The right calculations help engineers predict air velocity, pressure drop, and flow rate—factors that determine whether material moves smoothly or a system clogs before it ever runs.
This guide walks you through key core pneumatic conveying calculations every engineer should understand, why they matter, and how to apply them in real-world design—including choosing the right Roto-Disc valve or airlock to match your system.
Understanding the Basics of Pneumatic Conveying
At its core, a pneumatic conveying system moves dry bulk materials through a pipeline using air or another gas as the transport medium. The system’s efficiency depends on how precisely you balance material flow, air velocity, and system pressure.
Two main operating modes determine your calculations:
- Dilute phase conveying: particles are fully suspended in the air stream (higher velocity, lower material concentration).
- Dense phase conveying: particles move in slugs or waves at lower velocity and higher concentration.
Choosing the wrong mode—or skipping key design math—can lead to excessive wear, product degradation, or a complete system choke.
Key Parameters in Pneumatic Conveying Calculations
Every engineer should have these four parameters at their fingertips when sizing or troubleshooting a system:
1. Solid Loading Ratio
The mass of solids conveyed per mass of gas:
A higher ratio means a denser flow. It affects power consumption, pipe diameter, and equipment selection.
2. Saltation Velocity
The minimum gas velocity required to keep particles suspended and prevent settling. Operating below this velocity risks line blockages.
Typical ranges: 3,000–6,000 ft/min for light powders, 4,000–8,000 ft/min for granules or pellets.
3. Pressure Drop
Accounts for frictional losses in straight pipe, bends, fittings, and vertical lifts. Use the Darcy–Weisbach equation or empirical charts to estimate total head loss:
Blower or vacuum sizing is determined by pressure loss.
4. Pickup Velocity
The minimum air velocity required to entrain particles at the feed point is slightly higher than the saltation velocity. This is critical for ensuring smooth line startup.
Tip: For quick reference, the Engineering Toolbox provides standard velocity guidelines by material type.
Step-by-Step: Pneumatic Conveyor Design Calculation
Let’s walk through the steps used to size or verify a pneumatic conveying system.
Step 1: Define the Process Requirements
- Material characteristics: bulk density, particle size, abrasiveness, and moisture content
- Throughput: total mass flow (lb/hr or kg/hr)
- Conveying distance: horizontal + vertical run, plus the number of bends
- System type: pressure or vacuum conveying
These define your starting assumptions.
Step 2: Select the Conveying Mode
If your material is fragile or abrasive, lower-velocity dense phase conveying might be ideal. For lighter materials or long distances, the dilute phase offers simplicity and steady flow.
Step 3: Estimate Airflow and Velocity
Use the fundamental relationship:
Where:
Rearrange to solve for pipe diameter or required air velocity. Engineers typically aim for a gas velocity 20–30% above saltation velocity to ensure stable dilute-phase transport.
Step 4: Calculate Pressure Drop
Combine friction losses from:
- Straight pipes (Darcy–Weisbach friction factor)
- Bends and fittings (use equivalent length or K-values)
- Vertical lifts (gravity head)
- Feed and discharge losses
Sum these to estimate the total ΔP.
This value determines whether your chosen blower or vacuum pump can maintain the target velocity without surging.
Step 5: Check Energy and Equipment Limits
Blower horsepower, valve sealing pressure, and airlock throughput are directly tied to the pressure and flow values you just calculated.
For systems that require consistent pressure isolation between stages, Roto-Disc’s Airlock/Double-Dump Valve Assemblies offer a reliable alternative to rotary valves, delivering tight seals, minimal maintenance, and proven durability under vacuum or pressure-conveying conditions.
Vacuum Conveying System Design Calculation
Vacuum systems move material by suction rather than pressure. The airflow direction is reversed, but the math remains similar.
Scenario: Conveying 2,000 lb/hr of powdered resin over 60 ft with one vertical lift.
- Estimated pickup velocity: 4,000 ft/min
- Pipe diameter: 3 in
- Equivalent length (including fittings): ~90 ft
- Friction factor (smooth steel): 0.02
Using the simplified formula for friction loss:
Consider calculating a total pressure drop of ~6.5 psi and adding minor losses and a safety factor to size the vacuum pump accordingly.
Pro tip: Vacuum conveying systems generally require less air volume but higher differential pressure than positive-pressure systems. That impacts both energy use and airlock configuration at the discharge.
For negative-pressure conveying systems, Roto-Disc’s Roto-Flate® Inflatable Seal Spherical Valve provides bubble-tight sealing, preventing air leakage and ensuring stable system performance under vacuum.
Common Mistakes in Pneumatic Conveying System Design
Even experienced engineers can overlook subtle factors, including:
- Ignoring saltation velocity: leading to material buildup and line plugging
- Oversizing air velocity: causing product degradation and excessive wear
- Underestimating bends and fittings: each adds equivalent pipe length and pressure drop
- Mismatched valves or airlocks: poor sealing leads to air loss, backflow, and uneven feed
- Skipping field validation: pilot testing verifies your assumptions before scaling up
Turning Numbers Into Real-World Results
Pneumatic conveying calculations are more than theoretical—they’re the basis for everything that follows. Selecting the appropriate valves, diverters, and airlocks hinges on a clear understanding of flow rate, velocity, and pressure, guaranteeing consistent performance under load.
Our engineering team designs equipment for seamless integration into existing systems. This helps facilities minimize maintenance, maximize uptime, and ensure material flow exactly as planned.
Optimize Your Pneumatic Conveying System with Roto-Disc
A well-calculated conveying system begins with data and ends with durable, reliable components. If your team is evaluating system design or troubleshooting performance, Roto-Disc can help you size the correct valve or airlock to keep your conveying line efficient and leak-free. Contact us today to get started!