the cone, the other end free to rotate inside the casing. This "floating" tip of the conical rotor would undergo precession or "wobble", which caused wear where it meets the inside of the valve casing, becoming loose as a result, and leading to further problems such as air leaks and lubricant loss. Thus, the Thayer valve can have higher cleaning, maintenance and lubrication requirements than other valve designs. They can also be more difficult to disassemble and clean than a standard rotary valve, especially on double-valve bass trombones. Some players, especially bass trombonists, claim that more resistance enhances the response of low notes on the valve side (below E♭). This group finds playing open flowing designs like the axial flow valve to be more of a strain. Evolution and improvement Thayer filed several further patents in the 1980s which attempted to solve some of the initial design problems, as well as other innovations to reduce costs of manufacture and improve the speed of action. These involved using spring tensioners to hold the rotor against the casing to prevent air leaks, and using materials such as plastic or Teflon for the rotor, to reduce its mass and prevent corrosion issues. Cristian Bosc, Italian brass instrument maker, has improved the axial flow valve design by fabricating both the rotor and the valve casing from single pieces of solid brass with no soldered parts. This was to address leakage and corrosion problems. A 2011 patent granted to Michael Olsen of Instrument Innovations also greatly improved the valve by (among other things) mounting bearings at both ends of the rotor spindle. This increased the speed and reliability of the action, and eliminated the "floating rotor" design problem and its associated wear and precession issues. Vincent Bach use this design for their "Infinity Valve" on their "AF" trombones, which replaced their "T" trombones that used the older Thayer design. Aftermath The invention of the Thayer Valve kicked off an "arms race" among trombone designers and manufacturers that continues today. Newer valve designs include the relatively successful Swiss Hagmann valve found on trombones from many European manufacturers, the Christian Lindberg valve from Conn, the S.E. Shires Tru-Bore valve, the Balanced Valve System or "K" valve from Bach in the 1990s, as well as less successful designs like the Miller valve and the Yamaha "V" valve. This activity has also spurred many patents and refinements in traditional