Which of the following is NOT a type of compressor seal?

The correct answer is "transformer seal" because it is not a type of compressor seal. Instead, a transformer seal is associated with electrical transformers, where it serves to prevent the leakage of insulating oil and maintain internal pressure.

On the other hand, the packing gland seal, bellows seal, and mechanical seal are specifically designed for use in compressors. Packing gland seals use a packing material that is compressed against the shaft to prevent leakage. Bellows seals utilize a flexible, bellows-like material to create a seal that can accommodate motion. Mechanical seals consist of two flat surfaces, with one rotating and the other stationary, and are used in various applications to prevent fluid leakage. Understanding the specific roles and designs of compressor seals is crucial for their effective use in machinery.