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A question about G.W.R. engines

Discussion in 'Steam Traction' started by 240P15, Dec 11, 2017.

  1. Railcar22

    Railcar22 New Member

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    The farting sound you hear from a GWR steam loco is the realease valve for the braking system. When the vacum gets above 25" Mercury the valve releases a small amount of air into the vacum system to bring the vacum back down to 25" of Mercury. Our GWR Diesel railcar does it all the time, as we get 27" of Mercury
     
  2. 240P15

    240P15 Member

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    Thanks a lot for your explanation Railcar22! :)

    Knut
     
  3. MG 7305

    MG 7305 New Member

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    Thank you for this. I am looking at my "Handbook for Railway Steam Locomotive Enginemen"(1977 edition) p 150 fig 68. According to this diagram the only time a vacuum limiting (pepperpot?) valve would be in communication with the brake ejector would be when there is full vacuum in both the train pipe and the reservoir. The routing being vacuum limiting valve on the vacuum pump, retaining (triple) valve and thence to the train pipe and ejector. Have I got this right?


    Incidentally, is the lack of the retaining valve on combined steam and vacuum braked locomotives the reason that panniers and so on do not make this noise?


    Best regards


    Julian
     
    Last edited: Aug 25, 2019
  4. 1472

    1472 Well-Known Member

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    Firstly panniers and others fitted with the combination brake valve are capable of making this noise which incidentally appears magnified at the chimney. Not sure how that works on Railcar 22!!

    When the vacuum is first created the ejector is exhausting the train pipe & by drawing air past the IR band (on the brake cylinder piston) it also exhausts the reservoir side as the IR band shape makes it act like a one way valve. There are two vacuum limiting valves, one set at 25" on the air pump which is normally part of the train pipe system. The other valve is on the reservoir side and is set to 23". When a brake application is made the action of the pump is changed so that it continues to evacuate the reservoir side (thereby maintaining the force of the brake against any res side leaks). The retaining valve is the device which makes this happen and the difference between the 25" train pipe vacuum and 23" reservoir vacuum is essential to make this work properly.

    Recreating the train pipe vacuum using the ejector restores the retaining valve to the train pipe position for the air pump.

    Note the pump attached to the RH crosshead is strictly an Air Pump (as so described on the drawings) as it pumps air out of the system. Also a triple valve is part of an air brake system not vacuum.
     
  5. 240P15

    240P15 Member

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    Note the pump attached to the RH crosshead is strictly an Air Pump (as so described on the drawings) as it pumps air out of the system. Also a triple valve is part of an air brake system not vacuum.[/QUOTE]


    I guess it is this pump that gives this "phit-phit-" sounds (or how should I discribe it) while the engine is running?

    Knut:)
     
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  6. 1472

    1472 Well-Known Member

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    I guess it is this pump that gives this "phit-phit-" sounds (or how should I discribe it) while the engine is running?

    Knut:)[/QUOTE]

    Yes - the action of drawing small amounts of air out of the system & then exhausting it to atmosphere is what causes the sharp ticking noise as the valves lift and then return to their seat.
     
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  7. 240P15

    240P15 Member

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    Yes - the action of drawing small amounts of air out of the system & then exhausting it to atmosphere is what causes the sharp ticking noise as the valves lift and then return to their seat.[/QUOTE]


    Thanks! :)
     
  8. CH 19

    CH 19 Member Friend

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    Out of curiosity, I have noticed on most of the GWR locos that I have encountered, a vertical plate that rises from the rear of the crosshead guides to the boiler. At first I thought it was a boiler support but is it reinforcing for the crosshead guides. Hope I have the terminology right.
    I have not seen this on any other railways loco's and wondered if this was another GWR individualistic touch.
    Thanks

    Chris
     
  9. Jimc

    Jimc Part of the furniture

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    Its basically just the motion bracket, but my understanding is that the extension upwards provides support for the boiler if anything goes wrong at the front end. Its pretty much confined to the two cylinder types with extension frames. I don't believe there's any such arrangement on the Castles and Kings with through frames. I can't quite satisfy myself, with what I've been able to find quickly, whether the support is there on the modified Halls and 460 Counties, which also lacked extension frames.
     
  10. CH 19

    CH 19 Member Friend

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    Thanks for that, my interest was piqued when I saw a photo of an unclad boiler from a tank engine at the ESR and could not determine any fixing points.
    Chris
     
  11. Railcar22

    Railcar22 New Member

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    I guess it is this pump that gives this "phit-phit-" sounds (or how should I discribe it) while the engine is running?

    Knut:)[/QUOTE]
    Yes it is. The GWR designed it as a steam saving device, where the vacum is matined via a mechanical pump. Apart from Stanier designs, all other railway companies in the UK, used steam to maintain vacum during the course of each run.
     
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  12. Jamessquared

    Jamessquared Nat Pres stalwart

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    Wasn’t only Stanier on the non-GWR companies who used mechanical vacuum pumps - Maunsell fitted them to his engines (*). They were removed in the early 1930s, presumably because the hoped for savings in steam consumption didn’t balance the extra maintenance cost.

    Notable that in the same way Stanier was no doubt influenced by his prior time at Swindon, presumably the Southern connection was via Holcroft’s experience under Churchward.

    (*) certainly some of the King Arthurs and moguls; probably the H15s as well but I am away from references to check.

    Tom
     
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  13. 240P15

    240P15 Member

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    Stanier`s engines (at least some of them) had this mechanical pump mounted below the cylinders if I`m right?

    Knut :)
     
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  14. gwalkeriow

    gwalkeriow Well-Known Member

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    They were below the slide bars.
     
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  15. 240P15

    240P15 Member

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    Whilst we talking about vacuum brakes, I have read some place that some sort of "silencer" were tried out to reduce the loud noises from the vacuum ejector. Is this corret or I`m wide off the mark?
     
  16. LMS2968

    LMS2968 Well-Known Member

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    The LNWR also used a crosshead driven vacuum pump to maintain vacuum. This was a result of an agreement between the LNWR and GWR allowing the patent's use in exchange for the GWR's free use of water troughs and pick-up gear, a John Ramsbottom invention for the North Western. Quite a few early LMS types got the pump by this route before Stanier arrived, so the origin of the pumps on his early engines isn't so straight forward.
     
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  17. marshall5

    marshall5 Well-Known Member

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    I've seen some on Austrian narrow gauge locos but not in the U.K. AFAIK.
    Ray.
     
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  18. ross

    ross Member

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    Certainly a silencer was a feature of the Eames vacuum brake ejector used on a number of US narrow gauge locomotives. Typically the silencer was a sort of "tin can on a stick" affair, visible above the cab roof.
    [​IMG]
     
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  19. Hirn

    Hirn New Member

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    Thank you very much for this, I hadn't realised that the narrow gauge there used vacuum breaks, though I did know they were common on the steam hauled
    elevated railways.
    Presumably where there was through running a standard break - which came to be air pressure - trumped any other considerations.
     
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