In reading, I see lots of references to staybolts. Are staybolts used exclusively to hold the firebox within the boiler? Or are staybolts used in other places also? My understanding is that a staybolt is a large-diameter, very long bolt that is threaded only on the ends; correct?
I know that, looking fore to aft, there is water on both sides of the firebox, and above, forming sort of a horseshoe shape. But is there water below also? That appears unlikely to me, as the ashpan's placement would seem to make that impossible.
In, say, a big 4-8-4, how wide is the water space to the sides of the firebox? Like 3 feet?
An illustration I have seen shows the combustion chamber as (it seems) merely the forward part of the firebox. But I have read that a lot of engines had no combustion chamber. If an engine has no combustion chamber, does it also have no brick arch? In the referenced diagragm, the arch seems to be the demarcation between firebox and combustion chamber.
If there is more to the combustion chamber than I stated above, I woud appreciate a brief explanation of combustion chambers.
If our 4-8-4's boiler is "full" of water, how much vertical distance would there be, at the lateral midpoint, from the top of the water to the top of the boiler? Five feet? (Looking at photos and illustrations, I gather that this "steam gap height," if I may call it that, varies somewhat from fore to aft on many engines.)
Thanks.
Still in training.
LithoniaOperatorIn reading, I see lots of references to staybolts. Are staybolts used exclusively to hold the firebox within the boiler? Or are staybolts used in other places also?
Staybolts hold the inner liner of the water-shielded firebox from the outer wrapper, thereby defining the waterspace of the legs, backhead, and throat. There are thousands of them in a good-sized 4-8-4 boiler, spaced at the distance from each other needed to hold the pressure developed between the corresponding plate area when the boiler is in steam.
My understanding is that a staybolt is a large-diameter, very long bolt that is threaded only on the ends; correct?
It is not particularly large diameter (an inch or two), and is no longer than the corresponding waterspace plus plate thickness on either side. What is important is that (1) the inner thread is smaller diameter than the outer (or else the staybolt could not be inserted) and the threads on the two ends are 'keyed' together so that both ends screw in at the same time to hold the plates at the intended spacing. (There are special taps designed for this purpose)
There are also flexible staybolts (see the historical Flannery catalogue available on-line) which have a sealed ball-and-socket joint on the outer end and can accommodate thermal expansion as the firebox comes up to temperature.
Note the importance of making at least some of these bolts hollow inside, and what is done at the 'mouth' of hollow bolts.
I know that, looking fore to aft, there is water on both sides of the firebox, and above, forming sort of a horseshoe shape. But is there water below also?
In a typical boiler there does not need to be. The grate is carried at or above the level of the mud ring, so there is no 'fire' that isn't water shielded, and the ashpan takes care of itself.
There were boilers that provided water space a full 360 degrees, the Vanderbilt boiler (derived from marine practice) being a good example. The problem here is that few of these arrangements allowed for combustion primary air in anything like the amount or flow pattern required by a large boiler. An intermediate version of this (as seen for instance on the watertube firebox on the Baldwin 60000) is to have transverse water connections between the two sides of the mud ring below the grate, improving the convective flow upward in the legs (or at least such was the theory).
To be measured in inches -- probably no more than about 5", with the spacing tapered outward toward the top to allow for the effect of evolving steam bubbles. Any good cross-section drawing will show the shape of the waterspace in the legs, and most are dimensioned there.
An illustration I have seen shows the combustion chamber as (it seems) merely the forward part of the firebox. But I have read that a lot of engines had no combustion chamber.
Think of the 'combustion chamber' as an extension of the water-shielded 'double bottom' space forward of the firebox into a hollow section of the boiler barrel with no tubes inside. The rear tubesheet defines the forward end of the chamber, but not the forward wall of the firebox space.
