The conductivity probe and float switch are the top sensors used.
by Hydraulic Institute
August 23, 2019

How can seal leakage be monitored in submersible pumps?

The two principal places for leakage monitoring are at the bottom of the motor (for vertical shaft motors) or in the seal barrier fluid containment volume.

Two sensor types dominate the market: the conductivity probe and the float switch.

In order to detect liquid intrusion from all possible areas, it is beneficial to install the leakage sensor in the bottom of the dry motor compartment.

The float switch contains a small floating element. Under normal conditions, it remains at rest at the bottom, but when liquid enters, it rises. This rise can be detected by several electrical methods.

While reliable, float switches are position sensitive, so they are usually not used in submersible equipment that is subject to incline, such as in portable pumps. The conductivity probe senses the conductance of an oil-water mixture, beyond a threshold limit, that reaches the sensor.

In an inner seal of a dual unpressurized seal arrangement, change in the seal reservoir pressure can be detected by either blocking off the reservoir from the vent and noting the increase in pressure or using a pressure transmitter or switch. In an inner seal of a dual pressurized seal arrangement, change in the seal support system pressure can be detected by using a pressure transmitter or switch.

For more information about bearing wear detection and seal leakage monitoring, refer to ANSI/HI 9.6.5-2016 Rotodynamic Pumps – Guideline for Condition Monitoring at www.pumps.org.

Visit www.pumpsandsystems.com/training/HI/training to register for classes, or to purchase guidebooks or standards.

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