Submerged cargo pump (frank mohn) in details

 

1)     There are 3 concentric tubes.

a)     H.P oil (170 bar) supply pipe to hydraulic motor

b)     Return pipe (3 bar)

c)      Protective outer cofferdam

2)     After completing pumping, vertical discharge pipe will be left full of liquid.

3)     Stopping pump will allow liquid fall back to tank.

4)     To overcome this situation, a purging connections are fitted to clear the discharge pipe (and the cofferdam if there is leakage)

5)     Compressed air or inert gas at 7 bar will use to clear the vertical discharge pipe by pressurizing it from top & forcing liquid cargo up through small riser to the deck main.

6)     The cofferdam is also pressurized before the pump is stopped, to check for leakage. It is connected at the bottom of the pump.

7)     Seal above and below the chamber exclude ingress of low pressure hydraulic oil and liquid cargo from the tank respectively.

8)     The bottom seal is subject only to pressure from the head of cargo in the tank, not to pump pressure.