Vacuum Conveying Velocity Calculator
Determine saltation pickup velocity, required actual airflow CFM, solids-to-gas loading ratio, and estimated system vacuum for dilute phase pneumatic bulk transfer.
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Pneumatic Vacuum Conveying Principles & Saltation Physics
Dilute phase pneumatic vacuum conveying uses a negative pressure differential created by an exhauster or rotary lobe blower to entrain bulk particulate solids into a high-velocity air stream. Unlike positive pressure systems, vacuum systems pull product toward the receiver hopper, providing inherently dust-free operation even if minor line leaks occur.
Key Vacuum Conveying Formulas
- Volumetric Airflow Rate (ACFM):
ACFM = Superficial Pickup Velocity (ft/min) × Pipe Area (sq ft) - Solids-to-Gas Mass Ratio (μ):
μ = (Material Convey Rate in lb/min) / (Air Mass Flow in lb/min)
Where dry ambient air mass is calculated using actual air density at the pickup pressure (~0.070 lb/cu ft). - Saltation Velocity Consideration (Rizk Equation):
Air velocity must exceed the saltation velocity by at least 20-30% to prevent particles from dropping out of suspension and accumulating on the bottom of horizontal piping. - Filter Receiver Sizing:
Pulse-jet filter receivers require adequate cloth area to maintain an air-to-cloth (A/C) ratio between 3.5:1 and 5.0:1 CFM/sq ft.
Frequently Asked Questions
What is saltation velocity in pneumatic conveying?
Saltation velocity is the minimum superficial air velocity required to prevent solid particles in horizontal pipes from settling out of suspension and forming sliding dunes or stationary deposits.
What solids-to-gas ratio is typical for vacuum dilute phase conveying?
Typical dilute phase vacuum conveying systems operate with solids-to-gas mass ratios between 3:1 and 12:1 lb of solid per lb of air, with line vacuums ranging between 8 and 14 inHg.
Why does vacuum conveying require higher actual CFM at the pump than at the pick-up nozzle?
As the conveying air travels downstream toward the vacuum blower, pressure drops and the air expands. Consequently, the actual cubic feet per minute (ACFM) increases from the pickup point to the receiver separator.