Air Filled vs Oil Filled by Jason Fletcher

Air Filled -vs- Oil Filled by Jason Fletcher, PE
The long debate in the submersible wastewater industry has been which is better an air filled motor or oil filled motor. An oil filled pump is defined as having the motor cavity filled with oil, usually to cover the upper bearing and windings. An air filled pump is one the does not use any oil to fill the motor cavity. This article will tell what the advantages and disadvantages of each design and explain why Zoeller Company has chosen an oil filled type motor. "With a submersible pump, heat transfer is accomplished by direct conduction to the relatively constant temperature fluid being pumped. This more efficient heat transfer method (verses a dry mounted pump) results in a lower operating temperature for the motor and its internal components, and helps extend the life of the motor" - SWPA Handbook. Let’s take the above quote one step farther, if it is good to submerge the pump in sewage for better heat transfer then why not submerge the stator in oil for the same reason. Oil filled motors lower the winding temperature through extra heat transfer away from the stator, to the housings, and then out into the liquid. We all know that heat kills electrical components so anything that is done to lower the temperature inside the pump will give a longer lasting product. Other advantages include a more uniform winding temperature, therefore eliminating destructive hot spots in the motor and permanently lubricating the bearings / seals to extend life and lower temperature. The downsides to oil filling are the environmental consequences and a lower overall efficiency when compared to an air filled type motor. The environmental issue can be easily resolved by using a type of oil that is environmentally friendly J. The lower efficiency carries about a 2% increase in overall energy costs. Both of these penalties are pretty easy to offset when the pros of oiling filling are explored.

Air Filled -vs- Oil Filled
by Jason Fletcher, PE

     The long debate in the submersible wastewater industry has been which is better an air filled motor or oil filled motor. An oil filled pump is defined as having the motor cavity filled with oil, usually to cover the upper bearing and windings. An air filled pump is one the does not use any oil to fill the motor cavity. This article will tell what the advantages and disadvantages of each design and explain why Zoeller Company has chosen an oil filled type motor.
     "With a submersible pump, heat transfer is accomplished by direct conduction to the relatively constant temperature fluid being pumped. This more efficient heat transfer method (verses a dry mounted pump) results in a lower operating temperature for the motor and its internal components, and helps extend the life of the motor" - SWPA Handbook.
     Let’s take the above quote one step farther, if it is good to submerge the pump in sewage for better heat transfer then why not submerge the stator in oil for the same reason. Oil filled motors lower the winding temperature through extra heat transfer away from the stator, to the housings, and then out into the liquid. We all know that heat kills electrical components so anything that is done to lower the temperature inside the pump will give a longer lasting product. Other advantages include a more uniform winding temperature, therefore eliminating destructive hot spots in the motor and permanently lubricating the bearings / seals to extend life and lower temperature.
     The downsides to oil filling are the environmental consequences and a lower overall efficiency when compared to an air filled type motor. The environmental issue can be easily resolved by using a type of oil that is environmentally friendly J. The lower efficiency carries about a 2% increase in overall energy costs. Both of these penalties are pretty easy to offset when the pros of oiling filling are explored.