In a maximum distance relay method, what is one of the assumptions made?

In the maximum distance relay method, an assumption of 20 PSI of residual pressure is commonly used. This figure reflects a standard operational pressure that allows for adequate water delivery under normal conditions. Ensuring this level of residual pressure is crucial because it enables the assessment of how far water can be effectively delivered through the chosen relay hose, taking into account the necessary pressure drop over distance and any additional friction losses along the hose.

This assumption helps to maintain a balance between sufficient pressure at the end of the relay and the operational capabilities of the firefighting equipment being used. Other pressure levels may not provide an effective baseline for estimating performance, which is why the focus is on the 20 PSI figure in this context. Using this assumption, operators can calculate necessary adjustments to ensure reliable water flow to the firefighting effort at greater distances.