Some of the earlier engines (like Chicago Northwestern 4-4-0s purchased by that railroad in 1899 for the Fast Mail between Chicago and Omaha) had a distinctive bulge of the boiler at the center. Machining such a bulge would have been difficult given the limited ability of precision machining in that era). So what would have been the purpose?.. Why not stick with a simple cylindrical boiler?
Remember that it isn't 'machined' (as in lathed from a brass bar as in model construction), it is made up as specially cut and drilled/reamed sheets and then assembled as a hollow pressure vessel. There was little lack of ability to lay out, cut, or roll the relevant sheets; in fact, it could be argued there was far more empirical ability to do the necessary 'mensuration' in the late 19th Century than now...
The principal reason for wagon-top construction 'in the old days' was to keep a higher water level in the boiler when the locomotive traversed grades. With a pure cylindrical boiler, going upgrade might tend to expose the tubes at the front; descending might expose the crown. The 'taper' provides more room for the water level to equalize.
Another reason was to increase the steam separation from adjacent sections up to the dome, and then keep the dry pipe as high as possible over the 'boiling milk' that is what the water plus boiler chemicals resembles at full heat transfer.
Interesting Overmod.. thank you!
True of some modern locomotives too. If I remember correctly, the Centrals J3a had more of a bulge than the J!a. Am I correct?
Ulricha distinctive bulge
Possibly a Belpaire firebox?
timz Ulrich a distinctive bulge Guess you mean part of the boiler is tapered-- conical rather than cylindrical? With the largest diameter closest to the firebox? Or are you describing something else?
Ulrich a distinctive bulge
Guess you mean part of the boiler is tapered-- conical rather than cylindrical? With the largest diameter closest to the firebox? Or are you describing something else?
Yes, tapered, conical would better describe it..
There is a little more to his specific question, and part of this involves looking at the specific locomotives he referenced (which indeed produces slightly different answers).
I assumed that two 'representative' classes could be represented by class B locomotive 211 and class A 217, both of which have clear pictures on the Web.
These have a conical transition from the smokebox/first course to a larger cylinder (not taper) over a narrow (hence invisible from 'outside') firebox. There is likely a larger crown sheet in that rear barrel, and note in particular the radial-stay bolted waterspace on 217, almost what I would expect in a Vanderbilt firebox.
Looking at these engines it's easy to see why the OP thought they were machined. The evaporative part of a boiler is insulated with 'lagging' and covered with metal the British call 'cleading'. This is normally in sections held on with bands but here is carefully smoothed and the joints leveled to give a smooth -- and thoroughly machined-looking -- appearance.
Overmod
I still find it amazing that in the present gasoline and nuclear age the concept of a "steam boiler" is so distant from common understanding.
That's right boys and girls - "steam power" is not some antique form of technology lost to the past. Yes your automobile is cooled by a radiator with hot water - and when it leaks the steam is not a fire!
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Seriously now the steam boiler is a "pressure vessel" which means that it is specially designed to contain great force. Which in the event of a structural failure becomes a giant bomb. Contained within the "pressure vessel" is great storage of energy. Soooo - when the raging coal fire heated to fierce temperatures gives up that energy to the water - it in turn generates great pressure ----- and well you have the potential to do a GREAT DEAL of WORK!
Which is what a steam locomotive is all about.
Great care is taken to design the locomotive boiler - the quality steel is rolled into giant cylinders by huge rolling wheels or rollers. Rivets were used in most 20th Century locomotive construction because in that age of early welding technology - rivets were a safe and sure means of joining boiler parts.
Holes for rivets were carefully drilled and reamed to size and location so that when the huge boiler sections of steel were place together the rivets could be tightly inserted an then "riveted over." Riveting was a skilled profession - the rivet was heated to the correct temperature - usually a glowing orange - then a workman picked it up with tongs inserted it in the holes of the boiler and placed a large steel "buck" against its head. Then quickly a another workman would take a air hammer with special round cuped head and drive the rivet from the other end - forming another nice round head. Good riviters could draw the steel parts together tightly with the rivet. Many rows of rivets would secure the seems of the new locomotive boiler.
Step by step and piece by piece the boiler sections would be joined which included a squarish fire box construction which made room for grates and an internal fire.
THROAT SHEET and CROWN SHEET - Were placed inside the firebox where it joined the cylinderical boiler sections. These were the two parts called the "crown sheet" and "throat sheet." Sheets of steel they were. These two parts derived their names from what they did in the construction of the boiler. The "crown sheet" was the top of the firebox on the inside - it was exposed to the heat of the fire. The "throat sheet" was the front part of the firebox - on the bottom - that connected the round part of the boiler to the square firebox. These two steel parts took careful shaping so that when all rivited togeather a huge hollow pressure vessel was constructed that could contain a fire.
