Hello Everyone, I am working on a project with a friend and neither of us have any formal training in engineering but we generally are quick learners. We are both familiar with many of the gas laws and are trying to calculate the equalization pressure between 2 cylinders/vessels or tanks used in Fire Fighting and SCUBA diving. The second part of the task is to calculate the number of transfills or fills that can be accomplished with a bank of storage cylinders, but we can address this part after calculating equalization. The specific criteria we are working with are as follows for the pressure equalization part: P1 (Supply Cylinder Pressure) = 6000 PSIG Initial V1 (Supply Cylinder Volume in Liters) = 43.28 P2 (Receiver Pressure) = 0 PSIG Initial, 4500 PSIG Final after transfer V2 (Receiver Volume in Liters) = 9.06 I realize that the transfer of the air from one cylinder to the other will generate heat and there will be some loss of pressure after the receiver cools down, so if temperature will play a bigger role to be more accurate, we can use 70 degrees Fahrenheit as the ambient temperature. I am also not sure if the "Z Factor" or compressibility factor should be part of the equation to achieve a reasonably accurate equalization pressure between the 2 cylinders. I have spent days searching online to get a better understanding of how to calculate this and have seen a few different methods, all of which seem to have a different answer but I would like to achieve an accurate value if possible. Can someone please help me to determine how to accurately calculate the equalization pressure of the 2 cylinders and if I need more information to accomplish this part of the task?