Hydraulics & Pressure
Nozzle Reaction
Nozzle reaction is the backward push a flowing nozzle exerts on the crew, the equal-and-opposite force to the water leaving the tip. It rises with both the flow and the nozzle pressure.
The faster and harder water leaves the nozzle, the more it shoves back. Bigger tips and higher tip pressures both increase the reaction, which is why a high-flow line takes more firefighters to hold and why nozzle choice is a handling decision, not just a flow decision.
Reaction is felt at the tip, not at the panel. Extra pump pressure spent on friction loss down a long lay never reaches the crew's hands — the line handles by its nozzle reaction, not by the pump discharge pressure on the gauge.
Where this shows up
Calculator
Nozzle Flow & Reaction