Using superheated steam for the auxiliaries was in vogue for a while... you'd see a large steam pipe running from the smokebox to the turret, but seems to have fallen out of favour.

Did any engines survive to the end of steam with this feature? Do any operating engines still use that arrangement?

The header is steam tight as it's part of the feed from boiler to valves/cylinders. Steam flow in this case is: boiler -> dome throttle -> dry pipe -> superheater header (wet ports) -> superheater tubes -> superheater header (dry ports) -> delivery pipes -> valve cages/valves -> cylinders.

It had better be!

You'll notice that the element ends are ground spherical where they mate with the underside of the header -- that is to ensure they stay sealed even if they move around from thermal expansion (and they see a lot of that!)

In a locomotive with dome throttle, ANY appreciable steam leak between the throttle and the header will be mass flow lost to 'availability at the cylinders' but it is still in equilibrium with the overcritical water in the boiler, and just blows into the steam space without changing saturation pressure. Once it gets into the header, however, any leak in the joints will blow steam down across the front tubesheet -- this wastes the heat and mass of the steam, increases water rate, and can spoil the gas flow from flues and even tubes. The expanding steam also spoils some of the ejector action in the front end (much like excessive steam remaining in the cylinder at release going into and expanding in the exhaust tract) further wrecking draft. Yes, in severe cases, a blow from a superheater element can pressurize hot gas or luminous flame back toward the backhead, perhaps with little warning -- if it is from the 'hot' end of an element, the steam may remain a gas for a considerable time during expansion (doing much what you want it to do in a cylinder!) and will be further increase superheat in intimate contact with hot gas that may be at least as hot... effectively in counterflow.

With a front-end throttle, steam in the dry pipe is in equilibrium with the saturated steam and overcritical water in the boiler, but the steam in the elements is essentially at the same saturation pressure, also in equilibrium, and hence the elements cannot burn until truly 'crazy high' gas temperatures are encountered. The cost of this is that the throttle poppets and camshaft bearings must be steamtight as well as both ends of each element, as the steam traverses them all under what may be MAWP in order to get down those curved pipes to the steam chest.

In short, all of those little holes you see in the bottom of the header must have flexible but steamtight joints, and those joints (and the bottom of the header) will be bathed in hot gas through the flues (gratefully this is at below atmospheric pressure, but moving at high enough speed, and with enough particulates in it, that the outside of the elements that face the gas flow are often armored in a fancy proprietary hard alloy (one of which was mentioned in the 'historic alloys' thread, and for which I hope someone can find Superheater Company data on precise composition used). Note that pressure in the different cored passages in the superheater header are essentially at the same pressure, but the steam temperature is very different (by the amount of the superheat) and this has to be accommodated in the design and fabrication of the header.


is going to result in heat loss

Good concise description of the plumbing, thanks.

TrainDetainer,

Thank you for a brief concise description of the superheater plumbing.

~Wesley

After many months of work to rebuild the superheater elements and recondition and polish both sides of the ball and seat sealing surfaces the actual installation of the superheater elements only took three working days to complete and was a bit anticlimactic but very satisfying. Another major task checked off of the punch list!

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

With the superheater elements installed the exhaust nozzle could be fitted and the blower ring trial fitted.

The March status report is posted at https://www.alaskarails.org/pix/former- ... index.html

The mid-week crew led by Paul Dalleska is installing all of the air, steam, and water piping. They took the art of pipe fitting up a notch by making sweeping curves in the the piping to the air compressor in place of the original elbows.

It's too bad you guys were the victims of vandalism (or were they not very smart truck thieves?), that is money that could be spent on the locomotive.

The latest status report is posted at https://alaskarails.org/pix/former-loco ... index.html

An aerial view of the turret valves and valve spindle extensions being reassembled. The bronze u-joints are some that I cast and machined a couple of years ago. They are replicas taken from the Nathan drawings for the #1 size but are in bronze instead of cast iron. I've been told by the shop crew that they now need a couple of #0 u-joints so it's time to light the foundry off again.

This month Patrick Durand prepared a supersized status report. It's available at https://alaskarails.org/pix/former-loco ... index.html