Learn: Minor/local head loss
A fitting, inlet, bend or valve disturbs pipe flow and dissipates energy. A local loss coefficient K scales that loss to the velocity head in a specifically chosen reference pipe section.
What the formula is saying
Calculate v²/(2g), then multiply by K. The word minor describes the localized source, not a guarantee that its loss is small compared with straight-pipe friction.
Read the symbols in plain language
- K
- Loss coefficient
Loss coefficient. The coefficient multiplies a head quantity and does not itself have a length unit.
ratio / no unitA dimensionless ratio has no physical unit; 0.01 as a ratio is 1% when the percent option is selected.
- v
- Velocity
Velocity. Use the pipe velocity associated with the selected local-loss coefficient.
m/sUse m/s as the base unit shown here. K has no unit, velocity is m/s and gravity is m/s²; head loss is m. The velocity must be the same reference velocity used to define the selected K, particularly across changes in diameter.
- g
- Gravity
Gravity. Use the pipe velocity associated with the selected local-loss coefficient.
m/s²Use m/s² as the base unit shown here. K has no unit, velocity is m/s and gravity is m/s²; head loss is m. The velocity must be the same reference velocity used to define the selected K, particularly across changes in diameter.
- hm
- Result to find
Minor/local head loss. The coefficient multiplies a head quantity and does not itself have a length unit.
m
Sort out the units first
K has no unit, velocity is m/s and gravity is m/s²; head loss is m. The velocity must be the same reference velocity used to define the selected K, particularly across changes in diameter.
Assumptions before calculating
Treat the liquid as incompressible with constant density and use section-average velocity. The velocity-head coefficient is taken as 1; all elevations and pressures must use consistent reference levels.
Let’s solve one together
Read the given values, follow each operation, then check what the result means.
Read the supplied values as one complete study case. Find hm and explain the result in the stated output unit.
- K · Loss coefficient
- 1.5
- v · Velocity
- 2 m/s
- g · Gravity
- 9.81 m/s²
Compute the reference velocity head
Use the pipe velocity associated with the selected local-loss coefficient.
(2)^2 ÷ (2 × (9.81)) ≈ 0.2038735984 mScale by the fitting coefficient
The coefficient multiplies a head quantity and does not itself have a length unit.
(1.5) × (0.2038735984) ≈ 0.3058103976 m
Does this worked answer make sense?
At fixed K, doubling the reference speed makes the loss four times as large. A zero coefficient contributes no modeled local loss; it does not imply the whole system is lossless.
A second worked example — different values
A second case uses different data. Predict which way the answer will change, then calculate it without reusing the first answer.
- K · Loss coefficient
- 2
- v · Velocity
- 3 m/s
- g · Gravity
- 9.81 m/s²
Compute the reference velocity head
Use the pipe velocity associated with the selected local-loss coefficient.
(3)^2 ÷ (2 × (9.81)) ≈ 0.4587155963 mScale by the fitting coefficient
The coefficient multiplies a head quantity and does not itself have a length unit.
(2) × (0.4587155963) ≈ 0.9174311927 m
Now try your own values
Change a value or its unit. The same method will show your calculation, step by step.
Results update only when you calculate. The lesson example above stays unchanged.
Your turn — check your understanding
Solve this separate case yourself. Use only the values below; the two worked examples use different data. Give the requested result in the selected unit.
- K · Loss coefficient
- 0.8
- v · Velocity
- 2.5 m/s
- g · Gravity
- 9.81 m/s²
Find: Learn: Minor/local head loss
A hint, not the answer
Calculate v²/(2g), then multiply by K. The word minor describes the localized source, not a guarantee that its loss is small compared with straight-pipe friction.
K has no unit, velocity is m/s and gravity is m/s²; head loss is m. The velocity must be the same reference velocity used to define the selected K, particularly across changes in diameter.
Show the full practice solution
Compare the steps with your work; revealing a solution does not mark the lesson complete.
Compute the reference velocity head
Use the pipe velocity associated with the selected local-loss coefficient.
(2.5)^2 ÷ (2 × (9.81)) ≈ 0.3185524975 mScale by the fitting coefficient
The coefficient multiplies a head quantity and does not itself have a length unit.
(0.8) × (0.3185524975) ≈ 0.254841998 m
Avoid the common trap
Do not add K directly to a head in metres, use velocity rather than its square, or combine coefficients defined using different velocities without conversion.
When this method applies — and when it does not
Use a coefficient applicable to fitting geometry, opening, flow direction and Reynolds-number range. Interaction between closely spaced fittings may invalidate simple separate coefficients. Convert loss to pressure with ρg only when needed.
For study and understanding, not approval of a real structure, site operation or design. Apply the correct standard, National Annex and professional review to actual engineering work.
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Sources & further reading
References open in a new tab and explain the underlying principles. The teaching text and examples here are SimpleFlick’s own; the source organisations have not endorsed this calculator.
Reading focus: Minor/local head loss. Water-measurement principles; for discharge devices, read the orifice/weir chapters and the installation and head-measurement conditions, not only the coefficient formula.
- U.S. Bureau of Reclamation — Water Measurement Manual, 3rd edition (1997; revised reprint 2001)
- Dawei Han, University of Bristol — Concise Hydraulics (2008, Ventus Publishing)
Lesson updated: · Both examples and the separate practice case are checked against an independent high-precision numerical implementation. This verifies arithmetic for the stated model, not engineering certification.