4
Operation
(continued)
Magnetic Coupling Pumps
In normal operation, the magnetic poles
of the outer drive magnet remain aligned
with the magnetic poles of the inner
pump magnet. The motion of the motor
is smoothly transferred to the pump
shaft. If the torque load on the pump
exceeds the magnetic coupling
strength, then the outer magnets will
rotate past the inner magnets and the
magnetic poles will misalign. The outer
magnet will increase to a no-load motor
speed while the inner magnet remains
relatively motionless. Excessive noise
and vibration can be observed as the
poles of a decoupled magnet move past
one another.
The pump should be stopped
immediately if the magnets decouple.
Continued operation of the motor with
the magnets decoupled will reduce the
future strength of the coupling. The
magnets will not properly realign until
the motor has been stopped. Before
restarting the motor, one should deter-
mine the cause of the decoupling and
remedy the problem. Decoupling does
not necessarily indicate a pump failure.
It indicates that an instantaneous torque
requirement of the pump has exceeded
the strength of the magnetic coupling
supplied with the system.
Without disassembly of the pump it
can be difficult to determine whether the
magnetic coupling or the pump internals
are operating incorrectly. The following
is a list of examples that could result in
magnet decoupling:
• Blockage or restriction in the dis-
charge side of the system
• Discharge pressure in excess of
nominal conditions
• Too rapid acceleration or decelera-
tion of the drive system
• An increase in fluid viscosity
• Foreign particles impinging upon
pump internal components
• Increased friction due to a poorly
lubricating process fluid
The decoupling characteristic of mag-
nets can be a safety feature, preventing
inadvertent pump/motor overloads.
Magnets should be chosen so that their
decoupling torque is greater than the
pump input torque. This should include
any transient, starting, and stopping
conditions in addition to steady state
values.
The decoupling torque can vary with
different fluids, temperatures, operating
pressures, and magnet sizes. Accurate
sizing of magnets for a specific application
requires precise knowledge of several
operating conditions. Check with your
Zenith representative to see which 9000-
MD system is appropriate.
General Magnetic Coupling
Precautions
Both the inner and outer magnetic
rotors are very powerful.
Handle them
with care.
Danger!
Persons with cardiac pacemakers
should stay at least 8 feet from the
magnetic product at all times.
Do not
position hands or fingers so that
they may become trapped between the
two magnetic rotors, or between one
magnet and a metal object.
Do not
position the magnets near one
another unless assembling the pump to
the system. Both rotors should be fas-
tened to their respective shafts before
bringing them into proximity.
Do not
place the magnets near any elec-
tronic equipment or media that is sensi-
tive to magnetic fields (computers,
diskettes, credit cards, etc.)
When storing and assembling the
magnetic coupling, make sure that no
small metallic fasteners, pieces or other
foreign objects adhere to the rotors or
barrier cap.
If the magnets de-couple, stop the drive
system for the pump immediately.
Determine the cause of the excessive
torque requirement and remedy the
problem prior to re-starting the system.
WARNING
