As mentioned above, the air pressure P3 is balanced to the sea water pressure Pw on steady-state condition, P3=Pw+abt.15 kPa. Here, the sequential actions of the flow controller and seal ring on the transient state condition is shown in Fig.5.
1] When the sea water pressure increases from Pw to Pw+△Pw, the radial load on the aftermost seal ring also increases.
2] The clearance h between the seal ring and liner is reduced by increasing of radial load.
3] The air flow rate Q, which is set up at the time of installation of the system beforehand and discharging to the sea, is choked and reduced momentarily by the small clearance h.
4] The air pressure P3 in the air chamber is increased by this reduced air discharge Q.
5] The secondary pressure P2 in the flow meter is also increased by the rapid transmission of the increased air pressure P3.
6] The clearance C is spreaded so as to keep the constant air flow rate due to the function of diaphragm which acts to hold the differential pressure (P1-P2) unchangeable.
7] The secondary pressure P2 is reduced and returned to the initial value by this manner.
8] Then the air flow rate Q is actually controlled to come back to the set-up value with the higher air pressure P3+△Pw in the air chamber. Because the constant air flow rate assures the constant differential pressure on the seal ring by the function of seal ring itself.
9] The clearance h also get to return to the initial value due to the same flow rate.
10] The radial load on the seal ring obtains again the initial condition through the same differential pressure (about 15 kPa).
