| 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. |
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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. |
 |
 
|
Here are a couple of
3-D renderings of a Lempor
ejector.
The picture on the left shows
the full exhaust system with a
section taken out of the stack
to show the inside.
The picture on the right is a
closeup showing the 4 steam
exhaust nozzles (set an included
angle of 10 degrees, based on
Wardale's latest experiments),
the bellmouth entry, and the
mixing chamber (the lower,
straight portion of the exhaust
stack).
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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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