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Discussion Starter · #1 ·
Maybe this is just a balmy idea...


Has anyone ever tried to use two full tanks connected in series? On first blush it seems a shame to give up the reasonable-but-not-large-enough tank in the cab and replace it with one modestly larger in the tender. Is there any way to series one into the other to get a substantial gain in capacity? Is this even a reasonable thing to consider? I'm not sure how to get effective gas/fluid exchange between the tanks. Would you want to feed vapor from the tender tank forward into cab tank, or would vapor not transfer due to the pressure differential.

In a similar vane, it seems that it would be advantageous to have an off-engine auxiliarly fuel tank that could be used during intial warming so that you could leave the steam-up bay with a full fuel tank. (At present, I shut down the burner after warming and clearing the cylinders to refill the fuel, then fire up again before moving out. Certainly doable but a bit of a pain.) It seems to me that there should be some way to use a quick-disconnect line to allow safely disconnected an auxiliarly tank when everything is ready to go.

Please don't flay me too badly if these are just a stupid ideas.

Joe
 

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Hi Joe,
I'm quite sure I've seen the setup you propose used at least once. I can't remember the specifics from the top of my head, but worked fine. The idea of a track side large gas tank for starting is interesting. Of course the locomotives would need a valve to prevent gas from venting out when the tank is disconnected. Maybe a clack valve is all that's needed...
 

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Joe,

I'm entirely without expereince in live steam, so perhaps I'm as balmy as everyone else, but I suspect that it could be a dangerous idea.

I have always heard that a live steam loco is (or should be) designed to run out of fuel before it runs low on water. Increasing the fuel capacity, without a comparable increase in water capacity, could lead to a low water situation. Worst case scenario, you get a boiler explosion.

Now, if you're talking about increasing the water capacity as well, it sounds like a great idea. Would it not be possible to simply connect the 2 tanks via a flexible but semi-permanent coupling, with a single filler and a single outlet?
 

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>> I have always heard that a live steam loco is (or should be) designed to run out of fuel before it runs low on water. Increasing the fuel capacity, without a comparable increase in water capacity, could lead to a low water situation. Worst case scenario, you get a boiler explosion.




Just to reassure you as you are new to live steam, increasing gas capacity is unlikely to harm you or burst your locomotive UNLESS you panic.

The Instructions do make a thing about it, because that's how the author can avoid scorched paintwork, disappointed customers and warranty wrangles.


With a classic model Stephenson boiler dependent on it draught, as soon as the water runs out the draught stops and the fire goes out. Neat huh?

With these newfangled gas-in-a-tube jobbies, when the water runs out the train stops and the tube gets red hot. That's OK as far as it goes, because after all it got red hot when it was soldered up. You soon realise what's happened and turn off the gas. And THEN let it cool right down before doing ANYTHING else. If you panic and pump water into the boiler, there'll be a load Crack followed by a gentle hiss and a gloomy silence: you've beggared you boiler tube.


The earliest gas-tube boilers had no clack, no sight glass and often no pressure gauge. Drivers soon learned when the water was running low. The engine would get frisky, blowing off all the time as the boiler tube got hotter. It's unmistakeable when you know your machine. At that point, it's still safe to add water through the clack.


Boiler explosion in these sizes? There was a model steamship boiler explosion in London around 1912 - serious design fault. Not heard of any since. has anyone else?


In a big boiler, the danger point is when the crown of the firebox gets red hot and yields. The boiler is still largely full of water, which then generates many many times its own volume of steam. The rush of steam through a crack rips the whole thing apart with many tons of force, scattering metal and rapidly evaporating superheated water in all directions. Utterly lethal.

Now think of the backplate of your boiler when pressurised. 3 square inches x 40psi = 120lbf. A good kick in the teeth if you were leaning on it at the time, and a scalded hand if you had it in the cab, but not able to rip up copper like tissue paper.


Or look at it this way: if you've run out of water, there's no kick left in it at all. Just a fizz. And if you keep calm, not even a bill for a new boiler. But if you walk away from your dual-fuel locomotive for a natter, budget for a repaint. . .


David
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Discussion Starter · #5 ·
Posted By DKRickman on 09/25/2008 12:46 PM

I have always heard that a live steam loco is (or should be) designed to run out of fuel before it runs low on water. Increasing the fuel capacity, without a comparable increase in water capacity, could lead to a low water situation. Worst case scenario, you get a boiler explosion.

Now, if you're talking about increasing the water capacity as well, it sounds like a great idea. Would it not be possible to simply connect the 2 tanks via a flexible but semi-permanent coupling, with a single filler and a single outlet?


With proper monitoring and management of water and fuel, there shouldn't ever be a problem with running a boiler dry. And even if you did, it'd just pop a seam as David mentioned. Increasing fuel capacity out of necessity also requires continously monitoring water level and adding more as required -- that goes without saying. Fortunately I've got that already covered.
 

