What type of trapping mechanism depends on moving parts to maintain seal?

The correct answer is based on the understanding of plumbing traps and their operational mechanisms. Bell traps use a design that incorporates moving parts, specifically a float mechanism or a movable barrier, which enables them to maintain a water seal in the trap. This design allows the trap to adjust to changes in water levels and flow, which is essential in preventing sewer gas from entering a dwelling while ensuring proper drainage.

In contrast, other types of traps like full "S" traps, band traps, and antique traps typically rely on a static body of water to create the seal against sewer gases. These traps do not utilize moving parts and may be less effective in maintaining that seal under varying environmental conditions or flow rates. Understanding the functional difference between these trap designs is crucial in plumbing applications, particularly for ensuring compliance with codes and achieving effective drainage solutions.