KEVOS® MAKEOS · Hydraulics
Hydraulic Line Sizing (Velocity, Pressure Drop and Tube Rating)
Is this tube big enough for the flow, how much pressure does the line lose, and is the tube rated for the system pressure?
Sizing check of a hydraulic pressure, return or suction line: the least bore for the flow at your velocity limit (as the pipe size by velocity tool), the actual velocity, Reynolds number, friction factor and pressure drop through the line and fittings (as the pipe friction tool), the power lost, and the tube burst pressure by Barlow’s formula on the outside diameter with the working pressure rating at your design factor.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Flow | L/min | Flow through the line (for a return line from a cylinder, include the area ratio). |
| Velocity limit for this line | m/s | Velocity limit you design to (commonly about 0.6–1.2 m/s suction, 2–4 return, 3–6 pressure lines). |
| Tube bore | mm | Inside diameter of the tube. |
| Tube outside diameter | mm | Outside diameter of the tube. |
| Working pressure | bar | Highest working pressure in the line. |
| Tube tensile strength | MPa | Tensile strength of the tube material. |
| Design factor (burst ÷ working) | Ratio of burst to working pressure (often 4 for hydraulic tube; follow your standard). | |
| Line length | m | Length of the line. |
| Sum of fitting loss coefficients | Sum of loss coefficients of bends, fittings and valves in the line. | |
| Oil viscosity at working temperature | cSt | Kinematic viscosity at operating temperature. |
| Oil density | kg/m³ | Density of the oil. |
| Tube roughness | mm | Absolute roughness of the tube bore (about 0.0015 mm drawn tube). |
| Allowed pressure drop in the line | bar | Pressure drop you accept along this line. |
Method and formulas
- Least bore d = √(4Q ÷ πv_max); velocity v = Q ÷ (π d² ÷ 4).
- Re = v d ÷ ν; f = 64 ÷ Re laminar, Colebrook turbulent; Δp = (f L ÷ d + ΣK) ρ v² ÷ 2 (as the pipe friction tool).
- Barlow burst pressure p_b = 2 S_u t ÷ D_o with t = (D_o − d) ÷ 2; working rating = p_b ÷ design factor.
- Example: 60 L/min in a 16 mm bore runs at 4.9736 m/s, loses 3.0261 bar and the tube is rated about 279.55 bar.
Limitations
- Straight-tube rating; fittings, hoses and welded joints have their own ratings.
- Viscosity must be taken at the actual oil temperature.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Choose a tube size for a new hydraulic circuit
- Find why a return line runs hot or noisy
- Check a tube’s pressure rating against a pressure increase
Who it is for
- Hydraulic engineers
- Maintenance engineers
- Machine designers
What you get
- Least bore and actual velocity
- Pressure drop and power lost
- Tube burst and working pressure rating
Interpreting the result
- Pressure drop rises about as velocity squared in turbulent flow: one tube size up often halves the loss.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3024–3027, 281–286. Topic reference; no source tables or recommended settings are reproduced.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Hydraulic Line Sizing (Velocity, Pressure Drop and Tube Rating) calculator
