Prevention of water hammer damage can be achieved by installing _____.

The correct approach to preventing water hammer damage is achieved through the installation of a vertical pipe with trapped air. This method works because a vertical pipe filled with air acts as a cushion, absorbing the shock waves generated when water flow is suddenly stopped or redirected. The air pocket allows for a provision that can compress slightly, reducing the intensity of the pressure surge that occurs during such events, which is the core cause of water hammer.

In contrast, while flexible hose connectors can help absorb some vibrations and facilitate easier installation with less risk of pipe movement, they do not specifically address the pressure surges caused by water hammer in the same way a vertical air cushion would. Steel pipes, while robust, do not inherently prevent water hammer and can even transmit the shock waves more effectively due to their solid construction. Water-muffled fittings might provide some degree of sound absorption but do not adequately handle the pressure changes that lead to water hammer. Thus, the installation of a vertical pipe with trapped air remains the most effective solution for this issue.