Cabin Compressor is used for pressurization sometimes called an Engine driven compressor EDC. Blows the cabin up like a balloon, then you have the outflow valves that control the amount of air exiting the cabin so that the cabin does not become over pressurized and exceed psi limits. Safety valve is a backup to the outflow valve if this fails to open. Safety valve will open at a slightly higher psi than the outflow. the outflow constantly closes and opens to maintain pressure desired in the cabin eg 8000ft.
make sense?
Systems - good, questions very similar, the written ones are more current than the cybers. Make sure you keep up to date each night on the course or you will get behind.
A lot of info that you just have to jam in.