If I may add a little something here on the subject of superheating. I hope this come out right so here goes. It's a popular misconception had by some that superheaters are used to dry the steam before delivery to the engine cylinders. While superheaters do have that effect, the main purpose of superheating is to add heat to the steam. By definition, superheat is any heat added to the steam above generation temperature.

Steam @ 100 psig is 338* f, it's a fact of physics and steam and water can exisit in a boiler at this temperature. This is called the saturation point, hence the term "saturated steam". The term saturated steam has nothing to do with the water content of the steam, although it could be "wet", the saturated referance is to the steam temperature in relation to the pressure. Example: If the steam is leaving the boiler @ 338*f(saturation point) and running through the superheating bundles and being delivered to the cylinders @ 400*f, you would have 62*f of superheat.

The more heat available, the more work can be had out of the engine. The term used for the heat content of the steam is enthapy, which in simple terms is the number of btu's /lb. Superheated steam also has a higher rate of expansion in the cylinders and this is where the economy comes in. You can now get more work from a pound of steam while burning the relative same amount of fuel and it's basically free,as you're getting some heat recovery back from the spent gases of your fuel in the firebox in the superheater units. And as a steam locomotive is a total loss type machine by design, any heat recovery is a good thing as it affects the overall operating cost.

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Kelly -

So you have a locomotive equipped with superheaters and have decided that they are too expensive to replace for the benefits received, what do you do? Are they removable? Can they be "blocked off"? Or is the "curse" more trouble than the "cure"?

Les

I recently acquired two photos of Mountains CNR 6044 (Kingston)Winnipeg 1940 and GTW 6040 (Baldwin) in Chicago 1939. I was
surprised to see the GTW 6040 without the long linkage connecting to a front end throttle. Seems a big engine for a dome throttle or am I missing something here ?

Then why not convert the engine to a saturated engine. It would be cheaper than building units and would then be more cost effective for what you are doing.
Simply build jumpers, loops, for the superheater header. Then each superheater flue would have to probably have a restrictor added to slow the flue gas down. The restrictor would approximate in size/restriction what the unit would restrict by being in the flue.

this isn't new technology and has been done in the past

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Has anyone ever used modern alloys like titanium for the superheaters? Perhaps higher cost but perhaps longer life. Or would the FRA frown on something like this?

Bob

Another good example would be Frisco 4500 4-8-4's. Built pretty late in the game with dome throttles. Somewhere I recall reading the Frisco had scale problems with multiple throttle valves getting hung up and thus elected to go with dome throttle valves on these. Maybe someone else can expand on this thought.

The balancing chamber portion of the valves on a front end throttle has a fairly tight clearance and if the water treatment wasn't right on then scale could conceivably cause the throttle to jamb in either open or closed.

[quote="Kelly Anderson"] You bite the bullet and pay for new superheater units. It is possible to de-superheat an engine, but to do it right, you will need to replace both tube sheets, then replace the superheater header with a custon "T" to connect the dry pipe to the cylinder steam pipes. Then you still end up paying for new boiler tubes to go in your new tube sheets in order to save on new superheater tube to make new units.

Agreed. If the tube sheets and tubes were toast, conversion might be worth considering. I think choosing the locomotive to rebuild / replicate / design and construct / whatever based on the specific uses proposed for it is where the cost difference must be considered, just as one of many factors.

I suppose if Strasburg were to use 90 to pull AMTRAK to Harrisburg as well as run the usual tourist train, the benefit of superheaters would become evident. As I read the article, it took some considerable time and fire development before the heat transfer rate across the superheaters added enough extra heat energy to the steam flowing past (and the reduced amount of flowing steam based on reduced cutoff at track speed, at boiler pressure since the throttle would be open while the valves throttled the steam at the valve chest) to effect any significant greater efficiency.

dave

I think Kelly will agree that the Strasburg schedule and line profile never allow #90 to get hot enough to benefit from the superheaters. Even climbing the hill after Cherry Hill crossing you can't "cover the fire" completely without lifting the safeties, but if the fire remains light then the gas temperature remains low and the superheaters have little effect. The fire temperature also drops during the station stop.

My little live steam model had superheaters, made of copper, that burned out a few years ago and I have not yet replaced them. There was a noticeable performance drop, increase in coal consumption, and increase in wet exhaust afterward (that is - more oil spots on my glasses). The units are still sitting on the workbench as one of those projects to do. My little engine has the opportunity to run at speed with a hot fire.

I've fired several superheated engines that were under a good load, and a couple of saturated engines, although not under as much demand. The difference in water consumption however I felt was drastic, and in turn, the amount of fuel consumed. The rate of steam flowing through the superheaters at cutoff is a very good point, and agrees with recommended practice for operation. When a locomotive is under a full load and running square, the throttle can be wide open and the valve then controls the admission of steam "bottling up" steam in the superheaters. This allows even more transfer of heat from exhaust gas which is the great benefit.

If there were an ideal comparison to make a real world test, the two surviving Rio Grande K-27's are of each category. The #464 had it's superheaters removed after retiring as the Durango yard switcher and moving to California. #463 however remains superheated pulling trains over Cumbres Pass.

One thing that using super heaters changed was the make up of the cylinder oil used. They found that oils containing animal fats "Tallow" would not work as the fats would literally cook & harden making the oil unusable.
I was a Boiler Tech in the Navy & our boilers ran at 1275 Psi & 1000*F superheat. We looked for steam leaks with a broom & I have seen the straws on the head of the broom cut off from a leaking packing gland on a 1/4" drain valve.

Dave Huffman