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I have added extra capacity to a Ruby gas tank by adding an auxillary tank forward of the original. I added a copper pipe at the bottom of the original tank and connected it to the bottom of the auxillary, then added a copper pipe to the top of both tanks. What I made is a fill (bottom) and a vent (top) to the auxillary tank. When the original tank is filled so is the auxillary tank. When the fuel is used both tanks are at the same level until empty. Even if they did not empty equally the gas still comes out the the same. Doubled my run time with gas and use a Goodall valve for more water.

Thanks
Steve
 

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Discussion Starter · #7 ·
Posted By steveciambrone on 09/25/2008 2:38 PM
I have added extra capacity to a Ruby gas tank by adding an auxillary tank forward of the original. I added a copper pipe at the bottom of the original tank and connected it to the bottom of the auxillary, then added a copper pipe to the top of both tanks. What I made is a fill (bottom) and a vent (top) to the auxillary tank. When the original tank is filled so is the auxillary tank. When the fuel is used both tanks are at the same level until empty. Even if they did not empty equally the gas still comes out the the same. Doubled my run time with gas and use a Goodall valve for more water.



That of course make sense. The double connection makes the assembly perform as if it's a single tank

The following question is for the forum, not for Steve in particular...

In the case of a somewhat remote tank, it might not be practical to have two lines. What would happen if there was only a single pipe from the aux tank to the primary tank? You'd have to fill both tanks separately, of course. But would the fuel transfer properly from aux tank to primary during use? Would it be best to tap aux tank at the bottom (to transfer liquid) or at the top (to transfer gas)? I can't see that it should matter where a single line feeds into the primary tank.

Joe
 

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Let's think about the three distinct jobs a gas tank has to do.

The obvious one is to carry the liquid fuel around, and for that its Critical Success Factor is being pressure-tight.

This has a bearing on the type of connection between the two tanks.

The Aster Mogul has two tanks (in effect) - one for storage and one as an evaporator sump. A friend had a leak in the hose between the two, which caught fire. He turned off the burner, which made everything worse as the leak was now the only escape path for all of the hot gas. A massive gas jet launched itself out of the hole and the cab got well fried before the excitement died down.


So think about the integrity of the connection, and if there are flexible connections involved, where you need stop valves.


A less obvious job a tank has to do is to evaporate the liquid fuel into gas, and to do that it needs heat. Basically, it takes heat to turn liquid butane at (say) 70F into gaseous butane, still at 70F. The geek name for this is the Latent Heat of Evaporation.


And that heat has to come from somewhere, so another Critical Success Factor is being able to get heat from the outside world into the liquid. Because if you can't the evaporation will take heat from the liquid fuel itself, which will get colder and colder. Its vapour pressure will therefore fall, and by the time ice crystals form over it, butane will have ceased to evaporate at all, and you could pour into into a cup.


If neither of your tanks have a source of heat the train stops.

If both tanks have a good supply of heat - whether from the locomotive, from a water tank or just from the atmosphere if you live in a warm climate - you can connect top to top and shift the gas, or bottom to bottom and shift the liquid, and it will all work. But if one tank is nice and warm in the cab and the other is freezing in the tender, then it needs more thought because the cold tank won't be producing any gas. In that case I would suggest connecting both top to top and bottom to bottom. Then gravity alone can equalise the levels and enable the warm tank to do all the evaporation. But this considerably increases the number of potential leakage points. If you need two flexible connections, then you may need four stop valves to maintain integrity.



Finally, a tank has to be easy to fill. It must be possible to flush air out of it, and to vent any compressed gas that is stopping liquid entering. Sometimes self-venting filler valves can do this, and sometimes they can't. If you usually need to vent your tank by opening the burner valve, you also need an equivalent for the secondary tank too. If they are joined top to top, there's no problem, but if they are joined bottom to bottom, you may need a bleed valve on the secondary tank. It is important that this valve should be sufficiently distinct from your pipework stop valves to prevent it being opened by mistake.

So overall, my vote is for a single larger tank in a more suitable place, rather than a secondary tank in a different thermal environment, ESPECIALLY if flexible connections are needed to join the tanks.


What do other people think?

David
 

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I think that if the two tanks are connected at the bottom they would not work because the warmer tank would try to transfer all it's liquid to the cooler tank due to higher pressure. If the cooler tank is in the cab it would start feeding liquid to the burner, not good. On the other hand if the tanks are connected at the top the only gas would be transfered and the pressure would equalize. Should work. The tanks would have to be filled seperately.
 

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Discussion Starter · #10 ·
Good points, David.

Okay, persisting with the second tank idea for a bit...

The tank in the tender would be in a water bath. There would be a steam bleed line running back to the tender bath for warming. Given that the warming line is set to actually warm the water appropriately, it seems that there should be enough heat available to keep the aux tank vaporizing.

We connect the tanks top to top, so we're transferring vapor.

Each tank is filled separately, and each has a self-venting valve, so we shouldn't get a vapor lock anywhere.

There is a shutoff valve on the aux tank so it can be isolated, and the connection to the cab tank is through some sort of self-closing quick disconnects so that the tender could be uncoupled if necessary for servicing.

Does that work?

Does the tender tank need to be kept warmer (by the bath) than the cab tank is kept by its proximity to the burner for this to work?

