 Westinghouse Air Brake Company acquired National Electric, renamed 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 separate occasions over the rights to manufacture compressed air brake systems for streetcars.In 1933, working in his basement, Christensen discovered by trial and error that a ring-shaped piece of rubber in a groove one and a half times long as the minor radius of the ring made a reliable, tight seal of a piston sliding in a cylinder.