Knuckle couplers are a semi-automatic form of railway coupling that allow rail cars and locomotives to be securely linked together without workers having to get between the vehicles.
Originally known as Janney couplers (the original patent name) they are almost always referred to as knuckles in the US and Canada (regardless of their actual official model name, nowadays generally various AAR types in North America), but are also known as American, AAR, APT, ARA, MCB, Buckeye, tightlock (in the UK), automatic couplers (in some Australian states) or centre buffer couplers.
Types There are many variations of knuckle coupler in use today, and even more from the past. Some variants of knuckle couplers include:
Janney: the American original, a rather finicky coupler; reportedly annoying to make open and close. This design was obsolete by 1900.
MCB: In the latter 1880s the Master Car Builder's Association (MCB) were faced with choosing a standard from the multitude of mutually incompatible automatic coupler designs then on offer. They could not, with any effect, choose a single design, but favored Janney's. The patent holders either proposed, or were persuaded, to release their rights to the Janney coupler's mating profile, and in 1888 a slightly modified profile became the MCB standard. Thus the MCB standard initially specified only the interface between MCB automatic knuckle couplers, leaving all other aspects to open competition between manufactures. There were a number of revisions and additions to the standards over the next two decades, with extensive updates in 1899.Car Builder's Dictionary, 1906, p7. By then there were a great many variations of MCB couplers in use - an 1899 knuckle identification chart illustrates 78 mutually incompatible knuckles.Railroad Car Journal, July 1899 Further revisions to the standard followed through 1916, when what is now known as the AAR type D was recommended as the North American standard coupler. However some of the better MCB couplers remained in use for decades, and a few are still manufactured for non-interchange service or export.
The slotted-knuckle variation is a transitional type, used while converting from link-and-pin couplers to knuckle couplers. Here the vertically pivoted knuckle has a horizontal slot through its exposed width, with a vertical pin hole through the knuckle tip. With the knuckle closed and locked, a coupling link can be inserted through the slot and pined through the vertical hole, allowing coupling to cars fitted with the older link-and-pin system. Slotted knuckles were common in North America prior to 1900, in South Africa after 1925, and anywhere else during this conversion. They are rarely found after conversion is complete.
AAR: In the first decade of the 1900s there were upwards of 75 makes of MCB standard-compliant couplers in use on North American railroads. All of these could couple together. Practically none shared internal design or parts. Most were offered with multiple shank patterns to match different draft gears - the Tower coupler had 16.Car Builder's Dictionary, 1906, figs 1292-1956White, John H, The American Railroad Passenger Car, p566-577 With freight cars freely interchanged throughout the continent's standard-gauge lines, the problem of maintaining these couplers fell upon all roads, and prompt repair of damaged couplers was effectively impossible.
Circa 1913 the MCB Coupler Committee, in cooperation with five of the principal coupler manufactures, set out to devise a standard coupler for North American railroads, one that mated with existing MCB standard couplers, was up to the heaviest anticipated service, and of proven operational efficiency and long service life. The participating coupler companies agreed to each submit their best designs for rigorous testing under the MCB committee's supervision, to work together to eliminate weaknesses and combine the best features of each, and to freely share (among themselves) any patented features chosen or developed for the new standard. The result was the American Association of Railroads (AAR, successor to the MCB) Standard "D" coupler of 1916. This was upgraded to the No. 10 contour in 1918, which largely eliminated the MCB coupler's tendency to jackknife under buffing forces.Locomotive Cyclopedia, 1930, p880-883 A stronger version, the AAR type E was adopted in 1931, the principal change being an increase in knuckle depth from .
Both the D and E were essentially freight car couplers, and necessarily provided a degree of slack in their coupling, which is undesirable in passenger service. The type H tightlock passenger coupler was developed in the 1930s, made an alternative passenger standard in 1937, and the standard for new North American passenger cars in 1947. This design incorporates a pin and socket that flank what is essentially a type E coupler head. While it can still couple with the freight couplers, two Tightlock couplers, when coupled, form a nearly rigid drawbar between their car's draft gear, eliminating the impact associated with slack action.White, John H, The American Railroad Passenger Car, p571-574
The surge in North American freight car capacities in the latter 1900s, particularly that of tank cars, emphasized the need to prevent cars uncoupling in the event of a derailment. Several variations of the standard knuckle coupler incorporate shelves above or below the coupler head, to prevent vertical separation. The development of unit trains for moving coal or ore led to the substitution of rotary dumped gondolas for traditional hopper cars. These incorporate a rotating coupler and draft gear in one end, to allow the cars to be dumped without uncoupling them.
