Vauclain compound
Encyclopedia
The Vauclain compound was a type of compound steam locomotive
Steam locomotive
A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...

 that was briefly popular around 1900. Developed at the Baldwin Locomotive Works
Baldwin Locomotive Works
The Baldwin Locomotive Works was an American builder of railroad locomotives. It was located in Philadelphia, Pennsylvania, originally, and later in nearby Eddystone, Pennsylvania. Although the company was very successful as a producer of steam locomotives, its transition to the production of...

, it featured two pistons moving in parallel, driving a common crosshead and controlled by a common valve gear
Valve gear
The valve gear of a steam engine is the mechanism that operates the inlet and exhaust valves to admit steam into the cylinder and allow exhaust steam to escape, respectively, at the correct points in the cycle...

 using a single, complex piston valve.

Advantages and disadvantages

The claimed advantage for this arrangement, as with other compounding arrangements, was greater economy due to lower fuel and water consumption. In practice uneven forces at the crosshead produced excess wear, with increased maintenance costs thus offsetting any fuel economies. The integration of the compounding system into the smokebox saddle made conversion to conventional engines straightforward, so most Vauclain compounds were so converted and led normal lives thereafter. The only known operable example is Manitou and Pikes Peak Railway #4, which is preserved on-site along with the static display of its sister #5.

Design

The key to the Vauclain compound is its valve system. In essence, there is an extra system of valves, concentric with the usual middle steam passage in conventional single expansion piston valves. This passage connects the high pressure cylinder exhaust to the low pressure cylinder intake. The driving pistons are rigidly connected to either side of the crosshead, so that they move in concert. As high pressure steam is admitted to one side of the high pressure cylinder, the low pressure steam exhausted from the other side is passed through the valves to the opposite side of the engine and into the low pressure cylinder; finally the exhaust steam from the opposite side of the low pressure cylinder escapes through the center part of the valve to the blastpipe.

The high and low pressure cylinders were mounted in vertical line with each other, with the piston rods in parallel. Usually the low pressure cylinder was on the bottom, but clearance issues sometimes caused it to be put on the top. In the former case, the valve cylinder was mounted directly inboard from the high pressure cylinder; in the latter case, the valves were also placed inboard, but at a level between the two power cylinders. The placement of the valves necessitated an inside-connected valve gear, and the Stephenson pattern
Stephenson valve gear
The Stephenson valve gear or Stephenson link or shifting link is a simple design of valve gear that was widely used throughout the world for all kinds of steam engine. It is named after Robert Stephenson but was actually invented by his employees....

 was used (being the dominant type of the era anyway). One extra appliance required was a starting valve, manually controlled, which allowed admission of high pressure boiler steam directly to the low pressure intake. Without this, the low pressure cylinders would have to actually work against atmospheric pressure.

Each side of the locomotive had its own separate engine, as with conventional locomotives. This eliminated the connections between sides characteristic of cross-compound engines, where the low and high pressure cylinders were on opposite sides. The direct flow of steam between the high and low pressure cylinders on each side of the locomotive eliminated the need for a receiving chamber to store the steam. It also avoided subjecting the locomotive frame to unequal forces from separate high and low pressure sides. The whole package was compact and took up little more space than conventional equipment. Indeed, at first glance from the side the Vauclain compound can be mistaken for a conventional simple locomotive; the only giveaways are the unusual arrangement of the crosshead and (viewed from the front) the extra cylinder.

The scheme did not produce a more powerful locomotive; the maximum practical tractive force was governed by the weight on the drivers, and this did not change. The advantage was efficiency: the compounding reduced the steam required for the same performance. According to Baldwin's standard sizing tables, the high pressure cylinder on the compound was about 70% the diameter of the single cylinder of the conventional engine; therefore, steam consumption for the same stroke and degree of cutoff was about half that of the conventional engine. In practice lesser results were generally achieved, with Baldwin in 1900 reporting trials by various railroads showing fuel savings of 17% to 45%. In order to produce symmetrical forces, the low pressure cylinders had to be about 66% larger in diameter than the high, or about 20% larger than conventional cylinders; for small drivers this could lead to the clearance issues mentioned earlier, thus requiring the low pressure cylinders to be on top.

