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A mechanical seal is an assembly designed to seal the pump where the shaft passes through the pump cover. Tightness in such units comes by tight pressing along the end planes of two precision parts – rotating and stationary. To prevent leaks, the accuracy of the parts must be very high. This accuracy comes by grinding and lapping the contacting surfaces by the Water Pump Seals manufacturers.
If in dry pumps the mechanical seal has special design to prevent the pumped liquid from passing from the pumping room to the environment. Moreover, in submersible pumps the mechanical seal does not let water into the electric motor and prevents a short circuit. To increase the reliability against leaks, two end caps often place on the same shaft.
In this case, a coolant is additionally common, often oil, which in turn is a dielectric. And, when it enters the electric motor, does not lead to a short circuit.
Structurally, mechanical seals divide into dismountable and cartridge seals, balanced and unbalanced by Water Pump Seals manufacturers.
The materials of the friction pairs depend on the characteristics of the pumped liquid, temperature and pressure. All of them can be divided into soft and hard. Depending on the tasks, the following materials can be used in various combinations: silicon carbide, aluminum oxide, tungsten carbide, graphites impregnated with metals or synthetic resins.
Rubber (TPDM), Viton (FKM), Nitrile (NBR) can be used as a secondary seal. Reasons for failure, prevention and measures to maintain the performance of end and pumps in general.
According to Water Pump Seals manufacturers, the mechanical seal is the most accurate, fastidious and fastest wearing part in the entire pump. According to the statistics of the service center, 70% of all faults come with the mechanical seal. Moreover, the statistics of the end failure looks like this:
Wear (30%) – wear is a natural process that directly depends on the number of hours that the pump has worked. However, several other factors affect the wear rate, for example, high temperatures or abrasive inclusions also reduce the service life of the mechanical seal.
Water Pump Seals manufacturers say that to increase the service life, it is necessary to select mechanical seals with materials. Furthermore, these are more good to your application. There are a lot of such factors and for each specific case. Hence, we recommend that you contact a specialist.
Incorrect use (15%) is a case when the wrong selection of the end seal leads to hyper-intense wear (3-6 months). Moreover, it can be the loss of their properties of the secondary seals. For example, for oils and emulsions, it is necessary to use Viton (FKM) as a secondary seal material.
Dry running (15%) – the pumped liquid performs the function of cooling and partially lubricating the friction pairs. Hence, Water Pump Seals manufacturers suggest buying reliable seals. Furthermore, these seals have far better functions and life.
Prevention of such malfunctions is the systematic release of air from the pumping section through specially provided drain and correctly professionally tuned automation. As practice shows, most cases of dry running breakdowns are associated with the negligence or unprofessionalism of the adjusters or maintenance personnel.
Sticking of the seal (15%) – this includes both adhesion of rubber seals to the shaft and adhesion of the ground surfaces of friction pairs after a long downtime, which leads to the formation of roughness and chips at the moment the shaft breaks off the dead center.
Water Pump Seals manufacturers say, the seal is the most vulnerable and most often wearing part of any water pump, regardless of its design. If earlier, stuffing box packing was used to seal such equipment, today mechanical seals are used, which are more modern and reliable.
Mechanical seals ensure the tightness of the area. This comes where the shaft passes through the pump housing. It is due to tight compression at the ends of the rotating and stationary parts.
One of the rings of the seal presses by Water Pump Seals manufacturers against another elastic pressing element. It can be in the form of a bellows, a spring or a membrane. This which together with the sleeve forms a clamping unit that ensures a snug fit of the end surfaces.
An important part of the design is secondary seals made of different grades of elastomers, PTFE or rubber in a PTFE sheath. For fixing along the shaft and installing the seals, screws and drive pins are used, which are responsible for transferring torque from the shaft to the moving ring and preventing angular displacement of the stationary seal.
Seals of this type are used in both surface and submersible centrifugal pumps. In the first case, their function is to prevent leakage of the pumped liquid from the pump to the outside into the atmosphere. In the second case, a seal is necessary to prevent liquid or water from entering the engine.
Since maximum tightness is important for submersible pumps say Water Pump Seals manufacturers, they are most often equipped with two seals and use oil as a barrier medium, acting as a dielectric and eliminating a short circuit when water enters the motor.
The scope of use of seals for water pumps is quite wide, since modifications can be selected for different types of liquids: drinking and purified water, domestic and industrial waste water, as well as aqueous solutions of different composition, including those containing abrasive particles.