Compressed air can be directed wherever it needs to go by installed piping and valves, and the valves themselves can be hand-operated. Submarines do indeed car

Compressed air can be directed wherever it needs to go by installed piping and valves, and the valves themselves can be hand-operated. Submarines do indeed carry an emergency diesel generator, and they also have a fairly large battery, but the emergency main ballast blow system can be run off of nothing but previously-stored energy and a hand-actuated valve.