Hydraulics & Pressure
Nozzle Pressure
NP
Nozzle pressure is the pressure of the water as it reaches the nozzle, and it sets both how much water flows and how good the stream looks. Each nozzle type is designed around a specific tip pressure.
Different nozzles are built around different tip pressures: a smooth-bore handline forms a solid stream at about 50 psi, a standard fog nozzle wants about 100 psi, and a master-stream fog device runs around 80 psi. Pump pressure exists to deliver that tip pressure after the lay takes its cut.
Nozzle pressure is what the crew feels and what determines stream reach and droplet quality. Under-pump it and a fog cone collapses, reach falls off, and the line flows less than its rating — even though water is still coming out of the tip.
Where this shows up
Calculator
Nozzle Flow & ReactionLesson
Automatic Nozzles: The Flow You Can't Feel