Hot off the virtual press is the latest status report.

https://alaskarails.org/pix/former-loco ... index.html

Our appreciation of the Alaska Railroad's support can't be expressed too often. Last month three of their communications staff and 557 restoration crew members Paul and Terry packed the cab while they advised on the type of radios that would be needed and their installation.

The January status report has been posted at https://www.alaskarails.org/pix/former- ... index.html.

Saturday, February 1st, brought us closer to the first firing of 557's boiler following its overhaul. Three members of the volunteer crew completed the installation of 12 of the 30 superheater elements.

In the photo, what is behind the white half-moon shaped piece at the top? I'm curious about how the superheater tubes work, if there is a maze of pipes up there or just open space (obviously my knowledge of steam is limited).

What white half-moon shaped piece?

On a modern American locomotive, there is no throttle in the steam dome, only a dry pipe with its mouth raised as high as possible above 'priming' water level in the boiler underneath (with various methods of enhanced 'steam drying' separation.

The dry pipe connects forward to the BACK side of the superheater header, where it is directed into 'one end' of each of the superheater elements. These pass backward and forward much of the length of the flue, in some cases making several passes, and the exits are in separate passages in the neader that connect to the multiple poppet valves in the front-end throttle.

Steam fron the front-end throttle goes through the two large whitish pipes which go through the smokebox gas space to the steam chests above the valves.

Some of you may remember a certain amount of excitement in the power-boiler community about requiring safety valves on superheaters as part of the revived 'locomotive boiler code'. Those would be necessary on a British superheated locomotive, which has the throttle ahead of the superheater elements -- if there is any carrover into the elements, the throttle is closed, and the valve gear is set as close to mid as the combination-lever action allows, you have a 'seaparately-fired pressure vessel' and would need pops on it for safety. In the American system, pressure equalizes back from the elements through the dry pipe to the saturated steam in the boiler space, so a closed throttle merely expands hot steam back into the dome at saturation pressure -- near-perfect safety against bursting, with full saturation pressure steam throughout to preclude any 'burning' or overheating.

Sorry, I meant half-circle.

Exactly what I was wondering.

Drawings.

Mostly what Overmod said.

The piece you are asking about is the header. The dry pipe comes from the throttle which is under the steam dome, through the front tube sheet, and into the rear of the header. Half of the sockets that the superheater elements are connected to are for steam from the dry pipe. The other half are for steam that has passed through and been heated in the superheater elements and it then goes through the steam pipes on either side of the smoke box and on to the valves and cylinders.

We don't have a drawing of the header that shows the internal construction. The superheater assembly was apparently designed by and purchased from an outside supplier (the Superheater Company) as a kit of parts and is not an ALCO or Baldwin design/drawing so isn't available from the archives of those materials.

Excellent, thank you.

The white piece he's referring to is the baffle behind the delivery pipe flanges. I'm guessing it's purely to prevent eddys in the draft flow. If it were a coal burner it would keep cinders from piling up on the header a bit too.

And I was wondering if that is an enclosed compartment capable of withstanding pressure, like a boiler.

There are instructive descriptions and diagrams of superheater arrangements in the '47 Cyc (and, I suspect, in the '22 and '41 editions available as reprints, or the 50/52 that is online.

Fig. 3/726 (p.323) shows a type A header with connection to a dome throttle. This does not show the "intricate coring" that makes the four-pass arrangement work. 3.295 and 3.296 (p.328) show the arrangement for type A and type E respectively with a typical multiple-poppet front-end throttle.

Regarding the front-end vs. dome throttle difference, the Cyc discussion says (p.322)

The design philosophy for the S-160s was to build them cheap with minimum materials and labor. That probably influenced use of the dome throttle.

Nothing to do with pressure. Just smoothing gas flow up the stack. Will be interesting to see if 557 has a sectional petticoat or a long solid one with that stubby stack. That baffle would definitely be a help with the upper section of a sectional.

557 will maintain the original stack design s in the drawing above. I don't know if a decision has been made to extend the bottom. My recollection is that the oil burning conversion by the ARR in the 1950s didn't include a longer stack extension as called out for an oil burner.

A bit of S-160 trivia, the stacks for the U.S. specification locomotives were about 6" taller as in the U.S. there were no issues with low clearance in tunnels and under bridges as in Europe.

A different locomotive, but this site has some good photos of a superheater header removed from the locomotive. https://www.midcontinent.org/superheate ... tallation/

The smokebox itself, like almost the entire volume in the firebox, runs below atmospheric pressure -- this is key to how a Master Mechanic front end, for example, works. Effective draft (and operation with 'automatic action' across a wide range of exhaust mass flow, and proper cinder 'self-cleaning' action, are associated).

The header of course runs at saturation pressure in the passages 'feeding' the elements. For a front-end throttle, the passages at the 'ends' of the elements will be hotter, but at no higher pressure.

Some locomotives were built with both a dome throttle and a front-end throttle. This was primarily, I think, for safety against 'nightwalking' or creeping due to one or more warped or leaking poppets in a multiple front-end type, but it also had the benefit of allowing effective pressure reduction on high mass flow (like wiredrawing, but nowhere near the steam chests or valves) that could limit propensity to slip much like the receiver and passages to the LP engine on a large Mallet.

Interesting. So the header is steam tight?