Pipe-area scaling: the evaluation begins with defined process conditions, material data and equipment boundaries. Changing pneumatic conveying pipe diameter affects almost every part of the duty: gas velocity, required inlet volume, air-only friction, solids concentration, feeder performance and the pressure imposed on the blower. An area-ratio calculation can help compare possible bores quickly, but it is not a final capacity guarantee.
At the preliminary design stage, the main value of this calculation is speed. It can indicate whether a proposed bore change is too small to produce a meaningful improvement, large enough to require a different blower package or likely to move the system beyond its demonstrated conveying behaviour. The result should then be checked against the complete conveying route and material data.
The Preliminary Area-Ratio Relationship
When two duties are dynamically comparable, a first approximation may scale solids rate with pipe cross-sectional area:
Here, ṁs is the solids mass flow rate and d is internal pipe diameter. The relationship assumes that the new system can maintain comparable gas velocity, solids behaviour and pressure conditions. Those assumptions must be stated because they rarely remain perfectly true in an industrial modification.
The internal diameter—not nominal pipe designation—should be used. Wall schedule, lining and buildup can change the effective bore enough to affect both area and velocity.
What Must Remain Comparable
Before applying the screen, confirm that the material grade, moisture, particle distribution and feeder principle are representative. The proposed route should also remain inside the pressure and velocity region covered by the reference data.
If the new bore requires a major change in blower airflow, the receiver filter, valves and feeder leakage may no longer behave comparably. A large bore also changes the pressure gradient and can eliminate a low-velocity condition that was available in a smaller test line. Conversely, a smaller bore can raise velocity, air-only loss, wear and particle degradation.
Convert the Screen into an Air Requirement
The next task is not to accept the calculated solids rate. It is to determine how much blower-inlet air is needed to produce a stable velocity at the selected operating pressure. Gas expansion must be included because actual volume and velocity increase as pressure falls along a positive-pressure pipeline.
The critical locations are commonly the high-pressure inlet section, where actual gas volume is lowest, and the discharge region, where velocity may be highest. A bore that is acceptable at one end can be unsuitable at the other. Stepped-bore pipework may deserve evaluation when a single diameter creates an excessive velocity spread, but its purge and transition behaviour must also be checked.
Rebuild the Pressure Budget
Increasing diameter normally reduces air friction for a given actual velocity, yet maintaining that velocity requires more volume. The blower duty can therefore move toward lower pressure and higher airflow. Whether absorbed power rises or falls depends on the specific combination, not on diameter alone.
The pressure budget should include inlet and discharge silencers, air piping, feeder leakage, material acceleration, straight runs, bends, vertical lift, receiver and clean-to-fouled filter resistance. This total is compared with the selected model’s continuous operating data, not merely with a catalogue maximum.
Use the Calculation for Commercial Decisions
Area scaling is most useful for screening alternatives before detailed engineering. It can answer questions such as whether an existing blower is likely to have enough volume for an upsized line, whether a proposed throughput increase demands a new feeder and filter, or whether a smaller pipe would approach the pressure boundary.
The project record should label the result “preliminary” until material-specific calculation or testing confirms capacity. It should also state the expected normal point, maximum credible point and permitted control range.
Pasifik Blower selects positive-pressure two-lobe and three-lobe roots blowers from model-specific flow-pressure and power diagrams. Providing the internal bore, route, reference airflow, total differential pressure and material rate allows the area-ratio screen to be converted into an equipment duty without presenting a geometric estimate as a performance warranty.
Glossary
Area-ratio screen: Preliminary comparison based on the ratio of internal pipe cross-sectional areas.
Comparable duty: Operating case sufficiently similar in material, regime, pressure and velocity for a limited comparison.
Effective bore: Internal flow diameter remaining after wall thickness, lining, wear or deposits are considered.
Geometric estimate: Early calculation based mainly on dimensions rather than a complete gas-solid model.
Internal diameter: Actual inside dimension of a conveying pipe used for flow area and velocity calculations.
Scale factor: Numerical ratio used to transfer a preliminary result from one size or condition to another.
Velocity spread: Difference between the lowest and highest gas velocity along a conveying route.