Minor Loss from K Factor

Also known as fitting loss · K value loss

h_L = K \, \frac{v^{2}}{2g}

Worked example: 1.2 m lost at 3 m/s → K = 2.6151 — press Try an example to run it live, then adjust anything.

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Constant used — built into this formula, no need to enter

g_{n} = 9.80665\ \text{m/s}^{2}

Standard acceleration of gravity · exact

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Minor Loss from K Factor explained

Every disturbance a fitting imposes on the flow — the sudden turn of an elbow, the contraction through a gate seat, the wake behind a tee — dissipates some multiple of the velocity head. Crane Technical Paper 410 tabulates those multiples as K: about 0.9 for a standard threaded 90° elbow, 0.2 for a fully open gate valve, 10 for a globe valve, 0.5 for a sharp-edged pipe entrance, 1.0 for the exit into a tank. Water at 8 ft/s through that elbow loses 0.9 × 64/64.35 ≈ 0.90 ft.

Calling these "minor" losses is a historical joke that has misled generations. In a long transmission main they truly are minor, but in a chiller room or a pump skid — twenty elbows, four valves and a strainer in thirty feet of pipe — they dominate, often carrying three-quarters of the total loss. The other subtlety is the velocity: K is referenced to the velocity in the pipe of the fitting's nominal size, so for a reducing fitting you must be clear which of the two velocities the tabulated K assumes.

Minor Loss from K Factor formula

h_L = K \, \frac{v^{2}}{2g}

Where

$h_L$ = Minor head loss (m)
$K$ = Resistance coefficient
$v$ = Flow velocity (m/s)

Missing one of these? Work it out first, then come back

Minor head loss — Hazen–Williams Head Loss, Hydraulic Gradient
Resistance coefficient — Equivalent Length of a Fitting, Mole Ratio from a Balanced Equation
Flow velocity — Pipe Velocity from Flow and Diameter, Volumetric Flow Rate (Q = Av)

Part of these formula sets

Pipe friction losses

9 formulasDarcy–Weisbach, Hazen–Williams, friction factors, minor losses and equivalent length — every way the trade computes head loss in pipe.

Valve sizing coefficients

4 formulasCv, Kv, K factors and equivalent length — the four coefficients that turn a valve or fitting into a pressure drop at a given flow.