What is a Fixed Flow Nozzle? 

A fixed gallonage nozzle is a firefighting nozzle that provides a constant flow rate or gallonage and can flow a straight stream or fog pattern. These nozzles come in a range of pressure choices so that you can choose the option that is right for your fire department. 

How Does a Fixed Flow Fog Nozzle Work? 

The fixed flow nozzle uses the same formula as a smoothbore to calculate flows and pressures. 

GPM = (29.7) (d)2 (√NP) 

GPM: Gallons Per Minute 
29.7: a Constant 
d: Nozzle Orifice Diameter in Inches 
NP: Nozzle Pressure PSI (Pitot Pressure) 

You can see this demonstrated and explained in the video. 

How is a Fixed Flow Fog Nozzle Different from Smooth bore?

A fixed gallonage fog nozzle does differ from a smooth bore nozzle in another area, though. With a smooth bore nozzle, you cannot move to a fog pattern. You might gate your nozzle to create turbulence and break your stream, but this will reduce your flow rate. 

With a fixed gallonage fog nozzle, you can move your nozzle into a fog pattern, creating a consistent pattern without limiting your flow. 

Continue Learning 

Learn more about how smoothbore nozzles, automatic nozzles, and selectable nozzles work in the Firefighter Learning Hub!