Hello! I will try to formulate myself as clearly as possible, but english isn't my main language. I'm having trouble solving this problem that should be relatively easy to solve. Let's say we have a submerged pressure tank, constantly fed with air through a compressor, so it's maintained at a certain pressure Ptank. The pressure tank has a hole in it at a known height from the surface, and with a known diameter, so that air will leak out. I want to calculate the volume air flow through the hole [m3/s]. Can I use the formula to conclude if the flow is choked by using P* = Patm + rho*g*h P0 = the pressure in the tube (between 1 and 4 bar or something) gamma = 1,4 for air If the flow is proven to be choked, does this mean the air speed is 340 m/s through the hole? Can I then just multiply the speed with the area [m2] of the hole to get the volume air flow [m3/s]? I have tried using this formula but I can't seem to figure out Cd. Thanks in advance!