On this page of our guide to Layers of Fear 2 we have provided a detailed description of the riddle with vault door, which has to solved during the fifth act. You will learn how to manipulate the central regulator to unlock access to the vault.
You will get to the vault by exploring the sunken ship. You'll have to unlock it to continue your journey.
Start to rotate the central controller (in either direction) until the first blue light will flash (example is shown in the attached image). Stop for a moment in this position to save this movement.
In the same way, lit another two lights.
After solving the puzzle, open the vault (the handle on the left) and go inside.