Posted by Sean Chisham on February 23, 1999 at 09:14:58:
In Reply to: valve number five posted by Tom Caudron on February 23, 1999 at 08:10:29:
The 5 valve on a tuba serves much the same function as the other 4 valves. It lowers the pitch of the instrument by either a major 3rd or a flat whole step. It is used, primarily, in conjunction with other valves to provide better intune valve combinations when playing within the lowest octave of the tuba. There is a fingering chart off of the main page of TubeNet labeled "Tips" which has fingering charts demonstrating suggestions of which notes play more intune using the 5th valve.
There really is no mystery about having more than 3 valves. Each additional valve allows more choices in fingering combinations, I have even seen an 8 valved tuba before. I think the guy was a closet bassonist.
Orchestral literature is not the only place one will find lower notes which are aided by a 5th valve. Every genre that I have seen has had it's share of lower notes including solo, chamber, band, jazz, and orchestral.
When you boil it all down, valves are valves are valves. You press one and the overtone series of the instrument changes.