What is a mechanical seal used for?

Mechanical seals are used to prevent leakage between rotating and stationary parts in a wide range of applications. The mechanical seal in a pump prevents leakage of process fluid effectively by employing the following design principles.

1. Seal Face Contact: Mechanical seals rely on precise contact between two opposing seal faces i.e. stationary face and rotating face (they are considered as a primary sealing point between rotary and stationary parts), typically made from hard and wear-resistant materials like silicon carbide or tungsten carbide. These faces are carefully lapped to ensure a smooth, flat surface that promotes hydrodynamic lubrication and prevents leakage. Typically, mechanical seal faces are lapped to achieve a surface finish of Ra<0.2 µm or better. This level of smoothness ensures that the seal faces can maintain a tight seal while minimizing contact pressure and wear.
2. Hydrodynamic Lubrication: As the pump shaft rotates, a thin film of fluid is formed between the seal faces due to hydrodynamic lubrication. This fluid film prevents direct contact between the seal faces, reducing friction and wear, and maintaining a tight seal.
3. Spring Force: Mechanical seals employ springs or other mechanisms to maintain a constant force between the seal faces, ensuring proper contact and sealing even under varying pressure and thermal conditions. This spring force ensures that the seal faces remain in close contact, preventing leakage and maintaining sealing integrity.