High and low temperature-resistant nano ferrofluid is adopted (adaptable to water temperature of -10°C ~ 50°C, applicable to both fresh water and seawater environments). The base fluid uses perfluoropolyether (PFPE) oil, featuring corrosion resistance and shear resistance up to 15,000 r/min, matching the maximum propeller speed of the hydrofoil board and preventing atomization and loss of magnetic fluid at high rotation speeds.

Graphene modifier is added to the magnetic fluid to enhance lubricity, reducing the dynamic friction coefficient to 0.02 (compared with 0.15 for traditional sealing rings), further lowering motion resistance and motor energy consumption.

A combined structure of rare-earth permanent magnet + electromagnetic coil is used:

The permanent magnet provides a basic magnetic field (to maintain the initial sealing shape of the magnetic fluid), while the electromagnetic coil dynamically adjusts magnetic field intensity (range: 0.1 T ~ 0.8 T) based on feedback from pressure sensors.

Pressure sensor arrangement:

One high-precision water pressure sensor is built into each end of the propeller shaft sleeve and hydrofoil connecting shaft (measuring range: 0–10 bar, corresponding to 0–100 meters water depth), with a sampling frequency of 100 Hz to ensure real-time response to water pressure changes.

The cavity adopts a stepped diversion design:

The magnetic fluid filling area is divided into a main sealing chamber and an auxiliary compensation chamber. The main chamber provides primary sealing, and the auxiliary chamber stores spare magnetic fluid. When magnetic fluid in the main chamber decreases due to wear, it is automatically replenished via a micro electromagnetic pump, extending service life to 500 hours (three times that of traditional sealing rings).

Cavity material: titanium alloy + ceramic coating.

Titanium alloy is corrosion-resistant and lightweight; the ceramic coating (hardness up to HRC 60) covers the inner wall of the shaft sleeve, reducing wear during shaft rotation and preventing magnetic fluid leakage caused by cavity scratches.

For the hydrofoil’s maximum speed of 60 km/h, the magnetic field gradient distribution is optimized to form a magnetic fluid vortex sealing layer at the shaft rotation center, resisting water impact and preventing magnetic fluid overflow due to centrifugal force. Diversion grooves are added outside the cavity to deflect high-speed water flow sideways, reducing direct impact on the sealing chamber.

An elastic buffer sleeve (polyurethane material, 5 mm thick) is installed outside the sealing cavity, providing shock resistance and scratch protection. During minor collisions, the sleeve absorbs impact, avoiding shaft deformation and enlarged sealing gaps without destabilizing the magnetic field.

Anti-sedimentation dispersant is added to the magnetic fluid. A micro vibrator is installed at the bottom of the sealing chamber (automatically activated for 1 minute every 24 hours) to prevent ferromagnetic particle precipitation. A magnetic fluid circulation channel is also designed, driven by shaft rotation to ensure uniform distribution of the sealing layer.

The electromagnetic coil features low-power design: only 5 W during dynamic adjustment (0.3 W at static state). Friction energy consumption is reduced by 80% compared with traditional mechanical seals, with negligible impact on range (range loss < 3%).

A magnetic fluid filling port (with built-in one-way sealing valve) is reserved. Users can replenish fluid via a dedicated injector (every 100 hours, operation < 5 minutes) without shaft disassembly or professional repair. A sealing status detection chip is integrated to automatically verify integrity after refilling.

A magnetic fluid level sensor + magnetic field intensity detection module is integrated.

When fluid level drops below the threshold (remaining < 30%) or magnetic field is abnormal, a maintenance alert is pushed via APP, and the maximum motor speed is automatically limited to 40 km/h to prevent leakage caused by seal failure.