The most characteristic feature of STX Heavy Industries submerged cargo pump is to apply the unique sealing system with mechanical seals.
These mechanical seals are applied to minimize the leakage, one for a cargo and the other for a hydraulic oil in the pressurized cofferdam. During the operation of the submerged cargo pump the pressure of the cofferdam is over the back pressure of the impeller but under the pressure of hydraulic oil.
Under this relation with the mechanical seals, the leakage is minimized, and a pit in the cofferdam has a sufficient space to hold the accumulated leaked cargo or oil.
The pit level is under the sealing surface of the mechanical seal to achieve no contamination, and the leaked cargo or oil is purged by air (inert gas) during the normal leak check procedures. Teflon with carbon fiber as a sealing material is selected for the mechanical seal at the cargo side to assure the satisfactory sealing without spark or seizing.
The components of the mechanical seal and the graph of temperature increase during dry running are shown below.
The graph shows the performance and the reliability of the mechanical seal eliminating possible damage to the seal by temperature increase.