It is used to isolate the chamber where the liquid circulates from the outside. The mechanical seal is the part of the pump which is suitable for isolating two environments, among which there is a component with circular motion. For example, the mechanical seal serves to isolate the electrical part from the chamber where the liquid circulates. It is said that the seal is "mechanical" because it is the set of components pushed by a spring to prevent the liquid from reaching the electric part of the engine.