Yamaha Sousaphones Owner's Manual page 6

Nomenclature
■ Rotary Tuba
Main Tuning Slide
Water Key
■ Front Action Valves Tuba
Main Tuning Slide
Water Key
22
4th Valve
Mouthpiece
3rd Valve
2nd Valve
1st Valve
1st Rotary Valve
2nd Rotary Valve
3rd Rotary Valve
4th Rotary Valve
Mouthpiece
5th Rotary Valve
1st Valve
2nd Valve
5th valve pitch (amount pitch lowered)
3rd Valve
4th Valve
w/o sleeve
w/sleeve
Bell
Leadpipe
4th Valve Slide
1st Valve Slide
2nd Valve Slide
Bell
Leadpipe
1st Valve Slide
3rd Valve Slide
YFB-621 YFB-822
Export model
2/3 4/3
4/3 -
5th Valve Slide
YCB-822 YCB-861
2/3 4/3
4/3 -