Short answer
Flow rate and nominal diameter alone are not sufficient for a pressure loss calculation. The actual inside diameter, length, fluid properties, temperature, connections and flow regime are required. A single reliable loss value cannot be produced with incomplete data.
Technical explanation
The flow cross-section and volumetric flow rate determine the mean velocity, but flow resistance also depends on the line configuration and fluid behavior. Manufacturer selection guides address size, fluid and application conditions together. If a pressure loss curve in a catalog is based on specific test conditions, it must not be transferred directly to a different liquid or temperature. A connection of the same nominal size as the hose can have a different actual flow cross-section.
Topic-specific checkpoints
| Item | Description |
|---|---|
| Geometry | Actual diameter, length and line layout |
| Fluid | Density and viscosity at temperature |
| Flow | Flow rate and assessment of the applicable flow regime |
| Local resistance | Fittings, couplings, elbows and valves |
How to evaluate it in practice
In the proposed data form, collect the total hose length, actual inside diameter, list of connections and valves, flow rate, fluid density/viscosity information and temperature. Mark narrow passages and abrupt changes of direction separately. The technical lead should choose the calculation method and the sources of coefficients. A reliable pressure loss cannot be calculated with missing coefficients; this guide aims first to complete the necessary data. Plan separately how the calculation result will be checked against a measurement or a manufacturer curve.
Original editorial recommendation; not a clause of a standard.
Frequently asked questions
Do two hoses of the same diameter and length have the same pressure loss?
Not necessarily, if the internal construction, actual diameter, fluid conditions and connections differ.
Source coverage
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S021
Selecting a hose assembly? Remember STAMPED Swagelok Bangalore · accessed 2026-10-19 Size; Temperature; Application; Material; Pressure; End Connections; Delivery
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S024
Hose and Flexible Tubing, MS-01-180 Swagelok · accessed 2026-10-19 PDF pages 4–5 / printed 253–254: Nomenclature; pages 8–9: selection, installation and use