Smoke Stacks on Union Pacific Steam Locomotives

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Although not their true name, what are known to present-day railfans and modelers as "Sweeney" exhaust stacks first came to Union Pacific in the 1932-1934 time period. Most apparent on UP's 2-8-2, 2-10-2, and 4-6-2 steam locomotives, these so-called "Sweeney" exhaust stacks were merely the most visible part of the on-going effort by Union Pacific to improve the drafting of its steam locomotives, which resulted in more economical operation and increased reliability. A major part of the improvements were annular ports on the exhaust nozzles, similar to those originally designed by Don Sweney in 1899. The improved drafting included the flow of air across the grates in the bottom of the fire box, air flow through the flues, and through the smokebox, along with the nozzles for exhaust steam from the cylinders.

As a brief explanation, on a steam locomotive, the nozzle is a component within a locomotive's smokebox, sitting exactly under the exhaust stack itself. It serves to take the exhaust steam from the cylinders and direct it upwards into the exhaust stack, and to create a draft, or vacuum that improved the burning of fuel in the fire box. Throughout the history of steam locomotives, there have been numerous designs for nozzles, as well as what is known as a "front end", an apparatus meant to control the cinders that, by way of the flues, entered the smokebox from the firebox. Cinders exiting the exhaust stack was a constant concern because of the potential for starting line-side fires. Also, cinders meant excess air flow and unburned fuel, which was not economical in the operation of steam locomotives. Changes in the design of grates in the firebox, and the design of nozzles and front ends in the smoke box was an on-going effort by Union Pacific and other railroads to improve economical and reliable operation, and to prevent claims for damages caused by line-side fires.

The use of what is more correctly called the "Sweeney Nozzle" comes as early as 1899, and Union Pacific's efforts apparently began after the 20-year expiration of those applicable patents in 1919. There are references to the Sweeney Nozzle in the Decatur Review newspaper for December 15, 1899, noting that the Root & Van Deroort Engineering Company (also known as Root & Van Deroort Manufacturing Co.) had just received an order from Illinois Central for Sweeney Nozzles that were to be applied to five of its locomotives. The news item also noted that Mr. Van Deroort was on the IC's Freeport Division, equipping other IC locomotives with the Sweeney nozzle. An earlier reference in the October 20, 1899 issue of the same newspaper noted that the Wabash recently tested an installed Sweeney nozzle, and had placed an order with Root & Van Deroort to equip an additional eight locomotives.

These references in 1899 all refer to the apparatus as the "Sweeney" nozzle. But in fact, the design was patented in May 1899 by Don. R. Sweney. (Note the different spelling.) Sweney himself was a student at the University of Illinois at Urbana when he completed most of the design for his steam locomotive nozzle. He received his degree in 1896 and applied for a patent in October 1898. Don Sweney was born in February 1872, and died in September 1943, and is buried in Sheridan, LaSalle County, Illinois. A biography published in 1906 showed that at the time he was Road Foreman of Engines on CB&Q at Galesburg, and had started with CB&Q in 1899 as a draftsman.

View the Sweney 1899 Patent -- Note that the application was witnessed by W. H. Van Dervoort, one of the principals of the company, Root & Van Dervoort, manufacturers of the design.

The distinctive exhaust stacks known as "Sweeney" stacks on the Union Pacific were the most visible component of these on-going improvements for locomotives built in 1925 and before. It was many of these locomotives built before 1925 that later received Sweeney stacks and other non-visible improvements, beginning in the 1932-1934 time period. Locomotives built in 1922 and 1923 and later (the 7000-class Mountains and 5000-class 2-10-2s), were designed to incorporate many of the improvements, which were less visible because of their larger smoke boxes. (Review the chronology of Union Pacific's steam locomotive deliveries)

Beginning in 1939, the smoke stacks on many older steam locomotives (notably the 4-6-2 Pacifics, 2-8-2 Mikados, and 2-10-2s) were modified again, making the smoke stacks even larger in diameter. This was done as part of the modification that included UP's own design for what they called the "Multiple Jet Nozzle." Instead of the annular ports of the so-called Sweeney design, the newer Multiple Jet Nozzle had four round openings that were different for each class of locomotive. The major visual difference was that annular ported locomotives of the 1930s had a rim on their large smoke stacks, and locomotives with the more modern multiple jet nozzles were smooth and had no rim on their smoke stacks. They were also larger in diameter. These same multiple jet nozzles, and accompanying large stacks, were also used on UP most modern steam locomotives, including the FEF 4-8-4s, the 4-6-6-4 Challengers, and the 4-8-8-4 Big Boys. But being larger locomotives, their large smoke stacks were not as obvious.

