Water hydraulics
Fitting / local resistance loss
- where
- local pressure loss (Pa; the calculator shows kPa)
- sum of resistance coefficients
- fluid density (kg/m³)
- reference velocity (m/s)
Explain this equation
Works out the pressure lost through fittings, valves and other local resistances. Add it to straight-pipe friction loss for a circuit total.
K is the resistance coefficient for each fitting, summed for all of them. ρ × v² / 2 is the dynamic pressure of the flow, the pressure equivalent of its speed.
Each fitting loses a fixed number of velocity heads. That makes the loss proportional to K and to the square of velocity.
Sense check: K totalling 3 at 1 m/s loses about 1.5 kPa. At 2 m/s it is four times as much, 6 kPa.
Watch out: K values must match the actual fitting geometry and the velocity they were quoted against, often the inlet bore. Mixing reference velocities gives the wrong answer.
Enter your values to see the result.
Good to know
K values must correspond to the component geometry and stated reference velocity.
Sources
Results are arithmetic only. Worked examples are not recommended design settings. This library does not provide automatic gas pipe selection, live gas tightness tests, purging procedures, combustion acceptance limits, installation approval or commissioning certification. Manufacturer data and the applicable current method remain essential.