Rotor valve direction difference explained (?)

[Art Hovey]

Getting back to the original topic: The video shows a rotor appearing to block the input port of a valve when it is turned the "wrong" way. What it does not show is how the output port will appear to be blocked by exactly the same amount when the rotor is turned the "right" way.

Here's my theory about how the rotation issue may have been originated: On most rotary tubas the third and fourth valves turn the opposite way from the first and second so that the pushrods can be a bit closer together. Depressing the third or fourth valve puts a lot more tubing into play than does the first or second, so it takes more effort to get the air moving and vibrating in that longer tubing. Also, since the third and fourth valves are not used as often as the first and second, sometimes the air trapped in that tubing cools off a bit while waiting, causing a decrease in pressure which results in a "pop" when the valve is depressed. It is easy to blame both of those effects on the direction of rotation instead of on the real causes.

I suspect that an honest blindfold test would fail to show any difference due to reversal of rotation, but a good snake-oil salesman could easily convince most of us that it makes a huge difference.

[MartyNeilan]

...Also, since the third and fourth valves are not used as often as the first and second, sometimes the air trapped in that tubing cools off a bit while waiting, causing a decrease in pressure which results in a "pop" when the valve is depressed...

I am a big fan of getting valves vented, and this is one of the reasons.
(Admittedly, it is much easier to vent pistons than rotors.)