Cause Remedy
• See remedy in Cavitation; insufficient NPSH
(depending on installation) above.
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.
• 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.
8.4 The pump loses liquid after running for a short time
Cause Remedy
The suction lift or static lift is too high.
• Reduce the difference in height between the water
reservoir or water supply and the pump.
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 inlet pipe is not immersed deeply enough.
• Extend the inlet pipe so that the risk of sucking air is
eliminated.
Air or gases in the liquid.
• Remove the gas or air from the pumped liquid.
• See remedy in Cavitation; insufficient NPSH
(depending on installation) above.
8.5 The pump consumes too much power
Cause Remedy
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.
Air or gases in the liquid.
• Remove the gas or air from the pumped liquid.
• See remedy in Cavitation; insufficient NPSH
(depending on installation) above.
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.
• 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.
The viscosity or specific gravity of the pumped liquid
is higher than that of water.
• Use a larger motor. Consult Grundfos for
recommended size.
• Test the liquid for viscosity and specific gravity.
40
English (GB)
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