Pump motor shaft sheared off. Anyone seen this before?

[DavidArmenB]

I work with steel all day every day and this was a defective piece of steel from the get go. I zoomed in on one of the pictures where you clearly see a clean and dirty portion of the break. The outer circumference is a lighter shade whereas the center is darkened which means the last part of the broken shaft was just the outer part because that's the new break. The dark area was fractured long ago somehow most likely in the manufacturing process that is why it's darkened. This motor doesn't nearly have any kind of torque to cause this. The link @JamesW sent you may be very interested to get this into their hands .......

Are you referring to this outer portion by the “lighter shade”?

Because I thought that that was a groove in the cylinder. The shaft was thinner in that small section. Can anyone confirm if the motor shaft has that groove? I thought the darker portion in the center, with the slightly raised edge, was the shear zone.

 

[wireform]

If you're saying there was a groove there that explains the even circular portion but I can't say the shaft has that but many years ago we had a piece of round material that broke which stunned the team and it was a determined to be a defect in the material which to the manufacturer was one in a million. In your case for the shaft to break off clean like that was a defect in the grain from day 1.

 

[JamesW]

I do not think that the shaft would have a groove from the manufacturer, but I do not know for sure.

I suspect that there was probably a defect in the metal that allowed a crack to slowly propagate through the metal.

I would ask Lafert for a new motor.

 

[generessler]

My old pump developed a leak that eroded the seal plate like that. The motor could wiggle enough for the impeller to lock up, which it did, luckily with the motor at rest so the symptom was the pump not starting. I guess if it chose to bind hard while the pump was running at full tilt, the energy of the spinning rotor (~160 joules at 3450 rpm) had to go somewhere in a few milliseconds. But I agree it feels like a 1/2" shaft in good shape should absorb that without snapping.

 

[wireform]

I've seen a 3" crank shaft snap with similar coloration meaning, it was already broken internally for a while then the rest snaps at some unexpected point. There's no way a .625" shaft on a pool motor can break even with a dead stop.

 

[JamesW]

I guess if it chose to bind hard while the pump was running at full tilt, the energy of the spinning rotor (~160 joules at 3450 rpm) had to go somewhere in a few milliseconds.

Basically impossible that the shaft in good condition could break like that.

Even if you grabbed the impeller and made it stop instantly, the impeller plastic would break first and then the threads before good steel at 5/8" thick.

The corrosion indicates that the part was exposed for a long time and that the break was not sudden.

Possibly this is the final spot to break.

 

[JamesW]

https://www.halseymfg.com/assets/strength_of_standard_bolts_and_threaded_rods.pdf

 

[wireform]

Would love to see a good picture of the other portion of thr broken shaft.

 

[Jennifer_in_Clyde]

Wow- I'm surprised by the interest in this thread. A few other clues and thoughts for all of you metallurgists out there:

The shiny "ring" you see on the motor side of the fractured shaft is where the shaft is wider than the broken-off piece. Here is a picture that I captured from the Youtube video that was posted earlier in this thread (at around 14:01 in the video):

It appears that the shaft is machined in the area where mine fractured. The "ring" you are seeing is where the shaft was machined down to a narrower diameter, and the darker center is the area where the shaft sheared off, which is almost but not quite flush with the shiny machined surface. If you hold the two pieces together, the broken-off piece is only as thick as the dark center area.

The "corrosion" at the fracture point: After the pump stopped moving water I did not open it up for at least a week so the broken-off piece sat in salt water for awhile. After disassembly I waited a few hours before taking pics while researching the issue. I don't know if that has anything to do with what appears to be some corrosion on the sheared surface of the piece attached to the impeller.

Corrosion as a cause of the fracture and better pictures: The pump definitely had a small leak for a long time, but as others have said, I don't see how that causes a shaft to shear off unless there was also another defect that allowed water to penetrate the shaft. I'm just not buying the idea that surface corrosion alone had any impact on its structural integrity. I have tried (unsuccessfully) to get better pictures and I'm not inclined to spend a lot more time on this issue because I don't think anything short of a microscope and a Ph.D. will result in conclusive answers.

I may at some point send pictures to Lafert so they know about the issue, but I'm not going to ask them to do anything about it. In my view, this is Pentair's problem.

Anyway, I'm looking forward to getting a new Jandy pump installed soon.

Thanks to everyone who contributed to this thread.

 

[JamesW]

It almost looks like there are two different pieces of metal welded together.

 

[NCMike]

I have only seen the shaft shear off like that once or maybe twice.

There is a thread within the last year, but I cannot find it.

I think that I would replace the whole pump.

What did you do to your pool today?

At my target FC-7, I can smell it on my skin after a dip. That's your CCs because you didn't get out for a bathroom break. :ROFLMAO: How is 20? Nobody had a clue and there was no odor, even with 20 people in the pool. The bather residuals, shampoos, sweat, etc had to be making CCs...

www.troublefreepool.com

I think that was me. Mine was a Jandy pump. I was right under the 3 year warranty time frame for mine so they replaced it for free.

Anyway, I'm looking forward to getting a new Jandy pump installed soon.

I was going to say I wouldn't let this failure drive you away from Pentair, but it looks like you have iAqualink for automation so maybe that's why your going to Jandy. I wish I would have went with all Pentair equipment to begin with just because Jandy parts are so hard to come by and they don't want any homeowners working on anything themselves.

 

[Bill1974]

I have seen it on other styles of pump shafts. I am not sure of the construction of the shaft on this pump, but isn't not uncommon for the shaft to be made of two materials, carbon steel on the motor side and stainless steel on the pump side. They are typically joined by friction welding. Failure looks like typical cyclic loading failure (bending back and forth). Generally not an issue in pool pump, but if there isn't enough straight pipe on the inlet side this can be a contributing factor. I don't see a pattern suggesting there was a weld issue (if the shaft was welded). If there is an elbow too close to the pump inlet it causes a moment force on the impeller and this turns into a cyclic bending force every rotation of the impeller. If the force is high enough it's just a matter of time before it will fail.

 

[wireform]

I have seen it on other styles of pump shafts. I am not sure of the construction of the shaft on this pump, but isn't not uncommon for the shaft to be made of two materials, carbon steel on the motor side and stainless steel on the pump side. They are typically joined by friction welding. Failure looks like typical cyclic loading failure (bending back and forth). Generally not an issue in pool pump, but if there isn't enough straight pipe on the inlet side this can be a contributing factor. I don't see a pattern suggesting there was a weld issue (if the shaft was welded). If there is an elbow too close to the pump inlet it causes a moment force on the impeller and this turns into a cyclic bending force every rotation of the impeller. If the force is high enough it's just a matter of time before it will fail.

interesting

 

[Bill1974]

I am an engineer and have worked for a pump manufacturer (not pool pumps), and have seen this happen. I have see shafts bend and also see where the impeller will tighten if hit with a slug of fluid (the motor shaft keeps turning but the force on the impeller causes it to slow down or momentarily stop and the inertia of the rotor causes the impeller to tighten on the shaft, usually the pump would seize up at this point).