Axial flow valve

These drawbacks are especially noticeable on the trombone, since its characteristic timbre results directly from its cylindrical bore and almost straight construction with only two bends (not counting the valve tubing).

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 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.

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.

[2] 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.

[4] 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.

Thayer axial flow valve on a tenor trombone
Rotary valve in default (A) and engaged (B) positions. The airflow from mouthpiece (1) to bell (2) passes through two 90° bends when diverted through the valve ports or "knuckles" (6) into the valve tubing (3); 4. valve casing; 5. internal rotor; 7. rotor spindle.
Axial flow valve in default (A) and engaged (B) positions. 1. airflow, from mouthpiece; 2. airflow, to bell; 3. valve tubing; 4. valve casing; 5. conical rotor; 6. input (a) and return (b) valve ports; 7. spindle axis of rotation.
Two independent axial flow valves on a Shires bass trombone