History First design Janney was a dry goods clerk and former Confederate Army officer from Alexandria, Virginia, who used his lunch hours to whittle from wood an alternative to the link and pin coupler. The term buckeye comes from the nickname of the US state of Ohio, the "buckeye state" and the Ohio Brass CompanyOhio Brass Company which originally marketed the coupling.Ohio Brass company
In 1893, satisfied that an automatic coupler could meet the demands of commercial railroad operations and, at the same time, be manipulated safely, the US Congress passed the Safety Appliance Act. Its success in promoting switch-yard safety was stunning. Between 1877 and 1887, approximately 38% of all railworker accidents involved coupling. That percentage fell as the railroads began to replace link and pin couplers with automatic couplers. By 1902, only two years after the SAA's effective date, coupling accidents constituted only 4% of all employee accidents. Coupler-related accidents dropped from 11,710 in 1893 to 2,256 in 1902, even though the number of railroad employees steadily increased during that decade.
When the Janney coupling was chosen to be the American standard, there were 8,000 patented alternatives to choose from. The only significant disadvantage of using the AAR (Janney) design is that sometimes the drawheads need to be manually aligned.
During the transition period from link-and-pin couplers, knuckle couplers on many locomotives had a horizontal gap and a vertical hole in the knuckle itself to accommodate, respectively, a link and a pin, to enable it to couple to vehicles which were still equipped with the older link-and-pin couplers.
Changes since 1873
The knuckle coupler has withstood the test of time since its invention, with only minor changes: The current AAR contour dates back to the 1888 Master Car Builders Association (MCBA) design, which, in turn is based on the 1879 Janney patent. Buckeye coupler, a side-operated version of the MCBA couplerBuckeye coupler (scroll down) Type D coupler, adopted in 1916 by the MCBA (predecessor of ARA), had individual parts interchangeable, simplifying maintenance. Earlier designs had compatible profiles, but component parts differed between manufacturers, creating maintenance problems when cars were interchanged with other railroads. Type E coupler, adopted in 1930 by the ARA (predecessor of AAR), also had individual parts interchangeable, though not with Type D due to improvements. Still the most widely used design today. Tank cars carrying hazardous materials are equipped with Type E double shelf couplers.Tedrail Type F coupler, a vertically interlocking variation to prevent accidents, derailments and wrecks from disconnecting the coupler. Type F also includes versions with rotating shafts for hopper car rotary dumpers, such as on the Pilbara railways and Transnet Freight Rail's Sishen-Sandanha Iron Ore and Ermelo-Richards Bay Coal Terminal lines. Type H coupler, a "tight-lock" variation to reduce slack action and improve safety for passenger cars. Now under the supervision of the APTA (American Public Transportation Association). Improvements in metallurgy and casting techniques to increase maximum trailing load. Some narrow-gauge railways such as the Victorian Puffing Billy Railway use a three-quarter- or one-half-scale version of the Janney/MCB coupler.
Bazeley coupler Bazeley coupler 1905-1918 M.C.B. D Type established as the Universal M.C.B. standard, adopted 1915
Arthur James Bazeley (1872–1937), railway couplings inventor/design engineer; was born in Bristol, England, in 1872, and worked for the Great Western Railway until the age of 34 when he immigrated to Cleveland, Ohio, in 1906, where he worked as a mechanical engineer for National Malleable Castings, Co., inventing and designing improvements in the function, strength, and durability of the (MCB/ARA/AAR/APTA) Janney, knuckle, alliance couplers and other coupling devices/draw gear for the evolving heavier demands by US railways, as well as, National Malleable Castings' international customers in the United Kingdom, India, and many other countries building and expanding their railway systems. A.J. Bazeley was directly responsible for over 90 registered U.S. patents for railway automatic coupler improvements through design, under the coupler type names which included the "buckeye coupler", the "Sharon coupler", the "simplex coupler", the "climax coupler", the "Latrobe coupler", the "tower coupler", the "major coupler", the "Gould coupler", the "Pitt coupler", the "R.E. Janney coupler", the "Kelso coupler" and others.
A.J. Bazeley related railway inventions, U.S. patents and railway coupler mechanical drawings and illustrations filed and assigned to National Malleable Castings Company can be referenced by a patent search under "Bazeley, railway couplings" or "Arthur James Bazeley, railway couplings patents" which have been drawn/filed and provided by Roger Bazeley-USA, MSTM, MSID, CHSRM Mineta Transportation Institute, Transportation Industrial Designer. A.J. Bazeley Railway Coupling, Construction/Design Improvements and Draft Rigging related patents include: US 1193222, US 124622, US 1932719, US 1518299, US 1932503, US 2235194, US 1932440 and others.
National Malleable Castings in 1891 absorbed the Chicago Malleable Iron which was founded in 1873 by Alfred A. Pope and John C. Coonley, who operated similar companies in Ohio and Indiana. By the late 1880s, the company employed nearly 1,000 men at its 26th and Western Chicago works, which manufactured various railroad couplers and steel products for the railroad industries. In 1891, Chicago Malleable became part of the new National Malleable Castings Co., the Cleveland-based company, where Arthur J. Bazeley was employed as a senior design engineer, had additional manufacturing plants across the Midwest. National Malleable purchased the Latrobe Steel & Coupler's plant in Melrose Park, Illinois, in 1909. In 1923, when it had begun to supply the automobile industry, the company changed its name to National Malleable & Steel Castings. Its stock was listed on the New York Stock Exchange beginning in 1936