As you know, even with the effect of the brick arch lengthening the evolving combustion-gas plume coming off the grate, combustion may not have time to complete by the time it exits the nominal firebox volume (and in a normal boiler encounters the rear tubesheet and radiant combustion effectively ceases). The chamber gives a little longer time for radiant combustion to continue, and for radiant uptake to be made by the inner wrapper 'direct to water'.
If an engine has no combustion chamber, does it also have no brick arch?
The two have nothing to do with each other. Whether or not the arch is equipped with circulator tubes, its function is entirely inside the firebox, directing the flame from the forward part of the grate through a longer path while providing some reverberatory reflective effect downward on the fire to assist with fuel vaporization and lightoff.
In the referenced diagram, the arch seems to be the demarcation between firebox and combustion chamber.
It is, but you need to look at the path and expansion of the combustion-gas plume to see what is happening. Follow the fire around the arch and then forward into the chamber, winding up at the mouths of the tubes and flues going into the convection section.
If our 4-8-4's boiler is "full" of water, how much vertical distance would there be, at the lateral midpoint, from the top of the water to the top of the boiler? Five feet?
Keep in mind that there's not a real good answer to this question. The water in the boiler looks and behaves a lot like boiling milk being scalded, with much of the upper 'level' in the boiler being indeterminate between water and steam in composition. As soon as there is steam demand to the cylinders, the reduced pressure under the dry pipe causes 'swell' in the effective water level as the boiling 'nuclei' increase and start to coalesce.
Obviously the more water you can carry inside the shell, the more steam you can generate ... but you do NOT want to start carrying any actual water (especially if using caustic boiler treatment or you have high dissolved solids) over into the mouth of the dry pipe. This is true if the engine is on an upgrade or downgrade and the water level 'tips' or if speed changes and there is longitudinal slosh. (The Elesco centrifugal 'steam dryer' is intended to help with this, not "dry" the steam in some way).
Best solution is to maintain a high vertical separation, but do it outside the boiler space -- this was the point of Woodard's external dry pipe (as seen on the 8000 and early Super-Power designs) and the reason for high domes on Russian locomotives (where the vertical loading gage allowed it)
The limiting dimension is imposed by the effectiveness of the steam separation. The arrangement on the domeless boiler in the NYC Niagaras are an important thing to study in this connection -- especially as the results when the system didn't provide adequate steam separation could be spectacular.
Thanks so much, Overmod. I really appreciate your taking the time to explain it all so fully.
Man, I must have been having a senior moment when I wrote this: In, say, a big 4-8-4, how wide is the water space to the sides of the firebox? Like 3 feet? If we are giving up six feet of width to these waterspaces, on a machine that has to run on 4' 8.5" track, we'd be talking about a firebox which is a few inches wide! Or non-existant.
LithoniaOperatorIf we are giving up six feet of width to these waterspaces, on a machine that has to run on 4' 8.5" track, we'd be talking about a firebox which is a few inches wide! Or non-existent.
Well, we did have the discussion about the truly explosion- and impact-proof tank car design for compliant oil trains -- capacity inside the full-pen-welded shell six feet thick, about one barrel.
What I recommend you do is run, don't walk, to where you can access Google Books and download a copy of the 1922 Locomotive Cyclopedia. Most of the 'significant' tech questions have answers there, and it's free in PDF.
There is a rather famous reprint of the '41 Cyc that you can probably find for a reasonable amount, although the '47 is the gold standard for advanced modern steam if you can find and afford one. (There is a '50-'52 edition with information on Franklin valves and some other late developments not covered elsewhere, but already a great many steam-specific details are gone or their previous marketers out of business...)
LithoniaOperatorIf our 4-8-4's boiler is "full" of water, how much vertical distance would there be, at the lateral midpoint, from the top of the water to the top of the boiler? Five feet?
Can you find any cross-section drawings of boilers? All the tubes/flues are supposed to be under water, and the top front corner of the firebox has to always be under water, since the firebox sheet isn't thick enough to hold boiler pressure when it's as hot as it would get with no water over it.
