Hi there, I have been asked by my boss to the following question... I have a vessel (500L) that is pressurised to 0.8 barg. That vessel is then held at that pressure for an hour (It is a pressure hold test on the vessel). Over the course of that hour the pressure drops by 2 kPa. He has asked me to find out what sized hole (theoretically) would be in the vessel in order for it to drop to that pressure over the course of an hour. Assumptions: 1. The vessel is in an area of normal atmospheric pressure 2. The temperature of the vessel does not change during the operation 3. We are using air to pressurise the vessel I have some small experience with Chemical Engineering but this is not my current area of expertise so I am having trouble remembering how to do this. I have calulated the density of the air in the pressurised vessel at 0.8 barg and at 0.78 barg (- 2 kPa). The drop of air in the vessel is 10 L over the hour. That gives me a flowrate of 10L/hr. I am unable to work out the velocity in order to get the cross sectional area, and in turn the diameter of the hole. Any help on this would be much appreciated!