What type of cover is required for fill openings?

The requirement for a tight metal cover for fill openings is primarily based on safety and the prevention of contamination. Fill openings need to be securely sealed to protect the contents from contaminants, pests, and environmental factors. A tight metal cover ensures that no foreign materials can enter the fill space, which is especially important in systems that involve liquids or gases, as well as those that can be affected by changeable weather conditions.

Metal covers are durable, can withstand pressure, and provide a robust barrier against both physical intrusion and environmental damage. Using a loose fitting cover or less secure materials, like plastic or rubber, would not provide the same level of protection and could lead to issues such as spillage, contamination, or even safety hazards. Thus, adhering to the requirement for a tight metal cover aligns with maintaining safety standards and regulatory compliance in mechanical systems.