The Vacuum Curve

Every vacuum system operates along a characteristic curve that shows the inverse relationship between airflow and vacuum pressure.

Static Pressure (SP)

Measured in inches of water column (in. WC), static pressure represents the resistance to airflow in the system:

• Low SP (0-2 in. WC): Light-duty applications
• Medium SP (2-6 in. WC): General industrial use
• High SP (6-12 in. WC): Heavy-duty applications
• Very High SP (12+ in. WC): Specialized applications

Airflow (CFM)

Cubic Feet per Minute measures the volume of air moved. Higher CFM means more air capacity for capturing contaminants.

The Fan Law

Understanding fan laws helps predict system performance:

• CFM ∝ RPM: Airflow is directly proportional to fan speed
• SP ∝ RPM²: Static pressure varies with the square of fan speed
• Power ∝ RPM³: Power consumption varies with the cube of fan speed

System Resistance

Total system resistance includes:

1. Duct friction losses
2. Fitting losses (elbows, tees, reducers)
3. Filter resistance (if applicable)
4. Cyclone pressure drop
5. Pickup point losses

Optimization Strategies

Balancing pressure and airflow for optimal performance:

• Minimize duct length and fittings
• Use proper duct sizing
• Select appropriate fan type for application
• Consider variable frequency drives for flexibility