Tank to Pump

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.

A fire hose runs from a pump to a firefighter's grip on the nozzle; a red reaction-force arrow points backward from the hands and grows longer as nozzle pressure rises.

Nozzle reaction · interactive

GOOD · 75.8 lbfAt design pressure: an effective stream at the nozzle's rated flow, with the reaction the line is built to handle.

Nozzle type

Reaction force is the backward push you feel on the line — it climbs with both pressure and flow, so a master stream pushes far harder than a handline. The arrow length and the lbf figure are training estimates; follow your SOPs and the nozzle's own data.

Nozzle reaction is the backward push you feel on the line. Pick a nozzle and drag the actual tip pressure to see the recoil grow — and why a master stream demands far more strength than a handline.

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.

Formula

NR = 1.57 × D² × NP

Smooth-bore form: D = tip diameter; NP = nozzle pressure. For a fog nozzle the training form is NR = 0.0505 × Q × √NP, where Q is the flow. Both rise with flow and pressure.

Common questions

What is 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, so bigger tips and higher pressures are harder to hold.
Why does a high-flow line take more firefighters to hold?
Because more flow and higher tip pressure both increase the nozzle reaction. The line handles by the reaction at the tip, not by the pressure on the panel gauge, so a high-flow stream pushes back harder and needs more hands.

Where this shows up

See also