In a constant pressure relay, what psi should the source pumper and all relay apparatus maintain?

Answer: B — 175 psi (1,206 kPa)

In a constant pressure relay, maintaining a pressure of 175 psi is crucial for ensuring consistent and adequate water supply throughout the relay. This pressure is often chosen to provide an optimal balance between sufficient flow rates and minimizing the risk of excessive pressure that could lead to equipment damage or hose failure. A pressure of 175 psi allows for effective firefighting operations while accommodating friction loss over long distances and elevation changes that may occur in relay operations. The setup ensures that each apparatus involved in the relay can efficiently contribute to the water supply without compromising the operational integrity of the hoses and pumps. By adhering to this established pressure setting, firefighters can maintain reliable and effective water delivery to the scene, facilitating a swift response to the emergency at hand.