Use this Vacuum Hose Air Velocity Calculator to find air velocity in vacuum hoses. To ensure the continuous movement of dirt, sand, and gravel in a vacuum hose, it is crucial to maintain a high velocity airflow. For optimal results with dirt, sand and gravel, a velocity of 5000 fpm is recommended.

## To calculate the air velocity at the vacuum hose inlet:

1. Select Hose Type (standard or Low Loss)
2. Input hose diameter (inches)
3. Input vacuum flow rate (CFM)
4. Input hose length (feet)

Output is in velocity (fpm).

Here is a chart that lists the conveying velocity (fpm) to move different materials.

 Material Conveying Requirements Material Approx Weight Lbs. per Cuft CFM per lb. of Material Min Conveying Velocity (fpm) Suction Pickup (inches of W.C.) Ashes, Coal 40 42 4,500 3.0 Cement, Portland 100 35 7,000 5.0 Coal, Powdered 30 42 4,000 3.0 Corn Meal 40 38 5,400 3.5 Dust, Grinding 160 to 175 42 5,000 3.0 Lime, Hydrated 53 to 64 42 5,000 3.0 Plastic, Granulated 35 42 5,400 3.0 Sand, Dry 99 35 7,000 5.0 Sawdust, Dry 7 to 15 63 3,700 2.5 Wood Chips, Heavy 15 to 24 45 4,500 3.0 Wood Shavings, Light 7 to 15 73 3,400 2.0

Note:  The above chart is based on data for 4″ diameter pipes and larger.  However, it provides relatively good information on velocities and weights of materials.

Note: As a result of much testing our empirical data indicates that it is relatively easy to move up to 1 pound a second of mixed sand and gravel through a 2 inch vacuum hose.  Constant velocity is key to moving material.  For many of the materials listed 100 CFM plus is required to keep velocities high.  In addition, it will become evident that keeping hose length down to a minimum is a valuable control parameter.  Also we have found that higher suction (inches of W.C.) is the powerful boot that keeps material moving when it starts to clog hoses and thus keeps the velocity high.

In summary, small vacuums with good suction, flow over 100 CFM and vacuum in the 45+ inches of W.C., and short 2″ hose (20 feet or less) work well for conveying sand and gravel.  Once the material is airborne it will convey for long distances as long as the velocity is above threshold.