Pump cavitation

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  • Last Post 13 June 2019
Todd27 posted this 11 June 2019

I recently replaced a A.O. Smith 1 HP C48K2PA105 motor with a  A.O. Smith 1 HP Square Flange 48Y Up Rate EE Motor - UQC1102.  It is mated to a Sta-Rite Dura-Glas P2RA5E-124L that contains a C105-138PEB impeller and a C1-200PA diffuser.  At low pressures (i.e. 12 psi after backwashing) there is a noise in the Hayward multiport valve that sounds like stones are rattling around.  At higher filter pressures (18 psi), the noise goes away.  I think that I am experiencing impeller cavitation.


Is the replacement pump that I selected the correct pump?


If so, since I can't reduce the pump speed to eliminate the cavitation, can I change to a smaller impeller/diffuser to eliminate the cavitation, perhaps to a C105-92PS/C1-216P?

InyoRob posted this 13 June 2019

Yes, you do have the correct motor. The C48K2PA105 had a total HP rating of 1.25. That is the same as the UQC1102. Your existing impeller and diffuser are properly sized for the UQC1102. 

The sound from your multiport valve is usually caused by air in the system. If it doesn't work it's way out and continues to be a problem, I'd look for a suction side air leak.

Another cause of a rattling sound in the multiport valve is a bad spider gasket.

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