How does an amount of water inside a sealed tank affect a change in pressure of the tank if you open a valve that connects the tank to another tank at a lower pressure and twice the volume? We have to consider the problem with and without water in the tank. We have to consider the vapor pressure of the water, and the fact that when pressure is reduced in the tank, more water will turn to vapor in order to reach the vapor pressure. The initial difference in pressure between the two tanks is lower than 10 psi at max. The temperature of the two tanks may change a little, but we can assume that it is constant over a long period of time. I'm trying to figure out how to formulate the question and then answer it. Does anyone know how to work this problem? Is anyone familiar with accounting for vapor pressure in problems like these? Ultimately, I'd like to figure out the difference in final equilibrium pressures between the cases of (1) an amount of water in the tank and (2) no water in the tank.