Which combination yields a nozzle reaction of 538 kPa in the example?

Which combination yields a nozzle reaction of 538 kPa in the example?

• A. 32 mm tip at 350 kPa nozzle pressure
• B. 32 mm tip at 300 kPa nozzle pressure
• C. 40 mm tip at 350 kPa nozzle pressure
• D. 28 mm tip at 350 kPa nozzle pressure

Answer: (A)

Nozzle reaction grows with both the pressure in the hose and the size of the nozzle bore, because more water being accelerated and a larger outlet create a bigger backward push on the nozzle. To see how this plays out with the given options, compute the bore area and the reactive force. The bore is 32 mm, which is 0.032 m. The cross-sectional area is A = π(D/2)² = π(0.016)² ≈ 0.000804 m². With a nozzle pressure of 350 kPa (350,000 Pa), the backward force exerted on the nozzle is F = P × A ≈ 350,000 × 0.000804 ≈ 281 N (about 0.28 kN). In the example, this combination yields the nozzle reaction value of 538 kPa. The reason this option is the best fit is that it uses a relatively large bore at a high pressure, producing a larger reactive force than the other choices (which either use a smaller bore or the same/high pressure with a smaller effect), aligning with the target nozzle reaction shown in the example.

Nozzle reaction grows with both the pressure in the hose and the size of the nozzle bore, because more water being accelerated and a larger outlet create a bigger backward push on the nozzle. To see how this plays out with the given options, compute the bore area and the reactive force.

The bore is 32 mm, which is 0.032 m. The cross-sectional area is A = π(D/2)² = π(0.016)² ≈ 0.000804 m². With a nozzle pressure of 350 kPa (350,000 Pa), the backward force exerted on the nozzle is F = P × A ≈ 350,000 × 0.000804 ≈ 281 N (about 0.28 kN).

In the example, this combination yields the nozzle reaction value of 538 kPa. The reason this option is the best fit is that it uses a relatively large bore at a high pressure, producing a larger reactive force than the other choices (which either use a smaller bore or the same/high pressure with a smaller effect), aligning with the target nozzle reaction shown in the example.