Brochure

1717
1.2.3 Coupling and drive
The impeller is usually driven by an electric motor. The coupling between motor
and hydraulics is a weak point because it is dicult to seal a rotating shaft. In
connection with the coupling, distinction is made between two types of pumps:
Dry-runner pumps and canned rotor type pump. The advantage of the dry-runner
pump compared to the canned rotor type pump is the use of standardized motors.
The disadvantage is the sealing between the motor and impeller.
In the dry runner pump the motor and the fluid are separated either by a shaft
seal, a separation with long shaft or a magnetic coupling.
In a pump with a shaft seal, the fluid and the motor are separated by seal rings, see
figure 1.9. Mechanical shaft seals are maintenance-free and have a smaller leakage
than stung boxes with compressed packing material. The lifetime of mechanical
shaft seals depends on liquid, pressure and temperature.
If motor and fluid are separated by a long shaft, then the two parts will not get
in contact then the shaft seal can be left out, see figure 1.10. This solution has
limited mounting options because the motor must be placed higher than the
hydraulic parts and the fluid surface in the system. Furthermore the solution
results in a lower eciency because of the leak flow through the clearance be-
tween the shaft and the pump housing and because of the friction between the
fluid and the shaft.
Figure 1.9: Dry-runner with shaft seal.
Motor Shaft seal
Figure 1.10: Dry-runner with long shaft.
Exterior magnets on
the motor shaft
Inner magnets on
the impeller shaft
Rotor can
Motor cup
Motor
Motor shaft
Motor cup
Rotor can
Impeller shaft
Inner magnets
Exterior magnets
Figure 1.11: Dry-runner with magnet drive.
Motor
Long shaft
Hydraulics
Water level