It was very important that the condition of the boiler and firebox were maintained - as any thinning or weakness could result in catastrophic explosion when heated with steam. The boiler would be regularly checked for any imperfections in its structural integrity. Engines restored today must meet strict Federal Government standards in order to be put back into use.
Within the boiler were partitions - discs of steel dividing the firebox from the water filled boiler - into two sections of fire and water. These steel discs were called "flue sheets." The flue sheets were drilled with holes usually 2 or 2 1/2 inches in diameter. Inserted through the holes were the long steel "flues" or pipes that allowed the fire and smoke to pass from the firebox through the water filled boiler.
The arrangement of these flues was carefully designed to allow as much heat from the fire to pass into the water. Flues were attached into the flue sheets by a special process called "swedging" which is an old technology not used much today but very capable of sealing the flue pipes into the flue sheets - after swedging which is a form of metal spinning the flues were welded to the flue sheets.
STAYS - Actually, called "stay bolts" were like the rivets only that they were to hold the water filled boiler and firebox together. Stays were special long bolts with special threaded ends. These custom made "stays" were used to suspend the locomotive firebox inside the boiler. There were hundreds of these "stay bolts" every few inches that suspended the giant hot steel firebox within the cold water filled boiler. These "stays" required constant maintaince because they would break with continual heating and cooling related to the boiler temperature and pressure fluctuations.
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CONICAL SECTION BOILER - The shape of the steam locomotive boiler developed over time. The early "cylinderical boiler" was the easiest to produce. The "conical section" or tapered boiler - allowed a larger firebox to fit into a standard cylinderical size boiler. This design change resulted because of the work engineers were constantly doing to develop more power from the existing boiler designs they worked on.
This very important change related to the "conical boiler" came at the very end of steam locomotive design era and was specifically related to this "conical section" change. This design - remember the word - "Combustion chamber" - was a major design break thru of the 1930s and 1940s - and was why the New York Central Hudson boilers mentioned went conical in shape.
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After much study - it became apparent to the engineers, that the fire in the firebox was not burning - not completing the combustion of the coal gases. So - What to do? Well, what happened was not immediately obvious.
In the new "conical boiler design" - the water section of the boiler - the "flue section" was changed and made entirely much smaller and shorter in size. In place of this, the firebox was made much larger and given a "combustion chamber" - which ment that the firebox itself was entirely extended into the forward part of the boiler.
Now in the new designs - the firebox took up most of the space internally within the locomotive boiler itself - and the coal gases of the burning fire were much more thoroughly burned! Horsepower and performance were greatly increased!
The J1 and J3 New York Central engines featured this major difference - boiler design change - as did most steam locomotives late in the steam era. Conical boiler sections ment big husky performance difference.
Here are some specifications:
NYC J1 Hudson - boiler major diameter 88 inches
NYC J3 Hudson - boiler major diameter 91 1/2 inches - conical section
NYC J1 Hudson - flue tube length 20 feet 6 inches
NYC J3 Hudson - flue tube length 19 feet 6 inches - short for cc chamber
NYC J1 Hudson - combustion chamber - none
NYC J3 Hudson - combustion chamber - 43 inches - within conical boiler
NYC J1 - firebox size - 130 inches X 90 inches
NYC J3 - firebox size - 130 inches X 90 inches - same as before
NYC J1 - firebox grate surface - 81.5 square feet
NYC J3 - firebox grate surface - 81.5 square feet - same as before
NYC J1 - boiler heating surface evaporative area - 4,484 square feet
NYC J3 - boiler heating surface evaporative area - 4,187 square feet - less
NYC J1 - super heater surface - 1,951 square feet
NYC J3 - super heater surface - 1,745 square feet - less
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I hope you appreciate this illustration. The NYC J3 had significant performance increases with a reduction in boiler flue length - reduction in amount and length of the boiler superheaters - and reduction in heating surface evaporative area of the boiler. All this with the addition of a firebox "combustion chamber" and conical boiler design which turned this famous steam engine into a real modern high performer - it was fast and now much faster!
The conical boiler design means something in old photos.
If you ever look at the design of the Pennsylvania Railroad T1 duplex engines the shocking amount of water tube boiler compared to firebox combustion size with chamber is just OUTRAGEOUS - marked by a conical boiler section design.
- Dr. D
At the risk of giving the intern a stroke, it should be noted that, except for nuclear submarines, steam engines are fading out from marine service, being replaced by some incredibly large slow-turning diesel engines.
Just to remind the folks who are 'new' to the list: "Dr. D" is one of the people who restored PM 1225 back in the day, so he knows about this firsthand.
