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Vac Brake Application Valve

Discussion in 'Steam Traction' started by CymruGarratt, Apr 29, 2019.

  1. CymruGarratt

    CymruGarratt New Member

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    Can anyone assist please? I'm looking for a driver's vacuum brake application valve, possibly d.m.u. type, for use on an Austerity saddle tank I'm helping to restore. If someone can point me in the right direction I'd be very grateful.
    C-G
     
  2. Steve

    Steve Part of the furniture Friend

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    Charles Adams used to supply a neat valve designed for industrial locos. Not sure how to contact him now, though. Alternatively, a ball valve is just as good, if not as railway like
     
  3. gwalkeriow

    gwalkeriow Well-Known Member

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    I saw Charles last Friday, should I ask him?
     
  4. CymruGarratt

    CymruGarratt New Member

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    Thanks, it certainly wouldn't harm. We already have a simple on-off pepperpot valve in place, but have been told on good authority we need the three position type that is on-off-lap. Ideally the ejector steam supply needs to be cut off when braking so that it isn't working against the system, as it were.
     
  5. gwalkeriow

    gwalkeriow Well-Known Member

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    PM sent with email address.
     
  6. weltrol

    weltrol Member

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  7. Steve

    Steve Part of the furniture Friend

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    Well, that wouldmake a lot of vacuum braking systems far from ideal, then. I would go back and ask the good authority why it is so important to cut off the ejector from the train pipe. I don't think any system isolates the steam supply to the injector, by the way. LMS ones don't isolate the ejector and BR vacuum brake valves only do it when a full application is made, which on a heritage railway is likely to only be in an emergency, otherwise the braking will be quite severe. The same applies to Dreadnought and SJ brake valves. Charles Adams brake valve is one that simply lets air into the vacuum pipe and does not isolate the ejector. Such systems are fitted to majority of industrial locos.
    If you still want to pursue a valve which cuts off the ejector from the train pipe, you can do it with a three port ball valve relatively cheaply.
     
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  8. CymruGarratt

    CymruGarratt New Member

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    Thanks Steve,
    That's an interesting take on matters. Perhaps the advice we've been given is in error, or perhaps over-elaborate for our needs. At most our loco will be hauling 4-5 Mk 1s at 20-25 mph on a preserved railway, so an over elaborate system is probably not required. It might save us a few pennies too!
    Thanks for your advice!
     
  9. brennan

    brennan New Member

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    A DMU brake application valve looks nice but an industrial ball valve will do just as well as the design provides adequate proportionality. I assume you are using a penberthy type ejector. You will get 21 inches on five coaches but it will be a bit slow and if your drivers are used to a Gresham and Craven or GWR type of ejector there will be a learning curve. Make sure you install the ejector with the train pipe connection at the top otherwise they are prone to filling the train pipe with water and also fit a drip valve to the lowest point of the loco train pipe. A pressure gauge between the steam control valve and the ejector will help matters as it can be marked with the most appropriate pressure that is found by trial. Penberthy ejectors work at 60 psi and too much steam will throttle the nozzle and you get less vac, not more. As boiler pressure drops ( should, of course your fireman allow this!) the driver can adjust the pressure accordingly. Opening the application valve will easily overcome the ejector and the brake can be "set" in the normal manner to achieve a controlled stop. Bear in mind that , unless you have also fitted a vacuum brake cylinder to the loco, all the braking is done by the train and while five coaches will stop it, one coach on a wet rail won't.
     
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