A jointed-boiler locomotive was a variant of the Mallet

articulated locomotive An articulated locomotive is a steam locomotive (rarely, an electric locomotive) with one or more engine units that can move independent of the main frame. Articulation allows the operation of locomotives that would otherwise be too large to neg ...

, in which a flexible coupling was introduced midway along the length of the boiler casing, which allowed the boiler to bend laterally when the locomotive was on curved track. ATSF jointed loco 3322

Six such locomotives, all of

2-6-6-2 Under the Whyte notation for the classification of steam locomotives by wheel arrangement, a is a locomotive with one pair of unpowered leading wheels, followed by two sets of three pairs of powered driving wheels and one pair of trailing wheel ...

wheel arrangement, were built for the

Atchison, Topeka & Santa Fe Railroad The Atchison, Topeka and Santa Fe Railway , often referred to as the Santa Fe or AT&SF, was one of the larger railroads in the United States. The railroad was chartered in February 1859 to serve the cities of Atchison and Topeka, Kansas, and ...

in 1910 and 1911. The first one built, number 1157, was assembled by the AT&SF in their Topeka shops from two 2-6-2’s (numbers 1051 and 1125). All the rest were built new by Baldwin Locomotive Works.

Design

In a conventional Mallet, the rigid boiler is fixed to the rearmost of the two engine frames, with the front of the boiler supported on a sliding bearing over the pivoting front engine such that when the locomotive traverses a curved track, the front (

smokebox A smokebox is one of the major basic parts of a steam locomotive exhaust system. Smoke and hot gases pass from the firebox through tubes where they pass heat to the surrounding water in the boiler. The smoke then enters the smokebox, and is e ...

) end of the boiler overhangs toward the outside of the curve. The jointed boiler, with the front half rigidly fixed to the front engine, eliminated this overhang. This new design was intended to reduce track wear, especially on curves where the outer rail carried a greater load, and to improve the riding characteristics of the locomotive.

Construction

The two boiler sections served different functions: The rearmost section with the

firebox Firebox may refer to: *Firebox (steam engine), the area where the fuel is burned in a steam engine *Firebox (architecture), the part of a fireplace where fuel is combusted *Firebox Records Firebox Records was a Finnish record label based in S ...

generated and

superheated A superheater is a device used to convert saturated steam or wet steam into superheated steam or dry steam. Superheated steam is used in steam turbines for electricity generation, steam engines, and in processes such as steam reforming. There are ...

the steam. The forward section contained a reheater (for low-pressure steam serving the front engine),

feedwater heater A feedwater heater is a power plant component used to pre-heat water delivered to a steam generating boiler. Preheating the feedwater reduces the irreversibilities involved in steam generation and therefore improves the thermodynamic efficiency of ...

and

. The large flexible joint in the boiler casing carried only combustion gases, at or slightly below atmospheric pressure. Steam and water to the front section were delivered by pipes external to the main casing, with pivoting

elbows The elbow is the region between the arm and the forearm that surrounds the elbow joint. The elbow includes prominent landmarks such as the olecranon, the cubital fossa (also called the chelidon, or the elbow pit), and the lateral and the media ...

in high-pressure steam lines, and hoses in water lines, as flexible connections. ATSF 1159 bellows

Two designs of the large flexible coupling were used: * A double

ball joint In an automobile, ball joints are spherical bearings that connect the control arms to the steering knuckles, and are used on virtually every automobile made. They bionically resemble the ball-and-socket joints found in most tetrapod animals. ...

assembly consisting of cast iron sleeves, fitted one within the other and provided with compression straps to keep the joints air-tight while allowing lateral movement. * A

bellows A bellows or pair of bellows is a device constructed to furnish a strong blast of air. The simplest type consists of a flexible bag comprising a pair of rigid boards with handles joined by flexible leather sides enclosing an approximately airtig ...

joint, similar to a

concertina A concertina is a free-reed musical instrument, like the various accordions and the harmonica. It consists of expanding and contracting bellows, with buttons (or keys) usually on both ends, unlike accordion buttons, which are on the front. The ...

, consisted of several pairs of concentric tapered steel rings, each

rivet A rivet is a permanent mechanical fastener. Before being installed, a rivet consists of a smooth cylindrical shaft with a head on one end. The end opposite to the head is called the ''tail''. On installation, the rivet is placed in a punched ...

ed to its neighbor along alternating inside and outside edges. This design proved less successful because coal cinders would accumulate in the folds and force the seams open when the bellows was compressed. These were soon replaced with ball joints.

Performance

The locos worked well enough that they remained in service for 15 to 18 years, but the hoped-for improvements in riding and track wear were not as good as had been hoped. The complicated construction required high maintenance, and no further examples were built. Jointed boilers were however included in Baldwin’s

patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A ...

ed but unbuilt 1913 proposals for massive 2-8-8-8-8-2 quadruplex and 2-8-8-8-8-8-2 quintuplex locomotives.”What Might Have Been,” ''

Trains In rail transport, a train (from Old French , from Latin , "to pull, to draw") is a series of connected vehicles that run along a railway track and transport people or freight. Trains are typically pulled or pushed by locomotives (often know ...

'' Magazine, August 1951

References

{{reflist 2-6-6-2 locomotives Atchison, Topeka and Santa Fe Railway locomotives Baldwin locomotives Mallet locomotives Steam locomotives of the United States Railway locomotives introduced in 1910