A pitot gauge reads 8 psi on a smooth and round hydrant outlet of 4-1/2 inch ID. What is the approximate flow in gpm?

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Get ready for the NICET Level 3 ITM of Water-Based Systems Test. Practice with flashcards and multiple choice questions, each with hints and explanations. Prepare for success!

Multiple Choice

A pitot gauge reads 8 psi on a smooth and round hydrant outlet of 4-1/2 inch ID. What is the approximate flow in gpm?

Explanation:
Discharge from a smooth-bore hydrant outlet is estimated using a practical formula that links flow to the bore diameter and the velocity pressure read by the Pitot. The common form is Q ≈ K × D^2 × sqrt(P), where D is the discharge bore in inches, P is the velocity pressure in psi, and K is a coefficient that accounts for the discharge setup. Here, D = 4.5 inches, so D^2 = 20.25. P = 8 psi, so sqrt(P) ≈ 2.828. Multiplying gives 20.25 × 2.828 ≈ 57.2. Using the typical coefficient K ≈ 27 for this context yields Q ≈ 57.2 × 27 ≈ 1,540 GPM. The closest provided option is 1,539 GPM. Note that using a larger constant (for example, around 29.7) would push the result toward about 1,700 GPM, which isn’t among the choices, so the option around 1,540 GPM reflects the coefficient used in these problems.

Discharge from a smooth-bore hydrant outlet is estimated using a practical formula that links flow to the bore diameter and the velocity pressure read by the Pitot. The common form is Q ≈ K × D^2 × sqrt(P), where D is the discharge bore in inches, P is the velocity pressure in psi, and K is a coefficient that accounts for the discharge setup.

Here, D = 4.5 inches, so D^2 = 20.25. P = 8 psi, so sqrt(P) ≈ 2.828. Multiplying gives 20.25 × 2.828 ≈ 57.2. Using the typical coefficient K ≈ 27 for this context yields Q ≈ 57.2 × 27 ≈ 1,540 GPM. The closest provided option is 1,539 GPM.

Note that using a larger constant (for example, around 29.7) would push the result toward about 1,700 GPM, which isn’t among the choices, so the option around 1,540 GPM reflects the coefficient used in these problems.

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