Whisperflo flow rate problem

I was working on a pool filtration system today for a condominium association in Huntington Beach. It had 3″ plumbing feeding two identical 2 HP Pentair whisperflo pumps on a 70000 gallon swimming pool. One was making a lot of noise so I checked and replaced the pump trap lid o-ring, and checked all the inlet side plumbing for leaks. I ran each pump (which feeds its own 60 sf filter before tee-ing back into a common 3″ return) separately to compare flow rates. The quiet pump was moving nearly 140 gallons per minute, whereas the noisy one was only moving about 85 gpm. I pulled apart the volute to inspect the impellor, which did have one clogged vane. I also noticed the diffuser had come unglued at the funnel. The diffuser could still be put back in place, but it was in two pieces. I have seen this before on older whisperflos. The flow rate went up to about 100 gpm, but is still significantly lower than the other pump. I checked amp draw on both pumps, close to the same at 9.9 A. I am wondering if the broken diffuser is the problem and am going to replace it next week.

UPDATE Jan 17, 2012 This morning I replaced the separated diffuser in the pentair whisperflo wfe-8 pump I posted about last week. The flow rate jumped from a little less than 100 gallons per minute to almost 140 gpm AND the pump noise dropped dramatically! It’s actually bearable to be in the equipment room with that pump running now.

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