Giesl ejectors and what they do

Giesl ejectors and what they do

By Ernest H. Robl 

Why do some Austrian steam locomotives (and those of a few other countries as well) look like that a giant squeezed their smokestack into a flat oblong shape?

Because they were fitted with Giesl ejectors, an invention of the Austrian locomotive designer Dr. Adolph Giesl-Gieslingen, that came very late in the steam era.  This device both improves the efficiency of the steam locomotive and reduces fuel consumption.

As this device was invented when steam was already on its way out in most countries, it’s amazing that so many locomotives – even some narrow gauge steamers – were fitted with it.  On the other hand, in Austria steam survived in revenue service into the 1970s (narrow-gauge steam into the 1980s) and many steam locomotives still underwent major rebuilds, including being fitted with entirely new boilers, through the late 1960s.  And, that was when many of them also received Giesl ejectors.

This was a result of the fact that Austria’s railways, still trying to recover from WW II, were pursuing a dual strategy.  They were trying to rebuild and electrify lines as fast as possible, including purchasing all the new electric locomotives they could afford, while at the same time making existing motive power last as long as possible.



Detail view of a catalog illustration of an HO Roco model of an Austrian BR 38 steam locomotive fitted with a Giesl ejector.

Why didn’t the Giesl ejector become more popular in the rest of the world?  In part because it came so late in the steam era that in many countries – particularly where the railroads could buy all the new diesels they needed – there wasn’t much interest in improving the efficiency of steam locomotives that were already scheduled to be scrapped in the near future.

So, what exactly does the Giesl ejector do?


Okay, before we get to specifics, we first need to look at how steam locomotives in general work.

What you see emerging from the smokestack of modern (relatively speaking, meaning at least early 20th century) steam locomotives is actually a mixture of steam and smoke.  Yes, you will sometimes see the steam locomotive venting steam from the cylinders, when the engineer has opened the cylinder cocks, but during normal operation, the steam that has been used in the cylinders also goes out the smokestack.

The reason for this is the use of the blast pipe, usually located in the center of the smokestack.

As the steam rushes out the blast pipe, it creates a vacuum that pulls the air along with it.  That air is coming from the firebox where fuel is being burned.

Increase the draft of air through the firebox, and you will provide more oxygen to the combustion of fuel, and you get a better burning fire.

What Giesl-Gieslingen did

What Giesl-Gieslingen did was to invent a better blast pipe – or actually an arrangement of multiple blast pipes.  Rather than venting steam through a single blast pipe, the Giesl ejector uses a series of blast pipes in a fan-shaped oblong smokestack.

This produced an even better draft through the smokebox and the firebox.  Studies showed an increase in 5-15 per cent in the power of steam locomotives (depending in part on the specific locomotive design) and a corresponding decrease in the amount of fuel needed.


Detail view of a catalog illustration of a Roco HO model of an Austrian BR 152 steam locomotive fitted with a Giesl ejector.  (The Austrian series 152 was a variant of the class 52 German war locomotive with a riveted instead of welded frame.)


The inventor of the Giesl ejector was born in 1903 and died in 1992 after a long life devoted to railroad technology.  And, he even had an American connection.  Giesl-Gieslingen graduated from the Technical University of Vienna with a degree in engineering.

Prior to WW II, he spent several years in the U.S., studying locomotive design at the New York Central — and married an American woman in the process.  He also became proficient in English during the time.

Giesl-Gieslingen returned to Austria just prior to WW II.  After the war, he began looking at how to get more out of the initially very inadequate pool of locomotives left to the new Austrian Federal Railways.  That was when he finalized the design of the Giesl ejector, for which he also received a patent.  Sadly, many of the railroads outside of Austria that adopted Giesl ejectors — particularly in the then East Bloc — did so without honoring the patent or paying royalties.

Giesl-Gieslingen served as professor emeritus at the Vienna Technical University in his later years.


In Austria, Giesl-Gieslingen is known as much for being a prolific author and out-and-out railroad enthusiast, as for his invention of the Giesl ejector, which gave locomotives a distinctive look.

In addition to writing many technical papers, Giesl-Gieslingen wrote three books on steam locomotives for a publisher of popular railroad literature.  He also contributed to many other works and, with his knowledge of English, also translated some railroad-themed pieces written by others.

The most famous locomotive

Probably the most famous locomotive fitted with a Giesl ejector is also one on which the Giesl ejector is not all that obvious.

Most fans of European railroading are aware of the one-of-a-kind East German high-speed steam locomotive 18.201, built to test the running characteristics of new higher-speed German coaches.  But, when most looked at that famous — and currently still operable — locomotive, they just noticed that it has a rather large oval smokestack.


Catalog illustration of one of several HO Roco versions of the still-operable 18.201.  (The versions differ mostly in the lettering applied over time, but also include a short-term special red paint scheme.)

The reason the Giesl ejector is not obvious is that, due to the very large boiler and the need to stay within European clearances, the ejector is set deep into the smokebox.

So, now, when someone asks why some steam locomotives had or have flat smokestacks, you can tell them why.


3 Responses to Giesl ejectors and what they do

  1. Jessica says:

    A steam injector is typically used to deliver cold water to a boiler against its own pressure using its own live or exhaust steam, replacing any mechanical pump.

  2. Karl Brand says:

    During the early 1920′s, David M. Lewis patented (US Patent Office 1539124) a draft appliance to produce a continuous draft and more effective draft. Did Giesl improve the Lewis appliance or is the Giesl exhaust ejector a completely different invention? The Lewis Appliance saw limited use in the US. I know that the Frisco applied the Lewis Draft Appliance to its Alco-built (1910), 2001-class, 2-8-8-2 Mallets.

    • Ernest Robl says:

      As far as I know — and have been able to determine — the Giesl ejector is a completely different device. It still sends out a blast of steam with each piston movement — only the blast is sent out through multiple pipes, increasing the vacuum draft from what would be produced with a single pipe.

      – Ernest

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