the lead loco drops the vacuum a bit too low!! 8-[
     
  13. James Green

    James Green New Member

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    I have know GWR ejectors to be quite noisy.
     
  14. Nigel Clark

    Nigel Clark Member Loco Owner

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    As twr12 says, at Swanage we use a thin compressor type oil in the pump lubricator, this seems to work quite well. With regards the retaining valve, yes it gets full of gunk and needs regular cleaning to prevent the valve sticking.

    Another issue with the pump is the amount of leakage on the rolling stock you're hauling; the pump will only overcome a small amout of leakage. Apart from sticking air clacks another major cause of a weak pump can be the pump-rod gland leaking by so you end up with it pumping out at one end only.

    GW loco vac cylinders have a flat rubber 'band' around the piston head, can be tricky to get these to sit properly when putting the piston back in the cylinder apparently. Any rust/rough surface on the cylinder wall will shave/tear the band giving you leakage past the head.
     
  15. burnettsj

    burnettsj Member

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    Surely that's a problem with the stock, not the engine?
     
  16. James Green

    James Green New Member

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    When you blow it up to 25 inch do you then shut the ejector once you are on the move?
     
  17. 1472

    1472 Well-Known Member

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    Yes once you are moving.

    Those inexperienced with GW locos waste water/steam/coal if they dont!
     
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  18. baldric

    baldric Member

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    A good ejector should create 25in of vacuum, personally once the train is moving I shut the ejector off, the pump should maintain the vacuum but this depends on how much of a leak there is, speed and wheel diameter. A small wheel means the pump will pump more for a given speed than a large wheel. If the vacuum starts to fall just top it up with the ejector, saves stewm compared to having the ejector open all the time and is quieter.
     
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  19. James Green

    James Green New Member

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    And deafen everyone!
     
  20. threelinkdave

    threelinkdave Well-Known Member

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    I'm new to this forum so this issue may welll have been addressed elsewhere. Had a GW loco tailing an 8 coach train with an SR leading. My brake in the middle of the train showed 23 inches soon after starting off. The pepper pot was probably working but over 8 coaches there was a gradient with 25 at the back likely. Stops were not smooth. When the GW engine cast off at Bewdley pulled the strings and all was then OK
     

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