I have a pipe. At its end I have mounted pressure meter. Of course there is no circulation. Water pressure meter is a kind of stopper for water. I know diameter of the pipe, and I know its pressure in static. How can I find velocity of water and its quantity $Q$ in that particular place (where pressure meter is) if I remove pressure meter and continue existing pipe with pipe of the same diameter?
As I understand $$Q = v(velocity) * S.$$ Then... I need velocity to count Q.