As a small note: you would not use riveting to 'draw' courses together; they are temporarily bolted up in position firmly so that no undue stresses are created or allowed in the process of forming the seams. I believe it is set I'll common practice to 'calk' the seams afterward to minimize the chance for corrosion to get started as the boiler thermally cycles in subsequent service. Do not miss the point about careful taper reaming of the through holes before the rivet is set.
There is more about the 'combustion chamber' thing that needs to be said. These things have very little to do with actually permitting more combustion, although they do allow a longer combustion plume. (Remember that combustion is almost all below atmospheric pressure in even the largest locomotive boiler, and consider the gas speed and hence dwell time in the length represented by the chamber compared to how much practical oxidation of unburnt fuel occurs in that time.)
What the chamber does best is greatly expand the radiant heating surface, where practical heat transfer is a fourth-power function of temperature (mathematically, see Stefan-Boltzmann for why). Meanwhile, at 'correct' front-end proportions, the maximum length of 'convective' heat-transfer tubes and flues is somewhere in the 20 to 21' range (whether or not counting something like the Chapelon or Porta sectional-boiler regions) so there is no point in making the convection section any longer than that, or very much shorter on locomotives of any particular length. So all the additional length goes in the boiler, but not in the firebox with its weird stresses and thermal cycling and proportions largely fixed by grate area ... better to put in a cylindrical section with neat radial staybolts and controlled waterspace characteristics.
Very late Lima practice involved what they called a 'double Belpaire' chamber where the inside cross section was not cylindrical but a kind of cushion shape that provided more radiant absorption area and room for a few more tubes/flues (at the cost of restricting driver diameter to about 76" for normal Eastern clearances). Work on this proceeded as far as construction of a large-scale model, which survives in a museum collection. Had Col. Townsend had any takers for the long-compression Franklin "type C" proposal we might have seen all-welded versions of this construction in the late '40s.
As a T1 note: the original Baldwin duplex proposal had a GA about 102-104 Sq.ft. Kiefer's C1a which implicitly reflected about 4 years experience when the design was finalized (in April 1945) used the same dimensions as the Niagara; I confess I might add the 'extra length' (for the middle cylinder block, which was not 'necked' to reduce rigid wheelbase as the Q2's was) as chamber but see Le Massena's article on this in Trains in the '80s. The replica would almost certainly benefit from a 'rightsized' firebox but due to complex reasons very extensive redesign of many parts would be involved in making even relatively minor increases in firebox geometry, so the smaller (and implicitly somewhat more 'economical') dimensions will be kept, with optimized circulation making up some of the foregone combustion efficiency.
BTW, it might be mentioned why staybolts were generally made of iron and not steel. I leave this for Dr. D as it's an interesting thing metallurgically. For those with technical interest (and perhaps something of a masochistic streak) look at the translation of the Tross article on the Wasatch Railroad Contractors site and some of the controversy over 'fillet-welded staybolts' ...
Terrrific explanation. Worth saving on my hard drive.
How about the two PRR K5s compared to the K4? Was PRR ahead or behind the times in the design of these two late Pacifics?
Hey, I know about riveting. I saw it in a Three Stooges film!
In my opinion the K5 was among the very best of Pacific designs. Unfortunately it came about just AFTER PRR spent money on All Those K4s, but just BEFORE adoption of mechanical stoking or Eksergian et al. balancing improvements. With low effective FA. (And we need not go into the problems with "Mussolini" as shared with every other locomotive Baldwin saddled with Caprotti gear.)
In my opinion it would NOT have benefited from being a Hudson for much the same reasons that NYC Mountains didn't need to be 4-8-4s (see Dr. Leonard for his well-reasoned take on this). Snyder preheaters and Cunningham circulators would likely allow for all the marginal increase in steam at pressure the chassis could practically use at speed.
But this would still leave PRR short, perhaps well short, of what it needed for longer axle-generator-equipped consists at high speed, which would involve at least eight drivers higher than 72" and at that point you are well into double-axle trailing truck country. Or the 'perfected' direct-drive turbines with Bowes-drive rotational speed matching...
... or of course E units and the like.
CSSHEGEWISCH At the risk of giving the intern a stroke, it should be noted that, except for nuclear submarines, steam engines are fading out from marine service, being replaced by some incredibly large slow-turning diesel engines.
Interesting. It was my understanding that for marine service such as cruise ships who's voyages involve a lot of "stop and start" ship handling diesels or diesel-electric power was the norm, but for cargo ships (of most kinds) steam was still preferred since it's more efficient than diesel for long voyages with little or no stops or starts, that is, "get it up to speed and leave it there" cruising.
Leo Ames will have the definitive word on this, but modern large-displacement diesels have been preferred to steam for almost all new ship construction for some time now.
