In terms of valve sizing, what should the relationship be between multiple high-pressure safety valves mounted on a boiler?

The correct choice emphasizes a crucial safety aspect of maintaining high-pressure safety valves on a boiler. Each safety valve needs to be sized appropriately to handle the potential pressure buildup. When multiple valves are installed, it is critical that they can collectively handle the maximum capacity that could be generated within the system.

By specifying that the smaller valve should have a maximum relieving capacity of 50%, it ensures that if conditions arise that require the operation of these safety valves, the combined relieving capacity is adequate to prevent overpressure scenarios. This design consideration reduces the risk of the larger valve failing due to overload while maintaining the integrity of the system.

In scenarios involving multiple safety valves, simply having them the same size or relying solely on the larger valve could lead to unsafe conditions where the total relieving requirements could exceed the capacity of the valves in an emergency situation. Thus, proper sizing ensures efficiency, safety, and adherence to engineering standards in pressure vessel applications.