Air Permeation Units

An APU's objective is to increase a material's flow rate to the required process rate. The Diamondback APU promotes flow when a powder loses its entrained air during storage, when the desired flow rate exceeds a powder's measured flow rate, or when air pressure at the hopper outlet is large relative to air pressure in the bin.

Diamondback Technology's air permeation unit dramatically accelerates powder flow rates up to 1,000 times faster than untreated powders.
It achieves this by injecting controlled air at strategic points in the hopper, compensating for air loss during storage. This prevents an excessive influx of air at the hopper outlet, a factor that can impede solids flow. The APU maintains precise control over air pressure and flow, ensuring a consistent powder flow rate that eliminates issues like flooding, flushing, and flow limitations.

Typical Applications

  • Eliminates feeder starvation when used in conjunction with an arch-breaking Diamondback Hopper

  • Enhances a Diamondback Hopper's ability to break arches in solids that set up with time

  • Eliminates flow problems with powders such as fly ash, ground ore, powdered polymers, fine dry coal and coke, talc, titanium dioxide and other pigments, cement, sawdust, flour, alumina and powdered metals


  • Material-specific factory setting

  • Complete manifold and tubing for direct hookup to Diamondback Hopper APU ports

  • Available with two, four, six, or eight injection ports

  • Special clean-out nozzles for periodic APU post cleaning

  • Installation, operation, and cleaning manual

A picture of the front of an electrical box.
A diagram of the process of air pressure.

Understanding Air Permeation

In hoppers with converging geometry, powder compaction occurs as solids pressure changes. This leads to increased bulk-specific weight. The highest compaction level typically happens at the transition between the vertical bin and the converging hopper. This compaction pressurizes the air in the gaps between powder particles. As solids flow, the powder expands, often below atmospheric pressure.

At the hopper outlet, atmospheric air rushes in to counter the low pressure in the gaps. This influx of air creates an upward force that hinders solids flow. It results in a solid surface forming at the hopper outlet, causing the powder to descend slowly in small clumps, a condition known as a "limiting rate condition." The most severe limiting rate occurs when solids remain in the bin, and air pressure at the highest solids contact point (top of the hopper) equilibrates with atmospheric pressure.

The actual limiting rate varies based on factors like how quickly the bin is filled and how long it stands before initiating flow. The APU addresses this by injecting the missing air into the gaps that would otherwise be filled by air entering from the bottom of the bin outlet. Complete air replacement can lead to significantly accelerated solids flow rates, often surpassing the maximum anticipated flow rate by several orders of magnitude.