What pressure defines the nozzle reaction force in smooth-bore nozzles?

The nozzle reaction force in smooth-bore nozzles is defined by the nozzle pressure. This pressure is crucial in understanding how the water flowing out of a nozzle generates a force that acts in the opposite direction, pushing the nozzle backward. The nozzle pressure is the pressure within the nozzle as water exits it, and it is this pressure differential that creates the reaction force.

In a smooth-bore nozzle, which is characterized by a simple cylindrical design without any internal obstructions, the flow is fully developed and primarily influenced by the nozzle pressure, resulting in a predictable and calculable reaction force based on the flow rate and nozzle diameter. This enables operators to properly manage and control the nozzle during operation, ensuring safety and effectiveness in firefighting or other applications.

Dynamic pressure, while related to the velocity of the fluid, does not directly define the reaction force in this scenario. Static pressure refers to the pressure within a fluid at rest, which may not contribute to the reaction force when the fluid is in motion. Friction pressure relates to energy losses due to friction within the system, but it is not the primary force responsible for the reaction in a smooth-bore nozzle. Therefore, the nozzle pressure is the key factor in determining the nozzle reaction force.