What seal is not used on a refrigeration system?

Mechanical seals are primarily used in rotating equipment and are not typically found in standard refrigeration systems. Refrigeration systems primarily rely on O-rings, gasket seals, and flange seals to provide effective sealing. O-rings are often utilized at joints where components of the system come together, ensuring a tight fit to prevent refrigerant leaks. Gasket seals serve a similar purpose, filling the space between static surfaces to create a leak-proof barrier. Flange seals are used where two flanged components meet, often requiring a gasket or O-ring to maintain pressure and prevent escape of refrigerant.

In contrast, mechanical seals are designed more for dynamic applications like pumps and compressors, where there is relative movement between parts that could breach the seal. The unique applications of seals used in refrigeration systems highlight their specific functionalities and limitations in these contexts. Thus, mechanical seals do not play a role in the standard configuration of refrigeration systems, making this the correct answer.