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A.0100.301 – IM-FIP/08.00 EN (02/2014)
7.2 Impeller
This guide is designed to help you to identify typical application problems that now and
then occur in flexible impellers during normal use.
Rubber is a “living” material and impellers should be kept in a dark and cool place for
long term storage. The impeller life is strongly reduced by frequent dry running excessive
pressure and/or temperature. It is advised to operate between +10° to +50° C to obtain a
long life.
Problem 1
Pieces are missing from vanes/tips, especially in
centre of impeller.
Edges eaten away, hollowed out.
Pitting on ends of impeller.
Causes
Cavitation, i.e. pressure too low at pump inlet, fluid
evaporates locally.
Precautions
Reduce pump speed. Increase inlet pipe diameter.
Reduce inlet pipe length and restrictions.
Problem 2
End faces hard, polished, cracked, looks like carbon.
Some or all vanes completely missing in severe
cases.
Causes
Dry running.
Precautions
Do not run more for than 30 seconds without liquid
in the pump. Stop the pump as soon as liquid is
exhausted. Arrange the pipe work to trap liquid in the
pump on the discharge side. Prevents dry running
for several minutes. Install a dry running protection
device, i.e. an electronic pump guard.
Problem 3
Vanes cracked half way up their height. Pieces of
vanes are missing.
Causes
Normal end of useful life. Excessive outlet pressure
reduces impeller life. A crease on trailing side of each
vane can indicate excessive pressure. Liquid temp
above 55° C reduces impeller life.
Precautions
Reduce the discharge pressure by reducing the
pump speed and/or increase the outlet pipe diameter.
Reduce the pipe length and restrictions. Reduce the
liquid temperature.
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