HELP how to simulate my problem?

Romain

Hello, Could you please tell me how to simulate this following problem: I have a tube(100mm) full of oil at 8bars, on the left side the tube is closed by a wall which is hooked to a spring(so the wall can move), on the right side there is a winnow, and behind this winnow there is oil at 20bars. I want to open the winnow and see the movement of the wall with the spring until pression is stabilize to 20bars.The problem is that there is not really a flow of oil, the oil at 20bars "push" the oil at 8bars until the pression is stabilized. Please, what is the good configuration of simulation for this problem? because I find values completly false. Thanks,regards