When pumps are required that can be submerged, they quickly become indispensable: Submersible pumps – also called underwater pumps (or U-pumps for short). They are frequently used for water supply and wastewater disposal. These pumps are not only indispensable for extracting water from wells, shafts or open waters, but also for removing chemicals and other substances from a wide variety of barrels and containers.
But not all submersible pumps are the same. A distinction must be made between two types of submersible capability!
Submersible Pumps
A submersible pump is a pump whose housing may be submersed completely, mostely including the driving motor (= submersible motor pump). The term includes several pump types, which work with different materials handling technologies. The most common type of submersible motor pump works according to the operational principle of the centrifugal pump.
The pumps are available in stationary and mobile variants. It is easiest to distinguish them based on their construction: shaped like a rod for stationary use, for example in wells and shafts, and in the classic shape, by contrast, for mobile use, for example as a wastewater pump for drainage or emptying a basement. Mobile versions also usually have a handle or a bracket on top of the housing so that they can be fastened and carried easily.
Special motor housings are used to protect the drive against damage due to being submersed in the fluid handled. The drive construction distinguishes itself from pumps that are not or are only partially submerged in the fluid (so-called dry-runners, semi-submerged or immeresed pumps). Another special feature of submersible motor pumps: Since the drive is completely submerged in the fluid handled, that fluid is also used to cool the motor.
In the B2C sector, submersible motor pumps are often just called submersible pumps. However, this term is misleading since in the B2B sector it also includes pumps whose housing is only partially submersed in the fluid handled. With these units, the motor may have no contact with the fluid. This is accomplished by having the motor set up so that it works dry; that is, with a long drive shaft at a distance from the pump housing.
Special ATEX models of submersible motor pumps fulfill the requirements for explosion protection. They are used with hazardous fluids. In order to protect the pump against especially corrosive or abrasive media, submersible motor pumps are also available in other special versions.
To explain it shortly:
Submersible Motor Pumps
Usually these pumps are meant: pumps that are completely submerged with motor inside the liquid.
These are the also so-called underwater pumps or u-pumps.
Since the pump and the pumping mechanism are already completely surrounded by the liquid and a permanent flow is possible, these pumps are not self-priming, only normal sucking.
Immersed / Semi-Submerged Pumps
At these pumps only the pump head is vertically submerged in the liquid. The motor is still dry outside above. The pumps are also only normal sucking, not self-priming.
Another type of this pump is a horizontally dry mounted pump and only a suction pump is immersed in the liquid. These pumps have to be self-priming to bleed the suction line to be able to start the pumping process.
Submersible pumps for wastewater and other contaminated fluids
The most frequent application of submersible motor pumps is drainage and wastewater disposal. If the pumps are used in this sector, they are called wastewater pumps. These units, which are frequently mobile variants, can pump contaminated water, wastewater, and other fluids even if they have greater solid content – for example, gravel, stones, or other typical wastewater components such as wet wipes and feces.
Pump manufacturers equip wastewater pumps with a specially developed impeller, which is especially suitable for such requirements. Typical are free-flow impellers, which are least subject to disturbances thanks to their large free flow space. Since they are comparatively inefficient, however, other designs with other impellers are offered: Multi-channel impellers, diagonal impellers, and other types.
Wastewater pumps are usually not self-priming since they are nearly always surrounded by the fluid they are handling when they are in use. However, they often have a float switch that protects the pump against dry running and also enables automatic regulation of the fill level.
Submersible pumps for drawing water from wells and shafts
Well pumps typically work below the water level, so it’s mainly submersible motor pumps that are used for this application. These submersible pumps, often called U-pumps, handle water in countless private, municipal, and industrial wells and cisterns around the world, providing household water, water for sprinklers in agriculture, and also drinking water.
While normal submersible pumps usually have a maximum head of about 10 meters, some submersible pumps are designed so that they can draw water that lies even deeper.
Use as drum & container pumps
In the B2B sector, a wide variety of water often has to be pumped, but also other pumped media, such as acids, alkalis and other chemicals & substances, often from IBCs and other containers or pits. This usually requires extraction from above in submerged form. Since the depth to be mastered is usually very small, the submersible pumps are used as so-called immersion pumps or even properly as barrel pumps or in complete drum emptying systems.
In contrast to other centrifugal pumps, submersible motor pumps have clearly delineated areas of application: They are used primarily as wastewater pumps for wastewater disposal, for general drainage, and for water supply and watering tasks from wells and cisterns. Thanks to their special construction, mobile submersible pumps can usually be recognized at first glance: These compact units were developed for flexible use so that they can be pressed into service quickly wherever they are needed.
Submersible motor pumps are not just used for household water and wastewater, but also in underground construction and mining, where the serve to keep construction pits and tunnels clear. In agriculture, submersible motor pumps are used to fill water systems. Mobile submersible pumps are used in disaster assistance, by fire departments, and in general flood protection to drain basements and keep buildings dry. In case of floods, they are in a position to pump the wastewater out quickly.
Watering pumps are usually mobile submersible motor pumps so that they can be lowered into fluid containers without a problem. They are used in agriculture to water the fields or “rain” on them. This type of pump is typically operated unregulated.
A rare application of submersible pumps in industry is the handling of cooling water. These pumps are usually regulated when supplying a heat exchanger: The pump capacity and head depend on the construction and the heat stream to be dissipated in the cooling system. More usual for this application are pipe and spiral housing pumps.
Even if submersible pumps are usually used for various types of water, they are clearly in a position to handle other non-critical, low-viscous fluids as well, and also chemicals – depending on the used materials for the different components.
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