Submersible wastewater pumps are essential equipment in water supply and wastewater disposal systems, such as sewage treatment plants, factories, and even domestic sewage collection systems. These pumps collect solid-contaminated liquids from wells, ponds, and reservoirs and transport them to the electrical grid. A key component of these pumps is the mechanical seal, which prevents leaks between the rotating shaft and the pump housing.
The main function of mechanical seals
In a submersible pump, the motor and pumping section are immersed in the fluid. Therefore, any leak between the rotating and stationary parts can cause water or wastewater to enter the motor and potentially cause malfunctions. In this case, the mechanical seal acts as a watertight barrier between the fluid and the motor, preventing costly breakdowns.
Mechanical structure of the sewage pump seal
A mechanical seal consists of two polished surfaces: a stationary surface and a moving surface. These surfaces are typically made of wear-resistant and corrosion-resistant materials such as carbon graphite, silicon carbide (SiC), tungsten carbide (TC) , or stainless steel (SS)
. Between these two surfaces is a thin layer of fluid that provides lubrication and sealing.
The main components of mechanical seals are:
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firm seat
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round surface
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Spring or spring set
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Elastomer or O-ring
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Retaining ring
Double mechanical seals are commonly used in submersible sewage pumps to ensure complete sealing and extend the service life of the equipment.
Why use double seals?
A double seal consists of two sealing components: one between the pumped fluid and the housing, and the other between the housing and the environment. The space between the two seals is typically filled with oil or an inert fluid. This design offers several important advantages:
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Completely prevents contaminated fluids from entering the engine.
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Reduces friction and wear on sealing surfaces.
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Better cooling and longer lifespan.
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Reduces the risk of leaks under harsh operating conditions or high pressure.
Types of mechanical seals for sewage pumps
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Single seal:
Suitable for light applications or relatively clean fluids. Low initial cost, but less durable and reliable. -
Double seal: the most common seal type for industrial submersible wastewater
pumps . It offers high resistance to abrasive particles, aggressive gases, and liquids. -
Cartridge seal:
The seal is delivered fully assembled and ready to install. This reduces installation errors and shortens repair time. -
Fan type:
has a metal sleeve or bellows, can withstand high vibrations and axial movements, suitable for pumps with high operating temperatures.
Factors that influence the service life of mechanical seals
To ensure optimal performance of a mechanical seal, the following points must be observed:
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Quality of the pumped fluid:
The presence of solid particles, sand or chemicals can lead to rapid wear of the sealing surfaces. -
Operating temperature:
High temperatures can reduce the flexibility of O-rings and lead to premature leaks. -
Installation method:
The slightest error during installation, such as shaft misalignment or excessive pressure on the spring, can cause cracks to appear on the sealing surface. -
Proper lubrication: When using double seals, it is very important that there is a sufficient amount of clean oil in the space between the seals .
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Material:
By selecting a suitable material depending on the type of liquid (acidic, alkaline, corrosive, with solid particles, etc.) the service life can be extended.
Advantages of using high-quality mechanical seals in submersible pumps
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Completely eliminate sewage leaks and environmental pollution.
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Extends the life of the motor and bearings
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Reduction of maintenance costs
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Maintaining pump efficiency over a longer period
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Reduce the number of unexpected system shutdowns
Signs of mechanical seal failure
Professional tradesmen often recognize flood damage by several signs:
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Water or oil leaks from the back of the impeller
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The pump vibrates or makes unusual noises.
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Engine overheating
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Pump power or low pressure
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The oil in the cavity has changed color or is contaminated.
If these symptoms are observed, the pump should be immediately disconnected from the circuit and the seals checked or replaced.
Methods for regular maintenance
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Check for leaks regularly:
The overflow chamber and connections should be checked every few months. -
Change your engine oil between fill-ups: Keep it clean and free of contaminants. It’s recommended to change it once a year .
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Shaft alignment:
Check the alignment of the shaft and impeller each time the pump is opened and closed. -
Use genuine parts:
Counterfeit or inferior seals can fail quickly and cause serious engine damage.
Tips for choosing the right mechanical seal for your wastewater pump
When purchasing or replacing a mechanical seal, consider the following features:
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Pump type and manufacturer brand (e.g. Flygt, ABS, KSB, Ebara, Leo, etc.)
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Pump shaft diameter
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Liquid type and solid content
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Operating temperature and pressure of the system
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Seal type (single, double, cartridge, etc.)
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Surface materials and synthetic rubber
Concepts and designs for septic tanks
Finally
Despite their small size, the mechanical seal of a submersible wastewater pump plays a crucial role in preventing wastewater from penetrating sensitive motor components and extending their service life. Proper selection, careful installation, and regular maintenance reduce repair costs and system downtime. In water supply and wastewater treatment applications, factories, power plants, and industrial plants, high-quality seals from reputable manufacturers ensure reliable and leak-free pump operation.