Name: fire extinguisher nozzle flow and pressure
Uploaded: 2025-02-13T15:43:18.000Z
Duration: 1 min 12 s
Channel: JoVE

A fire extinguisher uses pressurized water to generate a powerful stream through a nozzle.
The water inside is stored at a much higher pressure than the surrounding atmosphere, forcing the water to flow when the extinguisher is activated.
Fluid dynamics equations are applied to determine how fast the water exits the nozzle and how much is expelled over time.
The first step involves understanding the pressure difference between the interior of the extinguisher and the pressure outside the nozzle.
This pressure difference drives the water&#39;s movement. By applying Bernoulli&#39;s equation, which relates pressure and velocity, the velocity of the water as it exits the nozzle is calculated.
The smaller nozzle diameter causes the water to accelerate as it leaves, transforming pressure into velocity.
After calculating the exit velocity, the flow rate is determined. The flow rate is calculated using the continuity equation, which ensures that the amount of water flowing through the nozzle is consistent.
The flow rate is calculated by multiplying the velocity of water by the nozzle&#39;s cross-sectional area.

design example: flow through a fire extinguisher

Design Example: Flow Through a Fire Extinguisher

A fire extinguisher that uses pressurized water relies on fluid dynamics principles to generate a high-velocity stream capable of suppressing flames. The water is stored at a much higher pressure inside the extinguisher than the surrounding atmosphere. This pressure difference forces the water to flow rapidly when the extinguisher is activated, and the behavior of the water as it exits the nozzle can be understood using fundamental equations of fluid dynamics.
The key to understanding how the water accelerates lies in the pressure difference between the inside of the extinguisher and the outside environment. Bernoulli's equation, which relates pressure and velocity, calculates how fast the water will exit the nozzle.
<img alt="Bernoulli's equation, fluid dynamics, pressure and velocity, formula, educational physics." src="/files/ftp_upload/18047/18047_Equation_1.svg" style="text-align: center; height: 45px;" data-altupdatedat="1762173717000" data-alt="Equation 1" />
According to this principle, as pressure decreases, velocity increases. This means that the high internal pressure within the extinguisher is converted into the velocity of the water as it flows out. As the water approaches the nozzle, the decrease in nozzle diameter further accelerates the flow, transforming pressure energy into kinetic energy.
After determining the exit velocity of the water, the flow rate, or the volume of water expelled over time, is calculated. The calculation uses the continuity equation, ensuring that the water flowing through the system remains constant. The flow rate is the product of the water's velocity and the cross-sectional area of the nozzle.
<img alt="Flow rate equation Q=Av&#8322;, hydraulic engineering concept, formula image." src="/files/ftp_upload/18047/18047_Equation_2.svg" style="text-align: center; height: 40px;" data-altupdatedat="1762173717000" data-alt="Equation 2" />
Since the nozzle has a small diameter, the water is expelled at high velocity, providing a consistent and powerful stream necessary for fire suppression. By applying these principles, the performance of the extinguisher can be optimized to ensure effective operation.

A fire extinguisher uses pressurized water to generate a powerful stream through a nozzle.
The water inside is stored at a much higher pressure than the ...

design-example-flow-through-a-fire-extinguisher

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JoVE Core

Civil Engineering

Unit 1

Fluid Kinematics

KEY TERMS AND CONCEPTS

fire extinguisher nozzle flow and pressure

A pressurized water fire extinguisher uses fluid dynamics to create a fast stream of water. The water is stored at a much higher pressure inside the extinguisher than the surrounding air. When the extinguisher is activated, that pressure difference forces water to flow out quickly.

Bernoulli's equation helps predict the exit speed of the water. This equation links pressure and velocity. As pressure drops, velocity increases. In the extinguisher, the high internal pressure is converted into the water's speed as it leaves the nozzle.

The nozzle also plays an important role because its diameter becomes smaller near the exit. A smaller opening increases the flow speed even more. This turns pressure energy into kinetic energy, which is the energy of motion.

After the exit velocity is found, the flow rate can be calculated. Flow rate is the volume of water expelled each second. The continuity equation is used to keep track of how much water moves through the system, and the flow rate equals the water speed times the nozzle's cross-sectional area. Because the nozzle is small, the water comes out at high velocity and forms a strong, steady stream for fire suppression.

Fire Extinguisher Nozzle Flow and Pressure

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A pressurized water fire extinguisher uses fluid dynamics to create a fast stream of water. The water is stored at a much higher pressure inside the extinguisher than the surrounding air. When the extinguisher is activated, that pressure difference forces water to flow out quickly. Bernoulli's equation helps predict the exit speed of the water. This equation links pressure and velocity. As pressure drops, velocity increases. In the extinguisher, the high internal pressure is converted into the...

key terms and concepts

Explore how pressure, Bernoulli's equation, and nozzle size control the water speed and flow rate in a pressurized fire extinguisher.

Fire Extinguisher Nozzle Flow and Pressure | JoVE K12

JoVE Core Civil Engineering offers a foundational exploration of essential construction materials such as bricks, stones, steel, wood, and concrete, along with fluid mechanics topics like flow over immersed bodies, open channel flow, and dimensional modeling. It also covers key surveying concepts, including leveling, traverse adjustments, curve design, topographic mapping, and geospatial technologies (GPS & GIS). Science-in-action videos showcase laboratory research on materials, fluids, and surveying practices in real-world engineering systems.

Fire Extinguisher Nozzle Flow and Pressure

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