The axial flow valve, or Thayer valve, is a brass instrument valve design for trombone F attachments, patented in 1978 by Orla Ed Thayer. Designed with assistance from Zigmant Kanstul to replace the traditional rotary valve, it was a revolution in trombone valve and instrument design. Combined with open-wrap tubing, it eliminates the impedance caused by tight tubing bends, improving the airflow through the instrument and the open "feel" perceived by the player. Problem When engaged, a rotary valve deflects the air flow through extra valve tubing, using tight, small radius bends of at least 90° angles, leading to a stuffy response and audible tone colour changes, compared to the "open" instrument. These drawbacks are especially noticeable on the trombone, since its characteristic timbre results directly from its cylindrical bore and almost completely straight construction. Valve tubing aside, there are only two bends, one each in the slide and bell section. In contrast, the distinctly softer sound of other brass instrument families like the horns, saxhorns, and tubas is at least partially a result of their conical bore and their intricate construction with many bows and bends. The change in timbre and response in the valve section was also made more pronounced by the wrap of the valve tubing, traditionally in several tight loops to fit the length of tubing within the bell section, that was the norm until the 1980s. Invention The Thayer Valve uses a conical rotor (although the 1978 patent and early prototypes were cylindrical), with its spindle rotation axis parallel to the incoming and outgoing tubing. The airflow undergoes a maximum of 28° of deflection through the valve, which makes an F attachment's open-wrap tubing even more efficient. As a result, the response, tone colour and other playing characteristics are nearly unchanged from those of the open instrument, even on bass trombones with two independent valves fitted. Criticism There were several problems with early Thayer valve designs, noted by players and instrument repairers. Valves sometimes suffered from galvanic corrosion due to the use of unsuitable metals in the manufacture of different parts of the valve. Early valves used cast brass for the rotors, which made them heavy and slow to actuate; an initial solution to this problem was to use aluminium and other metal alloys for the rotor to try to reduce its mass. The conical rotor's spindle was only anchored at the wide end of