The sump pump at our parsonage died the other day, during a bad rainstorm while the Pastor and his family were on vacation (of course). Since no one was there to plug in the emergency pump that I had plumbed in, there was three inches of water in the finished basement when they got back. Ugh.
I replaced the Zoeller pump with a new one, and this time set up the emergency Little Giant pump so that it will go on automatically if the first one fails (why didn't I think of that before?!), but was curious as to why the original, all bronze pump had failed. It seemed to be running fine, but nothing was coming out. Turns out that, despite the fact that all the stainless steel parts were perfect after 16 years, the 1/2" motor shaft was only made of carbon steel, and had corroded off completely at the 3/8" section that was exposed to water, to the point that the bronze impeller was resting quietly in the bottom of the scroll, while the motor continued to run perfectly. You may well ask why the motor shaft wasn't stainless (I did) , but apparently Zoeller buys the motor rotor and stator as OEM assemblies from Emerson, and these only come with a carbon steel shaft.
Since the motor is undamaged except for the shaft, and all the bronze castings are perfect, I've decided to rebuild the pump as a backup. I can get all the parts I need from Zoeller, including a new motor rotor and shaft assembly, but I've decided to machine a new shaft out of 316 stainless and to press on the old rotor, to eliminate this failure mode.
I will still need to get the stub of the old shaft out of the impeller. I presume that, since the impeller is all bronze, I can just drill it and spin it out with an Eazyout. It shouldn't be too badly siezed in the bronze. However, I was just wondering if something like muriatic acid or lye would attack the steel and leave the bronze alone. Any thoughts? I don't know anything about the type of bronze. Thanks.
-- Bob (Chief Pilot, White Knuckle Airways)