Cause Remedy
2. Make sure that the frequency is correct.
3. Make sure that all phases are connected.
Wrong direction of rotation.
• Compare the direction of rotation with the directional
arrow on the pump housing. If required, change the
direction of rotation by interchanging two phases in
the motor.
The impeller is completely clogged.
• Dismantle the pump and clean the impeller.
The inlet pipe is partially blocked.
• Remove any obstructions in the inlet pipe.
Air leak in the inlet pipe or flange.
• Replace or repair the defective pipe section or
flange.
Air leak in the stuffing box.
• Clean the flushing pipe. Replace the stuffing box
packing rings, if necessary.
Cavitation; insufficient NPSH (depending on
installation).
1. Increase the net positive suction head by placing the
pump in a lower position.
2. Pressurise the inlet vessel.
The impeller or wear rings are worn.
• Replace the impeller and/or wear rings. If necessary,
also replace the bearings and the shaft.
Defective packing rings.
• Replace the packing rings.
The non-return valve is too small or partially
obstructed.
• Replace or clean the non-return valve.
The non-return valve is too small or partially
obstructed.
• Replace or clean the non-return valve.
The inlet pipe is not immersed deeply enough.
• Extend the inlet pipe so that the risk of sucking air is
eliminated.
8.3 The pump does not create enough pressure
Cause Remedy
The speed is too low. 1. Make sure that the motor receives full voltage.
2. Make sure that the frequency is correct.
3. Make sure that all phases are connected.
Air leak in the inlet pipe or flange.
• Replace or repair the defective pipe section or
flange.
The impeller or wear rings are worn.
• Replace the impeller and/or wear rings. If necessary,
also replace the bearings and the shaft.
Defective packing rings.
• Replace the packing rings.
The impeller diameter is too small.
• Check with Grundfos if you can use a larger
impeller. If not, reduce the outlet pipe friction losses.
But be careful not to overload the motor.
Obstruction in pump housing.
• Dismantle the pump and remove the obstruction.
Air or gases in the liquid.
• Remove the gas or air from the pumped liquid.
39
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