Decide how good the powerplant is at producing steam Use the valve in case the turbine starts spinning too fast and you can't wait for the plant to cool down (turn on draw path to see the path steam-particles take) (Bottom variable on the generator is how fast the turbine is spinning (RPM-rotations per minute), the top one is how much energy it's producing every hour (MW/h-megawatt per hour), the middle one is how much energy the plant has produced so far (MW-megawatt)
Huge update within a few days, stay tuned! The more steam particles on screen the laggier it gets