Flow Loss Coefficient, K-Factor, and Head Loss Explained

In fluid flow systems, the flow loss coefficient (also called the head loss coefficient or K-factor) quantifies pressure loss due to fittings, valves, bends, and other disruptions. This coefficient expresses the loss in terms of dynamic pressure, providing a consistent way to evaluate how components affect energy in the flow stream.

Definition Using Dynamic Pressure

The pressure drop caused by a fitting is proportional to the dynamic pressure of the flow:

Where:
    \( \Delta P \) = pressure loss (Pa or psi)
    \( K \) = flow loss coefficient (dimensionless)
    \( \rho \) = fluid density (kg/m³ or slugs/ft³)
    \( v \) = flow velocity (m/s or ft/s)

Head Loss and Flow Loss Coefficient

The head loss equivalent is derived from the pressure loss:

Where:
    \( h_L \) = head loss (m or ft)
    \( g \) = acceleration due to gravity

Relationship to Equivalent Length (L/D)

Engineers often approximate flow resistance using the equivalent length method, which expresses the energy loss of a fitting as an equivalent length of straight pipe:

Where:
    \( f \) = friction factor of the pipe (typically Darcy–Weisbach)
    \( L_e \) = equivalent length of pipe causing the same loss (m or ft)
    \( D \) = pipe diameter (m or ft)

Summary

• The flow loss coefficient (or K-factor) links flow disruptions to energy loss.
• It scales the dynamic pressure to compute pressure or head loss.
• Head loss is calculated as \( h_L = K \cdot v^2 / (2g) \), fundamental in pump and system sizing.
• The equivalent length method connects K to straight-pipe losses via the L/D ratio.

This understanding helps engineers estimate pressure drops more accurately and optimize piping systems for performance and efficiency.

Want to dive deeper? Explore our comprehensive list of flow loss coefficients for a wide variety of fittings, valves, pipes, and channel configurations above — perfect for quick design checks or system analysis.