Standard circulator pump A standard Grundfos UP pump has an asynchronous motor with a wet-running rotor. The whole shaft including rotor and impeller is operating in water. Consequently, the shaft seal requires absolutely no maintenance and is completely leakage-free. However, in asynchronous wet-runner motors the gap between stator and rotor is very important.

The stator must stay dry, while the rotor is running in water. Because the rotor can is a water-filled gap the ferritic rotor must be covered by stainless steel as well. Via all 3 the magnetic field has to be transmitted from stator into the rotor. However, not all these materials are good magnetic conductors and the water-filled gap cannot be reduced due to lime and sedimentation liability.

All small circulators have some losses like: • Iron losses (Motor) • Electro-magnetic gap losses (Motor) • Current heat losses / stator (Motor) • Current heat losses / rotor (Motor) • Mechanical rotor can losses Motor) • Bearing friction losses (Motor) • Impeller side friction losses (Pump) • Mechanical gap losses (Pump) • Impeller losses (Pump) • Entry and spiral housing losses   (Pump)