Submersible motor pump

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A submersible motor pump is a pump that is lowered into the liquid and thus completely enclosed by it.

history

Submersible motor pumps of today's design were created through the development of water-filled submersible motors.

The water-filled submersible motor was developed by Friedrich Wilhelm Pleuger in 1928 and was then used for the first time with the Pleuger submersible pumps in the construction of the Berlin subway to lower the groundwater level . In the further course of the company Pleuger (today Pleuger Industries) many other developments were advanced. For this reason, the term “Pleuger pumps” is still used today when referring to submersible motor pumps.

Many other manufacturers entered the market after the Second World War . In the 1970s, the Pleuger company built the world's largest submersible motor (50 inches in diameter ).

Areas of application

Submersible pumps are suitable for:

Construction

Well pumps have different diameters, depending on their performance characteristics, which the manufacturers usually specify in inches (for example 4 ″ well pumps). The exact diameter in mm can be found in the technical documentation for the respective pump type. Submersible motor pumps are designed to be used in narrow boreholes. The diameter of the submersible motor pumps ranges from 3 "(DN80 filter pipes) to 10" submersible motor pumps. Another special feature are the electric motors, which have been specially designed for this use. In contrast to commercially available standard motors, the motors have a slim design and are not cooled by air but by the surrounding groundwater. These motors are also filled with water inside and the motor winding is waterproof. The motor is pressure-balanced by a membrane. An underwater motor can also be used in very great water depths with correspondingly high external pressures.

Submersible motor pumps are available with a wide variety of performance characteristics. There are pumps with volume flows from less than one cubic meter per hour to several thousand cubic meters per hour. The delivery heights range from a few meters to delivery heights of 700 to 800 meters. Submersible motor pumps are made of gray cast iron, thin-walled stainless steel sheet (e.g. 1.4301, 1.4401, 1.4539), thick-walled cast stainless steel or thick-walled cast bronze . The correct material quality is selected depending on the quality of the conveyed medium. Submersible motors are available in outputs from 0.25 kW up to 5,000 kW for nominal voltages from 220 V to 10,000 V.

A submersible motor pump consists of several components, the submersible motor below, the pump hydraulics mounted on it, the check valve and a waterproof power supply cable. The electric motor and hydraulic part are connected to one another with a flange and a shaft coupling. The electric motor drives the shaft of the hydraulic part on which the running wheels are attached via the shaft coupling.

The pump inlet, which is provided with an inlet strainer, is also located between the electric motor and the hydraulic part. The inlet strainer protects the pump from coarse components that could enter the pump during operation (e.g. stones). The water flows into the pump via the inlet strainer and the impellers of the hydraulic part increase the pressure of the water. The more impellers the pump has, the higher the pressure with which the water leaves the pump.

The pressure outlet is located at the head of the pump, which is usually provided with a thread on 3 ″ and 4 ″ pumps. A flange is usually attached to larger pumps. In most pumps, a non-return valve is attached or integrated under the thread outlet so that no water can flow back into the well when the pump is not running. When the pump is switched on again, the considerable mass of the flowing water would cause a pressure surge in the pipeline system.

Installation of submersible motor pumps

So that the pump can be installed in a well without problems, the diameter of the well pipe should be a few millimeters larger than that of the pump. In the worst case, the pump can become jammed in the well pipe due to deposits or a deformation of the pipe in places due to root pressure or the power cable settles between the pump and the well pipe, which makes it difficult to pull the pump later.

As a rule of thumb, for example, the following can be assumed (manufacturer information must be observed):

  • DN 80 filter pipe: 3 ″ well pump
  • DN 100 filter pipe: 3 ″ well pump
  • DN 115 filter pipe: 4 ″ well pump

Before installing the pump, it is advisable to check the well pipe for free passage with a caliber. It is important to attach it to a sufficiently dimensioned (tensile force in the event of jamming) and in its entirety (including rope clamps, screws, shackles etc.) highly corrosion-resistant rope or a corresponding chain. Of course, the securing of the retaining means in the area of ​​the well head must also be carefully considered.

The pump should never be positioned directly in the area of ​​the filter tube, as the partial flow in a small area of ​​the filter tube causes turbulence in the groundwater, which can lead to the precipitation of substances contained in the water (iron, manganese, lime). The pump should be installed around one meter above the filter tube area so that the filter tube area is loaded evenly over the entire length. In this installation position, it is also ensured that the groundwater flows past the motor, which is located below the pump hydraulics, and cools it. If the pump has to be installed below the filter tube area, a suction protection jacket must be attached to the pump, which ensures a forced flow around the submersible motor.

It is advisable to use level sensors to protect the pump from running dry. The evaluation unit switches off the pump as soon as the probes are no longer immersed in the groundwater. In some submersible motor pumps, dry-running protection is already integrated in the pump itself, so that external monitoring is not required.

Design of the pump

The relevant characteristic diagram is decisive for the design of the pump. The pump should be operated in the normal state at the optimum point on the characteristic . Further requirements result from the expected durability and the load parameters (dirt, temperature, reduced air flow around the engine area).