Magnetic coupling

Magnetic couplings

The magnetic coupling is a special form of sealing that is possible without rotating seal surfaces. That is why these are also described as “seal-less pumps”. With the magnetic coupling, the product space and atmosphere are hermetically separated from each other through static seals; the torque is not transferred through a classic shaft connection, but rather only through magnetic field coupling from the drive to the pump. The magnetic coupling works without slip (synchronous magnetic coupling). This means that the pump speed always corresponds to the drive speed as long as the maximum transferable torque is not exceeded.

This form of sealing is always recommended if an escaping of medium must be avoided under all circumstances, for example, with toxic media. Since this seal variation is maintenance-free, it is often an attractive alternative to double seals. Furthermore, they are suitable for high system pressures (up to 700 bar), because both front sides of the shaft are exposed to the suction pressure and therefore no axial powers act upon the shaft.

Operating parameters

Suction side pressure: max. 700 bar(a)
Viscosity: 1 up to 30.000 mPas
Temperature: 450 °C

Structure of a WITTE magnetic coupling

Can
External rotor
Flange bearing
Hub
Internal rotor
Magnet external rotor
Magnet internal rotor

Can

The can can be designed in different ways.

Designs:

    Ceramic
    Glass
    Stainless steel
    Double-walled
    Plastic (GFK, CFK, PEEK)

All of the material used here may not be magnetized. The can is passed through in the bypass flow from pumped medium and is exposed to the suction side pressure of the pump.
External rotor

The external rotor carries the drive magnets and is coupled with the drive through a shaft-hub-connection. The external rotor covers the can radially, but does not touch it. The transfer of power to the gear pump drive shaft or the internal rotor is performed solely through the magnetic coupling with the external rotor.
Flange bearing

The separate flange bearing absorbs the weight force of the internal rotor so that the friction bearing of the pump is relieved. The drive shaft exclusively transfers the torque. Just like the friction bearing of the pump, this bearing will also be lubricated.
Hub

The hub connects the drive shaft with the internal rotor. The rotor is driven through the magnets. This makes it possible to hermetically seal the pumps.
Internal rotor

The internal rotor is the counter-piece to the external rotor; it carries the driven magnets and is connected with the drive shaft through the hub.
Magnet external rotor

The magnets from the external rotor are permanently connected to the external rotor and move the magnets from the internal rotor through magnetic fields.
Magnet internal rotor

The magnets from the internal rotor are permanently connected with this and absorb the magnetic powers from the external magnets to rotate the internal rotor. The magnets are covered with a stainless steel sheet to protect them from coming into contact with the pumped medium.