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Cause
The actual duty point of the pump lies to the right of
the specified duty point on the pump curve. The result
is lower head, higher flow and higher power
consumption.
8.4 The pump loses liquid after running for a short time
Cause
The suction lift or static lift is too high.
Air leak in the inlet pipe or flange.
Air leak in the stuffing box.
Cavitation; insufficient NPSH (depending on
installation).
The inlet pipe is not immersed deeply enough.
Air or gases in the liquid.
8.5 The pump consumes too much power
Cause
Cavitation; insufficient NPSH (depending on
installation).
The impeller or wear rings are worn.
Air or gases in the liquid.
The actual duty point of the pump lies to the right of
the specified duty point on the pump curve. The result
is lower head, higher flow and higher power
consumption.
The viscosity or specific gravity of the pumped liquid
is higher than that of water.
The shaft is bent due to damage.
Remedy
•
Install an orifice plate immediately after the outlet
flange. The orifice plate will raise the system
characteristic or increase the counterpressure thus
increasing the head and lowering the flow. The size
of the orifice plate must be adapted so that the
pressure corresponds to the required duty point.
Remedy
•
Reduce the difference in height between the water
reservoir or water supply and the pump.
•
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.
•
Extend the inlet pipe so that the risk of sucking air is
eliminated.
•
Remove the gas or air from the pumped liquid.
•
See remedy in Cavitation; insufficient NPSH
(depending on installation) above.
Remedy
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.
•
Remove the gas or air from the pumped liquid.
•
See remedy in Cavitation; insufficient NPSH
(depending on installation) above.
•
Install an orifice plate immediately after the outlet
flange. The orifice plate will raise the system
characteristic or increase the counterpressure thus
increasing the head and lowering the flow. The size
of the orifice plate must be adapted so that the
pressure corresponds to the required duty point.
•
Use a larger motor. Consult Grundfos for
recommended size.
•
Test the liquid for viscosity and specific gravity.
•
Check the deflection of the shaft. The total indicator
runout must not exceed 0.05 mm.
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