On Sun, 24 Jul 2011 02:45:43 -0700, Andy Dingley wrote:

On Jul 24, 9:29Â*am, Matty F wrote:

Does an 1891 Baldwin Steam tram have a superheater?

I would doubt it. There are two reasons why not.

Firstly, not much in 1891 was superheated. Superheating in steam locos
appeared slowly, from 1900.

Tried out much earlier, of course - possibly in the middle 1830s[1], certainly
in the 1840s - in locomotives. By that time it was moderately common in
marine and stationary plant (IIRC first application of superheating in a
stationary engine was about 1801). It provided a much greater boost to
efficiency in a low-pressure engine, of course.

It appeared according to the preference of
CMEs, some embracing it, others avoiding it. They mostly recognised the
efficiency advantages, but the problem was cylinder lubrication.

Again, less of an issue at low pressures, where steam temperatures were lower.
Most of the early (pre-1880s) attempts on locomotives were smokebox
superheaters, probably providing a fairly low order of superheat. Reasons
for non-adoption varied, but generally seem to come down to greater
maintainance costs and poorer reliability - much the same story as with
piston valves in locomotives in the same period (first adopted in a locomotive
in 1826, but in use in stationary plant slightly earlier).
All these early superheaters seen to have been mainly intended to avoid
condensation in the cylinder (Ahrons 1825-1925 is a good starting source
on them).
The smoke-tube superheater did, as you say, place much more severe demands on
lubricants.

The
high temperatures of superheating tended to break down the lubricants of
the period, leading to varnish buildup and sticking pistong rings and
valves. This was particularly a problem with slide valves - why the
piston valve also started to become popular around this time.

There'd been a brief flurry of piston valves on (UK) locomotives in the 1870s
- the younger Beattie on the L&SW and Bouch on the S&D notably[2], but none
were free of problems (piston valves on locomotives go back much further,
to Wilson's engine for the S&D in 1826). Interestingly, builders of lower-
pressure engines in marine and stationary applications seem to have made
piston valves work well much earlier than locomotive builders really did,
even though I'd have expected condensation in the valve to be more of an
issue with low pressures..

Secondly, superheating still doesn't work well in trams or shunters,
even today. Superheating requires a hot superheater element, which
requires gasflow past it. Fine on a long-haul run, but hard to achieve
with stop-start work, or long periods standing idle. Some superheater
designs also suffer if cycled between hot & cold and may start to leak.

Good summary.

[1] It's been suggested that the re-entrant smokebox fitted to the Dundee
and Newtyle locomotive "Trotter" in 1834 may have been a low-order superheater,
similar to some used in Germany later (can't recall ref. for this..)

[2] Bouch's machines for the S&D[3] in the early 1870s seem to anticipate
(or exceed!) best practice of 50-60 years later, with 13" diameter long (6.5")
travel, long lap piston valves serving 17" cylinders. Sadly, metallurgical
and lubrication problems with the valves made them near-useless, and Fletcher
rebuilt them with slide valves and inside cylinders, after which they did well
(obviously no problems with the boilers..).

[3] OK, strictly for the NER (Darlington Committee) by then.

--
From the Model M of Andy Breen, speaking only for himself