Niels Christensen

Niels Anton Christensen (16 August 1865 –5 October 1952) was a Danish-American inventor whose principal invention was the O-ring, the ubiquitous hydraulic seal.

Niels Anton Christensen was born on a farm in Tørring-Uldum Municipality, Denmark. He showed an early aptitude for mechanics and apprenticed to a machinist in Vejle, Denmark. After completing his apprenticeship, he entered the Technical Institute of Copenhagen, now the University of Copenhagen Faculty of Science. In 1891, at the age of 26, Christensen immigrated to the United States.^[1]

Christensen became a leading draftsman at Fraser and Chalmers in Chicago, a machinery manufacturer for industry, mining, and transportation. While working in Chicago, he witnessed an accident of a new electric railway, which resulted in two deaths and a number of injuries because the conductor was unable to stop the rail cars in time using the mechanical brake. Christensen decided to design and build a power brake. The Christensen air brake was successfully tested on Detroit's streetcar system, but an economic decline prevented Christensen from manufacturing and marketing the system.

He worked briefly on electrical systems for Chicago's Columbian Exposition and then was hired by the E. P. Allis Company of Milwaukee. While at E. P. Allis, he continued to develop his air brake for electric rail cars and streetcars. In 1896 he obtained financial backing that allowed him to make an experimental test apparatus. He also secured patents on the new valve mechanism. In early 1897, he founded Christensen Engineering Company, which initially operated in the Menomonee Valley at 718 Hanover. His operations were co-located with the Seamless Structural Company at the corner of Hanover and Burnham Streets.

George Westinghouse had developed an air braking system for steam locomotives and felt that Christensen's invention constituted patent infringement, suing him in December 1906. Westinghouse Air Brake Company acquired National Electric, renaming the company the National Brake & Electric Company, which refused to pay royalties to Niels Christensen. Christensen promptly countersued, starting a 24-year legal battle that went before the US Supreme Court on three occasions over the rights to manufacture compressed air brake systems for streetcars.

En 1933, mientras trabajaba en su sótano, Christensen descubrió por ensayo y error que una pieza de goma en forma de anillo, colocada en una ranura de una vez y media la longitud del radio menor del anillo, proporcionaba un sellado fiable y hermético para un pistón que se deslizaba dentro de un cilindro . Solicitó una patente estadounidense en 1937, la cual le fue concedida dos años después. ^{[ 2 ]}

Tras el ataque a Pearl Harbor , el gobierno de Estados Unidos adquirió los derechos de numerosas patentes relacionadas con la guerra y las puso a disposición de los fabricantes sin pago de regalías. Christensen recibió 75 000 dólares. Cuando la guerra terminó (formalmente en 1952) y los derechos de patente le fueron devueltos, a la patente solo le quedaban cuatro años de vigencia. Un litigio culminó con el pago de 100 000 dólares a sus herederos en 1971, 19 años después de su fallecimiento. ^{[ 3 ] [ 4 ] [ 5 ]}

• Hélice (1369399) – presentada el 6 de octubre de 1916; emitida el 22 de febrero de 1921 
• Controlador de potencia para frenos de vehículos (2150022) – presentado el 3 de noviembre de 1932; emitido el 7 de marzo de 1939. 
• Compresor de aire (2074980) – presentado el 17 de octubre de 1932; emitido el 23 de marzo de 1937. 
• Mecanismo de freno (2197068) – presentado el 10 de marzo de 1938; emitido el 16 de abril de 1940 
• Mecanismo de rueda y freno de automóvil (2172788) – presentado el 16 de julio de 1935; emitido el 12 de septiembre de 1939. 

• Weber, Robert John y David N. Perkins. Mentes inventivas: creatividad en la tecnología (Volumen 49. Oxford University Press. 1992).
• Christensen, Niels A. Patente estadounidense 2.180.795 (Empaquetado. 21 de noviembre de 1939)

• Retrato de Niels A. Christensen