Full definition
Mechanical seals are essential components in various industrial applications, primarily designed to prevent leakage in rotating equipment such as pumps, agitators, compressors, and mixers. These seals consist of two highly polished, flat faces: a rotary face that rotates with the shaft and a stationary face that remains fixed within the housing. The intimate contact between these faces is maintained by a thin lubricating fluid film, which serves to reduce friction and wear. The controlled leakage design of mechanical seals is a significant advancement over traditional compression packing, as it typically allows for leakage rates of less than 1 ml/hr, thereby minimizing environmental impact and enhancing operational efficiency.
The primary components of a mechanical seal include the rotary face, which is commonly made from durable materials such as silicon carbide or carbon/graphite, and the stationary face, which may consist of silicon carbide, ceramic, or carbon/graphite depending on the application requirements. Secondary seals, such as O-rings or elastomer bellows, are employed to further enhance sealing integrity. The spring mechanism, which can be single or multiple springs, ensures that the faces remain in contact, while the drive mechanism—utilizing set screws, pins, or clips—facilitates the connection to the rotating shaft.
Mechanical seals are classified into several types: single seals, which comprise one set of faces and are standard for most pumps; double seals, featuring two sets of faces with a barrier fluid for applications involving hazardous or toxic fluids; and cartridge seals, which are pre-assembled and pre-set for ease of installation. Compliance with industry standards such as API 682 for refinery pumps, EN 12756 (European standard), and DIN 24960 is critical to ensure reliability and performance in demanding environments. The selection of face materials must also consider compatibility with the specific process fluid to prevent degradation over time.