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Thread: J3A Hudson Steam Generation vs Usage

  1. #11
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    Default RE: J3A Hudson Steam Generation vs Usage

    Thanks for responding Jorge. In the US we generally refer to the safety valves as pop-offs because of the way they sound when they start releasing steam. And they can use quite a bit of steam, depending on how much the engine is being overfired for its needs.

  2. #12
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    Default RE: J3A Hudson Steam Generation vs Usage

    Jorge

    Thanks for clarifying the term for me. I had a feeling that Bill was referring to safeties, but needed to be sure.

    Bill

    Agreed that they can use a fair bit of steam when operating, but then that is their role, to ease the pressure. I think that Jorge has put his finger right on the spot here. If the differential between lift and reset is too big then there will be a major loss of steam during the safety operation. If you look at the default scotsman the pressure difference is 5 which can lose you a fair bit of hard won steam. The ESE and the Hudsons from the American classics set are set at 2 which makes for a much shorter lift time.

    The other major source of usage being the injectors can also be controlled to a degree by choosing smaller sizes to run with, or just using one of the larger size whether under Otto or Manuel control.

    Beer is not a matter of life and death. It is much more serious than that.
    mervyn.

  3. #13

    Default RE: J3A Hudson Steam Generation vs Usage

    I think I will keep posting in this thread. Sorry Bill but you are a good teacher!:-)

    Besides the quantity of steam spent on basic, injectors and safeties, you have to consider something Bill has pointed you out before, and that is very important in your design: the ideal fire mass.

    He mentioned that if you overburn, that is, if you constantly have a fire mass bigger than your ideal mass (by shoveling more coal than needed, your boiler produces too much steam and safeties open (and shut) quite frequently.

    In my Renfe 240-2591 (second version already up, but not in flightsim yet) in which I have to say Bill Hobbs has most of the good working resposibility of this engine, I decided to set my intital fire mass below the ideal (in the EngineVariables). This way the safeties won't pop-off upon starting the activity.

    But at the same time, this can put me into trouble because you have to start shoveling coal (R) to increase your mass near to ideal.

    Sometimes in the activity start-up I have forgotten to do this, and at the same time I have opened the regulator too much (without lowering the cut-off enough), depleting the steam in my bolier, the pressure goes much below working limits and then it will take a hell of a time to get to working pressure again. So you have to watch steam usage vs steam generation.


    Jorge

  4. #14
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    Default RE: J3A Hudson Steam Generation vs Usage

    Most of the locos I have been working on lately have been for mountainous terrain where extended grades of 2% or better (4% in one case) have to be tackled. That means running the loco full bore for long periods of time: throttle wide open, cutoff very wide, injectors on continuously, and continual firing. Under those conditions, having some "room" for the injectors and other non-exhaust uses of steam make a difference. If you have to stop the injector for too long to keep pressure up, you may melt the fusible plugs!
    On the prototype Cumbres pass run (4% most of the way), the poor fireman just opens the injectors and then shovels as hard as he can for the 1 1/2 hour ascent! There are 40sq ft grates on the K36's and 48sq ft on the K37. Those are hungry fireboxes. His only break on the way up is at the Cresco water tank.

  5. #15
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    Default RE: J3A Hudson Steam Generation vs Usage

    Jorge

    The firemass in all three places in the eng file are critical to the successful running of an engine whether auto or manual firing is used. The difference between Max and Ideal, if too large will seriously hamper the required generation of steam, especially when using Auto firing.

    Bill, I have come to the conclusion that your extra in boiler capacity and the UK method of extra in the exhaust capacity are coming at the same thing from opposite ends.

    What tonnage are you hauling up those grades, which engine type and at what kind of speeds?

    Beer is not a matter of life and death. It is much more serious than that.
    mervyn.

  6. #16

    Default RE: J3A Hudson Steam Generation vs Usage

    >Jorge
    >
    >The firemass in all three places in the eng file are critical
    >to the successful running of an engine whether auto or manual
    >firing is used. The difference between Max and Ideal, if too
    >large will seriously hamper the required generation of steam,
    >especially when using Auto firing.........

    Mervyn,

    Whatever I am saying here is with Auto off. I don't like running a steam engine with auto, except if the ENG has a wrong design.

    The value that is important is the ideal fire mass, which will depend mainly of the grate dimensions. You should stay as close to the ideal fire mass value as possible. Other than that you will be overburning or experiencing a lack of power.

    The value in the EngineVariables is your start value. The normal start up value should be the same as the ideal, but maybe you want to simulate a cold engine. You can do that, but it doesn't work well in MSTS, because you have zero fire mass but with the starting pressure.

    The maximum fire mass should be such a value that beyond that, you can't increase the mass even if you shovel more coal. However in MSTS when the fire mass depasses the maximum fire mass value, the pressure suddenly increases, the safeties open and it stabilizes a few Kg/cm2 (or psi) beyond the maximum pressure (the safety setting) above a possible melting point. In my opinion this is not right in MSTS, but you guys can correct me if I am wrong.

    BTW, no matter what value you have set to start the activity, the temperature will decrease as you shovel coal. It's normal as you have more fuel for the same amount of oxygen. What it isn't is that the temperature rate increase is the same. As you stop shoveling temperature increases again (you are not suffocating your fire anymore).

    Not everything has been said about the EngineVariables in this forum, as Bill and I have discussed before.

    Jorge

  7. #17
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    Default RE: J3A Hudson Steam Generation vs Usage

    Mervyn,
    For locos based on specific prototypes, I have tried to see if prototype tonnages could be hauled. Since these tend to be older locos, many times the tonnages will not seem impressive by modern standars: 180tons, etc. The speeds can drop to between 6 - 10mph with the cutoff set at whatever is just below slipping. Using F_Calc2 friction, you can see that it is a battle to stay ahead of the exponentially increasing friction that sets in below 6 mph. If you hit that, everything can be lost.
    You mention a wide variance between Ideal and Max fire masses. I have tended to keep the difference smaller so that it is easier to drop the steam generation rate when the loco is not working hard. This makes it more critical to keep the fire near the ideal level when working hard. I seldom have the Max more than 150% of the Ideal.
    Since I manually fire, I try to make it possible to keep from blowing of the safety valves when not working the loco hard. With a 150% difference between Ideal and Max, dropping the fire to 2/3rds or 1/2 Ideal really slows down steam production. For the same reason, I prefer a high value for the DraftingEffect: usually around 1.3 to slow down combustion when the loco is not drafting.

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