OK, by that logic it makes the most sense to build the new boiler without superheaters as the first boiler was built - saves a lot of hassle in the long run also.

dave

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Of course, if the ultimate goal here is to have cheap-to-operate motive power we wouldn't be talking about steam at all.

I'm approaching it from the entire picture, not just the financial one: sustainability and environmental impact. Steam is by nature inefficient in traditional Stephenson locomotives, but our business plans and missions lead us to use it anyhow. So, what can we do to increase efficiencies and reduce emissions without a lot of adverse consequences?

1. Make the combustion process more complete and cleaner.
2. Combust less in the first place for the same amount of power.
3. Use the power better.

I think we can find ways to accomplish these to some extent without breaking the bank in construction or maintenance.

dave

Greetings:
I think that some of the statements above would benefit from the caveat "but you really should do an analysis based on your own use/service for the given locomotive".
Some years ago, I "ran the numbers" on the initial cost/fuel savings ratio for installing a superheater on our No.40 (built as, and currently, a saturated locomotive).
No.40 uses about 25% more coal than No.97, about 30% more than No.3025 per day (on the road, not including banking, which would be the same regardless).
Based on my estimate for a header, units, new steam admission pipes and flue sheets verses the price we were paying for coal at the time; it was going to take about 30 years to amortize the investment (I didn't include maintenance, because, in my experience, when properly maintained and installed, they give little or no trouble).
We consume over 400 tons of coal per season.
Back then we paid less than $100./ton for low sulfur, low volatile, sized coal. For 2015, Valley will pay about $210./ton, in our bins, at Essex.
I wish that we weren't up against a deadline on completing the 1472 Service Day Inspection on No.40. If we had the time, I'd be thinking seriously about a modernization.
Be well,
J.David

The objective of superheat is to reduce initial condensation and wall effects - it does not raise the pressure and it is PSI which makes MEP which is translated by the running gear into HP. (a bit of Chapelon and EMD thinking here.)

For a given locomotive, one can make substantial gains in evaluating the steam and exhaust circuits for restrictions as well as steam tightness - especially in regards to piston and valve rings. As for condensation losses, improved insulation can yield a degree of improvement towards the same losses superheat corrects.

It's worth mentioning that the producers of Thermic Syphons and Security Circulators claimed both efficiency and maintenance benefits for their products. How well these were substantiated I don't know, but it seems reasonable that improved circulation in the boiler would allow a quicker rise to operating pressure (operational benefit) and maintain a more uniform temperature throughout the boiler, which would help avoid problems as noted with the 1385's current screwy tube arrangement (reduced boiler maintenance).

Like J David says though, any contemplated improvement should be analyzed on a life-cycle cost basis.

Only if your sole criteria is economic. Once you commit to steam that is already out the window. Intangibles may not be measurable, but that doesn't mean they are less real or important than what is easily quantified.

dave

Interesting discussion. On thermic syphons there are two studies, one from the University of Illinois Engineering Experiment Station. Since it was done for a commercial purpose, the report was jubilant of course. Prof. Dr. A. Giesl-Gieslingen made mince-meat of it! The report is online btw.
The second one is by British Railways on the Bulleid boilers for the Merchant Navy class light Pacifics. "Holland America Line" (!! hence my reaction) received a boiler without syphons. Both types of locomotives were tested in the Rugby test station and on the road. Official conclusion: it did not make any difference, taking syphons out was not cost effective neither was building them in! Also superheat was lower in the syphon boiler.
I would like to add that these syphons give a lot of trouble in the present fleet of heritage Bulleid Pacifics in the U.K.
Regarding superheat, I must take a position against the above remarks on superheat.
A locomotive is a heat-to-work conversion engine, the more BTU's/Joules you have in your steam the better it works! It is far better to use your fire for superheat than evaporate water and eject it as steam.
Overhere, a couple of years ago a small superheated locomotive was reboilered with a saturated version. The heritage owners highly regret that decision and intend to rebuild it back into a superheated version.
Kind regards
Jos Koopmans

Could anyone post a link to the studies on Themic Syphons mentioned in the post above?
Thanks,
Mike Tillger

Title: Tests of a mikado-type locomotive equipped with Nicholson thermic syphons : a report
Author(s): Schmidt, Edward Charles, 1874-1942; Young, Everett Gillham, 1888-; Schrader, Herman John, 1901-

https://www.ideals.illinois.edu/handle/2142/4241

I'll look for the British ones.
http://users.fini.net/~bersano/english- ... /BR-tests/
download: BR_P&E_No10_Orig_MN.pdf
The results/conclusions are on page 12

kind regards
Jos Koopmans

Jos, thank you for posting the links.

Mike Tillger

I'll throw my 2 cents worth in. On our locomotive, a small European 4-4-0 with a copper firebox between the frames, the super heaters are an absolute necessity! With our mainline trips where we run for a decent amount of time (around 45-50 minutes), it would be much more difficult for the fireman if they were not featured on the locomotive! Even with the units fitted, if the fireman is not attentive and knowledgeable, the boiler pressure can easily drop from 12 bar to 10 &1/2 bar if he is not careful. Super heaters may be a long term investment, but it must be considered that the locomotive might need them to keep up with the demands of service. If it is not really perceived that the 1385 will make any mainline trips if none at all, then the lack of super heaters would make sense. If mainline trips at speed are foreseen, then for the sake of steam consumption and the physical strength of the crew, super heaters could be a very worthy investment!

When our locomotive was originally built, it was fitted with a smaller boiler and no super heaters in the same mainline service we put it through regularly. I certainly feel sorry for the fireman on the long distance trains with the original configuration!

The smaller boiler is probably more responsible for the previously lower capacity than the temperature of the steam at the same pressure (presuming the same pressure here of course).

Strasburg's experience between saturated and superheated steam is probably what's most likely on a smaller museum or tourist operation with short trips and a small to medium sized locomotive not loaded to capacity. For long trips at heavy loads, the gains in efficiency could play out in practical ways......but unless we had identical locomotives, one converted and one not, we probably won't be able to run them in the same service with the same crews hauling the same loads to test different conditions to see what the optimum could be...and that's probably not going to be applicable to other locomotives anyhow.

For my money, if she was just going to run in museum service hauling a few coaches for short trips, I'd go back to saturated all else being equal. I would put the effort into insulation, better ring and packing design, and front end / drafting instead. I would like very much to work on projects in which ways to increase efficiency could be included, but the right economic opportunity to carry one out hasn't evolved yet.

dave

I must take objection to this passage, for it it were true, an efficient engine could have low boiler pressure as long as it had very high superheat. The function of heat is to make pressure, and the objective of superheat is to preserve pressure during expansion from various losses which cause the temperature to drop below the saturation temperature. Chapelon's tests on 160A1 as well as Stumpf's Unaflow engines (as built by the Skinner engine Company) show that steam jacketing the cylinders allows a saturated locomotive to achieve only a 1.5% to 3% loss in efficiency and 93% of the power compared to a superheated HP circuit without steam jacketed cylinders. (Chapelon Genius of French Steam p. 57.)

As such, I would build new steam jacketed cylinders that breath well for my little tourist engine which would give you a locomotive which was always ready to go with nice hot cylinders that did not shower everyone on a start, be able to use compounded cylinder oil, and not have the maintenance and capital costs of superheat.

Matt Janssen