This sequence is carried out instantaneously. The aftermost seal ring plays two important roles that one is an air barrier to seal the sea water by blowing the compressed air and the other is a detector to maintain the constant differential pressure without any additional sensor or transmitter to measure the change of the sea water pressure.
In case the sea water pressure on the aftermost seal ring decreases conversely to the above, the differential pressure is also kept constant by the similar way of the sequence which replaces the word "increase" with "decrease" and so on.
