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Cause
Wrong direction of rotation.
The impeller is completely clogged.
The inlet pipe is partially blocked.
Air leak in the inlet pipe or flange.
Air leak in the stuffing box.
Cavitation; insufficient NPSH (depending on
installation).
The impeller or wear rings are worn.
Defective packing rings.
The non-return valve is too small or partially
obstructed.
The non-return valve is too small or partially
obstructed.
The inlet pipe is not immersed deeply enough.
8.3 The pump does not create enough pressure
Cause
The speed is too low.
Air leak in the inlet pipe or flange.
The impeller or wear rings are worn.
Defective packing rings.
The impeller diameter is too small.
Obstruction in pump housing.
Air or gases in the liquid.
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Remedy
3. Make sure that all phases are connected.
•
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.
•
Dismantle the pump and clean the impeller.
•
Remove any obstructions in the inlet pipe.
•
Replace or repair the defective pipe section or
flange.
•
Clean the flushing pipe. Replace the stuffing box
packing rings, if necessary.
1. Increase the net positive suction head by placing the
pump in a lower position.
2. Pressurise the inlet vessel.
•
Replace the impeller and/or wear rings. If necessary,
also replace the bearings and the shaft.
•
Replace the packing rings.
•
Replace or clean the non-return valve.
•
Replace or clean the non-return valve.
•
Extend the inlet pipe so that the risk of sucking air is
eliminated.
Remedy
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.
•
Replace or repair the defective pipe section or
flange.
•
Replace the impeller and/or wear rings. If necessary,
also replace the bearings and the shaft.
•
Replace the packing rings.
•
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.
•
Dismantle the pump and remove the obstruction.
•
Remove the gas or air from the pumped liquid.
•
See remedy in Cavitation; insufficient NPSH
(depending on installation) above.
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