Which item prevents leakage past the hub of the resilient-liner plug valve?

The correct choice that prevents leakage past the hub of the resilient-liner plug valve is the diaphragm seal. This component is specifically designed to create a tight seal around the valve mechanism, effectively preventing any fluid from escaping. The diaphragm seal allows for a more reliable shut-off than some other sealing options, ensuring that the valve can maintain pressure and function properly without leaking.

In the context of valve design, the diaphragm seal offers advantages in terms of flexibility and adaptability to various pressure conditions, making it ideal for applications requiring a secure seal. This versatility helps accommodate wear and tear, while maintaining integrity over time—a crucial factor in water and fuel systems where leakage can lead to significant operational issues.

Other options like O-rings, asbestos gaskets, and graphite packing are also used in various plumbing and mechanical systems for sealing, but they do not provide the same level of effectiveness for the specific function of the resilient-liner plug valve in preventing leakage past the hub. Each of these alternatives has its own applications and limitations, which means they might work better in different types of valves or setups but are not the ideal choice for the scenario described.