22 Feb The Different Types of Submersible Pumps & What We Use Them For
Common Types and Typical Uses of Submersible Pumps
While it might be common practice to refer to a flowing river as an analogy to explain the behaviour of electricity, water and electricity are highly incompatible. Nevertheless, there are numerous situations when it is necessary to operate various types of electrical equipment underwater. Consequently, immersing an electrical appliance in water is a task that requires stringent precautions. Using suitable insulation techniques, we can safely heat the contents of a water tank or a kettle with an electric element. It should, therefore, come as no surprise that electric submersible pumps (ESPs) are safe, highly efficient, and widely used by various industries for many essential tasks.
How Submersible Pumps Function Safely Underwater
There are several ways to overcome this incompatibility and allow an electrically operated device to function safely underwater. The first and simplest of these is to ensure the drive motor remains clear of the water and only the functional components of the equipment are submerged. Whether immersed or not, the method most frequently used to transfer fluids is with a rotating fan-like structure, known as an impeller. The specially-shaped blades of the impeller in surface and submersible pumps generate centrifugal forces that draw fluid into a chamber through an inlet pipe and accelerate it before expelling it via an outlet pipe.
In each case, the impeller is mounted on a motor-driven shaft. The simple device mentioned earlier is commonly known as a vertical spindle pump, so-named because it has an unusually long, spindle-like driveshaft that extends beyond the liquid’s surface. The latter ensures the electrical components remain clear of any fluid that might cause a short circuit. In practice, it is more accurate to describe these units as semi-submersible pumps, and their primary use is to deal with flooding that often occurs in sub-ground level structures, such as basements. Typically, this type of device will remain inactive until the water level reaches a given height, at which point a sensor will activate it. When the level falls sufficiently, the sensor will automatically switch it off.
Fully Submersible Pumps
However, although the elongated driveshaft provides an effective workaround, it limits versatility. There are many instances in which the only viable option is to immerse the pumping equipment completely. There are two main ways to construct fully submersible pumps. The first method is to mount the motor in a hermetically sealed compartment within the outer casing. This arrangement isolates the motor’s components and the electrical wiring, thus eliminating any risk of contact with liquid either in the pump chamber or the external environment.
These hermetically sealed models are commonly installed in wells and boreholes. Positive pressure from the water above keeps the unit primed automatically and reduces the energy required to transport it to the surface. Being submerged also means they are not prone to cavitation and the cold liquid surrounding these submersible borehole pumps also helps prevent their motors from overheating. By contrast, a surface-mounted unit requires more power because it must lift the water without any help from the hydrostatic pressure that forces the liquid into the underwater models. The resulting reduced power requirements of these submerged units makes them a particularly economical choice for use in irrigation systems, on farms and smallholdings. It is often necessary to install a multistage model with two or more impellers for use in deeper holes.
Uses for Submersible Pumps
However, there are more uses for submersible pumps than water abstraction. The oil and gas industry employs ESPs extensively, and they have several advantages. The components operate efficiently even in casings with an external diameter as narrow as around 12 centimetres. Consequently, they are ideal for use in situations where clearance is minimal. Furthermore, they are heat tolerant and can be adapted to handle corrosive agents like hydrogen sulphide and abrasive sand, which are common contaminants in crude oil.
However, seals wear out, allowing leakage. Some submersible pumps are designed to operate without them to avoid this risk. Sealless models eliminate the need for a driveshaft and any form of mechanical connection between the impellers and the motor. Instead, they leverage electromagnetic induction to isolate an external motor housing from the pump chamber within and concentric rings of magnetics to serve as the connection. These units can be used submerged or dry and are the safest option for handling volatile combustible liquids.
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