What is the correct unitless coefficient for a smooth and rounded hydrant outlet commonly used in design calculations?

What is the correct unitless coefficient for a smooth and rounded hydrant outlet commonly used in design calculations?

• A. 0.70
• B. 0.80
• C. 0.90
• D. 0.97

Answer: (C)

The concept here is the discharge coefficient (Cd) used in flow calculations to account for real losses at the hydrant outlet. For a smooth, rounded hydrant outlet, Cd is typically about 0.90. This coefficient adjusts the ideal flow through the outlet area to reflect energy losses from turbulence and the vena contracta, giving the actual discharge: Q ≈ Cd × A × sqrt(2 g Δh) (or the appropriate head-based form). A smoother, well-rounded opening reduces losses, but you still don’t reach perfect efficiency, so 0.90 is the standard, realistic value used in design. Values like 0.70 or 0.80 imply more losses, and a very high value like 0.97 would be unusually optimistic and not representative of typical hydrant outlets.

The concept here is the discharge coefficient (Cd) used in flow calculations to account for real losses at the hydrant outlet. For a smooth, rounded hydrant outlet, Cd is typically about 0.90. This coefficient adjusts the ideal flow through the outlet area to reflect energy losses from turbulence and the vena contracta, giving the actual discharge: Q ≈ Cd × A × sqrt(2 g Δh) (or the appropriate head-based form). A smoother, well-rounded opening reduces losses, but you still don’t reach perfect efficiency, so 0.90 is the standard, realistic value used in design. Values like 0.70 or 0.80 imply more losses, and a very high value like 0.97 would be unusually optimistic and not representative of typical hydrant outlets.