Does an orifice control mass or volume flow? 5

[jennyrabbit]

I am trying to understand the effect of ambient pressure on venting a gas from a pressurized vessel. I understand that conductance of an orifice has units of torr-litre/sec. Does this mean that if there is a pressure difference of 1 psi, regardless of the absolute value of the input/output pressures, the same mass will flow? That is, if I hypothetically pressurized a vessel to 14 psia and vented it through a 1/16 inch diameter hole into a 13 psia ambient, the mass flow rate would be the same as if I vented that same vessel from an initial internal pressure of 4 psi into a 3 psi ambient? If this is the case, then an orifice controls mass flow. I'm having a hard time visualizing this as I am not a fluids person. I'm assuming that the gas is incompressible in this case, and flow is viscous. Any insight much appreciated.

 

[BigInch]

Or no flow.

http://virtualpipeline.spaces.msn.com

 

[jennyrabbit]

This post seems to have taken on a life of its own. ; )
As the original poster, I actually don't need anymore input..I got all I need! Thanks, and on to the next question! ; )