Airflow reference conditions: reliable decisions depend on stated operating conditions, material evidence and equipment limits. A statement such as “1,000 m³/h of air” is incomplete. It does not show whether the volume applies at the blower inlet, at a standard reference condition, at the compressed conveying-line inlet or at the receiver. The same air mass occupies different volumes as pressure and temperature change.
For pneumatic conveying, this distinction affects blower selection, pipeline velocity, feeder leakage and filter sizing. A reliable quotation must identify the condition attached to every volumetric flow value.
Common Airflow Descriptions
Project documents may use several labels:
- Actual blower-inlet volume: volume physically entering the machine at site pressure and temperature.
- Free-air delivery: volume referred back to specified ambient or intake conditions.
- Standard volume: volume at a declared standard pressure and temperature.
- Normal volume: another reference-volume convention whose conditions must be stated.
- Actual pipeline volume: local volume at a defined pressure and temperature inside the conveying circuit.
The words “standard” and “normal” are not self-defining. Different organizations may use different temperatures, pressures or humidity bases. The reference values must appear in the data sheet.
Converting Between Gas Conditions
For preliminary dry-air conversion where ideal-gas behavior is acceptable, the same mass flow at two conditions can be related by:
Pressures are absolute and temperatures are absolute. This is a condition conversion, not merely a change from m³/h to m³/min. A unit conversion changes the numerical unit while the gas condition stays the same.
Humidity and real-gas effects may require a more complete method for high-accuracy measurement or unusual gases. The blower and process designer should agree on the basis rather than applying an unexplained correction factor.
Why the Blower Uses Actual Inlet Volume
A roots blower is a positive-displacement machine. Its rotors displace the volume physically present at the inlet. If a process requirement is given as a standard volume, it must be converted to actual inlet volume at the site altitude, inlet temperature and intake restriction before model speed is selected.
At a high-altitude site, lower atmospheric pressure means a given air mass occupies more inlet volume. At a high inlet temperature, density also falls. A catalogue comparison made only in reference m³/h can therefore miss the actual displacement and motor-cooling conditions.
Why the Pipeline and Filter Use Local Volume
Conveying velocity depends on actual gas volume inside the local pipe bore. In a positive-pressure line, the gas volume near the inlet is reduced by pressure and may increase toward the receiver as pressure falls. Temperature rise also affects the expansion.
Receiver-filter area and cyclone inlet velocity should use actual volume at their connections. Using the blower reference flow directly can understate or overstate the gas load on separation equipment.
Feeder leakage should also be reported at a defined pressure location. A leakage value quoted as free air cannot simply be added to an actual compressed-pipeline volume without conversion.
A Clear Airflow Data Sheet
Every airflow entry should include:
- Numerical value and unit.
- Reference or actual location.
- Absolute pressure.
- Absolute or clearly convertible temperature.
- Dry or humid-gas basis.
- Gas composition if not ambient air.
- Normal, minimum or maximum operating case.
For measurements, the meter’s reported basis and compensation settings should be recorded. Two instruments may display the same unit while one reports actual flow and the other reports a standardized value.
Applying the Definition to Pasifik Blower Selection
Pasifik Blower’s published two-lobe and three-lobe portfolio spans approximately 30–9,360 m³/h and up to 1,000 mbar across all models. A portfolio flow range is meaningful only with the reference basis used by the applicable model diagram.
Final selection should convert the process air mass requirement to the model’s defined inlet-volume basis, then verify flow, differential pressure, speed, motor power and discharge temperature on the selected performance data. Stating reference conditions clearly prevents an apparently small notation issue from becoming a major commissioning shortfall.
Glossary
Free-air delivery: Delivered gas flow expressed as an equivalent volume at declared inlet or ambient reference conditions.
Normal volume: Gas volume expressed at explicitly declared normal reference pressure and temperature.
Standard volume: Gas volume expressed at explicitly declared standard pressure and temperature.