3.16 Components of the magnetic drive
3.16.1 Magnetic coupling
The magnetic coupling is transmitting the torque of the drive motor to the rotor shaft.
The magnetic coupling arrangement replaces a dynamic shaft seal and makes the pump 100 % leakfree.
The magnetic coupling consists of following components:
Outer magnetic rotor
Separation can
Inner magnetic rotor
The outer magnetic rotor is assembled on the pump shaft which is driven by the motor. The inner magnetic rotor is mounted on the rotorshaft inside the wet part of the pump. The separation can is situated between the outer and inner magnetic rotor and is sealing the pump hermetically. Permanent magnets are mounted on the inner and outer rotor of the magnetic coupling. The magnets on the inner magnetic rotor are completely encapsulated in stainless steel to prevent contact with the pumped medium. The magnets mounted on the outer rotor are open and protected against corrosion in contact with the atmosphere. The torque is transmitted by magnetic fields between inner and outer magnets which are passing through the stationary separation can. Inner and outer magnetic rotor are running synchronically without slip.
The separation can is a welded construction where the flange and bottom plate are welded to the thin walled pipe section. The can is designed for system pressures up to 25 bar. The section between the magnetic rotors is made of Hastelloy in order to minimize eddy current losses. The separation can is sealed against the intermediate cover by an
When the torque of the pump exceeds the maximum allowable torque of the magnetic coupling, the coupling slips. The slipping of the coupling is associated with excessive heat generation and strong vibrations, which can damage the coupling permanently and destroy the bearings. Therefore the drive motor must be switched off as soon as the coupling slips due to overload. This situation can be detected by following means
•Drop in flow output
•Drop of discharge pressure
•Reduced power consumption of the drive motor
The drive motor must be stopped in order to stop the slipping of the magnetic coupling.
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