What is NOT a characteristic of a true accumulator vessel?

A true accumulator vessel is designed to store energy in the form of pressurized fluid, and it typically operates within a defined range concerning its contents. The characteristic of having a normal operating level refers to the accumulation of fluid at specific points for optimal operation and efficiency.

Conversely, a true accumulator vessel should have capabilities such as high level protection and relief valve protection. High level protection is critical to prevent overfilling and potential hazards associated with excessive pressure. Similarly, relief valve protection is essential to safeguard the vessel from unsafe pressure levels, which could lead to catastrophic failures if not properly managed.

The state of being emptied is typically not characteristic of a true accumulator vessel since it functions to maintain a certain volume of fluid, allowing it to provide the intended energy storage. Therefore, the concept of having a defined normal operating level aligns with the standard functionality of an accumulator vessel, while the other options highlight safety and performance features that are integral to their design and operation.