FLEXIBLE IMPELLER GUIDE

[bob mitchell]

	Symptoms:	Pieces missing from blade tips especially in centre of impeller. Edges look hollowed out or eaten away. Pitting on ends of impeller.
	Cause:	Cavitation, i.e. pressure too low at pump inlet, fluid boils locally.
	Remedy:	Reduce pump speed. Increase inlet pipe diameter. Reduce inlet pipe length and restrictions. Reduce fluid temperature (vapour pressure).
	Symptoms:	End faces hard, polished, cracked, like carbon. Some or all blades completely missing in severe cases.
	Cause:	Dry running.
	Remedy:	Do not run for more than 30 seconds without liquid in the pump. Stop the pump as soon as liquid is exhausted. Arrange pipework to trap liquid in the pump on the discharge side. Prevents dry running for several minutes. Provide automatic liquid level/presence sensor.
	Symptoms:	Blades cracked about 1/2 way up their height. Some pieces of blade missing
	Cause:	Normal end of useful life Excessive outlet pressure reduces impeller life. Liquid too hot or too cold. A crease on the trailing side of each blade can also indicate excessive pressure.
	Remedy:	Reduce pressure and/or pump speed Increase outlet pipe diameter. Reduce outlet pipe length and restrictions. Can also be due to dry running (2) or swell (4).
	Symptoms:	Impeller too long, binds in pump. Blades much longer than hub. Rubber may feel soft and sticky.
	Cause:	Swell due to chemical attack, high temperature or long term immersion.
	Remedy:	Check rubber is suitable for all liquids pumped including cleaning agents; see Xylem Jabsco Liquid Compatibility Guide. Flush out pump after use. Drain for storage. Reduce liquid temperature. Avoid dry running (2).
	Symptoms:	Blades permanently and excessively curved.
	Cause:	Chemical attack Long term storage in pump. Normal end of useful life (especially nitrile impellers).
	Remedy:	Check chemical compatibility. Remove impeller for long term storage. Refit impeller to rotate in the opposite direction.
	Symptoms:	Worn blade tips and end faces. Worn impeller drive.
	Cause:	Cavitation, i.e. pressure too low at pump inlet, fluid boils locally (1).
	Remedy:	SEE (1) Above

    These illustrations are from www.xylemflowcontrol.com    -see "support" - illustrations much clearer on original site.