Common Types of Mechanical Seals

A mechanical seal, also known as end-face seal, is a widely used sealing device for rotating shaft equipment such as pumps, compressors and reaction kettles. Classified by structure, working conditions and materials, it is mainly divided into the following categories to meet the requirements of different industrial scenarios.

I. Classification by Structural Form

Single-End Mechanical Seal

It is the most basic and widely applied type, consisting of a pair of sealing faces (rotating ring + stationary ring). Featuring simple structure, low cost and convenient maintenance, it applies to working conditions with medium pressure ≤1.6MPa, temperature ranging from -20℃ to 150℃, non-corrosive and particle-free media, including ordinary clean water pumps and lubricating oil pumps. Its disadvantage is relatively poor sealing reliability, making it unsuitable for flammable, explosive, highly toxic and volatile media.

Double-End Mechanical Seal

Composed of two pairs of sealing faces, it forms a sealed cavity between the two end faces, where barrier fluid such as clean water and lubricating oil can be injected for cooling, lubrication and buffering. Divided into balanced and unbalanced types, it suits high-pressure (≤4.0MPa), wide-temperature (-40℃~250℃), toxic, flammable, highly corrosive or slightly particulate media, such as chemical pumps, high-temperature pumps and corrosive medium delivery pumps. It boasts stable sealing performance and high safety, effectively preventing medium leakage.

Balanced Mechanical Seal

Its structural design balances medium pressure acting on sealing faces, reducing face wear and extending service life. It is ideal for high-pressure conditions (≥1.6MPa), especially scenarios with low-viscosity media and drastic pressure fluctuations, such as high-pressure centrifugal pumps and compressors. Compared with unbalanced seals, balanced mechanical seals enjoy uniform face specific pressure, stronger wear resistance, and lower risks of face sintering and leakage.

Unbalanced Mechanical Seal

Medium pressure on sealing faces remains unbalanced, resulting in high face specific pressure. With simpler structure and lower cost, it applies to low-pressure conditions (≤1.6MPa) with high-viscosity and particle-free media, such as ordinary gear pumps and small centrifugal pumps. It suffers rapid face wear and short service life, and cannot be used under high-pressure and high-temperature environments.

Cartridge Mechanical Seal

All components including rotating ring, stationary ring, spring and sealing ring are integrated as a whole. Pre-assembled and debugged before delivery, it can be installed integrally on site without separate adjustment. It fits standardized equipment, batch installation and sites with poor maintenance conditions, such as large chemical units and mass-produced pumps. It features easy installation, high precision, reduced assembly errors and simplified maintenance.

II. Classification by Working Condition Adaptability

High-Temperature Mechanical Seal

Made of high-temperature resistant materials including silicon carbide, silicon nitride and hard alloy, as well as heat-resistant sealing rings such as flexible graphite and metal bellows, it withstands temperatures from 250℃ to 500℃. It is used for high-temperature medium conveying equipment including steam pumps and stirring shafts of high-temperature reaction kettles. Matching cooling systems are required to avoid sintering and abrasion of sealing faces caused by excessive heat.

Low-Temperature Mechanical Seal

Adopting cryogenic-resistant materials and sealing rings such as PTFE and low-temperature rubber, it adapts to ultra-low temperatures from -40℃ to -196℃. It applies to delivery equipment for cryogenic media including liquid nitrogen, liquid oxygen and low-temperature ethylene glycol. Attention shall be paid to preventing frost and ice formation on sealing faces that may impair sealing performance.

Corrosion-Resistant Mechanical Seal

Its rotating and stationary rings adopt corrosion-resistant materials like silicon carbide, ceramic and Hastelloy, while sealing rings are made of PTFE and fluororubber. It serves strongly acidic, alkaline and oxidizing media, such as acid-base pumps and electroplating wastewater treatment pumps in chemical industry. Proper materials must be selected according to medium properties to avoid sealing failure caused by material corrosion.

Mechanical Seal for Particulate Media

Manufactured with wear-resistant materials such as hard alloy and silicon carbide, and equipped with particle flushing devices, it prevents solid particles from entering sealing faces and causing scratches and abrasion. It is suitable for sand-containing and impurity-containing media, including sewage pumps, mine drainage pumps and slurry pumps.