CFD Basic Apparatus and Hydraulics Practice Test 2026 - Free Apparatus and Hydraulics Practice Questions and Study Guide

The main idea here is how the desired water pattern determines the pressure at the nozzle. A smooth bore nozzle is designed to deliver a solid, straight stream, which works best around 50 psi at the nozzle. That lower pressure keeps the water in a coherent jet without breaking it into a spray.

A fog nozzle, on the other hand, is meant to atomize water into a fine spray to blanket an area, and that requires more energy to break the water into droplets. To achieve that atomization and wide spray, the nozzle operates at a higher pressure, around 100 psi at the outlet.

So the statement that smooth bore nozzles typically run about 50 psi while fog nozzles run about 100 psi aligns with how each nozzle type is used and why their patterns differ. The other ideas—zero nozzle pressure, or nozzle pressure being irrelevant, or both types needing the same pressure—don’t reflect how nozzle design and spray behavior work in practice.