Why aren't the magnets in a water pump rotor afraid of water?

Some people wonder: How do the rotors in household circulation pumps, aquarium pumps, and car cooling pumps—which are constantly submerged in water—manage to keep their magnets intact? How is this achieved?

To answer this, we first need to understand: Are ordinary magnets vulnerable to water?

The answer depends on the material.

The most common materials used in water pumps today are neodymium iron boron (bonded) and ferrite (sintered/injection-molded). Neodymium iron boron magnets possess exceptionally strong magnetic force, but they contain large amounts of reactive iron and rare earth elements. When exposed to water, they rapidly oxidize and crumble, causing their magnetic strength to plummet. So why do neodymium iron boron magnets in water pumps last for years without issue? The answer lies in encapsulation and isolation, preventing the magnets from ever coming into contact with water.

Illustration shows radial rotor magnet

Ferrite material is inherently water-resistant. Its chemical structure is an oxide ceramic, representing iron's most stable oxidation state. It cannot undergo further oxidation or corrosion, remaining rust-free even after years of immersion in freshwater. Therefore, in small water pumps with low magnetic strength requirements (such as aquarium pumps or small circulation pumps), ferrite magnets can exhibit excellent water resistance even without perfect encapsulation.

Therefore, the water pump rotor magnets are “waterproof” thanks to corrosion-resistant magnetic materials and encapsulation technology.

Relevant water pump rotor magnets;

2 pole radial cooler pump ferrite rotor ring magnet OD 9mm x 10mm

Cooler Pump Rotor Magnet 4 Pole Ferrite 20x27mm in stock