Input data
Results
| # | Flow | Ref. | Diameter | Gauge pressure | Temperature | Line type | Density (kg/m³) | Mass flow (kg/s) | Velocity (m/s) | Velocity (ft/s) | Actual flow (m³/s) | Actual flow (ACFM) | Velocity check |
|---|
Formula used
The calculator estimates the mean air velocity in a circular pipe from the actual volumetric flow rate and internal diameter. The core relationship is:
v = Q / A
- v = average air velocity in the pipe (m/s)
- Q = actual volumetric flow rate (m³/s)
- A = internal cross-sectional area of the pipe (m²)
For a circular pipe, area is:
A = π × D² / 4
where D is the internal diameter in metres. When flow is provided at standard conditions (SCFM, Nm³/h), the calculator converts it to actual flow using the ideal gas relationship:
Qactual = Qstandard × (Pstandard / Pabsolute,line) × (Tline / Tstandard)
Assuming ideal gas behaviour for air, density at line conditions is:
ρ = Pabsolute,line / (R × Tline)
where ρ is density (kg/m³), R is the specific gas constant for air (approximately 287 J/kg·K), pressure is in Pascals and temperature in Kelvin. Mass flow is then ṁ = ρ × Qactual.
How to use this calculator
- Enter the volumetric flow and select the appropriate unit.
- Choose whether this flow is at actual line conditions or standard conditions.
- Provide the internal pipe diameter and select its unit.
- Select the line type if you want to compare with typical velocity ranges.
- Enter line gauge pressure and temperature, plus local atmospheric pressure.
- Adjust standard reference temperature and pressure if your company uses different values.
- Click Calculate velocity to compute pipe velocity, density and mass flow.
- Use Download CSV or Download PDF to export your calculations.
Example data table
The following example illustrates typical compressed air velocities in plant distribution lines. Actual acceptable limits depend on noise, pressure drop and application.
| Flow | Pipe ID | Gauge pressure | Temperature | Velocity (m/s) | Velocity (ft/s) | Density (kg/m³) | Comment |
|---|---|---|---|---|---|---|---|
| 1000 Nm³/h | 80 mm | 6 bar(g) | 20 °C | 19.5 | 64.0 | 7.5 | Typical main header velocity. |
| 500 Nm³/h | 50 mm | 7 bar(g) | 25 °C | 24.0 | 78.7 | 8.0 | Higher velocity in branch line. |
| 200 SCFM | 2 in | 5 bar(g) | 18 °C | 16.2 | 53.1 | 6.5 | Moderate velocity, acceptable for many systems. |
Compressed air velocity article
Understanding compressed air velocity
Compressed air velocity is a key design and troubleshooting parameter for plant engineers. Excessive velocity increases pressure losses, noise and leaks. Too little velocity can lead to water pooling and slow response in instruments. This calculator helps quantify velocity quickly so you can compare scenarios objectively instead of guessing. It also reinforces basic relationships between flow, pipe size and pressure for students or new technicians learning compressed air design.
Relationship between flow, area and pipe size
Flow, area and velocity are directly related. For a fixed flow, a smaller internal diameter forces higher velocity, while a larger pipe slows the air. By entering different pipe sizes, you can see how velocity changes and select a diameter balancing pressure drop, material cost and installation space.
Effect of pressure and temperature on velocity
Compressed air does not behave like an incompressible liquid. When you change pressure or temperature, the same standard flow produces different actual volumes and velocities. The tool converts standard flows, such as SCFM or Nm³/h, to actual flow using ideal gas relationships and your specified line conditions. This avoids manual conversions, unit mistakes and inconsistent reference conditions between different datasheets, compressor suppliers and plant standards.
Using line type to judge velocity levels
Different parts of an air system tolerate different velocities. Main headers can usually run faster than instrument or drop lines. By choosing a line type, the calculator compares the computed velocity against indicative design ranges and warns when the value is likely too low or too high.
Density, mass flow and energy considerations
Because air density increases with pressure and decreases with temperature, mass flow is not constant for a given volumetric flow. The calculator estimates density at your line conditions and multiplies it by actual flow. This gives mass flow, useful for compressor sizing and energy performance evaluations.
Checking velocities against design ranges
Checking calculated velocities against recommended ranges prevents common system problems. Velocities above guideline values increase turbulence, generate noise and accelerate wear in fittings. Very low velocities may allow condensate to accumulate. Using this calculator regularly supports better layout decisions and helps justify pipe size upgrades to stakeholders. Using clear numeric velocity targets also makes communication with contractors, consultants and operations teams less ambiguous during projects and troubleshooting work.
Using exports in engineering documentation
Exporting results to CSV or PDF extends the calculator beyond quick checks. CSV files allow you to compare several lines, operating points or upgrade options in spreadsheets. PDF summaries capture final design decisions or commissioning measurements, keeping a clear calculation trail for audits and maintenance teams.
Frequently asked questions (FAQs)
1. What units can I use for flow input?
Enter flow as m³/h, m³/min, L/s, L/min, SCFM or Nm³/h. Choose whether the value represents actual line conditions or standard conditions before calculation.
2. How is the pipe velocity calculated?
Velocity is calculated from actual volumetric flow and pipe area. If the flow is given at standard conditions, the calculator converts it to actual flow using temperature, pressure and the ideal gas relationship.
3. What velocity ranges are considered typical?
In many distribution systems, 6–20 m/s is typical for mains, 10–30 m/s for branches, and 5–15 m/s for instrument lines. The velocity check compares your result with these indicative ranges.
4. Why is very high velocity a problem?
High velocity increases pressure drop, noise, erosion risk and energy use. It can also worsen moisture carry-over. Very low velocity may cause poor response in control lines and water slugs in poorly drained piping.
5. What is the benefit of mass flow output?
Mass flow is the product of actual volumetric flow and air density at line conditions. It is useful for compressor sizing, energy calculations and comparing loads across systems operating at different pressures.
6. How should I use the CSV and PDF exports?
Export the table as CSV to analyse several scenarios in spreadsheets. Use the PDF export to attach calculation snapshots to reports, project files, commissioning documentation or maintenance records for future reference.