Looking For Improvements

Throughout its history, Union Pacific continued to make improvements to the designs it used. The Sweeney Nozzle of the 1930s, more properly known as the annular port nozzle, was just one of many designs to improve the drafting in a steam locomotive. One example from 1940 is a jointly-held patent given to Otto Jabelmann and Leonard Botteron, both of whom were Union Pacific employees. On April 15, 1941, they were awarded a patent for a smokebox design for coal-burning locomotives.

(View the Jabelmann-Botterton patent; Patent 2238057, April 15, 1941)

Known as the "Labyrinth front end", this design was installed in many locomotives, including the newer 4000 and 3900 class locomotives. But the design was a failure and within two years was being replaced by what is known as the "Modified Master Mechanic's front end." Research has not yet found if this Labyrinth front end design was installed in the older 5000, 3500, 7000 and 9000 classes before the program was stopped. However, a portion of the April 17, 1940 patent application describes the need for a design that improved the air flow on UP's steam locomotives, and reads:

The problem of smoke box arrangements for coal burning steam locomotives has long been a troublesome one, because of the importance of arresting burning cinders and the difficulty of doing so without impairing the draft or causing the rapid accumulation of cinders in the smoke box, or both.

In the past, recourse has been to have screen structures of a more or less complicated nature. These were objectionable, first, because they can rarely be made self-cleaning, and, second, because they so obstruct the smoke box that inspection of the tube sheet and inspection of the superheater, if used, are difficult. Attempts have also been made to adapt centrifugal separator principles but the resulting devices have unduly obstructed the smoke box.

The present invention provides a front end arrangement which has gone into actual use and demonstrated successful operation. It is wholly devoid of screens. It is extremely simple to construct and can readily be so proportioned that access for inspection and minor repairs may be had to all parts, and notably to the tube sheet, to the superheater, to the lift pipe and to the exhaust nozzle, without removing any parts in the smoke box.

Most of Union Pacific's work with improved smokebox drafting was produced under the supervision and design of Leonard Botteron in UP's Mechanical Department. In addition to the patented Labyrinth front end noted above, Botteron and Jabelmann held a patent for the four-jet exhaust nozzle that was used on so many of UP's later (built after 1935) steam locomotives.

(View the Jabelmann-Botteron patent; Patent 2273490, February 17, 1942)

In the application for that patent, they wrote:

In steam locomotives the draft on the fire is created by an ejector effect produced by directing the exhaust steam into a so-called lift pipe which is a flaring extension of the stack mounted in the smoke box. The exhaust being intermittent or pulsing, the action is severe and varies considerably according to the conditions of load and speed under which the locomotive is operating. The purpose of the present invention is to stabilize the draft, reduce back pressure, and in consequence materially improve and reduce maintenance costs.

John Bush wrote on November 30, 2014:

Personally, I believe that the word as we know it today, the "long e" pronunciation in "Sweeney" almost certainly resulted from the manner in which he pronounced his name, despite the single "e." While it's possible his name could have been misspelled by someone typing the patent, his own signature belies that.

Don Sweney did not design the large stacks utilized by engineer Leonard Botteron, hired by Otto Jabelmann. Botteron, through myriad experiments and tests, determined the stack dimensions which worked best with each class of engine in coordination with grate designs, tube diameters and lengths, nozzle diameters and many other elements to arrive at the best compromise drafting, back pressures, etc. I believe that the term "Sweeney stack" was simply an outgrowth of terminology used by UP mechanical department men who had decades before the end of steam taken part in these experiments and knew that annular-ported nozzles were of Sweney origin (even if they did have the guy's name wrong).

The work apparently started in the mid 1920s and resulted in the first of the 9000-class 4-12-2 locomotives being fitted with what was known as the Goodfellow Nozzle, a design patented in December 1913. In March 1927, the Goodfellow nozzle was adopted as Common Standard for use on other Union Pacific locomotive classes, replacing the plain or circular nozzles. The Goodfellow nozzle's major feature was four protrusions projecting into the exhaust stream that served to break up the exhaust jet and increase its movement within the smokebox. In combination with a larger diameter exhaust stack, the nozzle produced more horsepower and improved draft and heat convection.

Changing the design of the nozzle ports (larger, smaller, varying shapes), along with newer stack designs created a cyclonic effect in the exhaust steam which created more robust draft and burned coal faster and more completely, increasing heat release (BTU per cubic foot of furnace volume) and thus steaming rate.