Joe
 

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I made an auxillary tank because it used the existing tank, with limited space I was able to have the other tank remain small and fit easier than a single larger tank. If starting from scratch i would just build or buy a larger tank sized to fit.

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David
Good common sense approach in preventing unnecessary damage but on the other hand I know of several incidents where boilers have collapse due to running the boiler "dry"....so the moral of this double effort to ensure the water level extended is better than double the gas capacity.

Instead of two fuel tanks might think about a bit larger fuel tank or even better fire up and re-fuel prior to the actual run.


Joe


Track side fuel tank: a fellow steamer has just such an arrangement utilizing it for pre-warming allowing a full tank for the run time.


I have a photo some where.....




Posted By David Halfpenny on 09/25/2008 1:12 PM

>> I have always heard that a live steam loco is (or should be) designed to run out of fuel before it runs low on water. Increasing the fuel capacity, without a comparable increase in water capacity, could lead to a low water situation. Worst case scenario, you get a boiler explosion.




Just to reassure you as you are new to live steam, increasing gas capacity is unlikely to harm you or burst your locomotive UNLESS you panic.

The Instructions do make a thing about it, because that's how the author can avoid scorched paintwork, disappointed customers and warranty wrangles.


With a classic model Stephenson boiler dependent on it draught, as soon as the water runs out the draught stops and the fire goes out. Neat huh?

With these newfangled gas-in-a-tube jobbies, when the water runs out the train stops and the tube gets red hot. That's OK as far as it goes, because after all it got red hot when it was soldered up. You soon realise what's happened and turn off the gas. And THEN let it cool right down before doing ANYTHING else. If you panic and pump water into the boiler, there'll be a load Crack followed by a gentle hiss and a gloomy silence: you've beggared you boiler tube.


The earliest gas-tube boilers had no clack, no sight glass and often no pressure gauge. Drivers soon learned when the water was running low. The engine would get frisky, blowing off all the time as the boiler tube got hotter. It's unmistakeable when you know your machine. At that point, it's still safe to add water through the clack.


Boiler explosion in these sizes? There was a model steamship boiler explosion in London around 1912 - serious design fault. Not heard of any since. has anyone else?


In a big boiler, the danger point is when the crown of the firebox gets red hot and yields. The boiler is still largely full of water, which then generates many many times its own volume of steam. The rush of steam through a crack rips the whole thing apart with many tons of force, scattering metal and rapidly evaporating superheated water in all directions. Utterly lethal.

Now think of the backplate of your boiler when pressurised. 3 square inches x 40psi = 120lbf. A good kick in the teeth if you were leaning on it at the time, and a scalded hand if you had it in the cab, but not able to rip up copper like tissue paper.


Or look at it this way: if you've run out of water, there's no kick left in it at all. Just a fizz. And if you keep calm, not even a bill for a new boiler. But if you walk away from your dual-fuel locomotive for a natter, budget for a repaint. . .


David
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Posted By Charles on 09/25/2008 6:10 PM
David
. . . I know of several incidents where boilers have collapse due to running the boiler "dry"....


Do you know the mechanism please Charles? Was it pressure collapsing a red hot flue (it happens) or vacuum collapsing the barrel?

I agree it's best not to run out of water at all, but it will sometimes happen, and we could add the appropriate preventative measures to the common sense advice.


Such as:

If the locomotive stops with the burner still lit, don't panic. First and foremost don't put any more water in the boiler or you'll just crack the flue. Turn off the gas and leave it all to cool down completely. If you have vacuum-fill on your boiler, disable it immediately. To stop air pressure crushing your boiler as the last wisps of steam condense, open the boiler to the atmosphere somehow: try-cock, blow-down valve, safety valve, whistle or filler. Be wary as a boiled-dry boiler can be very hot in unexpected places.


Would that help?

As an aside, it is amusing to run a steamer in reverse as a Vacuum Engine as the steam in the boiler condensed - but not far ;-)




David
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Copper boilers do not fail like a full size steel boiler.

The Australians did a fine series of tests on copper boilers taking them to failure. Even boilers made to what the hobby would consider substandard did not fail violently. The well made boiler when overpressured sort of inflated like a balloon and failed at a seam then the pressure was exhausted.
While the testing was done well, I think in the real world conditions with the boiler in an engine and all the seals and fitting connected to the boiler and its normal fire source a model engines boiler would be hard pressed to reach 700PSI before enough steam leaks would occur to prevent the boiler from even geting close to the test pressures.

Running a boiler dry is only a problem for the boiler. But if your watching your engine you just go over and turn the flame off and you are fine. Ran enough engines dry to not worry anymore. When the water is gone so is any pressure, so no pressure to cause damage.

Thanks
Steve
 

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The Austalian tests were done as "Hydro-static" tests... i.e.: just pressurized liquid, no air, no gas, no heat, no steam... just water. Thus when the boiler shell failed there was nothing to continue expanding... it went "squirt" and was done. They reached pressures of 1,500 PSI (if I remember correctly) before failure. The center flue collapsed at around 500 PSI, and did so without a leak forming at the seam where the flue joins the ends. At the point of failure the boiler looked like a stubby football (American football, not Soccer).
 
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