What type of seal uses bolts to tighten its sealing element?

The packing gland seal is designed to provide a tight seal in various applications by utilizing bolts to compress its sealing element against a shaft or other surfaces. This compression creates a barrier that prevents leakage of fluids or gases. The ability to adjust the tension of the bolts allows for fine-tuning of the seal, accommodating wear over time and maintaining effective sealing performance.

Other sealing options mentioned, such as mechanical seals, rubber seals, and O-ring seals, function differently. While mechanical seals also prevent leaks, they do so through a different mechanism involving sliding surfaces instead of tightened bolts. Rubber seals and O-rings rely on their inherent elasticity and compressive fit within grooves, which does not necessitate the use of external tightening mechanisms like bolts. Thus, the unique design of packing gland seals, which specifically incorporates bolts for tightening, makes it the correct choice for this question.