BIZOMAT MAKEOS · Hydraulics
Pipe or Hose Size for a Target Velocity
What inside diameter keeps this flow at the target velocity?
Minimum inside diameter of a pipe, tube or hose for a flow at a chosen mean velocity, and the velocity in a selected actual bore.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Flow | L/min | Maximum flow in the line. |
| Target velocity | m/s | Design velocity for the line type (typical hydraulic guidance: suction 0.6–1.2 m/s, return 1.5–3 m/s, pressure 3–6 m/s). |
| Actual inside diameter to check (0 = none) | mm | Inside diameter of a proposed or existing pipe or hose. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Flow
- What it is
- The largest volume of fluid the line must carry each minute, for example the full pump flow.
- Units and format
- Enter a number in L/min: litres per minute. The form accepts 0.000001 L/min to 10000000 L/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 80 L/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The minimum bore rises with the square root of flow.
- Get it right
- Size for the peak flow; return lines from cylinders can carry more than pump flow.
What this means: Target velocity
- What it is
- The average speed you want the fluid to travel along the line, chosen from design guidance for the line type such as suction, return or pressure line.
- Units and format
- Enter a number in m/s: metres per second. The form accepts 0.000001 m/s to 100 m/s. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 4 m/s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A higher target velocity allows a smaller bore.
- Get it right
- Use guidance for your line type and fluid; suction lines need lower speeds than pressure lines.
What this means: Actual inside diameter to check (0 = none)
- What it is
- The inside diameter of a pipe, tube or hose you are considering or already have, to check its actual fluid velocity.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 25 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger bore lowers the actual velocity.
- Get it right
- 0 means no check. Use the true bore, not the hose dash size or tube outside diameter.
Method and formulas
- d = √(4Q ÷ (π v)), Q in m³/s.
- Velocity in a bore = Q ÷ (π d² ÷ 4).
- Example: 80 L/min at 4 m/s needs at least 20.601 mm bore.
Limitations
- Velocity guidance is not a pressure-drop check; long lines need the pipe friction tool too.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size hydraulic suction, pressure and return lines
- Size coolant and water pipes
- Check an existing hose for velocity
Who it is for
- Hydraulic and process engineers
- Maintenance engineers
- Design engineers
What you get
- Minimum inside diameter
- Velocity in the actual bore
Interpreting the result
- Choose the next standard size at or above the minimum bore.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3024–3027. Topic reference; no source tables or recommended settings are reproduced.
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