History

The Vauclain compound was introduced in 1889 through by its namesake and the then general superintendent of Baldwin and eventually president of the company, Samuel M. Vauclain
Samuel M. Vauclain
thumb|Samuel Matthews Vauclain was an American engineer, inventor of the Vauclain compound locomotive, and president of the Baldwin Locomotive Works. He was awarded the John Scott Award and the Elliott Cresson Medal by The Franklin Institute in 1891...

. Soon most Baldwin customers were operating some examples; a brochure from 1900 lists sales to 140 customers, including large fleets to such Class I railroad
Class I railroad
A Class I railroad in the United States and Mexico, or a Class I rail carrier in Canada, is a large freight railroad company, as classified based on operating revenue.Smaller railroads are classified as Class II and Class III...

s as the Baltimore and Ohio Railroad
Baltimore and Ohio Railroad
The Baltimore and Ohio Railroad was one of the oldest railroads in the United States and the first common carrier railroad. It came into being mostly because the city of Baltimore wanted to compete with the newly constructed Erie Canal and another canal being proposed by Pennsylvania, which...

, the Chicago, Milwaukee and St. Paul Railway, the Erie Railroad
Erie Railroad
The Erie Railroad was a railroad that operated in New York State, New Jersey, Pennsylvania, Ohio, Indiana, and Illinois, originally connecting New York City with Lake Erie...

, the Lehigh Valley Railroad
Lehigh Valley Railroad
The Lehigh Valley Railroad was one of a number of railroads built in the northeastern United States primarily to haul anthracite coal.It was authorized April 21, 1846 in the U.S. state of Pennsylvania and incorporated September 20, 1847 as the Delaware, Lehigh, Schuylkill and Susquehanna Railroad...

, the Norfolk and Western Railway
Norfolk and Western Railway
The Norfolk and Western Railway , a US class I railroad, was formed by more than 200 railroad mergers between 1838 and 1982. It had headquarters in Roanoke, Virginia for most of its 150 year existence....

, and the Philadelphia and Reading Railroad. Many other lines purchased one or two as samples. Vauclain was awarded the Elliott Cresson Medal
Elliott Cresson Medal
The Elliott Cresson Medal, also known as the Elliott Cresson Gold Medal, was the highest award given by the Franklin Institute. The award was established by Elliott Cresson, life member of the Franklin Institute, with $1,000 granted in 1848...

 of the Franklin Institute
Franklin Institute
The Franklin Institute is a museum in Philadelphia, Pennsylvania, and one of the oldest centers of science education and development in the United States, dating to 1824. The Institute also houses the Benjamin Franklin National Memorial.-History:On February 5, 1824, Samuel Vaughn Merrick and...

 in 1891 for the locomotive design; in recommending award, the reviewing committee wrote,
"Your committee, in conclusion, find that in view of the state of art, the Vauclain compound locomotive is a distinctly new and original type of locomotive. It is the most marked departure from the usual construction of engines, that has elicited general satisfaction wherever introduced, and in view of the reliable and satisfactory performance in service under the largest variations of conditions, immunity from total disablement, ready adaptability within limits of space incapable of accommodating other compound engines, and general applicability to and utility in railway service, it is, in the opinion of your committee, deserving of recognition by the award of the Elliott Cresson Medal of the Franklin Institute, which they hereby recommend."