So how many inches of water do you need above the top of the firebox? Dunno -- three inches sounds minimumish. Especially if you're approaching a summit that will shift the water forward in the boiler.
On the subject of safety tank cars carrying only a single barrel of oil, what about the Jacobs-Shupert locomotive firebox?
https://books.google.com/books/about/Tests_of_a_Jacobs_Shupert_boiler_in_comp.html?id=d39MAAAAMAAJ
A staybolt-less design, it used some manner of corrugated spacers between the inner and outer firebox walls, I suppose in the manner that boxboard holds apart the top and bottom paper surfaces of a cardboard box.
The "word on the street" was that like so many other wonder inventions for the steam locomotive, it was a failure. The mode of failure is that it leaked.
It apparently wasn't a failure in preventing a crown-sheet-deprived-of-water boiler explosion -- see the above link. You are thinking, after they ran the crown sheet dry, you still had to replace the boiler. Yes, but the claim, based on their tests, is that you wouldn't have to replace the human crew.
Could this design have worked in the era of welded boilers?
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
Paul MilenkovicA staybolt-less design, it used some manner of corrugated spacers between the inner and outer firebox walls, I suppose in the manner that boxboard holds apart the top and bottom paper surfaces of a cardboard box.
It was actually very different. Think of a set of radiator elements (or Weil-McLain J boiler sections) made of plate and riveted at the inside and outside seams, with the firespace 'inside' the central space. There are pretty good drawings and explanations available, including Santa Fe drawings in the de Golyer collection.
The chief issue these had, analytically, was that they were designed in the years people thought of the firebox as a water-shielded space and not a fantastic way to convert radiant heat into large volumes of steam. They were vastly undersized for their substantial weight and fabrication/maintenance complexity, and had very little practical vertical circulation (although you can clearly see how easily this could be built in a quasi-LaMont forced-circulation configuration with the sections arranged for 'consecutive' circulation flow.) You can imagine how much weight a modern version, comparable to say a Lima Allegheny boiler, or a double Belpaire, would impose on its carrying truck or trucks...
But you need to be more specific to understand why nobody continued with this idea. It leaked because you had a 'plurality'. as they like to say in older patent discussions, of cross-riveted joints that couldn't be caulked, and that were practically speaking impossible to access for tightening -- you'd need something like a ship-grade hydraulic riveting apparatus, capable of being three-axis positioned on one of any of the thousands of inside or outside rivets ... with no guarantee that tightening the rivets would actually stop developed leaks at a seam. Pressure preferentially levered the sections apart, and the inside seams in particular were excellent starting points for corrosion (and the "horizontal" ones made nifty traps for sludge and solids that came out of solution). Just how anyone thought they were going to clean the insides of the thing escapes me to this day -- perhaps hang the whole thing vertically, as in Alco's heat-relief tower or as boiler shells are fabricated on a bullnose, with a dip tank underneath. You can imagine the fun
Note that you would NOT attempt to seal-weld the leaky seams, not if you wanted to stay sane long-term. Doing so in the age before shielded-gas autogenous welding (something that ATSF in particular actually tried in a distressing range of situations!) would cause all sorts of problems, including propagation of stress raising from the doubtless-poorly-reamed holes for all the transverse rivets.
I actually developed a kind of improvement patent for how you put the firebox and boiler in a rotating fixture and use a traversing head to do 'downhand' submerged-arc welding for good deep-penetration continuous welds on both the inner and outer seams ... using technology that was mainstream in the late '40s when such boilers would have been tried. The approach should work reasonably well when the section pieces are formed using modern shipbuilding techniques and reasonably jigged and braced before welding commences.
The actual point, though, is that a good waterwall firebox does everything a Jacobs-Shupert does, at much lower cost and probably lighter weight, and is easier to build as a LaMont with somewhere around 6x the circulation mass flow of water compared to the steam mass at the throttle. And defined steam separators and circulators. Etc. That hasn't stopped some very smart people from continuing to have interest in a welded Jacobs-Shupert architecture.
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