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Submersible borehole pump

Submersible borehole pumps are a type of submersible pump. They are centrifugal pumps driven by a submersible motor. As they usually draw in the fluid directly without a suction line, they must constantly be submerged in the fluid handled.

Submersible borehole pumps are designed as single-stage or multistage pumps which are rigidly coupled to the submersible motor. The motor can be arranged on top or underneath the pump, depending on the application.

They are employed as submersible borehole pumps for use in tank farms and as cavern pumps, for example. Their most common application is that of a borehole pump. Borehole pumps are more cost-efficient than deep-well turbine pumps, especially for large installation depths, as their rising mains have a simpler design. See Fig. 1 Submersible borehole pump


Submersible borehole pump: Combined with water-filled wet motor to form a submersible borehole pump set Fig. 1 Submersible borehole pump: Combined with water-filled wet motor to form a submersible borehole pump set

To meet the typical conditions of a borehole, submersible borehole pumps are designed with a small diameter and a large axial length.

The motor, which is usually installed underneath the hydraulic stages, is a water or oil filled squirrel-cage motor (e. g. submersible motor), which is sealed off from the pump by a mechanical seal or another similar shaft seal. A suction strainer is fitted between the pump and the motor.

As the pump set is inaccessible during operation it must be entirely maintenance-free. Particular attention must be paid to the bearings absorbing radial and axial forces. The plain bearings, which are lubricated by the fluid handled or the motor fill, are commonly made of carbon, bronze, synthetic resin-impregnated hard fabric, ceramic or hard metal.
Depending on the requirements, the pump casing, impellers and diffusers are made of cast iron, bronze, aluminium multi-alloy bronze, chrome nickel steel or plastic.

A check valve (see Valve) is fitted at the very top of the pump set. The fluid handled (see Flow rate) is guided through this valve to the riser, from which the entire pump set is suspended.

The power cable is routed out of the motor through a cable gland and up along the outside of the pump and inside the riser to the top.

The principal applications of submersible borehole pumps are irrigation, maintenance of groundwater levels in open-cast and underground mining or construction pits, pumping tasks in water-supply wells and in the offshore, geothermal energy or deep-sea mining sectors.

The pump sets have to be matched to each application, especially when the fluid to be handled contains sand and contaminants.