This popularity, however, was short-lived. Significant maintenance difficulties appeared, particularly with uneven forces wear on the crosshead guides. The two cylinders were supposed to be proportioned so as to do equal work (with the low pressure being three times larger than the high); but since the steam passed between the low and high pressure cylinder is always expanded, even before cutoff, the force produced in the low pressure cylinder varies differently from that in the high pressure cylinder. The complex valve assembly and the starter valve also led to increased maintenance costs. The introduction of the superheater
Superheater
A superheater is a device used to convert saturated steam or wet steam into dry steam used for power generation or processes. There are three types of superheaters namely: radiant, convection, and separately fired...

 was the final nail in the coffin, as it increased efficiency further and was much easier to maintain.

All of the compounding machinery was contained in the valve chest, which in American locomotives (in the days before one piece cast frames) was integral with the smokebox saddle. The whole unit therefore could be unbolted and replaced with conventional single expansion cylinders. That was the typical fate of Vauclain compounds: when the time came for a major overhaul, the compound machinery and Stephenson valve gear were removed, and the engine was rebuilt with superheating, Walschaerts valve gear, and conventional cylinders.

Ironically, two of the four surviving Manitou and Pike's Peak Railway locomotives were converted to compounding after experience with M&PP #4, built in 1893 and at present the only operating Vauclain compound. (Vauclain himself had travelled to the line to deal with operational issues with the original engines in their pre-compounding state.) All six steam locomotives of the line were of this type.

Europe

The Vauclain system was also used in Europe and a Danish example (DSB 996) is preserved at Railworld
Railworld
Railworld is a railway museum in Peterborough.http://www.railworld.net/ It is located beside the Peterborough Nene Valley railway station but it is a separate organisation.-Exhibits:Alco switcher...

, Peterborough
Peterborough
Peterborough is a cathedral city and unitary authority area in the East of England, with an estimated population of in June 2007. For ceremonial purposes it is in the county of Cambridgeshire. Situated north of London, the city stands on the River Nene which flows into the North Sea...

, England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

.

New Zealand

Seven Vauclain compounds were supplied to the Wellington and Manawatu Railway Company (WMR) which operated the Wellington - Manawatu Line
Wellington - Manawatu Line
The Wellington and Manawatu Line is an unofficial name for the section of New Zealand's North Island Main Trunk Railway between Wellington and Palmerston North...

 in New Zealand. WMR No. 13, built in 1894, was the first compound in New Zealand and the first narrow-gauge compound in the world. In 1908 No. 13 was classified as the NZR Oa class
NZR Oa class
The OA class, built by the Baldwin Locomotive Works for the Wellington and Manawatu Railway in New Zealand, consisted of a solitary steam locomotive. Ordered in 1894, it entered service in August of that year as No. 13 and was the first narrow gauge Vauclain compound in the world...

 when the WMR was nationalised. Later Vauclain compounds purchased by the WMR were the NZR Na class
NZR Na class
The NA class was a class of two steam locomotives that operated on the privately owned Wellington and Manawatu Railway and then the publicly owned national rail network in New Zealand...

 (No. 14 of 1894 & No. 15 of 1896); NZR Nc class
NZR Nc class
The NZR NC class was a class of two steam locomotives built by Baldwin Locomotive Works built for service on New Zealand's private Wellington and Manawatu Railway...

 (No. 5 (1901) & No. 18 of 1904); NZR Oc class
NZR Oc class
The OC class, built by the Baldwin Locomotive Works for the Wellington and Manawatu Railway in New Zealand, consists of a solitary steam locomotive. Ordered in 1896 as an externally similar but more powerful version of the OA class locomotive ordered in 1894, it entered service in June 1897 as No....

 (No. 16 of 1896); and NZR Bc class
NZR Bc class
The BC class comprised a single steam locomotive that operated on New Zealand's national rail network. Built for the Wellington and Manawatu Railway and classified simply as No...

(No. 17 of 1901).

Although standard-gauge compounds usually had the larger low-pressure cylinder on each side below the high-pressure cylinder, this was reversed on narrow-gauge locomotives with the low-pressure cylinder above the high-pressure cylinder to provide greater clearance from platforms.
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