OK, I have been trying to find the answer to this question for a while, and no one seems to know.
The following Super Power 2-8-4 locos where built from the same design and are nearly identical (except for small road specific items, headlights, tender sizes, etc.):
NKP S class
Pere Marquette N class
C&O K-4 class
Virginian BA class
All the same frame, boiler, cylinders, etc, etc, EXCEPT for one major functional feature. Among these locos there are three different steam dome/sand box configurations - WHY? does anyone out there know?
The C&O locos all have a forward sand box.
The NKP locos all have a forward steam dome.
The first groups of PM locos are the same as the NKP locos, later PM locos are like the C&O locos.
The Virginian locos have the steam dome "burried" in the sand box.
Date of construction is not the answer, some of the earliest where NKP, the last one built was a NKP.
The DT&I heavy 2-8-2's, which were built during this same period, and which are very similar in design, have the forward sand box.
All these locos had front end throttles so steam dome location should not have had much effect on performence? Or does it?
Inquiring minds want to know? Does anyone have any factual data on this? Or, any thoughts?
Sheldon
Thoughts:
Steam domes tend to be in the middle of the boiler (front-to-back-wise) because at that location, on a grade, there is minimal effect on the distance of the intake pipe above the water level of the boiler. You have to maintain some distance to keep water from going down the pipe with the steam--generally considered a bad thing.
So, why move the steam dome towards the front of the boiler (as on the NKP loco)? You will get more steam space because there will be less of the steam pipe inside the boiler taking up space. More steam space is always better. Don't know how much better, but better.
The chance of passing water down the steam supply pipe is higher with more steam flow. A locomotive has a higher steam flow going uphill compared to downhill. So, with the steam dome placed forward, there will be more water level clearance going uphill than down. And that extra clearance will help minimize the likely extra water flow caused by the high steam flow pulling it along. That, of course, is theory. I don't know how these various 2-8-4's really compared with regard to passing water down the steam supply pipe.
The sand domes then just land in the empty space on the boiler. Except for the Virginian loco where the sand dome wraps around the steam dome. With this loco, there's a consequent greater boiler surface area (the steam dome) in contact with the sand (to keep it warm and dry).
Ed
Ed came up with some good points. The biggest point on placement and size is up to the superintendent of motive power of the purchasing company. Personal preference was a much larger factor in steam locomotive building. Locomotives were all a custom built product and very little was mass produced. All were built by contract and some were even bid on if the railroad had no preference in a particular builder. Just because most of the running gear was the same it could have been a specification that afforded some discounts from the builder. Dome placement and other appliances were placed on to customer specs and the railroad tended to keep the same looks as earlier steamers. Sand domes were placed on the boiler to customer specs but also existing sanding facilities dictated where the sand domes were placed. Why change the configuration of existing facilities for just a few new steamers. A hogger could fill the sand box at the same time the tender is picking up fuel or water.
Lima was the only builder touting it's Super Power locomotives. They were good locomotives for the intended service they were designed for. Super Power was a last chance advertisement by Lima to fend off the up coming diesel onslaught. Factor of adhesion and tractive effort is the determining factor when it comes to power.
Pete
I pray every day I break even, Cause I can really use the money!
I started with nothing and still have most of it left!
Ed and Pete,
Thanks for your thoughts, all good info, some of which I had allready considered.
Pete,
Your statements about railroad preference and the custom nature of steam locos is something I am well aware of and I'm sure it played some roll in this specific issue. And your statements are generally correct. However, all these railroads were in one way or another tied to the Van Sweringen brothers and their Advisory Mechanical Committee (AMC), who was directly responsable for this design.
So unlike many other situations, the AMC, the War Production Board, and the needs of these lines all worked together to make them more "standardized" then most steam other than maybe the USRA locos.
So this steam dome placement issue must have been a subject of debate among the various users and or LIMA and AMC design engineers. The theory Ed suggests does fit the nature of some of the users. The NKP and PM are basicly flat, dome placement could be optumized for shortest path to the super heater and throttle. The C&O had steeper grades, the forward position may have been a concern. The Virginian had grades, but purchased these locos for their flat territory - but maybe kept in mind they may be needed in the mountains at some point. The later PM locos were built at the same time as some of the C&O locos, maybe they really didn't care much and LIMA gave them a deal to stay with the C&O design?
We should also keep in mind that the steam dome placement on ALL of these locos is forward of the boiler center and forward of the typical locations on most earlier designs.
Super Power - true, only LIMA "advertised" it. But it does have a technical definition and many non LIMA locos are considered Super Power locos - N&W J, A, and Y6b, Big Boys and most later 4-8-4's, regardless of builder. Super Power is a loco that can make more steam than it uses at medium to high road speeds, is balanced for those speeds, and has a good factor of adheasion - usually 4 or better.
These locos typically have - large fireboxes, combustion chambers, front end throttles, type E superheaters, high boiler pressures, 69" or larger drivers, feedwater heaters and represent all the final advancements of steam power. Also many state of the art 4-8-2's, like those on the B&O and NYC, are considered Super Power. And surely the DT&I 800 class 2-8-2's are "Baby" Super Power.
In fact, most of the "Super Power" locos where actually built by the other two builders, dispite the fact that LIMA was the company that put all these ideas togethr in a successfull package for the first time.
Ed, your theory is by far the most logical possible explaination I have at this point. And, as noted above, it does fit the operational conditions of the roads in question.
Thanks to all, hopefully others may be able to offer more info.
ATLANTIC CENTRAL The C&O had steeper grades, the forward position may have been a concern. The Virginian had grades, but purchased these locos for their flat territory - but maybe kept in mind they may be needed in the mountains at some point. The later PM locos were built at the same time as some of the C&O locos, maybe they really didn't care much and LIMA gave them a deal to stay with the C&O design? We should also keep in mind that the steam dome placement on ALL of these locos is forward of the boiler center and forward of the typical locations on most earlier designs.
The C&O had steeper grades, the forward position may have been a concern. The Virginian had grades, but purchased these locos for their flat territory - but maybe kept in mind they may be needed in the mountains at some point. The later PM locos were built at the same time as some of the C&O locos, maybe they really didn't care much and LIMA gave them a deal to stay with the C&O design?
All the concern about steam dome location and grades is pretty much immaterial. Yes it may be important when the locomotive went up the hill on the westbound trip, but at some point its going to have to come DOWN the hill on the eastbound trip. So if you optimized the steam dome location for the uphill trip, you have sub optimized it for the downhill leg.
Dave H. Painted side goes up. My website : wnbranch.com
Dave,
Please note my comment regarding this as extracted from above.
7j43k The chance of passing water down the steam supply pipe is higher with more steam flow. A locomotive has a higher steam flow going uphill compared to downhill. So, with the steam dome placed forward, there will be more water level clearance going uphill than down. And that extra clearance will help minimize the likely extra water flow caused by the high steam flow pulling it along. That, of course, is theory. I don't know how these various 2-8-4's really compared with regard to passing water down the steam supply pipe.