Vertical submersible pump for sea water

Salt water and the use of anodes.

Salt water by nature is very corrosive, if the wetted metal parts are exposed to the air they will corrode. (Fact.) by fixing a block of pure zinc to the submerged pump parts like a pump bell or volute once the pump is energised or started, the EMF caused by the rotation of the motor the salt water becomes a huge battery, and any exposed parts will corrode very quickly, impeller turbulence can introduce air into the vortex of a pump, (in fact it does this anyway) because as you may know water is one part Hydrogen and two parts oxygen H20.

Zinc being a very high conductor of electricity with very low resistance, it will attract any EMF because electricity will always take the line of least resistance, by doing this it will attack the anodes and eat them away via Galvanic effect (corrosion) which saves the pump parts from corrosion by Galvanic effect.

You can keep most metals in salt water and they will not corrode away but, as soon as you add oxygen /air they will corrode very quickly. This is why zinc anodes are called sacrificial anodes, because they are eaten away and not the pump.