Q: What is the K-factor method for minor losses?

Minor (local) losses from fittings and valves are expressed as ΔP_minor = K × ρv²/2. The resistance coefficient K is tabulated for each component: standard 90° elbow K≈0.9, long-radius 90° elbow K≈0.4, fully-open gate valve K≈0.2, check valve K≈2.0, sharp entrance K≈0.5, exit K≈1.0. The equivalent length method gives the same result via K = f × (L_eq/D).

Q: How is pump power estimated from pressure drop?

Required pump shaft power is P = Q × ΔP / η (W or kW), where Q is volumetric flow rate (m³/s), ΔP is total pressure loss (Pa), and η is pump efficiency (typically 0.60–0.85). This tool displays a reference value assuming η = 0.75. In real design, also check pump curve intersection, NPSH, and system head including elevation change.

Question 1

What is the Darcy-Weisbach equation?

Accepted Answer

The Darcy-Weisbach equation ΔP = f × (L/D) × (ρv²/2) is the most widely used formula for pipe friction pressure drop. Here f is the dimensionless Darcy friction factor, L is pipe length, D is internal diameter, ρ is fluid density, and v is mean flow velocity. The friction factor depends on Reynolds number Re and relative roughness ε/D, read from the Moody diagram or computed via Colebrook-White for turbulent flow.

Question 2

How is the Colebrook-White equation solved?

Accepted Answer

The Colebrook-White equation 1/√f = -2log(ε/(3.7D) + 2.51/(Re√f)) is an implicit transcendental equation. It is solved iteratively (Newton-Raphson or fixed-point iteration) or via the explicit Swamee-Jain approximation f = 0.25/[log(ε/(3.7D) + 5.74/Re⁰·⁹)]². This calculator uses iterative Colebrook-White with convergence tolerance Δf < 1×10⁻⁸.

Question 3

What is the K-factor method for minor losses?

Accepted Answer

Minor (local) losses from fittings and valves are expressed as ΔP_minor = K × ρv²/2. The resistance coefficient K is tabulated for each component: standard 90° elbow K≈0.9, long-radius 90° elbow K≈0.4, fully-open gate valve K≈0.2, check valve K≈2.0, sharp entrance K≈0.5, exit K≈1.0. The equivalent length method gives the same result via K = f × (L_eq/D).

Question 4

How is pump power estimated from pressure drop?

Accepted Answer

Required pump shaft power is P = Q × ΔP / η (W or kW), where Q is volumetric flow rate (m³/s), ΔP is total pressure loss (Pa), and η is pump efficiency (typically 0.60–0.85). This tool displays a reference value assuming η = 0.75. In real design, also check pump curve intersection, NPSH, and system head including elevation change.

Pipe Pressure Drop Calculator

Theory Notes