Which type of intake relief valve is NOT included in the common types?

The correct choice identifies the gravity intake relief valve as not being a common type of intake relief valve found in practice. In fire service and water supply systems, intake relief valves serve the vital function of managing pressure within the piping and preventing issues such as backflow or over-pressurization.

Common types of intake relief valves include piston, Waterous intake relief systems, and combinations, which are widely recognized and employed in various firefighting and water delivery scenarios. Piston valves use mechanical components to operate, often providing precise control over pressure levels. Waterous intake relief systems are specifically designed to cater to the needs of fire apparatus, allowing efficient pressure management tailored to firefighting conditions. Combination valves typically incorporate features of different types to provide flexibility and functionality.

In contrast, the gravity intake relief valve is less commonly referenced in contemporary firefighting systems. This type of valve would primarily rely on gravitational force to operate, which may not be effective or reliable in the variable conditions encountered during firefighting operations. It does not meet the specific operational needs and standards that the other types provide, which is why it is not included among the common variants. Understanding the types of valves and their functionalities is essential for effective fireground operations and safety.