why do pumps fail?

[rsarvis]

What is failing when pumps fail? And why is it hard to make pumps that are more reliable and last longer? Or am I just buying cheap, poorly made pumps? And is there no fixing a pump that's just stopped working (where there isn't any buildup that appears to be stopping it)? The sedra on my skimmer isn't working properly; I took it out and played with it a little, at one point it was working in a 5-gal bucket, but i put it back in and it didn't work...

 

I've had several power heads fail (hydor koralia, maxijet, etc) and now the sedra.

[davelin315]

My own thoughts are that since pumps that seem to lock up without any signs of build up are that the impeller has become unbalanced and therefore the magnetic field surrounding the impeller is causing it to stick rather than spin. Once the impeller becomes unstable, it continues to cause issues. Of course, I have only verified this a few times as the impellers either locked the pump up or eventually wore down and snapped after having to be restarted over and over again.

[rsarvis]

My own thoughts are that since pumps that seem to lock up without any signs of build up are that the impeller has become unbalanced and therefore the magnetic field surrounding the impeller is causing it to stick rather than spin. Once the impeller becomes unstable, it continues to cause issues. Of course, I have only verified this a few times as the impellers either locked the pump up or eventually wore down and snapped after having to be restarted over and over again.

 

I see... so a) what causes them to become unstable (and why doesn't that happen in other motors?), and b) there's not much you can do about it other than buy a new impeller (or pump)?

[Origami]

The only issues I've had with several pumps are:

 

1) Calcium carbonate build up along the shaft and inside the impeller. Friction there raises the temperature, lowering the solubility of calcium carbonate. This causes deposits which bind and slow up (or stop) the impeller. Sometimes getting the two separated is difficult. After that, a good soaking is required.

 

2) I've had at least one pump (an old one from ZooMed) stop because of what I assumed to be swelling of the plastic inside the impeller causing binding. I'm assuming that this was the case because long soaks in an acid solution to dissolve calcium buildup was not working. I finally resorted to drilling the impeller out with a twist drill (to a size slightly greater than the shaft) to get it to work again.

 

3) I've had the wiring break on at least one pump (inside the potted motor block). In this case, there was a voltage leak near the pump and the impeller showed no signs of even being under the influence of the motor block, so I assumed that the wiring was bad. The only solution here was to toss out the pump.

[Integral9]

I've got a couple MJ-600 that completely stopped for no determinable reason. Drive shafts were easily removed and all cleaned and still the pump refused to start. I tossed the pumps but kept the rest of the parts... Maybe I should have kept the pumps and tossed the impellers... I wish I had the time to figure what the problem was.

 

I think either what Origami said and the pump fails due to overheating as the flow of water through it slows beyond it's ability to transfer heat away from the motor or it's the magnets on the impellers. There I'm thinking the magnets on the impellers either get reversed, neutralized or somehow destabilized from the motor constantly alternating the magnetic field around them causing them to spin.