Oh well....
Some of the big marine diesels have about 50% thermal efficiency. The best with steam is about 46% with ultracritical steam conditions.
A potentially even better solution would be a combined cycle engine.
There are still boilers on ships of the Scotch marine fire tube type usually, but only used for hotel steam.
I understood that some LNG tankers used boil-off loss gas to fuel boilers.
MidlandMike I understood that some LNG tankers used boil-off loss gas to fuel boilers.
CSSHEGEWISCHCould the same fuel source be used to supply modified marine diesels?
Technically, but there are complications.
As previously noted you cannot run a Diesel engine on 'straight' natural gas; you would need a proportion of continued diesel injection for polynucleate compression ignition, and this would likely involve different phasing and timing through the relatively large number of injectors per cylinder in those large engines.
Whether the boiloff consumption gives actual fuel savings overall (it can't be vented to atmosphere as it is a more potent greenhouse gas than CO2) rather than being used in service boilers is another question, to which the answer is probably in specialized maritime sources I haven't yet read.
It might make more sense to use gas (combustion) turbines which are perfectly happy to run off natural gas. Ship propulsion would involve a lot less cycling of pwer than locomotive use and improvement in efficiency can be derived from a combined cycle plant or steam injection.
There are natural gas fueled multi-piston engines, such as those used in gas compressors.
Brayton-cycle gas turbines are the 'topping' part of the combined-cycle plant (gas turbine shp and then Rankine-cycle steam bottoming) referred to previously.
Be very careful to distinguish compression-ignition (Diesel) engines from any kind of spark or laser ignition. Most commercial natural-gas engines I was familiar with used spark to ignite the fuel, whether port-'injected' or carbureted. These may look very much like similar Diesel engines in a manufacturer's range unless you know to look for the details. A millwright like tdmidget can likely tell you all the detail you want to know.
A problem here is that the LNG 'boiloff' is restricted to what the insulation permits, and insulation has become very, very good in the past decade. I would be surprised if the loss is sufficient to supply most of the ancillary load, let alone that needed for ship cruise propulsion. I would also be surprised if it were economical to use the compressed and liquefied product as a streaming source for propulsion power instead of using a more normal (energy-denser, warmer, etc.) liquid or liquid carrier fuel.
MidlandMike There are natural gas fueled multi-piston engines, such as those used in gas compressors.
Agreed. NWT Power uses these Natural gas fired engines in their Inuvik Plant. They have for at least 10 years IIRC. They are Wartsila engines built for the purpose and as far as I know don't use any diesel fuel. They replaced Mirrlees diesel engines which had been in sevice for many years and had finally succumbed to the effects of sulphur rich fuel from the Norman Wells refinery.
Charlie
Stay bolts are special bolts with a small hole drilled through most of the middle of it's lenght. This hole allows the visable leaking of steam or water if the bolt develops a crack. Hopefully this leakage will be noticed before the bolt breaks compleatly and the bolt will be replaced before failure.
The purpose of the stay bolts is support the crown and walls of the fire box so they do not deform from the boilers pressure. Since the shape of the firebox is not sutable for a pressure vessel they need stay bolts to strengthen them.
Thank you foir your interesting discussion. And, almost every power plant in operation uses some kind of boiler.
54light15 There are still boilers on ships of the Scotch marine fire tube type usually, but only used for hotel steam.
Not entirely true. Fire tube boilers yes, Scotch Marine boilers not usually. Most cargo ships today, having large, slow speed diesel main engines, will have an exhaust gas boiler fitted in the main uptake (and sometimes in the auxiliary engine uptakes too) to supply steam while underway. In some ships this exhaust gas boiler will also have the capability of being fired with oil when the main engine is not in operation. In other ships a separate, packaged, fire tube boiler is fitted somewhere in the engine room to supply steam when the main engine is shut down.
Oil tankers transporting crude oil and / or heavy oils generally use water tube boilers to supply the relatively large volumes of steam for cargo heating and tank cleaning operations. It is my understanding that clean product tankers do not require much, if any, steam for cargo operations and therefore are not fitted with large boilers, but may have a small boiler for hotel services.
The use of boil off gas to fire the boilers of the first generation of steam turbine powered LNG tankers was almost universal.
When LNG tankers began to be powered by low speed, direct drive diesels, most also employed boil off gas as main engine fuel, with a small amount of diesel or heavy oil (somewhere between 2% and 10% I believe) used to initiate combustion.
Newer ships do not use boil off gas as the tank insulation is so efficient that there is insufficient boil off gas to use as fuel. Instead, the ships are fitted with a re-liquidfaction plant and the boil off gas is returned to the LNG tanks as a liquid. This process makes the buyers of the gas happier as they now get a full load of LNG.
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