I'm a little unclear on the differences between a Type e and type a superheater.
It appears from drawings, that the type e uses smaller flues, thus can there can be more superheater units extended into the flues, vs the type a, thus giving more surface area.

It seems in both, the steam only makes one "trip" from the headed in the front to rear of the elements then back, with neither going from the manifold, to the rear of tubes, then back to manifold, then back into another set of super heater elements then back to manifold that leads to branch pipes.

Type A makes four passes through each superheater unit, a compact bundle of four closely-packed tubes inserted in one large flue (5-3/8" or 5-1/2" dia flue).

Type E uses smaller flues (3-1/2" usually) with one in-and-out pass in each flue, but the superheater unit has four passes, into and out of FOUR separate flues. The bundles are more unwieldy to handle.

Type E's multiple passes deliver hotter steam-- usually about 250-300 degrees hotter than superheated steam from a Type A arrangement.

Maintenance costs were usually lower on Type A superheaters, and such late era locomotives as RDG T-1 4-8-4s and UP FEF-3 4-8-4s (844) have Type A systems.

Howard P.

So the superheater headers, from photos I've seen, appear to be quite complicated and vary in their internal passageway arrangement as to the path the steam takes through it, and how the bundles are arranged as to which bundles are "1st pass", "2nd pass" etc and and how the steam moves between these passes via the header. Is that roughly correct?

I seem to remember someone telling me that one (I think type E) was found to provide too much superheat, or something to that effect.

Either type of superheater system could provide very high superheat temperatures depending on how it was designed. When C&O 614, with a Type E superheater, was first returned to service, they had problems with high superheat temperatures causing problems with the valve rings until they switched to a valve oil formulated for the higher temperatures. I imagine Mr. Rowland can elaborate.

The Pennsylvania T-1's had Type A superheaters, but they were also known to produce very high superheat values.

Ideally for maximum power and efficiency, you want the superheat temperature as high as the cylinder lubricant will handle.

Later German and I believe British locomotives injected the lubricant onto the rubbing surfaces of the valve bushings and cylinders rather than atomizing the oil and spraying it into the highly superheated steam. This allowed the use of higher steam temperatures as the lubricant wasn't as prone to break down when injected in this way. On the SAR Class 26 4-8-4 no. 3450, "the Red Devil", David Wardale went so far as to add cooling passages around the valve bushings. Saturated steam was run through channels which cooled the surfaces where the valve rings rode, keeping the lubricant temperatures safe despite having very high superheat temperatures.

While it is hard to find reliable first hand information I myself rely on the
"Standard Publication"
"Röll:Encyclopedia of Railroading" 10 Books Germany/Austria 1912-1923

It is available online:
http://www.zeno.org/Roell-1912/

This is the most scientific compilation of railroading available at that time.
If you are a native german language speaker it is very helpful!

I try to translate the most interesting parts about A vs E superheaters.
See below the drawings from that books.

First both are German W.Schmidt inventions.
Type A is called the regular superheater and I think it is widely known how it works.
Type E is called superheater for full occupation, that is what the encyclopedia says about:
Very usefull for saturated to superheated conversions when the original tubes are 2.5" or
larger then no retubing necessary.*
No damper needed because the smaller tubes can not tansport as much heat as larger ones,
also the the danger of burning the superheater elements is diminished this way.
For new build locomotives it is recommended to use this type in small, commuter and
branch line locomotives. The ability to reach the high temperatures faster make it
favorable to switching and commuter locomotives.

Now my opinion why some american locomotives with type E overheated. The american way
to make everything bigger did not calculate the correct lenght of the superheater elements,
one feet shorter and the temperature would be excellent!

*I know that Sierra 18 and Nevada Norhern 40 and 93 were superheated with aftermarket
Franklin piston valves. Anybody know if they use type E heaters and the original tubing?