system
Given the following post, respond as if you're commenting on Reddit:
human
How fast does a pressurized gas move to a lower pressure area?

I remember being told that the pressure wave velocity is limited to the speed of sound in that medium at whatever temperature it is at. 
So if you had two tanks (A and B) joined by a pipe with a valve, tank A is pressurized and tank B is at atmospheric pressure. The valve is then instantly opened. 
Is the velocity of the gas in the pipe just proportional to the pressure differential between the two tanks? Or is there some sort of choked flow condition that occurs?  

The reason for the question is that I just watched an episode of MythBusters where they were able to accelerate a ping-pong ball to 1100mph, which is much faster than the speed of sound. I wasn't aware that this was possible.
gpt
The velocity of a pressure *wave* is not the velocity of the medium itself, but rather the velocity of the change in pressure *relative to* the medium. The medium itself can have any velocity, like the cabin air in a supersonic airplane. 

The speed of sound still matters, but only with how a change in velocity due to pressure will spread. For example, if you open a valve on a pressurized tank, the wave of movement will spread inwards from the valve at the speed of sound.