Busted motor, again!

[jkalan]

This may be a case of stupid owner tricks, but I have managed to break my motor twice in the last year or so (most recently today).
To reproduce (in preparation for emptying the basket):
1. Shut off pump (by going into service mode)
2. Turn on the pump after waiting a few seconds (to let the heater cool down while I brush out the basket that is going in).
3. Hear an awful gurgling/priming sound followed by a large pop/crack

It appears that the motor has tried to unscrew itself from the impeller, ramming the impeller into the housing and putting sufficient force (not torque) on the shaft that the back of the motor housing breaks. It looks as if someone had taken a hammer to the impeller trying to knock the shaft out the backside of the motor.

The first time I had attributed it to a build up of DE in the impeller housing causing the impeller to get stuck. Today, the only thing I can think of is that maybe I didn't wait long enough for the water to stop moving around before starting the pump again.

In any event, part of the housing has detached as well.

I think I will be ordering a new motor and impeller assembly tomorrow. Has anyone seen this happen before? How can I avoid it in the future?

The motor is an AO Smith Centurion B130, 2 HP uprated to 2.4. The pump housing is a Jandy JHPU2.5. This particular motor is less than a year old.

 

[JasonLion]

I have never seen anything quite like that. It is almost as if the motor is turning backwards, forcing the impeller to unscrew as it spins instead of tightening it further as it normally would.

 

[lovingHDTV]

I'd have to agree with JasonLion with it being the wrong motor.

I googled ao smith centerion b130 and it appears to be a 2 hp CW (clock wise) rotation threaded shaft motor. I tried the motor lookup at AO Smith's website but it did not recognize the B130 motor. Must be a different model number on the plate.

Is this the original or a replacment motor? The impeller looks like mine which requires a CCW (counter clockwise) rotation motor. That would definitely explain why it is unscrewing. I'm not even sure that a pump would work if it was running backwards.

Hopefully one of the motor/pump experts will know for sure.

 

[lovingHDTV]

I looked around a little on this and found the service manual. It says that you need to turn the impeller CCW to remove it so it would use a CW motor.

I'm baffled as to how it would spin the impeller off.

 

[jkalan]

The pool builder came out today and replaced the motor, impeller and impeller housing. Thank goodness for the warranty!

I did call around to see if anyone had seen or heard of this happening:

- Everyone I know who has a pool or works on pools - never heard of it
- Pool builder service desk - never heard of it
- Pump manufacturer - never heard of it
- Local authorized motor distributor - never heard of it, but ... the motor in question (AO Smith B130) is a capacitor-run motor. The big lump on the top of the motor enclosure is a capacitor, but not a start capacitor. Apparently pool pumps don't need much torque on startup. But, because it has so little torque on startup, if the motor is moving just a little bit backwards then energizing it WILL spin it backwards... aha!
- Pool builder service technician (i.e. the guy who replaces these) - (paraphrase follows) - "... oh, yeah, I've seen this happen, in fact, I've done it myself. If the motor is spinning (he didn't say if backwards was a requirement) when you turn it on then it will do that." His opinion is that this is a design flaw and to make sure that everything has settled down before turning it back on.

So, in the future, I will make sure to give the whole system plenty of time to settle down before I turn the pump on.

Hopefully this bit of advice will be of value to the TFP community and spare someone a few days of still water.

 

[JasonLion]

That is interesting. If there is a little bit of air in the filter it will push some water back through the pump when the pump turns off, which could set the impeller spinning backwards.