A type of valve used in musical (brass) insturments.
French Horns have 3 or 4,
Tennor Trombones may have one, (modern)
Bass Trombones 1 or 2, and
Tubas, when rotary valves are used, 3 to 5.
Please excuse the crudeness of the following ASCII Art, but I think that as bad as it is, its better then trying to explain the operation in words:
(open/unengaged)
| /\ | | |
| | | | |
| | \ __ | |
\ \_/##\_/ /
/# ###### #\
/# /\ #### #\
|## | ## ##|
|## | ## ##|
\# | #### #/
\# | ###### #/_____
/ / / \##/ \
/ / \_________
| /\ |
| | |
| | |
(closed/engaged)
| /\ | | | |
| | | | | |
| | \ __ | \/ |
\ \ \_/ \_/ /
/# \ /____ #\
/### \ ###\
|#####################|
|#####################|
\### _____\ ###/
\# / _ / _ #/_____
/ / \__/ \ \_____\
/ / \______/__
| /\ |
| | |
| | |
Yes, those are supposed to be circles.
The exact angle/arrangement of the tubing varries, though it would be unusual if the main tube was not in straight alignment. This allows for the least restriction most of the time.