| One of the most important
components of
virtually all steam locomotives is the
exhaust system. Early steam
locomotive builders such as George
Stephenson discovered the principal
upon which virtually all steam locomotives
built since have used. They
found that directing the "waste" steam
exhausted from the cylinders at
the end of each stroke up the boiler's
chimney greatly increased the
air flow through the fire. This caused the
fire to burn hotter and
faster, allowing a locomotive boiler to
generate dramatically more
steam than stationary boilers of similar
size.
As locomotive design progressed, builders
realized that
the proportions and configurations of the
chimney and the exhaust pipe
had a significant effect on how well the
exhaust system worked. A major
concern was the effect of back-pressure
on the performance of
the locomotive's cylinders. The locomotive
exhaust could be built with
a small exhaust nozzle, which caused the
exhaust steam to jet up the
stack at high velocity, which would
produce excellent gas flow through
the boiler (draft). However, this small
nozzle would impede the flow of
the exhaust steam from the cylinders,
causing excessive back-pressure.
This back-pressure saps power from the
locomotive's cylinders, reducing
the locomotive's performance. Good draft
increased the locomotive's
power, but high back-pressure could cancel
this out.
This was the chief task of locomotive
exhaust designers:
how to produce the maximum draft while
producing the minimum
back-pressure on the cylinders.
Until the 20th century, the physics of
gas flow were not
understood and the theories and laws which
could be used to design
exhaust systems did not exist.
Consequently, early locomotive exhaust
systems were developed through a process
of trial-and-error.
 |
This exhaust
system, from a
locomotive in New Zealand, is
similar to that of many 19th
Century
locomotive exhaust systems. The
steam nozzle is at the bottom,
and it
exhausts through a "petticoat"
and finally up through the main
chimney
(the separate petticoat was a
20th century development). This
chimney
includes a spark arresting
apparatus, which forces the
exhaust gases
through several turns in order
to make sparks and cinders drop
out into
the bottom of the spark
arrestor. |
| This drawing shows
a typical
locomotive exhaust system from a
U.S. steam locomotive built in
the
20th century. The drawing shows
a cross-section of the smoke box
at the
front of a locomotive boiler
(the boiler would be to the left
of the
view). The steam nozzle is at
the bottom of the smoke box,
exhausting
its steam jet up the stack which
is at the top. The drawing also
illustrates the empirical design
formulas which were used to size
the
components. After building
hundreds of exhaust systems,
designers
decided that the proportions of
the components listed above
would work
best for most locomotives under
most conditions. |
 |
 |
This drawing shows
an early Kylchap
exhaust. Chapelon used the
exhaust splitter developed by
Finish
engineer Kylala, which divides
the exhaust stream into four
parts. The
Kylchap draws in gases from more
than one level of the smokebox,
which
Chapelon believed to be an
important feature in providing
an even gas
flow through the many tubes of
the boiler. Later Kylchap
exhausts used
two levels of entrainment and
two or even three stacks. |
| The Kylala exhaust
splitter was an
important part of the Kylchap
exhaust system. |
 |
 |
In the U.S.,
several railways
developed improved exhaust
systems using annular exhaust
nozzles and
larger stacks.
Plan View of Annular Exhaust
Nozzle (above)- Sectional
Views of
Smokebox (left)- Known as a
"Waffle Iron" exhaust on the
N&W
|
| The Lemaitre
Exhaust was developed by
Lemaitre, a mechanical engineer
from the NORD Belge. The
Lemaitre
featured 5 nozzles in a circular
pattern exhausting up a large
diameter
stack, with a variable area
nozzle exhausting up the center. |
 |
|
|
In the late
1940's, Dr. Adolph
Giesl-Gieslingen developed a new
exhaust design called the Giesl
Ejector. He patented this device
and it was applied to thousands
of
steam locomotives all over the
world. The Giesl Ejector
featured a
series of small in-line nozzles
exhausting up a thin, oblong
chimney.
drawing courtesy Stuart Kean |
 |
This drawing shows
the Kylpor exhaust
system developed by L. D. Porta
from the Kylchap as applied to
the
2-10-2s of the Rio Turbio
Railway in Argentina. |
| Finally, this
diagram shows the
Lempor (Lemaitre-Porta) exhaust
developed by Porta and applied
to many
locomotives. Porta also
developed an extensive theory
describing the
performance and design of these
exhaust systems. |
 |
 |
One of the most
recent new exhaust
systems was developed for the
Garratt locomotives of the
Rhodesian
Railways. These were known as
"pepperpot" exhausts and were
later
fitted to many Garratts which
were overhauled and restored to
service
in the early 1980's in the new
country of Zimbabwe. This nozzle
arrangement was used in
combination with a larger
chimney, and was
developed as alternative to
Giesl exhausts experimentally
fitted to
Garratts in the 1960's. The
pepperpot exhaust was preferred
because (1)
it was locally developed (the
Giesl was proprietary and
royalties had
to be paid for its use) and (2)
the Pepperpot was less
susceptible to
unauthorized tampering which
tended to cause problems with
the Giesls
in normal service. |
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