I have recently been experimenting with pressure to generate a mass flow and discovered something really bewildering. First let me explain the procedure. I use large stainless steel tanks filled to about 3/4 with water so there is a large enough capacity. I then pressurize the system with nitrogen to about 30 Bar using a high pressure regulator. The pressure in the nitrogen tanks is about 150 Bar. I also record the tank pressure with respect to time. Now, when I plot the Data on a graph I see a pressure drop in the tank and it settles at about 25 Bar, which is not good for the constant mass flow I desire. Question: Why is it that the regulator is unable to keep the pressure more or less constant at 30 Bar? Why is there a drop in pressure?