Submersible pump surprise

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- Salmon Egg
  
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posted
15 years ago

Sat, Apr 4, 2009 1:36 AM

I had a failure of a small submersible pump used for hydroponic nutrient solution. To my surprise, the hot to neutral resistance was about eight megohms. I decided to investigate further. The impeller seemed to turn easily.

Then, as I took the pump apart further, I got my real surprise. Apparently, this pump kept water from seeping into the motor area by immersing it in some kind of oil. All of a sudden oil was all over the place as I broke the seals. That makes sense because the oil and the O-ring seals are going to help prevent water from seeping into a volume with just air in it.

This was a cheap pump, Is this the typical technology for submersible pumps? What other technologies are used? I presume that the oil was a cheap mineral oil. How likely is it that it would be something more toxic?

Well, I certainly learned a messy lesson.

Bill

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- Mike Lamond
  
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posted
15 years ago

Sat, Apr 4, 2009 4:44 AM

The only submersible pumps that I have any experience with are used in sewage pumping stations, like the one they swapped out on an episode of "Dirty Jobs." These also have oil-filled motor housings with a separate dry terminal compartment. On their website, ITT Flygt just refers to the oil as "environmental oil." It would have to be suitable for use with the Class H temperature rating on the windings. One options is a level switch at the bottom of the motor housing that senses water accumulation to give a seal leak alarm.

A brief search on deep well pumps for drilled water wells turned up plenty of online distributors, but no real data on what, if any, fill oil is used.

Mike

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- James Sweet
  
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posted
15 years ago

Sat, Apr 4, 2009 9:43 AM

Every direct drive submersible pump I've seen has been made that way. I've taken apart two, one had water intrusion and the other burned out the motor. That second one was a real mess, burned oil full of flakes of burned insulation enamel.

The other type you find once in a while, particularly those little fountain pumps, have the stator potted in epoxy and the rotor is immersed.

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- John Gilmer
  
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posted
15 years ago

Sat, Apr 4, 2009 8:04 PM

The same is true of "deep well" water pumps. They are filled with oil. In the case of potable water pumps the oil is certificed as being safe for human consumption. That's important because when you deep well pump is about to completely stop working the first "inkling" is that you find bits of plastic and OIL in your drinking water.

The "terminals" in deep well pumps are just leads which are connect to the power leads by water proof connectors.

These pumps are often installed such that they are 100' or more under water (the driller seeks out an aquifer which is under slight pressure -- once he punches through the water level rises). I can only assume that there is enough "soft stuff" in the pump to permit internal and external pressures to equalize.

Some pumps don't use oil but use WATER as a lubricant. They still don't want any old water in touch with the bearings but when the seal fails at least you don't get oil in your drinking water. Just before you pump stops working you will find pieces of pump in your drinking water.