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Engineering Toolbox/Minor Loss / K Coefficient

Pressure, Level & Process

Minor Loss / K Coefficient

Calculate local pressure loss through fittings, valves and similar components from a supplied total loss coefficient, or infer an effective K-value from a known pressure loss.

Local-loss calculation

Use actual line-condition volumetric flow. Supply K from the appropriate component or engineering basis.

Do not treat the prefilled K-value as a fitting specification. K varies with component geometry, opening, Reynolds number and the source convention.

Field use

Add local losses without hiding the coefficient basis.

Useful for elbows, tees, reducers, valves, strainers and similar components after an appropriate K-value has been established from a recognized source or manufacturer.

Calculation basis

ΔP = ΣK · ρv² / 2
h = ΣK · v² / 2g

Local/minor losses are separated from straight-pipe Darcy-Weisbach major loss. Multiple components may be represented by a total ΣK only when their K-values are valid for the selected engineering basis.

Scope: steady, single-phase screening. Excludes compressibility, flashing, multiphase flow, interaction between closely spaced fittings, detailed valve characteristics, and any automatic fitting K-table. Standard-condition gas rate must first be converted to actual line-condition volumetric flow.

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