Initiating a nozzle change can be daunting task and is a topic that has a lot of opinion tied to it.
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In the well-read October 2007 Fire Engineering Article “How Kinks Affect Your Fire Attack System” Jerry Knapp along with Tim Pillsworth, Christopher Flatley, and Doug Leihbacher go into great detail how kinks affect your fire flows.
In this video Jerry Herbst reviews the points to consider when conducting your own nozzle evaluation.
Both inline gauges and piezometers can be used to measure psi in your fire flow system.