Water damage on submersible motor pumps and how to prevent it.

Watertight cable connections at the pump casing

The benefits of submersible motor pumps are clear to see: They are much more compact than conventional tubular casing pumps of the same hydraulic performance. No extra buildings or housings are required for the motors, and they are easier to handle regarding maintenance and installation. Only: How safe is it to operate these pumps continuously submerged in and surrounded by very dirty water? Is there a risk of fluid entering the pump, causing short circuits or damage to the motor?

Generally speaking, this risk affects all pumps with a submersible motor but only in the event of a defect, such as a missing test port screw, a fractured pump body, old and brittle sealing elements or a faulty casing. Other examples are damaged or incorrectly seated O-rings, grooved shafts or improperly lubricated or even incorrectly seated shaft seal rings. In these cases, too, water can enter the motor space. Bearing in mind that submersible pumps that are permanently installed in waste water tanks are out of sight when performing important tasks such as protecting basement rooms from backflow, maintenance is key. Maintenance can prevent all of the above.

If the pump is not mechanically damaged, no water can enter the pump. The pump is monitored by various sensors. In the event of any damage leading to water entering the pump, the pump will be stopped via the monitoring sensors.

Watertight connection: How to prevent water from entering via the cables

All of KSB’s submersible motor pumps (for instance the Amarex KRT and Amacan type series) are fitted with an absolutely watertight cable entry. Even if the cable insulation is damaged during installation or operation, this patented system protects the pump against ingress of the fluid handled into the motor space and into the terminal box. 

The insulation of the individual cable cores is stripped and the wire ends are tinned. This section is fixed in the cable gland system with spacers and then completely embedded in synthetic resin. A rubber gland provides additional sealing. This sealing concept is used for both the power cable and the control cable.

Naturally, all of KSB’s submersible motor pumps meet the requirements of enclosure IP68 (International Protection). The first digit, the 6, stands for “dust tight” and the second digit, the 8, signifies “suitable for continuous immersion”.

When the pump is installed in the discharge tube, it is necessary to mechanically support the cables’ own weight and at the same time protect them against flow turbulence. For this purpose KSB has developed a patented cable holder. The cables are attached to a support rope with rubber profiles. The support rope is then fastened to the discharge tube cover with a turnbuckle and shackle. In the case of an open discharge tube, it is fastened to a cross-beam. This ensures that the cables have a long service life and the cable entry into the motor housing is absolutely tight.

Double mechanical seal for protecting the motor against dirty water

The shaft is sealed by a double mechanical seal. Mechanical seals are indispensable for sealing rotating shafts. They make sure that the fluid handled remains in the system, prevent emissions and thus protect the environment from contamination. High-quality shaft seals in the form of mechanical seals also ensure maximum economic efficiency and operating reliability for pumps. This is crucial because the majority of repairs arise due to sealing problems.

Submersible motor pumps are fitted with mechanical seals in tandem arrangement with a liquid reservoir and high-quality, wear-resistant contact face materials for many years of trouble-free operation.

Monitoring by float switch and sensors

The mechanical seal is monitored by a float switch. Various sensors emit a warning at an early stage, before damage may occur. They monitor vibrations, moisture in the motor and connection space, and the temperature of motor winding, coolant and bearing.