Why mechanical seal and how to choose?
For more than 100 years, a variety of sealing materials, such as fillers, have been used to reduce the amount of liquid leakage from the liquid pump housing along the main shaft. The oldest seal design is still widely used in current liquid pumps because of its low starting cost and familiarity with the factory staff. However, due to environmental issues, the use of packing seals has gradually become unacceptable, especially for liquids that are more common and corrosive in modern processes. More and more packing seals are replaced by mechanical seals.
Packing seals are mainly used for low viscosity liquid pumps such as clean water pumps. In addition to being used in reciprocating pumps, packing seals can also be used in rotating applications. The packing sealing structure is simple, convenient in operation and maintenance, and low in cost. The disadvantage is that the power consumption is large, the sealing reliability is poor, and the shaft is easily worn during use. It should not be used for flammable, explosive, valuable or toxic liquids. The mechanical seal has a long maintenance period and can be automatically compensated after the end face is worn. Under normal circumstances, it does not require frequent maintenance and has good shock resistance. It is not sensitive to the vibration of the rotating shaft, the yaw and the deflection of the sealed chamber.
Mechanical seals are suitable for a wide range of applications. They can be used for low temperature, high temperature, vacuum, high pressure, different speeds, as well as various corrosive media and abrasive media. For the“zero leakage”requirement of many factories today, packing seals cannot meet this requirement, and frequent replacement or maintenance will cause great loss to the plant.
The basic principles of selection are:
1. According to the pressure of the sealed cavity, it is determined that the sealing structure adopts balanced or unbalanced type, single end or double end.
2. According to the working speed, it is determined to adopt rotary or static type, fluid dynamic pressure type or non-contact type.
3. According to the temperature and fluid properties, determine the friction pair and auxiliary sealing materials, and correctly select the mechanical seal cycle protection system such as lubrication, flushing, heat preservation and cooling.
4. According to the effective space for installing the seal, it is determined to use a multi-spring or single spring or wave spring, built-in or exterior.
5. According to the characteristics of different liquids, seal material should be different. Tungsten Carbide and Silicon Carbide are common to use. Then how to choose ?
The advantages of Silicon Carbide are mainly:
A.Self-lubricating is better than hard alloy,
B.The cost is lower than that of cemented carbide;
The advantages of Tungsten Carbide are mainly:
A.The scope of application is wider than that of silicon carbide.
B.The toughness is stronger than silicon carbide. It is not easy to be broken when assembled. The advantages and disadvantages of the two are basically complementary. Therefore, it should be considered as comprehensively in the selection.
BONVE Rotary lobe pump and Homogenizer mechanical seals are designed by experienced experts. They are made of different structures and materials according to the characteristics of different liquids, and has reliable interchangeability to ensure safety and no leakage.