Research and testing continued on Union Pacific and on other railroads, and by early 1930, a new nozzle design had reached its final form. Known as the "Annular Port Nozzle," it was very similar to the nozzle designed and patented by Don R. Sweney in 1899. Although somewhat successful with Midwestern roads that burned Illinois coal, the Sweney patent had expired in 1919 and this newer annular port nozzle used several features for its improved design, including changing the shape of the port openings. A design for an annular port nozzle used by Norfolk & Western is shown in the 1922 Sixth Edition of the Locomotive Cyclopedia of American Practice. According to the authors of The Union Pacific Type, Volume 2, page 14, "This nozzle is often referred to in UP circles as the Sweeney type."

William Kratville and Harold Ranks wrote in Motive Power of the Union Pacific, page 159, in their discussion of UP's 7000-class, "Large stacks and Sweeney Nozzles were applied to many of the type in 1932, the 7002 being equipped in March of that year, the 7006 in 1934."

In a discussion of Sweeney stacks on Trainorders in May 2006, John Bush wrote:

It was a UP development as part of their modified Master Mechanics front end arrangement to produce the smokebox draft with less back pressure. By increasing the size of the nozzles, the back pressure was reduced, but so is the exhaust steam velocity and its ability to fill the stack evenly with a continuous vacuum. A larger diameter and taller stack helps with this. Most UP medium size power had UP style stacks (wide, slight taper and no lip a top edge), but the Sweeney stack is noticeably tall and large. It looks obviously oversize on smaller power like the 2-8-2's and heavy 4-6-2's.

These very large stacks generally known as the "Sweeney" type were a part of UP's drafting experiments which extended from a major effort commencing about 1936 until the onset of WWII and then continuing in fits and starts for nearly a decade after. Actually, this "drafting" experimentation was an on-going part of steam design and UP had tried many different nozzles and arrangements by the time the effort resulting in these stacks was initiated.

Although the annular port "Sweeney" nozzle was adopted by UP on an apparent limited basis, it appears that Union Pacific continued to use the patented Goodfellow nozzle (patent expired in 1933) on older locomotives, based on the drawing 443CA23171, dated 6-6-39. This helps explain why not all locomotive classes on Union Pacific received annular port nozzles, and the accompanying and distinctive large exhaust stacks.

Based on the dates of available drawings, it appears that the large "Sweeney" stacks were applied to locomotives equipped with the UP-designed "Multiple Jet" nozzle, a design that was used on all of UP's later (post-1940) steam locomotives.


Gordon McCulloh wrote in A History of Union Pacific Steam, page 124 (2014 edition), talking about the improvements to the 5000-class 2-10-2s, "Original 1917 smoke stacks were 22-inches inside-diameter (ID) and 22-inches tall. Starting with the TTT-5s, the ID was reduced to 20-3/4 inches. Circa 1932-33, Firebar grates and Sweeney nozzles were added, and stacks were increased to 27-inches ID and 23-inches high. In 1941 stacks were widened further to 31-1/4 inches ID and shortened to 20-1/4 inches, displaying a pronounced taper. Multiple jet nozzles were applied and coal burners were fitted with Labyrinth front ends. This became standard on large power built before 1925. These changes improved draft and reduced erosive wear."

A comparison of available drawings, dated in 1939 and 1943, shows that all of the larger exhaust stacks used with annular port "Sweeney" nozzles on all locomotive classes had a total stack length (combined interior and exterior) of between 67-1/2 and 77-1/4 inches. They were all about 32 inches inside diameter at the top. These unique stacks are not as apparent on the newer locomotives, with their larger diameter smokeboxes. It is the older locomotives, like the 2-8-2 Mikados and 4-6-2 Pacifics with their smaller smokeboxes that the large exhaust stacks are so apparent. To attain the length needed for the annular port nozzles to be effective, the stacks themselves stuck out further on the older locomotives.


Stacks and Nozzles -- Digital images of several representative drawings, from the UtahRails Collection.

More Information

Kratville, William W., and John Bush. The Union Pacific Type, Volume II, William W. Kratville, 1995; companion to The Union Pacific Type, Volume I, William W. Kratville, 1990.

Kratville, William W., and Harold E. Ranks. Union Pacific Locomotives, Volume II, Barnhart Press, 1960; companion to Union Pacific Locomotives, Volume I, Barnhart Press, 1960.

McCulloh, Gordon. A History of Union Pacific Steam, Gordon McCulloh, 2014.