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Basic Common Sense on Sealing
Release Time:
2022-03-20 16:06
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Fundamentals of Mechanical Seals
Mechanical seals are widely used due to their excellent sealing performance, stable operation, minimal leakage, low frictional power consumption, extended service life, and negligible wear on the shaft—qualities that enable them to meet a variety of operational requirements. However, they feature a relatively complex structure, demand high manufacturing precision, come at a higher cost, and can be inconvenient to maintain.
Principles and Their Components
Mechanical seals, also known as face seals, feature at least one pair of end faces that are perpendicular to the axis of rotation. Under the action of fluid pressure and compensating mechanical (or magnetic) forces, these end faces maintain close contact and relative sliding against another opposing face, effectively preventing fluid leakage. The tight fit between the end faces creates a minuscule gap, through which the medium flows to form an extremely thin liquid film. This film generates resistance, effectively sealing the system while simultaneously lubricating the end faces, ensuring long-term sealing performance.
Basic Components
Stationary ring and rotating ring (dynamic ring and stationary ring), typically featuring a ground surface, are also referred to as the friction pair.
A supplementary buffering mechanism primarily composed of elastic elements.
Auxiliary Sealing Ring
A transmission component that drives both the moving ring and the shaft to rotate together.
Classification of Mechanical Seals
Categorized by Purpose
By equipment type, these can be categorized into pumps, reactors, centrifuges, fans, submersible pump motors, chillers, internal combustion engines, cooling water pumps, marine pumps, and others.
Classified by working principle
Logarithmic configurations of sealing faces: single face, double face, and multi-face. Among these, the double-face configuration is further divided into axial double face and radial double face.
According to whether the fluid pressure acting on the sealing end face results in unloading or no unloading, it can be classified into: non-balanced type, partially balanced type, and fully balanced type.
According to whether the stationary ring is mounted on the inner or outer side of the sealing end face, it is divided into internal-mounted and external-mounted types.
Spring settings are classified as internal spring types when the spring is positioned within the fluid, and external spring types when it is placed outside the fluid.
According to the number of compensation mechanism springs, it is classified into single-spring type and multi-spring type.
Mechanical seals are classified into rotating and stationary types, depending on whether the elastic element rotates along with the shaft.
If the leakage direction of the sealed fluid between the sealing end faces aligns with the centrifugal direction of the rotating shaft, it is classified as an outward flow type; otherwise, it is considered an inward flow type.
According to whether the sealing faces are in direct contact, mechanical seals are classified into contact types; otherwise, they are categorized as non-contact types, which can further be divided into hydrostatic and hydrodynamic types.
Based on the presence or absence of corrugated tubing, it can be classified into non-corrugated and corrugated types. The latter further includes several subtypes, such as metal corrugated tubing, PTFE corrugated tubing, and rubber corrugated tubing.
High-temperature mechanical seals, medium-temperature mechanical seals, ambient-temperature mechanical seals, and cryogenic mechanical seals.
-50, 80, and 200 are commonly used temperature thresholds.
By sealed cavity pressure
Several conditions including ultra-high pressure, high pressure, low pressure, normal pressure, and negative pressure.
0.8, 5, and 15 MPa are commonly used dividing lines.
Can be classified according to speed.
Several scenarios such as ultrahigh-speed, high-speed, medium-speed, and low-speed commonly use 2, 10, 30, and 100 m/s as the standard dividing points.
According to the characteristics of the medium, there are specifically designed mechanical seals for particular applications.
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