Concept reference

Minor Losses and K Values

C.1Plain-language definition

A “minor” loss is energy dissipated where the flow turns, separates, accelerates or mixes. The name describes long pipelines where straight-pipe friction dominates; inside a compact station, fittings and valves can own much of the loss. A K value is a measured or modelled count of velocity heads, not a universal label attached to a symbol.

C.2Governing relation or decision logic

hm = K Vref²/(2g) and hminor,total = ΣK · Vref²/(2g) only when the coefficients share the same reference velocity. Equivalent length uses Le/D = K/f, so it inherits a friction factor and is not constant across every flow and roughness.

C.3The failure to name

Summing K values referenced to different diameters silently corrupts the schedule. Generic coefficients can also hide valve type, opening, reducer geometry or manufacturer-specific behaviour; a half-open valve is not the tabulated fully open device.

C.4Field review checklist

• Inventory every entrance, transition, branch, valve, bend and exit crossed by the flow path.
• Record the coefficient source, configuration and reference velocity.
• Separate alternative and simultaneous paths before summing.
• Test whether station losses remain “minor” at each design flow and valve state.

C.5Where it fits in the course

See §4.1 for K values and §4.5 for a station loss schedule.