A submersible pump is designed to work underwater or other fluids. The motor of this pump silently spins down in wells, deep pits, boreholes, and sewage tanks. It is also used to clear floodwaters in waterlogged areas. This pump can also move out solid, semi-solid, or slurry particles.
However, it is a common question whether a submersible pump can also function in a dry condition, without being submerged in liquids. The answer in short is “No” because the motor’s life can be drastically shortened if it is not submerged in fluid while spinning.
Problems that may occur if a submersible pump runs dry
Submersible pumps can be allowed to work in a relatively dry condition, but not for a long time. The following problems are likely to arise if a submersible pump function is used for dry applications.
- Shorter lifespan – The motor of the submersible pump will be overheated if exposed to air while spinning. The heat capacity of air is much lower than water. So, the heat generated by the motor cannot be easily dissipated in the air, compared to the heat dissipated the motor is submerged in water. Thus, the lifespan of the motor reduces due to inadequate cooling, improper insulation, and a steady rise in temperature.
- Dangerous overheating – If the motor of a submersible pump is too much heated due to less cooling, fire may break out in this machine. All the internal parts of the motor can be destroyed by this fire, making the pump totally unworkable.
- Damage of lubrication – A submersible pump is duly lubricated, and all its parts are sealed to keep the device safe underwater. When the pump operates in a dry condition, lubricated bearings of this pump may be damaged due to overheating. Moreover, oil in the motor may start leaking out due to the change in the orientation of the pump from submerged to dry application.
- Corrosion of coatings – All the parts of submersible pumps are coated with corrosion-proof materials that protect the machines from rusting underwater. But these coatings may act differently out of water and start corroding in moist air.
- Difference in mechanical properties – A submersible pump is designed to bear the water pressure or buoyancy. When it is brought to function in the air, the absence of this pressure may cause failure of its proper operation. The mounting style, mechanical stress, and vibration rates also differ to a large extent when a submersible pump is used in a dry condition.
- Issues in electrical features – The electrical cables and connectors of a submersible pump are typically designed to work underwater. The electrical parts may not function as required when the pump is operated out of water. The moisture present in the air condenses on the electrical features of this pump, which present an environment different from that within water or other fluids.
- Less efficiency – If a submersible pump is forcibly operated in dry conditions, its efficiency decreases rapidly. Thus, it will cease to be useful within a shorter time than its expected longevity.
Limited cases when submersible pumps are used in dry conditions
Submersible pumps can be used in dry conditions for a short time, only in certain specific occasions. However, utmost care must be taken in such conditions to avoid accidents.
- Double purpose motor – Motors of some submersible pumps are specially designed to operate both underwater and in little water where a major part of a pump remains in air. However, the operation time of such pumps in air should be limited, for which the data sheets of the manufacturers need to be followed.
- Testing of the pump motor – Only a low load is acceptable while using a submersible pump in a dry condition. The pump can be tested above water, just to check its functionality as per the guidelines given by manufacturers. Prolonged operation and heavier loads in a dry environment can damage these pumps.
- Highly humid environment – If the air contains a very high percentage of humidity, it resembles water to some extent. Hence, it becomes easier for a submersible pump to function in such an environment though it is not fully safe to operate for a long span.
- Motors of low power – Small submersible pumps contain much smaller motors compared to large pumps. A small submersible pump has a low-power motor, which produces much less heat that can be dissipated in air. Thus, such pumps can be used in dry conditions, though for a limited period.
- Pumps installed with modifications – Some submersible pumps can be installed after adding some special features. These pumps are modified to operate safely above water as well. Extra cooling facility in air, bearings lubricated again with air-friendly grease, reconfigured electric cables are provided to the motors of these pumps while installing. However, the installation of such pumps can be done only by highly skilled engineers, who have thorough knowledge of the pump mechanism.
Conclusion
Precautions should be taken to use a submersible pump in dry condition. It is not always possible to replace the motor of the pump with a suitable one that can run safely in the air. In that case, it is best to consult the manufacturer of the pump, who can guide regarding the installation of extra modifications.
The addition of extra fans or blowers can help in cooling the motor in the air, to lower of risk of overheating. Lubrication of bearings with compatible grease and the use of adapted cables in the motor are other precautionary steps. Special temperature sensors can be added to the motor to check the rise in temperature while operating in air. The feature of automatic shutdown can also prevent accidental fire in the pump motors.
The submersible pump should bear much less load in the air, compared to that underwater. Still, continuous monitoring is needed if a submersible motor should be used in dry condition, to avoid hazards of accidents. However, it is best to use submersible pumps underwater, with controlled exposure to air if needed.