What must all valves be clearly identified by?

All valves must be clearly identified by the manufacturer's name and service conditions to ensure proper operation and maintenance within a system. This identification helps engineers and operators understand the specific application for which the valve was designed, including its intended use, operating pressure, temperature, and any special characteristics related to the fluid it controls. Knowing the manufacturer’s name also aids in sourcing replacement parts or support for maintenance issues, ensuring that the correct components are used for optimal safety and efficiency.

The other options, while they may provide some useful information, do not capture the critical need for identification that directly relates to operational safety and functionality in an industrial context. Color coding and shape can assist with quick visual identification, but they may not provide comprehensive details regarding the valve's specifications or manufacturer. Weight and size are practical considerations, but these factors alone do not convey essential operational information. Price and brand are not relevant to the identification required for the safe and effective use of valves in any power engineering application, as they do not reflect the critical operational parameters that affect performance.