Conveying-air velocity: reliable decisions depend on stated operating conditions, material evidence and equipment limits. Commissioning converts a pneumatic conveying design into a documented operating window. The objective is not to find the highest airflow or to copy a generic minimum velocity. It is to demonstrate that the actual material reaches the required throughput without progressive deposits, excessive pressure, unacceptable damage or operation outside the roots blower envelope.
Prepare the Measurement Basis
Every airflow reading must state where and under what conditions it applies. A blower inlet volume, a normalized flow and an actual pipeline volume can represent the same gas mass flow with different numerical values. Instruments should be suitable for the expected pressure, temperature, dust exposure and turndown.
Before testing material, confirm:
- Airflow-instrument range, units and calibration status.
- Pressure sensors at the blower and critical pipeline locations.
- Inlet and discharge temperature measurement.
- Feeder-speed or mass-flow indication.
- Receiver-filter differential pressure.
- Blower rotational speed and motor-current feedback.
- Relief, non-return, alarm and shutdown functions.
The test sheet should identify the pipe internal diameter used in calculations. Nominal pipe size alone may not represent the actual bore.
Establish the Air-Only Baseline
Operate the empty line through its planned speed range with the receiver and filter in normal service. Record blower inlet flow, line pressure, temperature, motor current and filter differential pressure. Compare the measured clean-line resistance with the design expectation.
An unexplained difference should be investigated before solids are introduced. Possible causes include a partly closed valve, incorrect pipe bore, leaking joint, obstructed filter, instrument error or an unexpected fitting. This air-only baseline later helps distinguish pipeline and filter changes from gas-solid resistance.
Introduce Material in Controlled Steps
Begin at a conservative feed rate supported by the conveying design or material test. Hold airflow steady long enough to observe repeatable pressure and receiver behavior, then adjust one variable at a time. For each point, record:
- Average and short-term solids rate.
- Effective conveying airflow.
- Pressure at the feed point and selected downstream positions.
- Blower speed, current and temperatures.
- Filter differential pressure and cleaning activity.
- Product condition and receiver discharge.
- Evidence of deposits after a planned stop or inspection.
The trial duration must represent hopper cycles, filter loading and thermal stabilization. A few minutes of apparently smooth transfer may not reveal slow accumulation.
Confirm the Critical Pipeline Sections
Actual gas volume generally increases as pressure falls along a positive-pressure line, so gas velocity often rises toward the receiver. The lowest velocity may occur near the feed point, but feeder leakage, added air, pipe steps and temperature changes can alter the profile. Bends, upward inclines and the base of vertical lifts also need attention because particles can decelerate or concentrate there.
Velocity should be calculated from the measured or corrected airflow at each relevant condition using the method established in the dedicated inlet-velocity article. Commissioning acceptance should not rely only on the receiver-end value.
Define the Accepted Operating Window
The final setting should provide a validated margin above unstable deposition while avoiding unnecessary velocity. Excess air can raise power, bend wear, product attrition, noise and receiver-filter load. Too little air can cause dunes, fallback, pressure cycling or blockage.
The handover record should define:
- Approved airflow and solids-rate ranges by material grade.
- Normal pressure, temperature, speed and current bands.
- Maximum filter differential pressure before intervention.
- Start-up and shutdown sequence.
- Alarm and trip thresholds.
- Response to feeder loss, receiver fault and rising pressure.
- Baseline values for future condition monitoring.
A relief valve remains a protective device and should not discharge as part of normal capacity control.
Link the Test to the Pasifik Blower Curve
Commissioning data should be compared with the model-specific performance curve for the installed two-lobe or three-lobe Pasifik roots blower. Normal operation and credible maximum resistance must remain within approved pressure, speed, motor-power and discharge-temperature limits. The portfolio-wide limit of up to 1,000 mbar is not a substitute for the selected model’s curve.
When the process operating window and blower envelope overlap with appropriate margin, the plant gains a defensible production setting. When they do not, the cause may be the feeder, pipeline, receiver, filter or original duty definition; increasing speed without that diagnosis can hide the problem only temporarily.