Different Types of Submersible Pumps and Their Many Uses

Pumping equipment is widely used to transport a range of liquids from drinking water to crude oil and even corrosive chemicals such as sulphuric acid. When handling these more aggressive fluids, suitably resistant materials are essential when manufacturing the equipment’s internal components. Sometimes, however, the potential danger can be external rather than internal.

Such is the case with electrically powered submersible pumps. Although water is often used as an analogy to explain the flow of electrons responsible for an electric current, in most circumstances, the two are highly incompatible. Consequently, special design features are necessary for electrically powered pumping machinery to operate safely when submerged in a conductive liquid such as water.

One option that can sometimes be effective is to locate the electric motor above the surface of the water and employ an extra-long drive shaft to rotate one or more impellers. This is the principle behind the semi-submersible units known as spindle pumps. These units are used mainly to deal with flooding and may either be operated by hand or set up to begin working automatically when the floodwater reaches a pre-set level. While this can be a highly practical means to cope with unexpected leaks or flooding in a basement located below the water table, there are many instances in which only a fully immersed unit will provide a viable solution.

Most often, the challenge for manufacturers is to prevent the liquid inside a unit from leaking out, whereas, in submersible pumps, it is the risk of liquid leaking into the unit that poses the challenge. In the conventional units, seals at the entry point of the driveshaft serve to limit the risk of leakages. Over time, however, these seals can become worn, especially when exposed to corrosive or abrasive fluids. If a worn seal should result in a leak, this could lead to serious consequences if allowed to persist.

However, the consequences of even a small volume of water leaking into the electric motor of a submersible pump would be immediate and are likely to be far more destructive. While it may sound like a contradiction, these underwater units overcome the possibility of leakage by dispensing with the need for seals. In a conventional pump, it is the need for a driveshaft to transfer rotational energy from the motor to the impellers that is the source of the problem. A seal between the shaft and the pump housing is only a temporary solution. Friction alone results in gradual wear and, eventually, the need to replace it.

The innovative design of submersible pumps eliminates the need for a driveshaft. Consequently, those potentially leaky seals are also unnecessary. The rotary action of an electric motor is the result of a phenomenon known as electromagnetic induction, in which a moving magnetic field produces an electric current in a stationary coil. The designers have leveraged this same phenomenon to develop a pump that requires neither a driveshaft nor seals. In these machines, the coupling between the electric motor and the impellers is magnetic rather than mechanical.

In submersible pumps, the motor is mounted in an outer housing, separate from the impeller shaft, and drives a cylinder composed of magnets with their like poles aligned. The impeller housing resides within that cylinder. In addition to the impellers, its shaft supports a second cylinder of magnets with poles opposed to those in the outer cylinder. As the motor turns the outer cylinder, the inner one rotates in unison, driving the pump’s impellers in the process. The only access to the impeller chamber is via its inlet and outlet ports. Therefore, there is no possible way that water could leak into the motor housing.

The applications for submersible pumps are manifold. In a growing number of homes, on farms, in remote areas and in businesses such as plant nurseries, where water consumption tends to be high, much of the water used is obtained from underground sources rather than purchased from municipalities. When suitably treated, borehole water can be safe to drink. More often, it will be used for relatively mundane tasks such as watering lawns, washing cars and driveways, while farmers will use it to feed vital irrigation systems.

In industry, dewatering of flooded mine works is another crucial task for these devices. Other common uses include powering domestic water features and public fountains, to name just a few. A wide selection of world-class submersible pumps is available in South Africa from Prochem Chemical Pump Manufacturers.

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